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is the journal of the Departments of Botany and Zoology, Victoria University of Wellington, and Victoria University Press, New Zealand, and is published twice a year.
Joint Editors:
ISSN 0041-3860
Keywords: Introduced birds, mammals, distribution, population numbers, environmental effects, control, farming.
Thirty three species of introduced birds and thirty two species of introduced mammals are now widely accepted as a part of New Zealand fauna. The history of the introduction of these vertebrates into New Zealand is documented, and consideration is given to their effect on the native vegetation and fauna. The status of introduced mammals in the late 1940's (Wodzicki 1950) is compared with the present, and the success of control is discussed. Improved technology and the high export value of quality animal products led to a population decline of certain mammals as farming became commercially viable. While the distribution of many introduced mammals has expanded, population numbers have generally decreased since the first survey. A notable exception is the possum.
New Zealand is a marginal fragment of the ancient continent of Gondwanaland. The long isolation of New Zealand has resulted in a considerably diverse flora which has been derived from two sources. Firstly, from ancient species that were present when New Zealand formed a part of Gondwanaland. The remainder consist of species which arrived during the subsequent isolation.
Although some browsing herbivores such as the moa (Greenwood and Atkinson, 1977), native pigeon (Hemiphaga novaeseelandiae) and takahe (Notornis mantelli) had an influence on the vegetation, the New Zealand flora developed in the absence of browsing mammals. Since the arrival of man the indigenous vegetation has been modified by destruction and fire, through the introduction of mammals, and by the establishment of many exotic plant species.
The long isolation of New Zealand has also given rise to a considerably diverse endemic fauna. There are sixty-five native species of extant land and freshwater birds of which 57% are endemic (Bull & Whitaker, 1975). New Zealand's long isolation is also shown by the archaic endemic genus of frogs Leiopelma; the tuatara Sphenodon punctatus, the so-called “living fossil”; and the existence of only two terrestrial mammals, the two bats.
Editor's Note: This paper was originally presented to an International Conference on the theme ‘Man as a Biogeographic Factor’ organised by the Société de Biogéographie in Paris, 18-22 October, 1982 and published in French (C. R. Soc. Biogéogr. 59 (2): 231-256, 1983). The English translation is published here to make it available to New Zealanders as an update to Wodzicki (1950).
Man arrived in New Zealand in three influxes. The first arrivals were the Polynesian settlers who probably came as early as the tenth century A.D. (Davidson, 1976), and brought with them two mammals, the Maori dog and kiore rat.
Centuries later, Captain Cook arrived on the 6th October 1769. From 1792, for about 20 years, European sealing and whaling gangs ruthlessly destroyed their quarry until the animal stocks became exhausted. European rats and mice were presumably introduced into New Zealand by the sealing and whaling ships. Finally the first large influx of European settlers took place in the 1840s and with them came the remaining introduced terrestrial vertebrates of New Zealand.
Table 1 shows the composition of the New Zealand vertebrate fauna including terrestrial, freshwater, native and introduced species. The table also illustrates the success of establishment of the various vertebrate groups, which varies considerably.
The origin of vertebrate introductions is of interest. Fig. 1. depicts these introductions and shows that the largest number of successful introductions came from the British Isles and Europe. Comparatively fewer came from the continent of Australia and the Pacific Islands. Obviously sentimental ties of the settlers with their country of origin has prevailed and this is shown by the large number of introductions from Europe. The dates of introduction of freshwater and terrestrial vertebrates are shown in Table 2. The prehistoric period prior to Captain Cook's visit had only two introductions (kiore or the Polynesian rat and the kuri or Maori dog). The largest number of introductions occurred about a quarter of a century after the settlement of New Zealand in the 1840s when most of the settlers were already established.
A total of 144 bird species were introduced by man into New Zealand between 1840 and the present day and of this total 33 species have survived and are now part of New Zealand's avifauna. The 33 introduced species
In considering the effects of the introduced birds on New Zealand's ecosystem several aspects have to be mentioned. The first is the effect foreign bird species may have had on the native bird fauna. It is claimed that avian diseases introduced by the new arrivals may have caused the disappearance of some susceptible native species. Turbott (1961) reported that aggressive behaviour and predation occurred between native and exotic bird species although only in a few cases. Another consideration is interspecific competition between the native forest species and the introduced bird species. According to Turbott (1961), only three introduced species, the blackbird (Turdus merula), the song thrush (T. philomelos) and the chaffinch (Fringilla coelebs) are found in the native forest, all being more common along the forest edge than deep in the forest (Kikkawa, 1966). The hedgesparrow (Prunella modularis) is found only in the forest edge and the redpoll (Carduelis flammea) is present in the subalpine scrub zone.
Although the destruction of native forest by man has reduced or even eliminated certain native species, other native species entered modified environments and are now found together with introduced species. For instance in the Kaingaroa exotic plantation there are vigorous populations of native and introduced species (Gibb, 1961).
Williams (1953), in his survey of introduced passerines on offshore islands of New Zealand, reported that 10 or 11 out of 13 species then established in New Zealand were self-introduced to the various islands up to 885km distant. These self-introductions occurred within 30 or 40 years of their liberation in New Zealand.
Over a century has elapsed since the liberation of most introduced birds in New Zealand and the distribution and populations of most have for some time remained static (see Table 3). Nevertheless, a few species are still subject to changes in distribution and numbers. The rook ( Corvus frugilegus), which was introduced to North and South Island has spread considerably since 1969, although for several years it remained static in its distribution. The rosella (
Introduced species in New Zealand display several characteristics that contrast with the same species in its native country. For instance in New Zealand the goldfinch is a very common bird whereas in England it is fairly local and generally in low numbers. Introduced species in New Zealand tend to have high population densities and therefore more intraspecific competition occurs (Dr P. Carduelis flammea) and yellowhammer (Emberiza citrinella) the plumage of New Zealand specimens is significantly brighter than comparable specimens from Europe (Mr
The birds introduced into New Zealand may be divided into agriculturally important species, game birds and others. The destruction of wetlands occurred at the same time as forest destruction and reduced numbers of the native waterbird species such as the grey duck (Anas superciliosa). To satisfy the demands of sportsmen the following game birds were introduced: mallard ( Anas platyrhynchos), Canada goose (
As in their countries of origin, birds introduced into New Zealand are at times considered to be pests to crops. Dawson and Bull (1970) have found that serious damage is done by nine species of introduced passerines to various fruit and fruit buds. Some bird species, e.g. the starling (Sturnus vulgaris) are considered both noxious and useful on the New Zealand agricultural scene. Orchardists consider it to be a pest but in pastoral areas this species is beneficial as it preys upon grass grub (Costelytra zealandica).
A special class of birds influenced by man are the self-introduced Australian birds, which have colonized New Zealand in recent years and are established in this country. An early example is the Silvereye ( Zosterops lateralis), large flocks of which migrated to New Zealand in the 1850's.
More recent migrants include the spur-winged plover (Vanellus miles), the white-faced heron ( Ardea novaehollandiae), the welcome swallow (
The 32 species of mammals introduced and established in New Zealand belong to seven orders. These mammals were introduced for a variety of reasons, the majority for sport (Table 4). An interesting characteristic of a number of species was their ability to penetrate into the native forest and to become established there. It should be added that the New Zealand native forests grew and developed without browsing mammals. Their populations expanded rapidly and contributed to the destruction of forests and the initiation of erosion. However, other introduced species took to the man-made pastoral country and increased rapidly until they became a menace to farming in hilly areas. More recently in certain species a combination of high technology and high prices for animal products has resulted in a simultaneous decline of animal populations and a rise in export earnings from the animal products.
A denizen of Australia and the greatest wildlife pest of New Zealand at present, the possum was repeatedly liberated from Australia between 1858 and 1930 to establish a fur industry. The subsequent spread of this species was greatly enchanced by numerous liberations of New Zealand stock in both islands, particularly between 1890 and 1930 (Pracy, 1962).
The first map showing the distribution of possums in New Zealand was produced by Wodzicki (1950). At this time possums were well distributed in both islands and Stewart Island but there were still large areas without possums, such as North Auckland, most of the central North Island, the central South Island and the west coast of the South Island. At present possums have expanded north of Auckland and from Urewera to the East
The effect of the possum on the vegetation has been the object of several studies as discussed below. Possums have been found to thrive in a variety of habitats including native bush, Pinus radiata, orchards, pasture, scrub and urban gardens. In exotic plantations when the trees are growing they suppress the underneath shrub layer and the possum populations decline. However, when the trees become mature more light is available to the shrubs and the possum population increases (Clout, 1977).
Alice Fitzgerald (1981) provided a list of native plant species eaten by the possum and found eight native species which occurred regularly in the
Elytranthe sp.), rata (Metrosideros robusta) and fuchsia ( Fuchsia excorticata), and thus actually
The problem of bovine tuberculosis in the possum is even more important. The first case of tuberculosis in possums was reported in 1970 and since then the disease has been discovered in 23 general localities (Julian, 1981). In 1982 $430,000 were spent controlling tubercular possums (Mr
It should be mentioned that possums are also an economic asset. As soon as possums were established in the last century, possum skins were exported. Since 1970 the price of skins has risen and in 1980 the skin trade was worth 23 million dollars (N.Z. Yearbook, 1981).
In recent years possum farms have been established in New Zealand. The ranching of possums on farms produces skins which fetch higher prices $18–$20 per skin) than the skins of wild animals ($6–$8 per skin) (N.Z. Dept. Statistics, 1980).
Like so many mammal species introduced into New Zealand the possum requires control to reduce damage caused to forests, and also the infection of cattle with tuberculosis.
The control of possums is largely in the hands of Pest Control Boards and commerical trappers. Where skins are of high quality the trappers make deep inroads into their numbers but where the skins are of poor quality, the trappers leave large numbers behind. The very wide spread of possums in both islands makes, despite the existence of satisfactory techniques, an efficient control very difficult and costly. As Freeland and Winter (1975) suggested, in Australia the possum is not a pest for two reasons: firstly the flora has built many chemical defences and secondly there are other marsupials that the possum has to compete with.
In summing up, we can say that the possum is the only introduced mammal species that is still unmanageable.
Twelve species of marsupials were introduced into New Zealand between 1858 and 1870 but only six wallaby species and the possum (Trichosurus vulpecula) became established (Wodzicki, 1950). Five species (Macropus bicolor, M. dorsalis, M. eugenii, M. parma and Petrogale penicillata) are found on Kawau Island and on a few other islands in the M. eugenii) is present in the Rotorua area, North Island. The sixth species (M. rufogriseus) is located in South Canterbury, South Island. Populations of the dama wallaby (M. eugenii) near Rotorua, and the red-necked wallaby (M. rufogriseus), near Waimate have expanded considerably in recent years. The parma wallaby (M.parma), nearly exterminated in its homeland, Australia, is found in satisfactory numbers on Kawau Island.
Wallabies compete with sheep for food and also cause damage to young trees. Stomach contents of wallabies in South Canterbury included native trees, shrubs, ferns and various grasses and weeds (Wodzicki, 1950). With regard to control, in the Waimate area, $70-90 per hectare was spent in one year on wallaby control to ensure that trees grew high enough to prevent browsing (Mr K. Miers, pers. comm. 1982).
Problems are caused if wallabies are kept as pets as they are often taken to new areas where they can establish themselves if they escape. For example at Lake Hawea in the South Island, wallabies released during the 1930's and 1940's built up a substantial population. The cost of their control thus far is about $100,000.
Hedgehogs were introduced from England between 1869 and 1900 to the South Island and between 1900 and 1909 to the North Island. They were introduced to control various insects and other garden pests. The spread of hedgehogs was much assisted by man who continued to liberate them in new localities (Wodzicki, 1950).
Brockie (1975) has found that over 250 frost days per annum or rainfall exceeding 2500mm/year limits hedgehog distribution. In comparison with distribution maps of hedgehogs in the late 1940's (Wodzicki, 1950) it appears that hedgehogs have colonized all suitable areas in both islands. According to Dr R. E. Brockie (pers. comm. 1982) at present the population is static.
With regard to the food of the hedgehog Brockie (1959) has shown that slugs, moths, caterpillars, snails, millipedes, frogs and earwigs make up most of the food of hedgehogs and that the diet varies with habitat. A particularly interesting finding is the lack of predation by this species on ground nesting birds, although hedgehogs are a minor nuisance to farmers by carrying off chicken eggs.
During the long voyage from Europe to New Zealand many parasitic fleas and tapeworms of the hedgehog were lost. However, the scab mite disease spread widely in New Zealand hedgehogs during a population peak in 1970. A ring worm from hedgehogs sometimes affects children and the hedgehog is also a maintenance host for Leptospirosis ballum (Brockie and Till, 1975).
Three mustelids—the weasel (Mustela nivalis), the stoat or ermine (M. erminea) and the ferret (M. putorius) were liberated in New Zealand (Wodzicki, 1950; Marshall, 1963) between 1867 and about 1897 for the biological control of rabbits.
The distribution of the three species of mustelids varies greatly. The ferret and weasel are both locally distributed with the distribution of the ferret being related to that of rabbits. Stoats are the most common mustelid, as shown by Marshall (1963).
Recent publications provide details of the food of the mustelids in New Zealand (Marshall, 1963), particularly in forests of Fiordland (King and Moody, 1982). The principal foods of stoats were insects, mice, birds (10-20 species) and mammals such as rats and possums. Also, of considerable importance was the fact that stoats “did not eat significantly fewer birds when there were plenty of mice” (King and Moody, 1982). However, the real effect of mustelids on birds remains unknown. Ecological studies in the Orongorongo Valley, near Wellington by the
The problem of mustelid control has recently been reviewed by King and Moors (1979). Drawing on the results achieved in the control of mustelids in England, they doubt whether trapping, particularly in National Parks, will lead to their extermination. Active management of rare native birds would be the alternative.
Finally, the latest economic development with regard to mustelids is fitch farming. Within the last few years approximately ten farms have been established. Imported ferrets from Scotland have been bred with New Zealand feral animals to improve fur quality and colour (Dr C. M. King, pers. comm. 1982).
Since the introduction of the house cat in the early whaling days, the species has become feral and colonized most of mainland New Zealand and some islands. It occupies a wide range of habitats from sea-level to 1500m. (Collins and Charleston, 1979). Feral cat populations are probably self maintaining although straying cats may augment the feral numbers occasionally (Fitzgerald and Karl, 1979). In mixed forest of the Orongorongo Valley near Wellington the food of feral cats has been found to consist primarily of small mammals such as rabbits, rats, mice and even possums and stoats. Although several species of bird are eaten, they form only a small part of the diet. However cat predation has been suggested as one of the reasons for the decline of ground-feeding bird species in the past (Fitzgerald and Karl, 1979). On Stewart Island the continued survival of the rare flightless parrot, the kakapo ( Strigops habroptilus) is threatened by feral cats. The cats are estimated to kill 25-50% of the population of 100 kakapo, reducing an already endangered species (Mr H. A. Best, pers. comm. 1982). Recently the Wildlife Service, Department of Internal Affairs, New Zealand eradicated a long established population of feral cats from Little Barrier Island, a wildlife sanctuary. This has resulted in a dramatic increase in native bird species, in particular the endangered stitchbird (
A recent survey has found that feral cats are definitive hosts for several sporozoa parasites including Toxoplasma gondii and Sarcocystis both of which have a wide range of intermediate hosts including sheep (Collins and Charleston, 1979) and therefore may be of economic importance to the meat industry.
Four species of rodents have been introduced into New Zealand; the kiore (Rattus exulans), Norway rat (R. norvegicus), the ship or black rat (R. rattus) and the house mouse (Mus musculus). The kiore has been reported to have been brought to New Zealand by Maoris. It is assumed that the Norway rat came ashore during the first visit of Captain Cook but the ship rat arrived later and was not widely distributed until the 1880's (Atkinson, 1973). The house mouse apparently established itself during the early 1800's (Thomson, 1922).
All three rodents introduced from Europe soon became widespread. An account of the present distribution of the four rodent species was recently
The mouse is very widespread and is also present on several outlying islands.
Rodents have a very important effect on birds and reptiles as reported by Atkinson (1978). Predation by kiore has been reported on seven bird species, by the ship rat on 10 species and by the Norway rat on nine species. It will be of particular interest to note that nine bird species have been brought to local extinction by ship rats but none by kiore and Norway rats. Fig. 4 illustrates predation by the three rat species on various bird groups (Atkinson, 1978).
Other groups of vertebrates are also subject to predation by the rodents. The effects of kiore on the tuatara (Sphenodon punctatus) and other reptiles have been described by Crook (1973) and Whitaker (1978). It was found that tuataras were “common” on islands without kiore. On islands with kiore, tuataras were rare and often only old large specimens were present. Similarly the diversity of the lizard fauna was reduced in the presence of kiore. No research work has been carried out on the effect of kiore on frogs but it is very likely that they are subject to predation by this species too.
The house mouse is generally distributed through the main and many outlying islands, usually in low densities (Fitzgerald, 1978). However in beech forests where the trees seed irregularly, mice populations will erupt in a good seed year (see e.g. King, 1982).
The rabbit is of particular interest as it became a pest in New Zealand very soon after its liberation. The presence of rabbit for over a century has proved to be a most expensive undertaking with regards to control.
The numerous and deliberate liberations of rabbits in the North and South Islands were due to the desire to export rabbit skins. The liberations took place between 1864 and 1905 and the rabbits multiplied quickly to the effect that “as early as 1869 rabbits were reported as a nuisance in Southland and in Marlborough and Central Otago by 1878” (Wodzicki, 1950).
Rabbits spread more slowly in the North Island because of large forested areas, different patterns of land development and fewer extensive open tracts. It is believed that between 1920 and 1940 rabbits had occupied all the areas suitable to them in both islands.
The relationship of medium and heavy infestations of rabbits to soil types in the North Island was provided by Dr N. Taylor (Wodzicki, 1950). Rabbits affected farming mainly through the reduction of sheep-carrying capacity and the depletion of soils through erosion. It is estimated that fifteen rabbits eat the same amount as one sheep, although this probably overestimates the requirements of a hill country ewe and underestimates the consumption of a rabbit (Wodzicki, 1948).
Rabbits cannot survive in long grass and this may be the reason that the largest rabbit populations occurred in sheep country. Gibb et al. (1945) considered that if other agencies deplete the vegetation, rabbits may become the dominant cause of erosion. Rabbits do not penetrate native forests but they must have crossed them in order to reach the open tops. On the other hand rabbits are known to be present in exotic forests where they eat the foliage of newly planted trees.
In an experiment carried out by Gibb et al. (1969) in the hill country of Wairarapa, indices of rabbit sign were used to measure changes in density in two areas carrying sparse rabbit populations, one with and the other without rabbit control. At the end of a three year period both areas carried similar rabbit populations although the age structures were different and it was suggested that predators were able to control the rabbit population in the protected area.
The damage done by rabbits forced the settlers to form organizations to control the pest and as early as 1876 the Rabbit Nuisance legislation was introduced. Another important step to control rabbits was the introduction of the “natural enemy” in the form of ferrets, stoats and weasels. Although these predatory animals can control rabbits under special circumstances (Gibb et al. 1978), their harmful effect on native bird life was and still is of great ecological significance.
Myxomatosis was introduced in 1951 to control rabbits but failed as there was no vector to spread the virus.
At present Pest Boards have replaced the Rabbit Boards and the control of other mammals is included in their activities. The methods used now include trapping, fumigation, dogging, night shooting and poisoning. The spreading of poisoned 1080 bait by aeroplane has proved to be the most
A recent development has been the establishment of rabbit farms for meat and fur. In 1980 the pest legislation was changed enabling the rabbits to be kept commercially and as pets.
The European hare was introduced repeatedly onto both islands of New Zealand from 1851 for food and sport. Protected at first, the species increased quickly in numbers and soon spread. Wodzicki (1950) stated that hares had occupied all suitable areas in both islands from sea level to snowline but were most abundant on the east coast of the South Island. According to Dr
The hare, despite coming under the jurisdiction of the Agricultural Pest Destruction Council, has never become a significant pest in New Zealand, although the species can cause damage by nipping off new growth in young trees.
At the beginning of this century 130,000 whole frozen hares were exported and later during the 1940's many skins were exported annually (Wodzicki, 1950). In recent years live hares have been air freighted to France for $80–$90 each to restock game farms (Dr
Wild pigs were first introduced into New Zealand by Captain Cook in 1773 and later more were liberated by the early settlers. Pigs were also released on various outlying islands as food for castaways (Wodzicki, 1950).
The latest information on wild pig distribution is given by Challies (1976). It shows that wild pigs are more widespread in the North Island than in the South Island, where pigs are absent on the West Coast. In comparison with the distribution maps of Wodzicki (1950), the areas with pigs appear to have become restricted (Mr P. C. Nelson, pers. comm. 1982).
The main vegetation damage caused by wild pigs stems from their feeding habits. Several plant species, particularly those with succulent roots, such as ferns, are uprooted. Rudge (1976) provided information on animal remains in the faeces of pigs on Auckland Islands. Among these remains were feathers of Antarctic prions (Pachyptila desolata).
At present local control operations are required from time to time to reduce wild pig predation on lambs and cast sheep, damage to young plantations, agricultural crops and pasture. Otherwise pigs are hunted for recreation or for meat.
Goats were first liberated by Captain Cook and for more than a century more introductions followed.
There were three main reasons for liberation of goats: (i) as a supply of
Feral goats have spread widely and their recent distribution has been given by Rudge (1976). A comparison with the distribution in 1947 (Wodzicki, 1950) shows that goats have extended their distribution on the two main islands (Fig. 5). On the other hand, goats have been exterminated from 12 of the 23 outlying islands where they were liberated.
An account of the feeding habits of the goat and of its effect on the vegetation of islands has been given by Turbott (1948). A goat population left uncontrolled on Great Island, Three Kings Islands for 35 years, reduced a flora of 143 species to only 70 species. Similar destruction was observed on Kermadec Islands by Sykes (1969). Goats are known to feed on the foliage of most trees and plants and can destroy all vegetation. They can reach otherwise inaccessible foliage by climbing on leaning tree trunks.
The relationship of goats to deer is of interest. In North-West Nelson Forest Park deer have been removed by helicopter hunting. As soon as the deer disappeared goats moved in. On the other hand in Southern Ruahine mountains, when goats were shot out, deer came in (Dr M. R. Rudge, pers. comm. 1982).
It is likely that feral goats will eventually be exterminated from further outlying islands, particularly those whose fauna and flora is of special value. According to Dr Rudge the number of goats on the mainland has been reduced by control measures of the Forest Service, but their distribution remains the same. The low export value of goats normally prevents the use of helicopters in their control. The only commerical use of feral goats is in Hawkes Bay and Taranaki where goats are mustered and their meat is exported, with a value of $0.5 million per year to the Caribbean, Pacific Islands and South East Asia.
Despite the economic control applied in these areas the populations remain static.
Sheep (Ovis aries) were introduced into New Zealand along with cattle (Bos taurus) and horses (Equus caballus) as domestic stock by the early settlers (Thomson, 1922). Because the land was not fenced the animals roamed free and some, escaping periodic mustering, became feral.
In comparison to the situation in the late 1940's when there were several herds in the North Island (Wodzicki, 1950), feral horses are now found only in the Kaimanawa Ranges where a reserve has been established to protect them. Small populations of feral cattle exist only on Campbell and Enderby Islands although in the past they were present in remote areas of the mainland (Taylor, 1976). Feral sheep are still distributed in isolated local areas of the mainland and on one inshore and three outlying islands (Dilks and Wilson, 1979). Some of these populations exhibit features of scientific interest. For example the “merino × longwool” sheep on Campbell Island are resistant to footrot, have a low ratio of secondary to primary follicles in the wool and have increased body temperatures (Rudge, 1982).
Unfortunately some of the feral populations of cattle and sheep are on reserves and their presence conflicts with reserve management policies. Other herds are present on private land and as this is cleared of scrub the animals are eliminated.
Overall the populations of feral farm animals are declining but moves have been made recently to preserve particular breeds so that their unique genetic qualities may be drawn on for future domestic stock (Rudge, 1982).
Himalayan thar (Hemitragus jemlahicus) and chamois (Rupicapra rupicapra) were liberated as game animals near Mt. Cook in the South Island of New Zealand. The thar was released in 1904 and the chamois in 1907 (Wodzicki, 1950).
Since then the thar has spread north and south to occupy the middle region of the Southern Alps (Caughley, 1970). The chamois increased more rapidly and has dispersed along the Alps at a rate of approximately 10 kilometres per year (Christie, 1964), believed to be the fastest dispersal rate for any game animal in New Zealand (Riney, 1955). The distribution of both species in the late 1940's (Wodzicki, 1950) is compared to that of the late 1960's (Harris, 1970) in Fig. 6 and 7.
Both species can feed in places inaccessible to red deer (Riney, 1955). Chamois eat a variety of grasses (Christie, 1970) while thar is known to eat out high altitude pastures (Howard, 1965). As both animals live in areas where erosion has accelerated they may be having a prominent effect on the habitat.
The effect of chamois and thar on the alpine environment of the South Island made control mandatory. Between 1936 and 1968 official control accounted for over 82,000 chamois and 30,000 thar (Harris, 1970). Many additional thousands of chamois and thar were shot by sportsmen, and helicopter hunting has now virtually eliminated the thar.
Red deer were liberated in New Zealand for sport, with 29 recorded liberations between 1851 and 1910 in the North, South and Stewart Islands (Wodzicki, 1950).
Red deer expanded their range considerably between 1924 (Forbes, 1924), 1947 (Wodzicki, 1950) and the present time (Fig. 8). They now occupy almost all forested areas. Exceptions in the North Island are parts of the East Cape area, North Auckland, Coromandel Peninsula and the Mount Egmont area. In the South Island the area between Franz Josef and Fox Glacier remains free of deer (Mr K. Miers, pers. comm. 1982).
Most of the deer are found in native forests but substantial numbers live in Pinus radiata forests, e.g. Kaingaroa Forest. The steadily increasing deer population had a dramatic effect on the native vegetation, which had evolved without the presence of browsing mammals. The structure of some forests has been modified by the destruction of the lower tiers of vegetation. By selective browsing the animals have altered the floral composition, with browse-resistant plants replacing palatable species (Howard, 1965). Accounts of the effect of high deer populations on native and exotic forests were given by Wodzicki (1950), and Clarke (1972) who described the habitat destruction resulting from the presence of deer. Possums, by defoliating forest canopies open up the forest, make it less impenetrable for deer, which inflict further serious damage (Wallis and James, 1972).
Red deer were protected after their first liberation in 1851. The damage to vegetation, which became apparent in many parts of the country, led to the removal of protection in 1930 and a year later to the implementation of deer control. This was carried out all over the country firstly by shooters of the Department of Internal Affairs and later of the Forest Service. From 1931 to 1968 a total of 1,067,434 deer were destroyed by Government shooters, although plenty of deer still remained in the forests.
By 1968, because of rising velvet and venison prices, commercial interests had largely taken over the control of deer. This led to a drastic reduction of deer numbers, mostly in the South Island but also in the North Island. According to Dr I. Atkinson (pers. comm. 1982) the removal of large numbers of deer had the most marked effect on the vegetation in alpine areas. As deer move between the forests and the alpine areas the effect is also noticeable in the forests although less pronounced.
Hunting by helicopter has allowed a feral and noxious animal to become a source of a considerable revenue. The total export of venison (feral and farmed) in 1979-1980 amounted to $5.9 million, a total of 1,063 tonnes of which 100 tonnes were farmed venison. (1981 New Zealand Yearbook). West Germany is the main market for New Zealand feral venison which is considered to be of the finest quality.
The high prices obtained for New Zealand deer products on overseas markets provided the incentive for the establishment of over 3,000 deer farms (Fig. 9). It is estimated that a total of 1/4 million deer are present on
Red deer comprise 90% of the total farmed deer population while fallow and wapiti constitute the remainder. The red deer are the easiest species to handle and provide the most weight. Initially farms were stocked with wild deer caught from helicopters but now most stock is farm bred (Mr D. K. Yerex, pers. comm. 1982).
New Zealand farmed venison is sold overseas, mainly to Australia and America, countries which require licensed slaughter premises and meat inspection.
It is interesting to note that a wild, previously noxious animal species has not only become a source of considerable revenue but has been turned into a new domestic breeding stock.
Six deer species that have been introduced as game animals are of minor importance to New Zealand. They include the sika (Cervus nippon), virginian (Odocoileus virginianus), fallow (Dama dama), wapiti (Cervus
canadensis), sambar (C. unicolor) and the javan rusa deer (C. timorensis). These species were introduced at various times between 1864 and 1907 and are established in various localities in both islands with varying degrees of success (Wodzicki, 1950) (Fig. 10).
Perhaps the most successful species is the sika deer which has increased both in density and range. Because it is an intensive forager and can inhabit areas where food is limited, the species has managed to colonize areas where red deer are present (Mr K. Miers, pers. comm. 1982). Sporadic control operations attempt to keep the deer at manageable levels (Harris, 1970).
Wapiti which is restricted by natural barriers to an area in Fiordland, South Island, has continued to expand within this area since its release in 1905 (Meirs, 1970). The species is closely related to the red deer and hybridization occurs. Unfortunately the presence of the wapiti in Fiordland is thought to inhibit the expansion in range of the endangered native takahe (Notornis mantelli) and recently some wapiti have been removed from Fiordland. The private consortium responsible for the removal of the deer will receive half of the wapiti caught and these will probably be sold to deer farmers. The remaining deer are to be liberated in another area in the South Island for trophy hunting.
The distributions of both the virginian and fallow deer have remained static since 1950 although their densities have declined. Virginian deer are still present at Lake Wakatipu, in Fiordland and on the coastal fringes of Stewart Island where they have flourished (Harris, 1970). The Forest Service periodically carry out control programmes in an effort to reduce the deer populations (both red and virginian) on Stewart Island. Some fallow herds are presently on privately owned land and are thus afforded some measure of protection (Miers, pers. comm. 1982). This species is also used in deer farming although to a lesser extent than red deer.
The remaining sambar deer present in New Zealand are still found near their point of liberation. Because of their diminishing numbers they are now protected by the Forest Service in one area (Mr J.
The Javan rusa deer occupies the smallest range of deer in New Zealand, being present only in shrubland in the Rotorua District (Miers, pers. comm. 1982). They were accidentally introduced into New Zealand as sambar deer in 1907 and it was not until 1955 that they were recognized as a separate species (Harris, 1970).
Wherever any of these six species occur there is a noticeable alteration in the species composition of the flora. Fortunately, because of their limited distribution and small population densities their impact on the vegetation is slight compared to that of the red deer (Howard, 1965).
All the species mentioned are highly regarded as trophy animals for various reasons. The fallow buck is sought after for its palmated antlers and fine skin while the sambar is considered by many sportsmen to be the ultimate trophy because of its natural cunning (Harris, 1970).
In addition to the aforementioned species two other deer species were liberated in New Zealand, although both have now died out. The axis deer (Cervus axis) introduced during the 1860's and early 1900's, was last seen in Fiordland, South Island in 1948 (Harris, 1970). The moose (Alces americanus) was also liberated in Fiordland and in the early years following its introduction appeared to be successful. By 1924 the species was considered to be very scarce. The moose has not been recorded since 1954 when a single bull was shot at Wet Jacket Arm, Fiordland (Harris, 1970).
The aim of this paper has been to decribe the effects of man on the New Zealand environment brought about by the introduction of exotic birds and mammals. (See Table 1).
In trying to assess the present situation it is important to consider three points. Firstly, with regard to mammals, the changes between the late 1940's (Wodzicki, 1950) and 1980. Secondly, to view the presence of the introduced vertebrates in the light of the growing consciousness among the
The thiry-three species of introduced birds which have become established in New Zealand are now widely accepted as a part of the New Zealand avifauna. The majority of species arrived when the New Zealand landscape was undergoing modification from forest to pasture. As a result many new niches were established which could not be filled by the native species, but suited the new arrivals. Because of a lack of inter-specific competition a large number of these immigrants have become more successful in New Zealand than in their county of origin (Dr P.
The demise of the native bird fauna is generally accepted as being attributable to the destruction of the native forests and wetlands and the introduction of predators. However, some early reductions of native birds in unmodified forests have been attributed to diseases introduced by the exotic birds. Interactions between native and exotic species are limited. Only a few introduced species occur in the native forest and there is no indication that these species “drive out” native species.
Some species of introduced birds such as the rook ( Corvus frugilegus) have become pests. Others such as the starling (
Of the six successfully introduced gamebirds the mallard and the Canada goose have benefited greatly from the change in land use for farming purposes and their populations have expanded at an astonishing rate.
The self-introduced birds from Australia owe their colonization success to man. In the past many birds have probably arrived in New Zealand but have been unable to settle as the environment was unsuitable. When European man arrived and modified the environment he provided new habitats previously unavailable. It is therefore likely that New Zealand can expect more additions to the avifauna from Australia.
The introduction by man and establishment of 32 species of exotic mammals is a fact of considerable ecological and economic importance for New Zealand. New Zealand provides an interesting example of the effects, detrimental or otherwise, of introduced mammals in an ecosystem unused to either herbivorous or predatory mammals.
In comparing the ecological and economic situation of the introduced mammals between the late 1940's and the present, we see that their distribution has not changed much during these 35 years. One species (possum) has increased nationally, 13 species have increased locally (red, sika, fallow, virginian, Javan rusa, sambar and wapiti deer, goats, chamois and thar, dama, brush-tail wallabies and hedgehog). The distribution of 14 species (three species of mustelids, three species of rats, mouse, hare and rabbit, feral cat and pig, parma, red-necked and swamp wallabies) appears not to have changed significantly. Finally four species (black-striped wallaby, feral horses, cattle and sheep) have decreased in range and numbers.
For more than a century man has been conscious of the adverse effect of introduced mammals on both the man-made and the native environment and a good deal of research has been devoted to these problems. As early as 1867 rabbits were known to compete successfully with sheep leading to a depletion of pasture and eventually to soil erosion (Wodzicki, 1950). The
Finally, a study of the impact on the native vegetation by red deer (Cervus elaphus) and the possum (Trichosurus vulpecula) by Veblen and Stewart (1982) attempts to separate animal-induced changes from other types of vegetation change.
Another important aspect of introduced mammals in the New Zealand environment is the effect of rodents (ship and Norway rats) and carnivores (feral cats, weasels, stoats and ferrets) on the bird life. All native bird species in New Zealand have evolved in an ecosystem devoid of mammalian predators and as such are particularly vulnerable to any that are introduced.
Looking further on the essential changes which occurred between the late 1940's and present there has been a substantial transformation in the attitude of the public to the problems of introduced mammals. Today there is little emphasis on the “last rabbit, last deer” policy of the 1930-1968 era, as the public have come to accept the introduced mammals as part of the wildlife scene of New Zealand. This fact combined with a general increase in public awareness of nature conservation has lead to some interesting examples of introduced mammal management. The removal of some wapiti from Fiordland National Park and the protection of sambar deer in one small area are recent examples of this new attitude.
A new and important development in the management of some introduced mammals has been the innovation of helicopter hunting for deer and goats. An increase in the revenue from wild venison sold in Europe and velvet sold in Asia, led to the use of helicopters as a hunting tool. As a result there has been a substantial decline in wild deer numbers throughout New Zealand. However, this indirect form of control will continue only while high prices are paid for venison in West Germany. If the economics of our wild venison fail the uncontrolled deer populations could increase rapidly.
Within recent years the farming of certain wild mammals has attracted much money and attention particularly in the case of deer. At present deer farms number at around 3,000 and contain approximately 250,000 animals.
Unlike deer, the possum has not been controlled by hunting despite the skins being a valuable export article. Unfortunately good exportable skins usually come from areas with light possum populations and not from areas where control is required.
The Pest Destruction Council has relpaced the Rabbit Board and through its Boards controls rabbits, hares, wallabies, possums and rooks.
Finally, the concluding words may be devoted to a new and interesting aspect of introduced, feral farm animals (Dr Rudge, pers. comm. 1982): genetic conservation. The genetic base of our domestic animals is narrowing as breeding programmes reduce the range of genes available. Some of the feral farm animals display advantageous characteristics such as footrot resistance in sheep and these and less important genes should be preserved so that they can be drawn upon by animal breeders for future domestic stock. Unfortunately many New Zealand feral animal herds have already been exterminated.
We would like to record our sincere gratitude for the invaluable assistance and comments provided to us by Dr
We are grateful to the Cartographic Section of the Science Information Division, D.S.I.R., and the Photographic Section, Department of Zoology, for their co-operation and use of their facilities.
We would also like to thank Dr R. E. Brockie, Dr B. M. Fitzgerald and Miss C. J. T. Alderton who kindly read and commented on the typescript.
The typing of the drafts was kindly undertaken by Mrs J. Bedggood, Miss N. Black and Mrs M. Penning.
Taxonomy, morphology and distribution of Megaceros leptohymenius (Hook. f. & Tayl.) Steph., M. denticulatus (Lehm.) Steph. M. arachnoideus (Steph.) Steph. and M. flagellaris (Mitt.) Steph. are reported. Notes are given on other species recorded for New Zealand. Anthoceros coriaceus Steph. is transferred to Phaeoceros comb.n.
Keywords: Anthocerotae, Megaceros leptohymenius, Megaceros denticulatus, Megaceros arachnoideus, Megaceros flagellaris, Phaeoceros coriaceus.
Introductory remarks and key to the species.
Since all the species of Megaceros which occur in New Zealand are highly variable in their morphology, determination at species level is often difficult and particularly so in the case of incomplete herbarium specimens. Sometimes, too, different species of Anthocerotae grow intermixed.
The 4 species of Megaceros described below may be identified by the following key.
This species is widespread in New Zealand forests growing on the ground or on the bark of fallen trees. Frequently it has been confused with other members of the Anthocerotae. It is apparently endemic.
The species was named Monoclea leptohymenia by Hooker and Taylor (1844). Later Taylor (1846) transferred it to Dendroceros and still later Stephani (1916) transferred it to Megaceros. The type packet at the British Museum was annotated by Proskauer as containing a mixture of M. leptohymenius and M. denticulatus. A specimen of M. leptohymenius, accompanied by notes made by Stephani (sheet 7548) was available for examination by courtesy of the Curator of the Stephani Herbarium, Geneva. Specimens collected by Petrie and named by Stephani are in the National Museum, Botany Division DSIR and the Hodgson collection (MPN 18564). One of these (H 14) was found to be M. leptohymenius interlayered with Monoclea forsteri. In the William Mitten Herbarium at the New York Botanical Garden is a specimen (Colenso 2551) in the Phaeoceros laevis folder I consider to be M. leptohymenius, and also a New Zealand specimen on the same sheet tentatively annotated as M. leptohymenius by Proskauer and yet another collected at Auckland by Lyall and already annotated by Proskauer as M. leptohymenius.
Fresh material was obtained from Kaimanawa Forest Park, Tararua Range, Wellington Botanic Gardens, Abel Tasman National Park, Copland Valley, Westland and Stewart Island. It was maintained in culture at Massey University for up to three years.
There is a juvenile thallus which forks repeatedly giving branches of a rather uniform width of 0.1-0.2mm which spread out horizontally at a wide angle (Figs. 2 & 3). The margin is entire or almost so. In contrast the mature thallus is much larger with a horizontal spread of up to 5cm (Fig. 1). It is firm and rather thin, olive-green in colour and branched at a wide angle. The branches are ligulate, 3-10mm broad and up to 3cm long, with an irregularly crenulate margin. It may be supported by other bryophytes or anchored by rhizoids.
Plants may be monoecious but often are dioecious. In male-only plants the branches tend to be about 10mm broad and 6mm long. The antheridial cavities may be seriated in one or two rows, or irregularly scattered. Each contains a single large conspicuous antheridium with a spherical to oval body, up to 0.3mm long and 0.24-0.3mm broad, attached by a short stalk. Branches with archegonia tend to be longer. Since archegonia form singly behind the apex over a long period, there may be old unfertilised ones more or less seriated and widely spaced over a considerable length of the thallus. Later there may be sporophytes.
The juvenile thallus is up to 4 cells deep medianly and 3 cells deep at the margin. There may be only one large chloroplast per cell but more commonly it is constricted or dumb-bell shaped, or in older parts may have divided into two. The mature thallus is about 0.3mm deep medianly and gradually becomes thinner to about 0.1mm near the margin. Above and below are small cells containing either one or two large rounded chloroplasts or occasionally an elongated or constricted one. The larger central cells usually contain two, but occasionally four or even six, less conspicuous chloroplasts. Pores are present in both the upper and lower surface and scattered cavities contain Nostoc.
The slender capsule, 3-4cm long, is surrounded at the base by a thin, fleshy cylindrical involucre 3-10mm high. The capsule wall lacks stomata. It opens on one side below the apex by a lengthwise slit which broadens somewhat. It may remain in this condition until the spores are shed or later, due to curling and twisting movements in dry air, the capsule may partially split on both sides or the first slit may extend to the apex. The spores tend to hold together for a considerable time and are only slowly freed. When shed they are bright green due to a single large chloroplast, but become straw-coloured in herbarium specimens. They have a diameter of 34-36 microns. The triradiate face at a magnification of up to x1000 appears practically smooth but at x6000 a low surface meshwork is visible; the outer face has numerous papillate projections about 1.3 microns high (Fig. 4). The monospiral elaters, made of 2-3 cells, are 0.1-0.27mm long.
Particularly in autumn numerous new thalli arise on the edges and at times on the surface of old ones, appearing at first as finger-like projections which later fork repeatedly (Fig. 3). The old thalli then tend to disintegrate and groups of juvenile ones lie entangled in its remains and in any moss protonemata or rhizoids in the vicinity (Fig. 2). A rather similar type of regeneration occasionally takes place from the margin of the thallus of Phaeoceros laevis and can be distinguished only by the lack of repeated, regular forking at a wide angle and the form and number of the chloroplasts. Regenerates from other species of Megaceros at some stages of their development are also difficult to distinguish (see below).
Spores of Megaceros leptohymenius resemble those of Phaeoceros laevis but the presence in the former species of true elaters with helical thickening enables certain identification.
3. The presence, even in older parts of the thallus, of cells with only one chloroplast is unusual in a Megaceros.
4. A note on Anthoceros nostocoides Pears. This species was described and illustrated by Pearson (1923) from specimens which W. A. Setchell had collected at Pipiriki in 1904. As they were sterile, Pearson could not determine whether they belonged to Anthoceros or Megaceros. By courtesy of the University of California (Berkeley) the type U.C. 213714 was available for examination. Already it had been annotated by Proskauer who noted that “the shape and structure of the thallus and adhering diatom flora suggest this to be a growth form grown under constant trickle of water or at least under very moist conditions. Can be identified by reference to original locality only”.
When I visited Pipiriki on December 26, 1979, I found Megaceros leptohymenius growing on seepage banks alongside the track leading down from the site of the accommodation house to the landing jetty on the Wanganui River. The plants were sterile but some have been kept growing in culture and compared with M. leptohymenius from other localities. Since A. nostocoides in my opinion is a sterile form of M. leptohymenius, I consider that the name must be rejected.
This species is found on the floor of forests or shrubbery chiefly in the wetter and cooler southern regions and mountains of New Zealand, south of Mt Egmont, and also in Tasmania and south-eastern mainland Australia.
The species was described by Lehmann (1857) under the name Anthoceros denticulatus and transferred to Megaceros by Stephani (1916). A named specimen from New Zealand along with a description by Stephani (sheet 7545) was available for examination by courtesy of the curator of the Stephani Herbarium, Geneva. Another named New Zealand specimen, ex herbarium of Angstrom, is in the Hodgson collection (MPN 18565) and still others from both New Zealand and Australia are at the British Museum. Fresh material, obtained from Stewart Island and Mt Egmont, was observed in culture over 3 years.
The firm rigid olive-green thallus, up to 6cm long and 4cm broad, growing more or less horizontally and branching irregularly, resembles a large Aneura (Fig. 5). It is anchored to soil and rock by short rhizoids. Branches are up to 1cm wide. They have an irregularly lobed margin which, under a dissecting microscope, normally appears denticulate due to irregular, simple or forked, projections which typically are 2-8 cells high and 2-3 (or more) cells wide at the base, but sometimes these are little evident.
The plants studied were found to be dioecious although according to Stephani (1916) the species is monoecious. Antheridial cavities appear in groups behind the apices of male plants in September. Each cavity contains a single antheridium with a club-shaped head, up to 290 microns long and 220 microns wide, and a stalk 40-50 microns long. On female thalli archegonia appear in September in groups immediately posterior to each apex and may be so closely crowded as to touch one another. Later there may be sporophytes.
As seen in a transverse section the thallus is 0.7-1.3mm deep medianly but gradually becomes thinner to about .08mm near the margin. The small, upper epidermal cells are .03–.05mm deep with firm and at times somewhat thickened walls. In young parts each cell has one large chloroplast which is very variable in shape but is usually constricted or dumb-bell shaped (Fig. 6), in older parts there may be up to 4 rounded chloroplasts but sometimes an elongated or V shaped one. The lower epidermal cells also are small, being .01–.03mm deep; each has a single chloroplast except when rhizoidal. The central cells are larger, up to .12mm deep with thin but firm walls which often appear pitted due to prominent primary pit fields (Fig. 7) and
Nostoc colonies may bulge from the lower surface.
The capsule, up to 2cm long, is surrounded at the base by a firm, conical involucre 2mm high (Fig. 8). It opens by 2 longitudinal slits, at first located some distance below the apex, but later these gradually extend to the apex as well as downwards.
The spores, of diameter 26-34 microns, are green due to the dark green colour of the chloroplast. The outer face is verrucose with irregular knob-like thickenings as well as papillate projections; the triradiate face has papillate projections only (Fig. 9). The elaters, 105-275 microns long, are made of 2-3 cells and have a helical band of thickening.
Regeneration takes place from new growths arising at the margin and from the lower surface of the thallus, particularly after the shedding of the spores. These detach readily although normally the old thallus does not disintegrate immediately.
Although, in the dim light of the forest, vegetative plants of M. denticulatus are easily confused with Aneura alterniloba (Hook. f. & Tayl.) Tayl. which may also have a denticulate margin, the latter can be distinguished under a microscope by the oil-bodies and numerous small chloroplasts in the cells, and by the lack of blue-green algal colonies in the thallus.
This species is widespread in New Zealand forests and wet heathlands growing as irregular, greyish-green to olive green flat mats, up to 10cm in diameter, either on soil, on decaying bark and roots, or on other bryophytes. It is very abundant in Nothofagus forest on free-draining banks bordering the Waikareiti Track in Urewera National Park.
The species was first named Anthoceros arachnoideus by Stephani (1892), from specimens collected by Colenso in New Zealand, and later transferred to Megaceros (Stephani, 1916). By courtesy of the Curator of the Stephani Herbarium at Geneva a type specimen, as well as Colenso 1035 and sheet 7549 was available for inspection. On the latter is a dried specimen, a drawing of the thallus in transverse section, and notes written by Stephani. Isotypes, Colenso a 1260, are in the Hodgson collection (MPN 18589), in the National Museum, Wellington and in the British Museum. Other material was collected by Goebel during his visit to New Zealand in the summer of 1898-9. He first mentioned the species briefly
The broadly spreading, sometimes rather fleshy and sometimes very thin thallus, forks repeatedly and becomes irregularly lobed (Fig. 10). The ultimate branches, broadly obovate and up to 1 cm wide, often lie free of the substratum, whereas older parts of the thallus are attached by numerous rhizoids. The upper surface, when moistened, is yellow-green to olive-green in colour but, when not wetted, young parts often show a characteristic hyaline or whitish encrustation made from lamellae and crests or from clusters of branched filaments whose enlarged terminal cells are pale or colourless (Fig. 11 and 12). Further back these outgrowths tend to disappear and at times even near the apex they are not obvious. The margin at a magnification of ×5 appears crenate but at ×100 is highly irregular due to numerous multicellular protuberances similar to those on the upper surface. However, in plants of the high rainfall area of Fiordland and of dripping rock-faces elsewhere these are present only near the apex and sparsely even there.
Plants are monoecious. The antheridial cavities tend to be arranged in compact groups of 3 to 10 or more and are often located near the margin of the thallus. Each cavity contains one antheridium with a spherical head 0.19-0.25mm in diameter and a stalk 3-6 tiers of cells high. The numerous
The thallus as seen in a transverse section is usually 0.2-0.4mm deep medianly and 0.1mm towards the margin, but in the vicinity of the sporophyte it may be up to 1.3mm deep. Above and below are small cells, 13-30 microns deep; the upper ones have either one large chloroplast, which may be disc-shaped, elongated, constricted or dumb-bell shaped, or 2-4 smaller disc-shaped chloroplasts; the lowermost usually have two disc-shaped chloroplasts or occasionally an elongated or constricted one. The interior cells gradually become larger towards the centre of the thallus where they are 40-60(−145) microns deep. They have either 2-4(−8) rounded chloroplasts which tend to be pale in colour, or no discernible ones. On the lateral walls large primary pit fields, which are particularly well-defined near the base of a sporophyte, give a reticulate appearance. On the margin of the thallus and sometimes on the upper surface there are protuberances; on the lower surface in the posterior region there are rhizoids; while on both surfaces there are pores leading into cavities which later may become occupied by the blue-green alga Nostoc. At times the algal colonies become so large that they protrude from the thallus.
The surface and marginal filamentous outgrowths were examined in detail by Goebel (1906). He found that the hyaline appearance is due to a gradual reduction in the size of the chloroplasts from the base upwards until in the larger terminal cells of both main and lateral branches these are often no longer discernible. The arrangement of the filaments is such as to produce a spongy construction which is especially marked where they are crowded at points of forking of the thallus.
The involucre surrounding the base of the sporophyte is 4-11mm high. Its green fleshy base is up to 2mm wide but towards the apex it gradually
After the spores are shed thalli which have borne sporophytes tend to die off but regeneration occurs from the margin and at times from the surface of the old thallus. Marginal regenerates also arise copiously at times on other thalli. At some stages of their development the new thalli are difficult
M. leptohymenius but they tend to remain attached to the old thallus for a longer period, to develop rhizoids early and to show more rapid broadening of the branches along with arrangement in a fan shape.
Goebel (1906) interpreted the outgrowths as a whole as functioning in water retention and the hyaline terminal cells as functioning in water absorption. He related this to the lack of rhizoids in the anterior part of the thallus.
In New Zealand as elsewhere in its range this species is often found on wet rocks alongside streams and on decaying logs in shaded valleys. Rarely it is epiphyllous on fern fronds (Welt, H 8741). It occurs also, as demonstrated by Hasegawa (1983), in India, Thailand and Japan as well as being widely distributed through the Pacific Islands.
From a specimen collected by Rev. T. Powell in Samoa Mitten (1871) first described the species as Anthoceros flagellaris. Later Stephani (1916) transferred it to Megaceros. Sheet 7525 of Stephani's unpublished Icones was available for inspection. It contains a pressed specimen from Fiji and notes made by Stephani. Hasegawa (1983) gave a more detailed description and noted the great plasticity that he had observed while studying a wide range of specimens. He also provides a valuable list of the many synonyms which in the past have been applied to M. flagellaris. Previously it has not been recognised in New Zealand. Fresh material was obtained from the Akatarawa Valley, Wellington (collected by B. V. Sneddon) and from the Kahuterawa Valley near Palmerston North.
The thallus is rather firm with a smooth upper surface and when fresh is pale green, bright green or olive green in colour. Up to 5 cm long, it usually lies flat on the ground (Fig. 15) and is loosely attached by scattered short rhizoids arising from the lower surface. Repeated forking produces widely radiating branches 3-8mm wide, which may be broad with widened apices
Plants are monoecious. Antheridial cavities, each containing a single antheridium, 0.15-0.25mm in diameter, lie closely aggregated near the margin or, less commonly, scattered in the central region of the thallus. Numerous archegonia occur intermixed with the antheridial cavities or on separate branches and later there are, as a rule, many sporophytes.
The thallus as seen in sections is 6-11 cells deep in the broad median region but near the margin it is only 1-4 cells deep. All the cells are thin-walled but the surface ones are 13-16 microns deep while those of the interior are much larger being up to 87 microns deep and also considerably elongated in a lengthwise direction. The number of chloroplasts in the surface cells ranges from one near the apex to 4 or more in mature portions of the thallus while in the interior cells the number is also variable, normally more than 2 and at times as many as 14. Pores are present near the apex on the ventral surface and lead into cavities which may become occupied by Nostoc and produce bulges of the under surface.
The slender capsule, up to 8 cm long, is surrounded at the base by a smooth involucre, 0.5-1.3 cm high. It opens at first by a single slit below the apex and later usually by 2 which may extend right to the tip. The spores, of diameter 26-36 microns, are more or less globose but irregular in shape. The inner face in New Zealand specimens is papillate with short papillae and shows a weak triradiate marking. The spherical face is verrucose with a few warty projections amongst smooth papillae (Fig. 16). The elaters, up to 400 microns long, are usually made of more than one cell and have a single helical band.
A colony on a wet roadside bank at Rangiwahia, Ruahine Range, frequently showed geminate involucres and the capsules were short.
Multiplication takes place freely by adventitious development of new thalli from the margin or surface of older ones. The regenerative process and particularly the dedifferentiation of multiplastid cells was studied in detail by Burr (1969).
In some specimens from places outside New Zealand the warty projections on the spore coat are poorly developed or even absent, resulting in the spores being described as papillate (Hasegawa, 1983).
According to Stephani (1916) this is a plant of Brazil. Thus it is unlikely to occur in New Zealand although listed by Hamlin (1942) under the name Anthoceros aneuraeformis. However, see notes under Megaceros novae-zelandiae.
This species was first named Anthoceros grandis by Angstrom (1873) from a plant collected in 1852 by N. J. Anderson in Tahiti, and later transferred to Megaceros by Stephani (1916). By courtesy of the Curator of the Stephani Herbarium, Geneva the type (G 21931) was available for examination. Already in 1982 it was annotated by J. Hasegawa as being synonymous with M. flagellaris (Mitt.) Steph. Sheet 7531 of Stephani's Icones, containing a pressed specimen and a description was also kindly made available for examination.
The recording of the presence of M. grandis in New Zealand is based on identification, description and figures provided by Khanna (1944) from a specimen H 511 sent to him by E. A. Hodgson and now located in National Museum, Wellington. It was collected by M. flagellaris as does the specimen, although the
Megaceros collected by H. L. Hodgson in January 1940 from Mt Tauhara (MPN 18598). The capsules are mostly young but a few mature spores were found to be verrucose as in M. flagellaris In my opinion the specimens from Mt Tauhara represent M. flagellaris from a wet shady situation which is subject to flooding, as evidenced by the silt and diatoms on the plants.
This was collected by Aneura crispa, shady bases of cliffs, River Mangatawhainui, near Norsewood, county of Waipawa.” I have been unable to locate the type but the description of a plant “covered with masses of fine sparkling granules, as if frosted (or like soredia in some species of
This species was described and illustrated by Khanna (1944) from a specimen forwarded to him by E. A. Hodgson, who had collected it on papa rock (a silt-stone) in a creek in deep shade at Kiwi, Wairoa in April, 1935. The type, E. A. Hodgson 771, is now located at the National Museum, Wellington. According to Khanna the distinguishing features are the frequent geminate involucres and the short capsules.
However, my examination of the type showed that it corresponded with the form adopted by M. flagellaris in wet, shady localities. Elsewhere geminate involucres and short capsules have been found in M. flagellaris in such situations.
This species was described by Stephani (1916) from material collected in New Zealand. It was at first called Anthoceros aneuraeformis (Stephani, 1893) and later Megaceros aneuraeformis, under which name specimens are filed in the Stephani Herbarium, Geneva.
By courtesy of the Curator of the Stephani Herbarium sheet 7543 of Stephani's unpublished drawings was available for examination. The label reads “Anthoceros novae-zelandiae (olim aneuraeformis).” On the sheet are an outline drawing of the vegetative thallus and two descriptions. One description refers to a plant, regarded as the type (Bonner, 1962), which was collected by Helms in Auckland in 1888. The other description, which is closely followed by that of Megaceros novae-zelandiae (Stephani, 1916), is drawn up from a plant collected by W. N. Beckett in 1906 on Mt. Winterslow (Canterbury) on wet places on the ground and now filed as Megaceros aneuraeformis, Bryotheca E. Levier 5371, in the Stephani Herbarium. A duplicate specimen (Beckett 455), determined by Stephani as Anthoceros anueuraeformis and located in the Herbarium of Botany Division, Christchurch, was kindly made available by the Curator.
Although a detailed examination was not possible, this specimen was found to differ in several respects from Stephani's descriptions. The spores correspond with those of Megaceros leptohymenius, to which species I consider the plant belongs. However, specimens in the Hodgson collection (MPN 18596 and 18597) identified as Megaceros novae-zelandiae by E. A. Hodgson came from very wet areas; they are monoecious and have capsules and verrucose spores as in M. flagellaris.
This was first described as Anthoceros pallens (Stephani, 1892) from New Zealand material sent by Colenso; and later transferred to Megaceros (Stephani, 1916). Sheet 7549 of Stephani's Icones containing a pressed specimen and a description was available for examination by courtesy of the Curator of the Stephani Herbarium, Geneva. The later description (Stephani, 1916) was also consulted.
Differences between this species and M. arachnoideus, on the basis of Stephani's descriptions, are the small size (27 microns) and weaker ornamentation of the spores. This could be due to the immature state of such spores as remained in the capsule. The vegetative features, particularly the crested thallus with a laciniate margin, strongly suggest that there is not sufficient distinction from M. arachnoideus to warrant the erection of a separate species.
This species was described by Khanna (1944) from material collected by M. flagellaris. It corresponds in the monoecious condition, and in the form of the capsule, involucre and spores.
This was first named Anthoceros pellucidus by Colenso (1885) and transferred to Megaceros by Hodgson (1972). The type specimen, Colenso a 1362, was available from the National Museum, Wellington also an isotype in the Hodgson Herbarium (MPN 18592). The type was collected by
An examination of the specimens showed that they have a smooth surface and are monoecious. There are old antheridial cavities, and a few capsules containing elaters and verrucose spores. However, the narrow fronds which are mentioned in the description (Colenso, 1885) belong to Riccardia and the so-called gemmae represent cavities containing Nostoc. The species was not recognised by Stephani (1916) for an incomplete specimen sent by Colenso and now at the British Museum bears his comment “sterile; impossible to determine”. However, it is now considered to be M. flagellaris.
This was first named Anthoceros membranaceus by Colenso (1886) and transferred to Megaceros by Hodgson (1972). The type is at the National Museum, Wellington (H 7822) and an isotype is in the Hodgson collection (MPN 18593). These were collected by Colenso in 1884 “on logs in wet dark woods, near Norsewood, county of Waipawa, growing underneath large Aneura etc.” A specimen collected by Colenso and determined by Mitten in 1886 was also examined by courtesy of the British Museum. It is considered that the specimens belong to M. flagellaris.
Grolle (1983) has carefully examined the question of the usage of the name Phaeoceros. He concludes that, according to the Rules of Botanical Nomenclature and despite the recently expressed opinions of Schuster and
Anthoceros is correct for the black-spored species. All of these species were combined under the name Anthoceros in the earlier papers of this series.
However in the present paper the name Phaeoceros laevis (L.) Prosk. is used instead of Anthoceros laevis. Also Phaeoceros coriaceus (Steph.) Campb. comb. n. will replace Anthoceros coriaceus Steph. as used previously (Campbell, 1982).
The writer is indebted to the curators of the herbaria at the British Museum, the New York Botanical Garden, the Stephani Herbarium Geneva, the University of California (Berkeley), Botany Division, Christchurch and the National Museum, Wellington, for the opportunity to study herbarium specimens; to D. Havell, D. Pearce, B. Macmillan. A. Ratkowsky, B. V. Sneddon and H. Wilson for providing fresh material; and to J. Hasegawa for helpful information about M. flagellaris.
Publication No. 7 from the Evolutionary Genetics Laboratory, University of Auckland.
The logical structure of population genetics is discussed and its validity in the study of evolution is evaluated. It is argued that there are very serious difficulties with the accurate performance of genotype/form transformations. Alternatively, I suggest that evolution is a problem of individual form transformations not the genetic changes in population. Population genetics, according to the view expressed here, has a far more limited role in biological studies than that which it presently occupies.
Keywords: evolution, population genetics, Weiss, transformations, the “third view.”
The pages of Tuatara have recently been livened by a debate on the role of population genetics in courses on evolution. Saiff and Macbeth (1983) express the view that there is no need to teach population genetics in introductory courses on evolution, although advanced courses may include it as a “matter of history”. Hewitt (1983) has disagreed and argued that Saiff and Macbeth quote authors out of context and instead maintained “…that the failings of population genetic theory argue for more effort rather than less.”
There is currently substantial debate on aspects of evolutionary theory and since I am interested in this debate, and conduct courses in evolution, I would like to make the following comments.
Lewontin (1974) has provided a succinct outline of the logical structure of population genetics theory. This can be represented as:
Lewontin (1974) describes these states as:
T1: a set of epigenetic laws that give the distribution of form that results from the development of various genotypes in various environments.
T2: the laws of mating, of migration, and of natural selection that transform the phenotypic array in a population within the span of a generation.
T3: an immense set of epigenetic relations that allow inferences about the distribution of genotypes corresponding to the distribution of forms, F2.
T4: the genetic rules of Mendel and Morgan that allow us to predict the array of genotypes in the next generation produced from gametogenesis and fertilization, given an array of parental genotypes.
Essentially then, population genetics attempts to map a set of genotype distributions into a set of form distributions. It provides a transformation in population form space, and then maps these new forms back into populations of genotypes where a final transformation occurs to produce the genotypic distribution in the next generation.
Let us critically consider these transformations in turn:
T1. The path from the gene to form is, at least, a complex one. Perhaps it is best to examine the views, not of population geneticists who do not immediately concern themselves with this problem, but of a developmental biologist. Paul Weiss (1950) views this transformation as involving a number of levels (Fig. 2). He remarks “In dealing with the relations between genetics and development it is well to keep in mind that an organism is constituted like a system of Chinese boxes, in which larger ones enclose smaller ones in a descending series of magnitudes.” (Weiss, 1950). It seems likely that this was on Fritjof Capra's mind (1982 p. 108) when he said recently of genetic reductionism, “It ignores the fact that the
Interactions also occur within levels. For example non-allelic genes commonly interact and such interactions affect form. Similar interactions also occur between chromosomes. De Betham Anderson (1984), for example, has shown that in New Zealand lowland grasshopper Phaulacridium marginale the presence of heterochromatic B chromosomes affects rates of crossing-over in the autosomes. Similar interactions have been recorded in a number of cases (e.g. Naranjo and Lacadena, 1980: Miklos and Nankivell, 1976).
It seems then that there are a multitude of interactions within and between Weiss's levels. Hence it appears likely that it is difficult to provide an accurate T1 transformation and that T1 for generation 1 may well be different for T1 in generation 2 etc. As Lovtrup (1977) has argued in a multi-level system (like embryogenesis itself) any deviation at a lower level will result in larger deviations at higher levels. So over a large number of generations huge errors would be expected to occur.
T2 The transformational laws which operate to change form distributions within any generation represents a complex array of phenomena—the “laws of mating”, for example. What are these laws? In virtually all analyses mating is considered to occur at random! Patterns of migration are rarely considered. In fact Sermonti and Catastini (1984) have recently suggested that the “classic case” of natural selection, that of industrial melanism, is the result of a process of migration of moths, and the individual choice of environment by melanic and light-coloured moths.
T3 The ability to accurately infer the genotype distributions corresponding to the distribution of forms is dependent on an accurate knowledge of the T1 transformation. Indeed T3 is a reverse transformation of T1. Any errors in T1 will also result in T3 errors.
T4 The genetic rules of Mendel in a very real sense simply allow us to infer the movement of chromosomes at meiosis. A consequence of this movement is that certain predictable ratios of form arise in a limited number of cases. However as Lewontin (1983) has remarked many characters do not “Mendelise”. Also the phenomenon of meiotic drive will inevitably complicate this transformation in some organisms. So the plain fact is then that, in many cases population geneticists will encounter situations where genetic rules will not allow an accurate T4 transformation.
Milkman (1983) has argued that a central demand we must make of any population genetics theory is that “…it should be able to predict changes in allelic frequencies and phenotypic values…” This task is a difficult one to say the least. If organisms are indeed as multi-levelled as suggested by Weiss, accurate genotype/phenotype transformations will be difficult to perform. Hence any accurate prediction of changes of gene frequencies seems highly unlikely.
Finally in an interesting paper Kempthorne (1983) has recently critically reviewed the state of population genetics theory. After making some important criticisms Kempthorne agrees that “We have been quite unable, except under very limited assumptions, to develop theory of long-term changes, which is what we need if we are to apply the ideas to evolution.” He finally remarks “The overall task is extremely difficult but it has to be attacked.” This is so only if one considers that the whole populatior genetics approach is valid.
Historically population genetics has grown out of attempts to reconcile Darwinian views with Mendelism which was originally regarded as a competing theory (Bowler, 1983). This is reflected in Kempthorne's (1983) remark “… the aim of population genetics theory is to give an empirically validated theoretical basis for the process described in verbal terms by Darwin … “Hence as Hitching (1982) has pointed out, population geneticists consider evolution to be their specific domain. This is partly because commonly accepted definitions of evolution have been framed in neo-Darwinian terms. Evolution is almost exclusively regarded as changes in gene frequencies. Kempthorne (1983) remarks on this point, “The whole problem of evolution revolves around the production of new genetic types and the fitness of the genetic types in the population”. However, as is commonly agreed, even by neo-Darwinists, it is the organism's form which is important. This is surely a view with which most working biologists are sympathetic. The emphasis on genes by population geneticists is rationalised
In contrast however, if we see evolution as a change in form rather than a strictly genetic phenomenon, a different view arises. Genes are surely a component in such a system, but evolution is not a population problem, and most especially not a population genetics problem. It is a problem of the origin of form and therefore can only be understood in terms of the laws governing form transformation (Lambert and Hughes, 1984;). These laws are quite distinct from those regarding the origin of genetic variation.
Where then is population genetics left? I do not think that it is left as a purely historically interesting science. I think that it has a place but a far more modest one. Population genetics can be useful, for example, in the detection of morphologically very similar species (e.g. Lambert, 1982), and perhaps it has limited uses in aspects of human genetics. It is simply that population genetics is not a tool to investigate evolution. This essentially represents a third view (in the sense of Macbeth's (1976) third position) of evolution, the first being creationism and the second being neo-Darwinism. This view has many similarities with Hitching's (1982) “New Biology” where, it is argued the study of development will reveal fundamental laws of form and transformation (Goodwin, 1982), as opposed to the neo-Darwinian view that the study of genetic variation (usually populations of adult individuals) is sufficient to explain evolution.
Present Address: Department of Zoology, Victoria University of Wellington, Private Bag, Wellington, New Zealand.
Croizat had a low opinion of
form that occur. Croizat, on the other hand, believed that evolution as a process could only be adequately analysed if, in addition to the consideration of change in form, one took account of the geographical space where those changes occurred and the time of their occurrence. In this way the evolutionary changes described are treated in an explicitly dynamic manner, and at least some of the details of the processes involved are also presented.
Croizat used the term ‘Panbiogeography’ to described his method of investigating evolution in terms of its three components—Space, Time and Form. Panbiogeography basically involves the analysis of living and fossil records of the geographic distribution of different taxa to enable the changes of location through time made by different forms to be mapped. This is not to say that the taxa always moved themselves around over the surface of the Earth, for the surface of the planet changes as well as the living beings on it. As Croizat would put it: Earth and Life evolve together.
Croizat considered this aspect of biogeographical studies to be self apparent and was highly critical of other schools of biogeographic thought, particularly the biogeographic theories developed in the context of Darwin's theory of evolution. Indeed, Croizat appears to believe that Darwin was greatly at fault for not developing the ideas of panbiogeography himself.
Croizat (1964, 1981) even attempted to explain why he thought Darwin failed to discover panbiogeography. He (1964:637) wrote that:
In this article (()) indicates a notation by the present author.“He ((Darwin))
could not do it because he was not born to it. He had a science of dispersal ready-made in his hand in 1845, but when he began to think of it in term ((sic)) of general ideas he cracked up on the spot.”
Whilst he accepted that Darwin was a ‘very able observer’, Croizat (1964:637) concluded that
“He ((Darwin)) was on the other hand congenially not a thinker.”
This paper has two aims. The first is to show that Croizat's low opinion of Darwin's ability as a thinker is wrong. This in itself is unimportant but the attainment of the first aim will be used as a vehicle to introduce and discuss particular aspects of Croizat's work, which is the second aim.
The aggressive style Croizat habitually used can sometimes be blamed for obscuring the otherwise clear argument he presents. In particular, the rhetoric Croizat used when he critised Darwin for not discovering panbiogeography can be considered to be propaganda, designed to shock people out of what Croizat clearly believed to be unfounded hero worship. Sadly, in this case, the apparent wish to discredit Darwin, combined with Croizat's particular view of science, appears to have led him to make claims about Darwin for which there is no solid foundation.
An analysis of the arguments and statements behind Croizat's conclusion (cited above) will show that he had an unorthodox understanding of what is referred to by the terms ‘theory’ and ‘explanation’. This, on top of his inductivist view of science, made Croizat blind to alternative interpretations of Darwin's writings.
In the analysis much use will be made of direct quotation. Hopefully, this will, at the same time, illustrate both Croizat's style and wit, as well as convince the reader that Croizat's views are not being misrepresented.
Croizat repeated on numerous occasions his claim that Darwin had been very close to discovering panbiogeography. He (1981:505-506) stated that:
“Although Darwin proved incapable of formulating a viable theory of dispersal in the quoted text ((Origin of Species, 6th edition)), he nevertheless was not far from achieving that viable theory that he so grandly muffed when opening the door to the concepts of centre of origin, migration, and its means.”
He went on:
“The difficulty in understanding an intricate process and the mind's natural repugnance for paradox, readily account for the fact that an author who, like Darwin, has the correct solution of a major problem almost within his grasp, may eventually flounder into the inconsequential and erroneous instead of driving straight over the last few yards that still separate him from his goal.” (Croizat, 1981:509).
Clearly, Croizat thought that if Darwin had been a thinker of any standing he should have been capable of producing the theories that were, in fact, left to Croizat to invent. That Darwin failed, given the information available to him, Croizat found incredible and is one of the reasons behind his low opinion of Darwin's intellect. He wrote (Croizat, 1981:509):
“Darwin was one of the first naturalists to discover and report vicariance, nearly a century-and-a-half ago. But this epochal discovery fizzled out in his hands in a remarkable, even incredible way.”
Having established that Croizat thought that Darwin was actually incapable of producing a theory of panbiogeography we can now attempt to answer the question of why Croizat should have had such an opinion. This will require a consideration of what Croizat took to be a valid explanation and how this differed from his view of what constituted a theory. Such a consideration is necessary because it will allow us to appreciate how Darwin was able, quite validly, to reach conclusions quite different from those that Croizat believed to be obvious. It is plain that Croizat did not appreciate that his scientific methodology affected his view of Darwin's work. It will be shown that Croizat was wrong when he stated that:
“It is incredible that Darwin, master of factual observations of paramount biological significance, proved unable to reach obvious conclusions;.… It is
muff what in restrospect seems unmuffable, but this excuse can hardly apply in Darwin's case.” (Croizat, 1981:514, my emphasis).
Croizat was an inductivist. This claim is supported by the fact that he praised and supported a statement by S. A. Cain which included the following (Croizat, 1964:595):
“What is most needed in these fields ((zoogeography and phytogeography)) is a complete return to inductive reasoning with assumptions reduced to a minimum and hypotheses based upon demonstrable facts and proposed only when necessary.”
Unfortunately, the problem of determining whether Croizat was an inductivist or not is aggravated by Croizat's unusual usage of the term ‘deductive’. He wrote about Cain's usage of the term:
“…deductive for Cain basically refers to arguments rigged up to bolster aprioristic, theoretical assumptions. I have used the same adjective—unconventionally—in connection with reasoning which deduces ((induces)) the necessary conclusions from carefully observed facts of nature.” (Croizat, 1964:595).
In another discussion of his usuage of the terms ‘inductive’ and ‘deductive’ Croizat wrote (1978:210):
“I have already acknowledged that I applied the adjective ‘deductive’ in a sense contrary to convention (Croizat, 1964:595). Hence my use of the word may be equivalent to the ‘inductive’ of the learned world—an inversion for which I stand guilty.”
But he continued by demonstrating that he recognized the differences between induction and deduction and even claimed to have used both principles in the development of his ideas.
However, after making this claim he stated that (1978:211):
“I think that drawing a sharp line between what really is, or only seems to be inductive and deductive, except in rigid logic, is difficult.”
From all of this it might appear that Croizat was eclectic in his approach to making inferences about natural phenomena; that he was neither an inductivist nor a deductivist.
However this may be, Croizat's view of what was implied when a theory was refuted demonstrates that he believed theories and explanations to be produced inductively. In a revealing passage Croizat discussed the significance of testing a theory against new data. He was disagreeing with S. J. Gould who wrote that (Croizat, 1981:502):
“We are always ready to watch a theory fall under the impact of new data, but we do not expect a great and influential theory to collapse from a logical error in its formulation.”
Croizat (1981:502) replied to this by stating:
“In contrast to Gould, I would be inclined to believe that a theory falls under the impact of new data precisely because it is vitiated by some (one or more) logical errors in its formation. In my thought, a theory anticipates what the facts, when fully known, will demonstrate to be correct. Its failure when the facts tell otherwise, points to a logical error in its formulation.”
This claim, by Croizat, means that all falsified theories must have collapsed due to logical errors in their construction. For this to be the case each general theory must have been induced from a limited set of facts. If such a theory is then shown to be false the logical induction which produced it must have been in error. Hence, if the theory is falsified it must
As well as being an inductivist Croizat also had a rather unusual understanding of the properties of explanations and theories. That this was so is best illustrated by a discussion Croizat made about Darwin's theory of coral-atoll formation. Croizat (1964:603) wrote about this theory:
“This explanation is often miscalled a theory which does not strike me as justified at all. The term theory has been of course used in so many different meanings that it can hardly be but shop-worn, but I should think that it can in no place apply to a rigorous demonstration by which something is finally explained that once was obscure and unknown. As the reader is soon to see, Darwin indeed explained atoll-making, which of course means that he did not only theorize on its account.”
It is difficult to understand how a theory can fail to be explanatory, even with an inductivist view of science. But Croizat appears to believe that theories are always speculative, untried entities which are of doubtful use owing to their not being based upon (induced from) carefully observed facts of nature. ‘Explanations’, however, because they are so based (in Croizat's opinion), may be treated with respect. If this is the distinction that Croizat makes then his choice of example is very unfortunate. Darwin wrote concerning his theory of atoll formation (Barlow, 1958:98):
“No other work of mine was begun in so deductive a spirit as this; for the whole theory was thought out on the west coast of S. America, before I had seen a true coral reef. I had therefore only to verify and extend my views by a careful examination of living reefs.”
There is, in fact, no logical distinction between scientific theories and hypotheses. They can both be modelled crudely by the simple statement: If G and C then P; where G is one or more general laws, C are the initial conditions relating to a particular instance, and P is the prediction deduced from G and C. If P should turn out to be the case then the statements in G, given C, are said to explain P. Thus, all theories and hypotheses must be explanatory if they are to be scientific (testable). This, of course, does not mean that they must also all be true for it is commonly the case that some aspect of an explanatory hypothesis turns out to be false; but, happily, the responses to such discoveries often lead to the growth of science. It must be remarked, for completeness, that it is also true that not all explanations are hypotheses.
However the case may be with Croizat, he certainly treated what he termed ‘explanations’ with respect whilst ‘theories’ were definitely frowned upon. An example of this can be seen in Croizat's continued discussion of Darwin's coral-atoll theory. Croizat was uncharacteristically complimentary about Darwin when describing this theory. The reason for this unusual praise is soon found. In Croizat's (1964:604) own words:
“Darwin's explanation—not theory of course; this explanation holds good today and so it will into the future, in principle when not in every detail—amounts to the affirmation of one of the cardinal axioms of (pan)biogeography which I have worded as follows: Earth and life evolve together.”
Croizat praised Darwin for this particular theory because it implied a principle very close to Croizat's heart.
We are now in a position to appreciate Croizat's anaylsis of Darwin's biogeographic theories. Croizat gives a detailed discussion of the treatment
Croizat reprinted the following passage from the 2nd edition of The Voyage of the Beagle (Croizat, 1981:513-514):
“It is the circumstance that several of the islands possess their own species of the tortoise, mocking thrush, finches, and numerous plants, these species having the same general habits, occupying analogous situations, and obviously filling the same place in the natural economy of this archipelago, that strikes me with wonder… The only light which I can throw on this remarkable difference in the inhabitants of the different islands is, that very strong currents of the sea, running in a westerly and W.N.W. direction, must separate, as far as transportal by sea is concerned, the southern islands from the northern ones; and between these northern islands a strong N.W. current was observed, which must effectively separate James and Albemarle Islands. As the archipelago is free to a most remarkable degree from gales of wind, neither the birds, insects, nor lighter seeds would be blown from island to island. And lastly, the profound depth of the ocean between the islands, and their apparently recent (in a geological sense) volcanic origin, render it highly unlikely that they were ever united; and this, probably, is a far more important consideration than any other, with respect to the geographical distribution of their inhabitants.”
Croizat (1981:514) had the following to say about this passage:
“He ((Darwin)) perceived the importance of vicariance as a fundamental law of nature; he saw that “species” and “subspecies” (understood in the usual taxonomic sense) could not be discriminated absolutely, inasmuch as their limits are subject to the play of individual opinion; and he adopted ther happy term “representative” as applied to species and subspecies. He was assured that casual means of dispersal among the islands were of little importance; he was satisfied that the plants and animals of the islands were basically American in their relationships. Thus, he had the whole of evolution and panbiogeography snugly in his hands in 1836. All that remained for him to do was to reason, from his own observations in the light of the axiom that earth and life evolve together, that it could not be true that the ocean unbounded lay forever there, where the Galapagos now stand; that the islands could not have originated burning and lifeless, from the depths of the eastern Pacific, but do on the contrary represent the fragments, altered by late vulcanism, of an earlier history, of a former extension of the American mainland.”
From this it is clear exactly what it was that Croizat wanted Darwin to produce from the evidence before him. To Darwin, however, it would have been far from obvious that the islands could not have originated ‘burning and lifeless’ from the sea. To him a volcanic oceanic origin for the islands was strongly supported by a number of different sources of evidence which he could not ignore. We can see from a number of passages that Croizat quotes from Darwin's The Voyage of the Beagle that Croizat was aware of this diversity of evidence (Croizat, 1964:610-611):
“Seeing every height crowned with its crater, and the boundary of most of the lava-streams still distinct, we are led to believe that within a period, geologically recent, the unbroken ocean was here spread out… Why on these small points of land, which within a late geological period must have been covered by the ocean, which are formed of basaltic lava, and therefore differ in geological character from the American continent,.… And lastly, the profound depth of the ocean between the islands and their apparently recent (in a geological sense) volcanic origin, render it highly unlikely that they were ever united;”
Croizat dismissed Darwin's claim that the Galapagos were never united with the mainland despite Darwin's appeal to a wide array of geological evidence. Commenting on Darwin's account of the biogeographic position of the Galapagos, which included the passages from Darwin just quoted, Croizat (1964:611) stated that:
“It is right that he ((Darwin)) had the facts well in hand before he ever began to think of “Transmutation of Species”. It is true that he assumed for these islands an “oceanic origin”, but it is also true that he was aware of much that would, quite factually, not give easy comfort to this understanding.”
By claiming that Darwin had only ‘assumed’ an ‘oceanic origin’ for the Galapagos, Croizat is effectively ignoring and denying the stratigraphic evidence which Darwin produced and had to account for. That Croizat failed to see that Darwin had not just assumed a recent volcanic origin for the islands, but had rather tested this claim against field evidence, is due to the strange distinction Croizat made between theories and explanations. Croizat appears to believe that Darwin had only theorized (equals speculated) about, and had not provided an ‘explanation’ of, the present day distribution of the Galapagos biota. Of course, there can be only one true explanation (although it may never be found) and Croizat presumably believed that this could be discovered using induciton. It would appear that because Darwin did not produce the same explanation/theory as Croizat, the latter dismissed Darwin's efforts as incompetent. In fact, Croizat's explanation of the dispersal of the Galapagos biota is only an alternative explanation to that proposed by Darwin. What is required, instead of rhetorical attacks on either Croizat or Darwin, is some way of distinguishing which of the theories should be accepted and which rejected; it would appear that in the case of the Galapagos a geological test is required.
Darwin was aware that more than one explanation for the same phenomenon was possible. A result of this is that he put forward a number of possible solutions to the problem of explaining distribution patterns. They all, however, have a common assumption and that is that the same species cannot have been produced independently in two or more different places. The idea that Darwin was opposing when he wrote his On the Origin of Species was the so-called theory of Special Creation. This piece of information is required if one is to understand some of Darwin's statements. Unfortunately, Croizat appears to forget about Darwin's opposition to Special Creation; he quotes Darwin's Origin (Croizat, 1981:503):
“We are thus brought to the question which has been largely discussed by naturalists, namely, whether species have been created at one or more points on the Earth's surface. Undoubtedly there are many cases of extreme difficulty in understanding how the same species could possibly have migrated from some one point to the several distant and isolated points, where now found. Nevertheless the simplicity of the view that each species was first produced within a single region captivates the mind. He who rejects it, rejects the vera causa of ordinary generation with subsequent migration, and calls in the agency of a miracle.”
Croizat takes this to be Darwin's claim that the same species cannot evolve independently in more than one region.
As long as Croizat did not accept that the same species could evolve independently in different places the differences between his view and Darwin's reduces to the simple one of how vicariant distributions arise. Darwin does not deny that ‘means of dispersal’ can operate to enable species to cross barriers to free range extension, whilst Croizat believes that they do so only rarely. On the other hand, Darwin did not restrict himself to such explanations. Croizat (1964:631) quotes Darwin as saying, in the 6th edition of the Origin of Species:
“It seems to me ((Darwin)), as it has to many other naturalists, that the view of each species having been produced in one area alone, and having subsequently migrated from that area as far as its powers of migration and subsistence under past and present conditions permitted, is the most probable. Undoubtedly many cases occur, in which we cannot explain how the same species could have passed from one point to the other. But the geographical and climatal changes which have certainly occurred within recent geological times, must have rendered discontinuous the formally continuous range of many species. ((This describes a mechanism which Croizat would surely endorse.)) … Whenever it is fully admitted, as it will someday be, that each species has proceeded from a single birthplace, and when in the course of time we know something definite about the means of distribution, we shall be enabled to speculate with security on the former extension of the land.”
Following this, Darwin could not deny that it was possible for a species to obtain a vicariant distribution without one of the populations involved migrating away from the other.
Croizat was wrong to reject Darwin's explanation of the dispersal of the Galapagos biota, for it was a valid explanation which has received some corroboration from the field evidence. A corollary of this is that Croizat was also incorrect in his claim that Darwin was incapable of thinking (reasoning validly). In the context of the level of scientific development of his day (particularly geology) Darwin would have had grave problems had he produced only a geological or geographical explanation of the production of vicariant distributions.
Croizat was mistaken in his criticism of Darwin because his views of science made it impossible for him to understand what Darwin was doing. The differences between the Darwinian and Croizat's approach to explaining dispersal need to be clearly and explicitly stated; for example, it is unclear whether or not Croizat accepted the assumption that the same species cannot evolve independently in two or more regions. Only after the identification of differences can tests be made to see which account provides the most accurate representation of the development of the world's biota.
I would like to thank both Grant Gillespie and
Notes on some Anthocerotae of New Zealand (4) pp. 105-120
Never a serious scientist: the life of
see also
Mayr vs Croizat: Croizat vs Mayr — an enquiry pp. 49-66.
Some quotations from his works concerning “Laws of Growth”, compliled by
Introduction (to special issue “Croizat's Panbiogeography & Principia Botanica”) p.3.
Evolution by law: Croizat's “Orthogeny” and Darwin's “Laws of Growth”. pp. 14-19.
Was Darwin congenitally incapable of valid thought? pp. 127-133.
Principia Botanica: Croizat's contribution to botany. pp. 26-48.
Bibliography of the scientific work of
Population genetics and the ‘third view’ of evolution, pp. 121-126.
Introduced birds and mammals in New Zealand and their effects on the environment. pp. 77-104.
Never a serious scientist: the Life of
Principia Botanica: Croizat's contribution to botany, by
Bibliography of the scientific work of
Was Darwin congenitally incapable of valid thought?, by
Evolution by law: Croizat's “Orthogeny” and Darwin's “Laws of Growth”, by John R. Grehan, pp. 14-19.
see also
and Mayr, Ernst
and Population Genetics
Introduced birds and mammals in New Zealand and their effects on the environment, by
Notes on some Anthocerotae of New Zealand (4) (genus Megaceros), by Ella O. Campbell, pp. 105-120.
Mayr vs Croizat: Croizat vs Mayr — an enquiry, by
Population genetics and the ‘third view’ of evolution, by