Tuatara: Volume 23, Issue 2, July 1978
Two Biogeographical Frameworks: Implications for the Biogeography of New Zealand. a Review
Two Biogeographical Frameworks: Implications for the Biogeography of New Zealand. a Review.
‘Biogeography is like chess: he who really understands the game can tell in a matter of a few moves whether he stands before a genuine master or a pretentious patzer.’
— Croizat, 1977: 231
Biogeography is the study of the distribution of organisms upon the surface of the globe. It can be divided into historical and geographical/ecological biogeography: ‘… if our time scales are broad, then we are concerned with the subject matter of historical biogeography; if narrow, then it is the subject of geographical ecology that is of most interest.’ (Cracraft, 1974: 215). Biogeography is often divided into phytogeography (plants) and zoogeography (animals) but as the problems both face are essentially the same the division is not recognised in this paper. (See Croizat, 1958; Fleming, 1962, and Banarescu, 1975, for further discussion of this.)
Since the inclusion of two chapters on ‘Geographical Distribution’ in ‘The Origin of the Species by means of natural selection’ (Darwin, 1859) animal and plant distributions have usually been interpreted within the context of the ‘centres of origin’ concept. Darwin believed that species originated in centres from which they dispersed by either passive or active dispersal mechanisms:
‘When we feel assured that all the individuals of the same species, and all the closely allied species of most genera, have within a not very remote period descended from one parent, and have migrated from some one birth-place; and when we better know the many means of migration, then, by the light which geology now throws, and will continue to throw on former changes of climate and of the level of the land, we shall surely be enabled to trace in an admirable manner the former migrations of, the inhabitants of the whole world.’(‘Origin’, Chap. XV)
Darwin's biogeographic concepts were expanded and elaborated by a number of subsequent authors in books and papers which have had a significant impact on the development of biogeography. Some of the most important of these are ‘The Geographical Distribution of Animals’ (Wallace, 1876), ‘Island Life’ (Wallace, 1880), ‘Climate and Evolution’ (Matthew, 1915), ‘Antarctica as a faunal migration route’ (Simpson, 1940b), ‘Zoogeography: the geographical distribution of animals’ (Darlington, 1957), ‘Biogeography of the southern end of the World’ (Darlington, 1965), ‘Island Biology’ (Carlquist, 1974) and ‘Marine Zoogeography’ (Briggs, 1974). The fundamental assumptions underlying all Darwinian biogeography as noted by Croizat (1968a: 430) are. ‘(1) every taxon — the species first and foremost as the paragon of biological origin and related questions — comes into being in a center of origin of its own; (2) if “successful” it sooner or later outgrows it, and undertakes migration in order to occupy other regions of the earth, whether near or far; (3) the migration is accomplished thanks to appropriate means of dispersal. Since it is normal to find that plants and animals lacking said means are very widely distributed the conclusion is normally reached by orthodox — so called — phytogeographers and zoogeographers that means of dispersal are essentially mysterious.’
The centres of origin concept was challenged as early as 1901 (Croizat et al., 1974) but the concept was not critically analysed until the early 1940's in the work of Cain (1943, 1944). Cain demonstrated that none of the 13 criteria advanced for recognition of a centre of origin were of any real value in biogeographic studies.1 Cain's criticisms were to a large extent responsible for the rejection of the concept of dispersals from centres of origin by Leon Croizat and his formulation of the alternative vicariance approach to biogeography (Rosen, 1974a). Croizat has presented his views on the historical biogeography of terrestrial and marine biotas in five major works: ‘Manual of Phytogeography’ (1952), ‘Panbiogeography’ (1958), ‘Principia Botanica’ (1960), ‘Space, Time, Form: the biological synthesis’ (1964) and ‘Biogeografia analitica y sintetica (“Panbiogeografia”) de las Americas’ (1975) — and numerous papers. Vicariance biogeography basically conceives of present day biotic patterns as having arisen from the fragmentation of ancestral biotas due to geological and geographical change.
Croizat's work finds its immediate historical roots not only in the work of Cain but also in Rosa's theory of hologenesis (i.e. primitive cosmopolitanism of life) and two works by Andersen (1908, 1912) on bats. Biogeographical implications of hologenesis are that:
‘Orthodox biogeography is monogenetic, it states that each species and each group of species arises from a small number of individuals, in a very small area (center of origin), from which the species (or group) spreads by active or passive migrations, over the whole area of page 83 distribution — an area which, in general, was formerly much wider than at the present time.
‘Hologenesis on the other hand, is extremely polygenetical and leads to a biogeographical theory which is opposed to the former one. Without denying migrations, hologenesis ought to make as a basic principle of biogeography not a distribution arising from different centers, but a primitive cosmopolitanism succeeded by a process of localisation taking place at the same time as the multiplication and differentiation of species.
‘Working from this basis we are able, without always resorting to often unlikely migrations and without having to invent continents to explain very satisfactorily how sometimes the same species and more often different species of the same genus or family can turn up in zones which are distant from one another and discontinuous.'
(Rosa, 1933: 120)
Croizat (1963: 93) considered that Andersen's work on bats was ‘a model of biogeographic method and analysis’. During a period when Gadow (1913) and Matthew (1915) were advocating extensive migrations/dispersal of animals Andersen (1912) was astute enough to comment: … that the spreading of bats from one locality to another must obviously have been greatly facilitated by their possession of wings, may in theory appear plausible enough, but when tested on the actual distribution of the species and subspecies it proves to be of much less importance than commonly supposed; it rests, in reality, on a confusion of two different things: the power of flight no doubt would enable a bat to spread over a much larger area than non-flying Mammalia, but, as a matter of fact, only in very few cases is there any reason to believe that it has caused it to do so' (p. lxxvii) and ‘… the present distribution of the Megochiroptera has not been influenced to any great, and as a rule not even to any appreciable extent by their power of flight …’ (p. lxxviii).
Centres of Origin, Southern Hemisphere Biogeography, Continental Drift and New Zealand
‘During the past 5 years, however, the emergence of the theory of plate tectonics has provided a better understanding of the history of the earth's crust and, hence, a more reasonable basis for explaining many problems of biogeography.’
(Raven and Axelrod, 1972: 1379)
‘I have never been able to understanding why certain authors erected continental “drift” or the like into paragons of biogeography. Whether the Bay of Bengal came about because the Deccan and the Indo-Chinese Peninsula, respectively, did drift apart, or whether land once in between its current shores crumbled, is not a question to interest the student of dispersal very deeply. The student takes stock of the page 84 records of the geographic distribution of plants and animals, and objectively analyses them on a comparative basis, drawing the conclusions which the facts advise and common sense endorses.’
(Croizat, 1968b: 578)
One of the major problems in biogeography is finding an explanation for the faunal and floral resemblances between widely separated tropical and Southern Hemisphere temperate regions. There are two major ‘schools’ of thought on this problem: one, which traces the origin of its concepts of land connections of some sort during previous geological periods back to the work of Hooker in the 1850-60's (Hooker, 1860); and the other, which derives its view that present patterns of plant and animal distribution can be explained by progressive dispersal of life from an Holarctic center of origin along three independent routes into South America, Africa and the Indo-Australian region over a geography that is essentially modern from statements made by Darwin in chapter twelve of ‘The Origin of Species’.
Darwin believed that cold, glacial periods drove organisms from areas around the north and south poles into equatorial regions where they mingled together. When climatic conditions improved northern organisms were able to migrate southwards with the southern organisms; but southern organisms were unable to migrate into the Northern Hemisphere. This inability of southern life to migrate northwards he attributed to the great competitive, and hence ‘dominating’ powers of the northern organisms, such ‘powers’ having evolved in the northern plants and animals because they occupied the much larger land-mass areas of the Northern Hemisphere. Similarities between, and the presence of related organisms, in two or more of the Southern Hemisphere land areas was attributed to long-distance dispersal across water gaps.
Wallace (1876) presented the view that organisms had dispersed within the Holarctic region from Eurasia (Palearctic) to North America (Nearctic) via the Bering Land Bridge. From here animals migrated into South America, while they also migrated from Eurasia into Africa and along the Indonesian chain of islands into the Australasian region. Wallace (1880) adhered generally to a permanence of continental areas but was prepared to accept ancient land connections with regard to New Zealand and the Celebes which he class as anomalous islands.2
Matthew (1915) developed these ideas even further. According to Matthew the main groups of vertebrates arose in centres of origin in northern parts of the Holarctic and dispersed southwards along the three independent routes mentioned above. He believed that (1) animals disperse from large areas, into small areas, of land; based on the assumption that animals tend to disperse from continents to islands and not vice-versa, and (2) Matthew considered that alternations of arid and cold climatic zones in Holarctica resulted in the page 85 evolution of more competitive forms of life, i.e. inhospitable climates increase the force of natural selection and hence more progressive/advanced forms of life evolve in such areas. Because he believed in the permanence of continents and oceans the fact that there is more land in the Northern Hemisphere meant that animals dispersed from these regions into the smaller southern areas. New and more progressive animal forms evolved in northern areas, replacing the older primitive forms. These older forms were driven outwards from their centres of origin and survived as relict groups in the Southern Hemisphere.
Darlington (1957, 1965) modified Matthew's area-climate view of animal distribution. Arguing from the observable facts that larger land areas have more animals and that areas of favourable climate have more animal diversity, he suggested that animals disperse from large to small areas and from favourable climatic to unfavourable climate areas. Matthew's idea of dominant, competitive forms evolving under adverse climatic conditions was rejected by Darlington who argued that such conditions would result in cold-adapted tolerant forms. Darlington believed that dominant, more competitive forms evolved in warm climatic regions. Being an aprioristic believer in continental permanence (he admitted the possibility of continental drift/rafting in 1965 but so long ago that it could not have affected animal distribution) Darlington put forth the view that vertebrates (1957) and some invertebrates (1952, 1965, 1971) arose in the Old World tropics and dispersed from this centre of origin along three independent routes.
Simpson (1940 a and b) argued that marsupials had entered both South America and Australia by northern routes of entry. He also (1952) held that any biotic resemblances between widely separated continental areas could be explained in terms of the probability of long-distance dispersal.
All the above views depend on the idea of the permanence of continents and oceans through time. The recent widespread acceptance of the concepts of plate tectonics and continental drift/rafting have resulted in numerous reinterpretations of animal and plant distribution.3 For instance certain groups of carabid beetles considered by Darlington (1965, 1970) to illustrate his views can have their present distribution satisfactorily explained in terms of plate tectonics (see e.g. Jeannel, 1961; Noonan, 1973). Keast (1973) in an analysis of contemporary biotas showed that they were not inconsistent with what we know of the breakup of the large, original land mass Pangea and the two smaller super continents. Laurasia and Gondwanaland. A number of authors (e.g. Brudin, 1966, 1972; Cracraft, 1973 a and b, 1974; Fooden, 1972; Jardine and MacKenzie, 1972; Raven and Axelrod, 1972; Schuster, 1976) have interpreted present-day plant and animal distributions in terms of continental drift. Some (e.g. Brundin, 1966; Cracraft, 1973 a and b) postulate a southern origin page 86 for a number of groups and claim that these migrated northwards from an austral centre of origin. This apparently contrary view to the traditional Matthew/Darlington school is largely due to differences in systematic philosophy: the traditional school holding that primitive forms of a group disperse away from the centre of origin into peripheral areas and so are more likely to disperse, while Brundin (1966) maintains that primitive forms are less likely to disperse and hence remain nearer the centre of origin than advanced forms.
Despite the controversy between the advocates of these two viewpoints in recent years the differences that exist are not as significant as they appear to be from the polemical publications of Brundin (1972) and Darlington (1970). As correctly noted by Cracraft (1975), both involve the concept that as organisms evolve they disperse over the globe. Both schools have as their basis the recognition of centres of origin, dispersal mechanisms and pathways of dispersal, and interpret the biogeographic history of taxa within the context of this framework. Those who support continental drift as the key to historical biogeography merely apply the centre of origin/dispersal framework to a mobilist concept, as opposed to the Matthew/Darlington stabilist concept of past geography (Nelson, 1975). However, Matthew/Darlington biogeography is not incompatible with continental drift concepts. McKenna (1973) attempts a reconciliation and Noonan (1973) notes that Gondwanaland satisfies the criterion for Darlington's large land mass with favourable climates.4 Horton (1974), however, has challenged Darlington's dominance views and noted a number of cases where he considers animals have dispersed from small into large land areas.
Darwin, Hooker and Wallace discussed the origins of the New Zealand biota in their work. Hooker (e.g. 1860) considered that an Antarctic continental extension was needed to explain the similarities between the plant life of New Zealand, South America and the Sub-Antarctic Islands. Darwin regarded New Zealand as an ‘oceanic’ island, populated by dispersal over the sea, but he had doubts: ‘It is only against the former union with the oceanic volcanic islands that I am vehement. What a perplexing case New Zealand does seem: is not the absence of leguminosae, etc. fully as much opposed to continental connection as to any other theory? … The presence of a frog in New Zealand seems to me a strongish fact for continental connection, for I assume that seawater would kill spawn, but shall try.’ (Darwin, 1903: 418)
Hutton (1872: 228) disputed the Darwinian classification of New Zealand as an ‘oceanic’ island and commented that ‘The New Zealand fauna may be correctly called the remnants of a continental fauna.’ He attributed the origin of the New Zealand fauna and flora to migration across landbridges into New Zealand. In 1872 Hutton proposed that in the lower Cretaceous period an Antarctic continent extended northwards into Polynesia, connecting page 87 Australia with South America and perhaps South Africa; but in an important paper published in 1884 he wrote:
‘I now abandon the idea of an extensive Antarctic continent, because the soundings that have been lately taken in the Pacific Ocean have shown that such a supposition is highly improbable. At the same time, these soundings have made it clear how the connection really took place.’ (pp. 7-8.)
His mature view was that:
‘New Zealand, which formerly existed as the southern part of a continent extending through Australia to India, was isolated from Australia towards the close of the Jurassic period, but was attached to a South Pacific continent and received a stream of immigrants from the north. None arrived from the south because Fuegia was not then in existence. In the upper Cretaceous the land shrank to a size considerably smaller than at present. In the Eocene, elevating took place and New Zealand extended outwards in all directions but remained isolated from other lands. Plants and animals came in both from the north and from the south. In the Oligocene and Miocene periods New Zealand was, except for a short interval, a cluster of islands, but was upraised once more and obtained more immigrants from north and south during the Pliocene.’ (p. 273.)
Hutton conceived of biotic immigration into New Zealand as a series of ‘waves’ rather than as a continuous process and although Darwinian in his attribution of organisms to centres of origin outside New Zealand he was strongly opposed to long-distance transoceanic dispersal:
‘Our fauna and flora is indeed a standing protest against the views of those naturalists who would make the winds scatter abroad insects and seeds of plants over hundreds of miles, and who imagine land shells and lizards to float about on logs for days and weeks together without being killed.’ (p. 274.) Hutton's views on land connections as opposed to transoceanic dispersals to account for the New Zealand biota were supported by von Jhering (1892) and Hedley (1899).
Around the time that Hutton was invoking landbridges Wallace (1876) attributed the origin of New Zealand birds (‘still less does any other form of animal inhabiting New Zealand require a land connection with distant countries to account for its presence’, p. 431) and insects (‘The poverty of insect life in New Zealand must therefore, be a very ancient feature of the country, and it furnishes an additional argument against the theory of land connection with, or ever any near approach to either Australia, South Africa or South America’, p. 463) to trans-oceanic dispersal. Wallace later (1880) changed his views somewhat and accepted land connections between New Zealand and other land areas though at ‘a very remote epoch’.
Cockayne (1958) and Oliver (1925) both interpreted the origins page 88 of the New Zealand biota in terms of land connections and transoceanic dispersal. Most of the flora was believed to be derived from migration across direct land connections to the north up to the end of the Cretaceous period and by overseas migration from Australia, Tasmania and Antarctica when land in the New Zealand area was of continental dimensions and the Antarctic extended to the north within a few hundred miles of the New Zealand continent (Oliver, 1925). Then ‘On the breaking down of the land connection to the north the exchange of species between New Zealand and other countries was confined to such as could by chance cross a considerable stretch of ocean.’ (Oliver, 1925: 137.) Oliver also held that ‘The New Zealand continent not only received but gave to neighbouring lands some of its productions.’ (p. 137.)
In a series of papers Fleming (1949-76) and to a lesser extent Gaskin (1970, 1975) systematised and concretised a centre of origin dispersal framework as the biogeography of New Zealand. Fleming's method has been to group New Zealand organisms into categories according to his understanding of their presumed centres of origin.5 Fleming distinguished his categories according to the following criteria:
‘In this paper the term “element” is used for the sum total of organisms that came to New Zealand along a given dispersal avenue, but ecological bonds between the different organisms that used the same dispersal avenue are neither implied nor denied. Classification of organisms by dispersal avenues implies their immediate place of origin, but not their ultimate place of origin.’ (Fleming, 1963a: 15).
Three dominant elements — the Malayo-Pacific, the Austral and the Australian — are recognised and these ‘correspond with dispersal avenues that are still to some extent open, and with mechanisms that are still operating’ (Fleming, 1963a: 17). Less important elements (Fleming, 1975: 72) are: the Endemic element — ‘Groups that have no close relations in other countries to indicate their place of origin’; the Holarctic element — ‘A few organisms related to northern temperate forms, absent in the intervening tropics’ and the Cosmopolitan element — ‘Organisms so widespread that their particular route of colonization cannot be determined on available evidence’. The Austral element is subdivided (Fleming, 1962; 1975: 71-72) into Neoaustral (‘distributed by the West Wind Drift of air and sea’) and Paleoaustral (‘plants and animals more distantly related to those of other southern lands … which are no longer being dispersed … and which have such poor dispersal abilities that many biologists have considered they were distributed along land connections linking southern lands with Antarctica.’ Fleming (1963b: 382) clearly supported overseas dispersal for both the Paleoaustral and Neoaustral elements: ‘If the podocarps, Sphenodon, the frog Leiopelma, many invertebrates, Nothofagus, and perhaps ratite birds walked into New page 89 Zealand (and some of these organisms also into Australia) across an Antarctic landbridge from South America, lasting at least into the middle Cretaceous, we are left with problems almost as great as those solved. What kept out the land dinosaurs, the early mammals and the snakes from New Zealand? This question, rather than any geological or geophysical difficulties, inclines the writer to give wavering support to the view that the dispersal of Paleoaustral organisms, like that of the Neoaustral element, was across the sea.’
In his 1975 paper Fleming accepted that New Zealand was once part of Gondwanaland but continued to attribute at least some of his Paleoaustral element to trans-oceanic dispersal:
‘Some Paleoaustral organisms (e.g. Fuschia and the extinct penguins) were certainly distributed across the sea like their Neoaustral successors.’ (p. 76).
His views have been modified further in a recent paper and the Paleoaustral element is now attributed to overland dispersal(?):
‘New Zealand seems to have once shared with its neighbours common groups of plants and animals like the conifers Araucaria and Agathis and podocarps of several generic groups, the tuatara, … primitive frogs, ratite birds … and perhaps also lungfishes and monotremes. Most fragments of Gondwanaland seem to have remained fairly close until after early flowering plants such as the Southern Beech (Nothofagus) dispersed… . Many of the plants and animals common to Australia, New Zealand and South America probably dispersed at this time, including many invertebrates, such as those of the forest floor litter.’ (Fleming, 1976: 346.)
The Neoaustral element (‘though it is hard to know where to draw the line between these two groups’ p. 347) is still attributed to dispersal in the West Wind Drift.
Gaskin enthusiastically embraced both Fleming's biogeography (1970) and continental drift (1975). The origin of the New Zealand biota is seen within the context of three dispersal routes — ‘across the Tasman Sea from eastern and southern Australia and Tasmania, along the Melanesian Arcs and from Antarctica and South America’ (1970: 434). New Zealand is seen as ‘an island archipelago far enough removed from the nearest landmass to be considered oceanic, but with a large enough surface area to allow prolific speciation and evolution in isolation at least to the generic level. Although a number of ancient endemic elements of uncertain affinities exist, the majority of the precursors of present taxa came from outside New Zealand by way of pre-Cretaceous direct land connections of early and mid-Tertiary archipelogic links or of transoceanic dispersal by air or water throughout the history of the archipelago’ (1970: 434). Gaskin (1975) accepted continental drift but commented: ‘Providing the concepts of continental rifting and actual drift are not confused, new data from sea-floor or spreading and application of tectonic page 90 plate theory to the area do not very appreciably alter the previously published picture of the New Zealand Mesozoic largely developed by Fleming. In fact the fit between geological and biogeographical phenomena of the New Zealand region is improved’ (p. 94). These biogeographical phenomena that are vindicated by recent geological evidence according to Gaskin (1975: 87) are (1) ‘most precursors of present taxa probably originated outside New Zealand’ and (2) ‘The assembly of taxa was considered to have taken place over a time scale that allowed for migration over possible Paleozoic and early Mesozoic connections to other land masses, and via early to mid-Tertiary archipelagic links. Trans-oceanic dispersal by air and water from neighbouring continental areas and islands was thought to have played quite an important role at all times in New Zealand's history in assembly of the disharmonic fauna and flora of the Archipelago.’
To some extent Gaskin is quite correct in stressing the compatability of centres of origin/dispersal biogeography with continental drift. Just as landbridges, continental drift or expanding earth hypotheses are conceptually similar so are centres of origin/dispersal/migration frameworks; whether or not the migrations took place over dispersal avenues, along landbridges, joined continents, archipelagic chains or long-distance dispersal over water is irrelevant. It is illuminating to compare Fleming's (1962. 1975) conception of the origins of the New Zealand biota with e.g. Schuster's (1976) continental drift interpretation for certain plant groups.6 Similar dispersal routes are merely transferred from a stabilist to a mobilist view of past geography: ‘Numerous studies, especially recent ones that attempt reinterpretations of stabilist biogeographic patterns in terms of the newer data on continental drift, have been based on prior conceptions about world geography and not on the patterns exhibited by the organisms themselves’ (Cracraft, 1975: 235).
For over 100 years New Zealand ‘biogeographers’ have been preoccupied with irrelevant questions. They have approached the imposing amount of data that we possess concerning the distribution of life through a variety of geological preconceptions. Cockayne (1958: 418) commented: ‘The matter of ancient land connections, where there are now profound ocean depths, is the burning question in New Zealand biogeography.’ New Zealand ‘zoogeographers’ such as McDowall (1973: 91) have stressed the essential dependence, in their view, of biogeography on geological preconceptions: ‘Darlington, told by geologists that the continental positions had not changed, had to rationalize the distribution of animals on this basis. Now we are told that the continents have dispersed away from Gondwanaland, a large southern continent, and we will now have to establish a whole new set of rationalizations.’
Few (if any?) of those who have contributed to the annals of New Zealand biogeography appear to have taken seriously the page 91 following penetrating admonition of Skottsberg (1928: 914): ‘When confronted with a particular insular flora like that found on many islands in the Pacific our first thought invariably is: Where did it come from? and How did it get there? In our eagerness to answer these questions and our impatient desire to explain everything we have tried to form theories before enough is known not only of the geology and physical geography of the Pacific but even of the plants themselves, their taxonomy and geographical distribution. I am afraid that this is attacking the problem at the wrong end. It even may be worth while to ask why we always assume that everything there is in the Pacific must have come from some distant place. Nobody asks where the Chinese, or Malayan or Brazilian floras come from. We are quite satisfied to believe that they develop right where they are, that their early history goes back so far that it is useless, for the present at least, to ask any but general questions as to their origin.’ To such criticisms the orthodox biogeographer usually responds as follows: ‘He knows already that dispersal is the byproduct of “causal agencies”, of “distribution”, colonizing flights, “double invasions”, powers to cross salt water; he has read plenty of “authoritative” literature; he may even know everything of “darwinism”, “New Systematics”, etc. When coolly told that nearly everything of it … is worthless he cannot believe. Why? Darwin said it, Wallace did confirm it, Matthew repeated it, and so did Mayr, Guppy, etc., etc., between 1859 and this very day’ (Croizat, 1960: 1519).
Vicariance biogeography, as developed by Leon Croizat, frees the biogeographer from adherence to particular geological models and presumed centres of origin. It allows the biogeographer to construct hypotheses using the data of biotic distribution which can then be tested against a variety of geological hyptheses.
New Zealand biogeographers need no longer act as mouthpieces for Charles Darwin:
‘My chief qualification to present a lecture on this topic is that I am a thorough-going and unashamed Darwinian in my beliefs and in my approach to Natural History. Having said this, I can retire from the scene, except as a mouthpiece for Darwin and his contemporaries, for my intention is to present for your consideration an address composed very largely of quotations from Darwin's letters and books, and New Zealand illustrations of the principles he did so much to establish, some of them from work with which I have been associated’ (Fleming, 1958: 65).
The Two Frameworks: Areas of Conflict
‘Inferences in zoogeography are based on the proper evaluation of three sets of information: (a) the relative age of page 92 various taxa, (b) the determination of the dispersal capacity of taxa, and (c) the distribution of related taxa.’ Mayr (1965: 475).
‘… I trenchantly affirm (1) a botanist or zoologist does emphatically not venture on thin ice when he trusts the records of extant distribution. Beyond these records and the facts they display, nothing exists of which scientific biogeography may primarily take account. What is alive today will be fossil tomorrow, but, when fossil will not amount to a meagre fraction of its self alive; (2) living entities demonstrably go back to geological ages past.’ Croizat (1968b: 576).
‘The “zoogeographic” (and “phytogeographic”) approach is as follows: Hawaii is imagined in the very first place as the navel of the world in relation to a particular distributional “problem”, and its life is next subjected to dissection to find out what part of it is “oriental/polynesian”, “hawaiian (endemic)”, finally “american”. This established to the personal satisfaction of the inquirer, the “zoogeographic” and “phytogeographic” conclusion is next reached that Hawaii has received so many “casual colonizations” via the Western or the Eastern Pacific as the case may be — Hawaii, of course, is by “zoogeographic” pre-definition “oceanic” — and that, accordingly, this “proves” Hawaiian life to have “originated” from the Americas or from the Orient/Polynesia via “transoceanic conveyance”, whether by “rafts”, “stratosphere”, “endozoic means” and all the like.’ Croizat (1958; Vol. 1: 852-53).
The basic differences between the two biogeographical frameworks have been briefly covered above. In this section the differences between the two will be considered in detail with emphasis on the vicariance approach of Croizat.
A vicariance biogeographic model has as its basis the premises: (1) that distributions of a group can be represented as tracks connecting the range of all members of the group and (2) the overlap in individual tracks between two areas is a generalised track that represents the distribution of an ancestral biota that has been vicariated into two daughter biotas. Overlap of generalised tracks or the non-occupation of part of a generalised track is seen as evidence for dispersal. Croizat et al. (1974: 278) comment: ‘The general phenomenon of sympatry, including all cases of overlap (or coincidence) of distribution of unit taxa (definable, named populations) is itself evidence of dispersal. Sympatry is more prevalent among the members of more distantly related and therefore, relatively older taxa, e.g. between a fish species and a crustacean species. We assume that most sympatry of this sort, between distantly related species, was caused by dispersal in the remote past, before the formation of the most recent ancestral biotas, as estimated by the page 93 generalized tracks displayed by the modern world biota… . But regardless of the extent of broad sympatry (evidence of significant dispersal), we consider that vicariance underlies and antedates nearly all cases of sympatric distributions. Current practice in biogeography, however, involves an initial assumption of dispersal from a center of origin. But is it not reasonable that, before the causes and means of dispersal may be investigated in any specific case, evidence should first be found that dispersal has occurred?' It should be apparent by now that the concept of allopatric speciation is central to vicariance biogeography.
That a pan-Austral biota appears to exist was recognised over a hundred years ago (Hooker, 1860). This biota consists of not only the well known terrestrial plants and animals but freshwater organisms (recognised in a little known review by Brehm, 1936) and probably marine organisms as well. Within a vicariance framework this biota can be explained as the result of the breakdown of a widespread ancestral Gondwanaland biota, as opposed to dispersal from centres of origin whether trans-oceanic in the West Wind Drift, or overland via landbridges or joined continents. ‘There is no longer question here, with “migrations” over a “transtropical” connection, purely and simply of vicariant form-making in immobilism out of the ranks of ancestral populations antedating modern genera and species’ (Croizat, 1964: 285).
Freshwater groups in the New Zealand fauna that could be attributed to vicariance of an Austral biota include chironomid midges (Brundin, 1966), caddis-flies (Ross, 1976), mayflies (Edmunds. 1972, 1975; Tsui and Peters, 1975, stoneflies (lles, 1965; McClellan, 1975), nannochoristine mecoptera (Edmunds, 1975), Archichauliodes (Megaloptera), parastacid crayfish (Jeannel, 1967), numerous freshwater crustacea (Brehm, 1936), mussels (McMichael, 1958), planarian worms of the genus Neppia (Ball, 1974) and galaxiid fishes (Rosen, 1974b). There is no need to invoke southern dispersal routes via Antarctica from a South American (or other) centre of origin, as the majority of the authors cited above have, to explain the presence of these organisms in New Zealand. Edmunds (1975: 258) notes: ‘Whole communities of aquatic insects are seen to show the same geographic pattern. This pattern suggests strongly the past division of a single biota.’ Particularly relevant is the observation of Riek (1970) that adult nannocharistine Mecoptera do not disperse more than a short distance from the larval habitats.
The terrestrial biota could have included besides the well known members of about 49 families of seed plants (listed in Croizat, 1952), a large number of bryophytes (Schuster, 1976) and the following invertebrates: Peripatopsidae (Jeannel, 1967), the isopods Styloniscus and Notoniscus (Green, 1974), many spiders (Forster and Wilton, 1973), numerous groups of Carabid beetles (Jeannel, 1967), beetles of the pselaphid tribe Faronini (Jeannel, 1967), bugs of page 94 the families Enicocephalidae (Woodward, 1956) and Peloridiidae (Evans, 1959a), tabanid flies (MacKerras, 1957), solitary bees of the tribe Halictini (Moldenke, 1976) and proctotrupoid wasps of the family Scelionidae (Masner, 1968). Particularly interesting potential members of the ancestral biota are Nothofagus and intimate insect associates (Schlinger, 1974) and leaf hoppers of the tribe Cephalelini (Evans, 1959b) host specific on the monocot family Restioniaceae (Cutler, 1972). The radical difference between centres of origin/dispersal and vicariance biogeography is seen clearly in a comparison of the interpretations of Nothofagus by Schuster (1976) and Cracraft (1975) who both accept continental drift. Schuster (1976) traces Nothofagus to a North American centre of origin and then conceives of migrations southwards into South America, across Antarctica and up into the Australasian region. Cracraft (1975) conceived of common ancestors of the four Nothofagus species groups distributed over the various land areas where they now occur plus Antarctica prior to continental breakup. As a consequence of his hypothesis he stated that ‘… it is not necessary to advocate wholesale long-distance dispersal to account for the distribution of the genus around the southern end of the world’ (p. 248).
The New Zealand vertebrate fauna is traditionally seen as a waif biota (Caughley, 1964); ‘I think the evidence is strong that all the plants and animals that have reached New Zealand have done so across water’, Darlington, 1965: 107). Despite this interpretation the following New Zealand vertebrate groups could be descendants of an ancestral biota common to New Zealand, West Antarctica and southern South America (Cracraft, 1975): frogs of the family Leiopelmatidae, ratite birds of the infra-order Apteryges and penguins in the family Spheniscidae, while the diplodactyline gekkos could be traced back to a more widespread biota involving Australia too. Neither should the New Zealand skinks7 nor a large portion of the flying avifauna be excluded from the possibility of a general vicariance explanation. Croizat (1958: chapters XII-XIV) has analysed in a most suggestive manner a large number of bird groups whose distribution in the South West Pacific is usually attributed to trans-oceanic dispersal and the West Wind Drift.
The following statement by Deignan (1963: 268) is pertinent: ‘… when we make the mental effort to accept the fact that every fossil and every existing organism is merely the latest of almost countless links in a chain of earlier and gradually changing organisms, and that the earlier ancestral forms were already existing and presumably dispersed prior to the appearance of modern geography, the distribution of the Polynesian fauna whether represented by a flycatcher in the Palaus or a moa in New Zealand, whether by a frog in the Fijis or a flightless insect on Easter, may be readily explained.’
Generalised tracks for the world's biota have been constructed, following painstaking analysis of hundreds of animal and plant page 95 distributions, by Leon Croizat in his masterly synthesis of biogeography (1952-75). When consulting the maps in Croizat's work illustrating these tracks it is important to bear in mind the definition of a track (Croizat, 1960, 1615): ‘A “track” is expressed by a line on the map along which forms of closely related affinities are found. A channel of the kind should of course not be understood as tantamount to a line of flight and the like. Whether at sea or overland, a “track” stands for a chain of centers of form-making and distribution; each center arisen by fragmentation of the range formerly held by ancestors on a lower level of evolution than their descendents.’
Orthodox biogeography accords special weight to fossil evidence: ‘The classification of New Zealand organisms into biotic elements from their geographical affinities can be combined with paleontological data on their probable age in the biota to give a picture of changing biogeographic influences in later Mesozoic and Cenozoic time’ (Fleming, 1975: 76).8 On this basis some of Fleming's Neo-austral elements are stated to have dispersed late in geologic time because of their relatively recent appearance in the fossil record. Darlington 1957: 35) considers that in zoogeographic studies ‘The best clues, of course, are fossils — the right fossils in the right places — but even fossils must be interpreted judiciously’; but Cracraft (1975: 234) observes that although ‘his biogeography relies heavily upon them … one is never given a clear exposition as to how they are to be interpreted’. Fossils are used to support their interpretations by the above workers when they fit their preconceptions; when fossil evidence does not support these it is ignored. As noted by Forster (1961: 51): ‘It must be kept in mind that if the moas as a group had become extinct before the onset of the Pleistocene, we would have had only one single indication of their former presence in New Zealand — the late Pliocene record of Anomalopteryx antiquus… .’ It is not too much to ask Fleming to consistently apply and interpret fossil data, if he must use it, but we are told (1957, 1976) that the moas walked into New Zealand in the Mesozoic! But ‘genera like Astelia, Aristotelia, Laurelia, Fuchsia and Griselina, with strong claims to be considered Antarctic elements, appear so late in the record that they would require Tertiary land bridges if, indeed, they came by land’ (Fleming, 1963b: 372).
One of Croizat's many contributions has been the development of the principle that ‘age of fossilization is not the same as age of being’. Deignan (1963: 267) notes that ‘… if we forget this principle we could fall into the error of supposing that the duck-billed platypus, known fossilized only in the Pleistocene, is an animal of recent origin, rather than one whose ancestry, in platypodine facies, must go back to the earliest Tertiary or the late Cretaceous.’ This distinction between the age of being and age of fossilization leads directly to an important conclusion within Croizat's framework: ‘It is a cardinal page 96 error to ignore that most modern important genera, and even species in certain groups, are as old, when not older, as the geological events which have moulded the recent geography of India.’ (Croizat, 1968b: 588). Darlington (1957: 619) stated: ‘What does animal distribution tell about ancient lands and climates? The existing distribution of vertebrates and the fossil record as far back as it is clear (geographically) tell of many small changes in the world but no great ones’, which prompted Deignan (1963: 269) to reply: ‘I would comment that the “existing distribution of vertebrates and the fossil record” may indeed tell of no major change in geography or climate from the Tertiary or even from the late Cretaceous to the present day, but just as certainly the existing distribution of vertebrates and the fossil record (hippopotomuses in Madagascar, ratite birds in Madagascar and New Zealand, frogs in Fiji and so on) to say nothing of the existing distribution of such invertebrates as the Onycophora, indicate that very radical changes, at least in geography, have taken place since the Middle Cretaceous, and these distributions further indicate that the dawn of life must be pushed much further back than is customarily done.’ An essential part of Croizat's approach is that ‘Earth and life did evolve together and quite apace; and the present, whether by volcano, sparrow or daisy is but function of the past’ (Croizat, 1964: 147). His interpretation is thus entirely at variance with that of orthodox biogeography, the latter built around such concepts as centres of origin; chance, sweepstakes and filter-bridge dispersal; and the ‘S.S. Pleistocene’ (see Simpson, 1940a: fig. 6) — the former emphasising in situ development in response to tectonic change from the Mesozoic on. Croizat's views on an ancient origin for organisms that are conventionally regarded as recent find some support in the fossil record, whose sacrosanct role in biogeography he, ironically, has done much to demolish. Eocene and Upper Oligocene avian fossils are so ‘modern’ that they can be assigned to extant families and genera (Howard, 1950). With regard to lizards, which are generally regarded as ‘modern’ (e.g. Towns, 1974), Carroll and Galton (1977) note that (1) an essentially modern lizard fauna has existed throughout the Tertiary, (2) members of many modern lizard families are known from the late Cretaceous and (3) a fossil lizard, with an essentially modern cranial morphology is known from the Upper Triassic of China.
Vicariance biogeography is applicable not only to large scale, but also small scale, biogeographical problems such as the disjunction of life between coastal and inland stations. ‘If “coastal” forms are found inland … normally taking part in revealing association … the reason is that the coast once did reach inland. When geography and topography came to a change, the coast did vanish leaving behind plants that once were of the shore. In sum: it is not coastal life which has “immigrated” by “casual means” … It is on the contrary the coast itself which has “emigrated” away because of page 97 geological reasons leaving behind stranded inland the life that once grew by the shore’ (Croizat, 1964: 116-117). A large number of predominantly coastal plants are known to have disjunct inland populations, both individually and in association, in New Zealand (Burrows, 1964; Cockayne, 1906; Kirk, 1870). A satisfactory explanation for these is Kirk's suggestion of receding coastlines, extensively developed for Latin American situations by Croizat (1958a, 1964), rather than Burrows' (1964) competition hypothesis. Similarly, disjunctions between coast and mountains (noted for New Zealand by Davis, 1950, and Burrows, 1964) rather than reflecting ‘mode of dispersal and … the effectiveness of such dispersal’ (Davis, 1950: 96), nestle quite nicely in the Croization dictum that ‘the more it changes the more it remains the same’.
Fleming (1962: 95) made the following comment on the New Zealand alpine biota: ‘… the history of alpine communities remains an outstanding problem of New Zealand biogeography.’ As early as 1952 Croizat had made a simple, yet outstanding, contribution to what many still regard as the mysterious origin of alpine life: ‘As we see it, there lived in the pre-Andean lands of northern South America the progenitors of some 95 species of modern birds. As the Andes began to rise, the progenitors of 38 of these species were caught in the uplight and made “Andean”. As, on the other hand, these progenitors had alliances in the Pacaraima region before the uplift, we find today an “Andean” element in this region. The birds themselves did not budge; the earth, on the contrary, shifted under them’ (Croizat, 1952: 33; also 1971: fig. 1B). That ‘Earth and life do evolve together whether on a whole continent or within a few square yards of a mountain slope in the throes of very slow erosion or very gradual uplift’ (Croizat, 1964: 242-243) finds some corroboration from current thinking on the niche concept: ‘… a niche is an evolved, multi-dimensional attribute of a particular species population… . Since a niche is a set of relationships for a particular species population in a given community there is no need to postulate the existence of empty niches’ (Whittaker et al., 1973: 333) and ‘… as we use the term the niche is a phenotypic attribute of a population of conspecific individuals, a statistical entity that changes whenever the members of the population change in their response to the biotic and abiotic environment’ (Colwell and Fuentes, 1975). In contrast we can stress Fleming's (1962: 95) exposition: ‘The alpine-subalpine environment … offered colonizing organisms a variety of empty niches. Into this ecological vacuum … came colonists from several sources’ and Raven's (1973: 194) dispersalism: ‘In many respects the alpine and subalpine slopes of New Zealand were comparable with an island newly emerged in the sea at a great distance from land… . Those groups of plants which were efficient colonists … were the genera of plants that produced the large arrays of species that are such a notable feature of the New Zealand flora.’
Dispersal and Islands: Their Significance?
‘Disharmony in composition of an insular biota is considered a prime source of evidence for the occurrence of long-distance dispersal.’
(Carlquist, 1974: 6)
‘To insist “casual means”, “colonizing flights”, “stratospheric conveyance”, “migrations”, etc., are certainly not the prime agency of dispersal whether in Galapagos or elsewhere.’
(Croizat, 1964: 625)
‘The plant world of oceanic islands is described as a haphazard collection of waifs and strays, and this is said to explain why so few genera contain more than a few species. But would not the result be the same if the actual islands originated through volcanic activity on a sinking land?’
(Skottsberg, 1956: 379)
Wallace (1880) claimed that animal distribution could only be understood in the light of complete knowledge of means of dispersal. Means of dispersal are the major preoccupation of orthodox biogeographers: ‘Of prime importance in reconstructing the history of faunas is determination of the dispersal capacity of various types of animals’ (Mayr, 1965: 476), but of little consequence to the vicariance biogeographer: ‘Means of dispersal are hardly worthy of discussion, much as the contrary has always been taken for certain during the last century’ (Croizat, 1964: 213). The reasons for these completely contrary approaches can be sought in the question: ‘What is dispersal?’ Platnick (1976: 294) has clarified the issue by discriminating between dispersion, an ecological, and dispersal, an historical, concept: ‘Dispersion would be defined as a property of individuals, the process by which an organism is able to spread from its place of origin to another locality. Dispersal would be defined as a property of taxa, the process by which a species or other group is able to spread from its previously established range to a different range.’
Dispersalists make much of the fact that periodically certain insect and bird species are known to travel long distances across oceans. The argument usually runs: because the painted lady butterfly can cross the Tasman and a milkweed bug is a long distance migrant, therefore dispersal must play an important role in establishing biotic distributions. Such blatant sophistry fails to distinguish these cases as clear-cut examples of dispersion. Recent work on insect migration (Dingle, 1972; Kennedy, 1971) has established that although migration and diapause in insects are superficially different in that the former involves mobility, and the latter stability of the insect in relation to its habitat both involve a phase of suppressed development and the manifestation of both phenomena appears to be induced by the same environmental conditions. Furthermore migration is sometimes a pre-condition for diapause. Migration and diapause are similar in that they involve the synchronisation of activities to favourable page 99 periods. Migration permits this through escape in space; diapause through escape in time (Tauber and Tauber, 1976). Cases of insect migration are essentially ‘ordinary means of survival turned into means of dispersal’ (Croizat, 1964: 213).
Birds are the favourite group for analysis amongst zoogeographic dispersalists. Mayr (1940: 197-198) tells us that despite being ‘excellent flyers and thus capable of rapid and active spreading’ (page 197) ‘… most species of birds … are extraordinarily sedentary’ (page 198). The fantail flycatcher Rhipidura rufifrons is claimed by Mayr and Moynihan (1946) to be ‘one of the most successful transoceanic colonizers’ but Deignan (1963: 265) found it difficult ‘to accept … that any pair (of this species) … has ever voluntarily flown across even the narrowest arm of sea to establish a new colony.’ In spite of the massive evidence for sedentation in most bird species (Chapman, 1926; Deignan, 1963) both Falla (1953) and McDowall (1969) attributed most of the New Zealand land bird fauna to immigration, from Australia, across the sea.
Plant means of dispersal are considered to be of major importance in the writings of diffusionist phytogeographers. Various means of dispersal have been distinguished and a classification developed, for instance anemochores (dispersed by wind) and hydrochores (dispersed by water). But what we recognise as means of dispersal are not necessarily synonymous with effective dispersal and permanent establishment (Van Balgooy, 1971). Skottsberg (1928: 917) claimed that: ‘All evidence is contrary to the assumption that the present Pacific flora, with the exception of already widespread species of the seashore is travelling from one island to the other.’ It is well known, of course, that weedy strand plants are readily dispersed from island to island. Surprisingly(?) Fosberg (1955) discovered real geographical variation in such ‘good’ dispersers as Lepturus, Pandanus and Lepidium, leading him to comment (1963: 277): ‘The fact that strand species are common and widespread has always been regarded as showing that the sea is not an effective barrier for these species, but, on the contrary, is a means of dispersal. Now, our finding of geographical variation suggests that there is some isolation and hence, to some extent an effective barrier.’9
Evidence to the contrary is suppressed by dispersalists. All manner of life is rafted across the sea on logs or whirled through the sky in the wind. Dogmatic assertions based upon the inviolable role of dispersal in biogeography are made. McCann (1953) would allow ‘no explanation other than oceanic drift for the distribution of geckos in the Pacific’. Even the New Zealand frogs, which vexed the committed dispersalist Darwin, have climbed on logs and put to sea: ‘The New Zealand frogs are relicts of too ancient a group to make speculation on the migrations of their ancestors profitable, but these ancestors probably come from Australia by flotation’ page 100 (Myers, 1953: 16)! Many orders of insects happily wing their way around the Pacific. Cautious workers are ignored: ‘Overwhelming evidence in the literature as well as the Museum's ship trapping supports the theory that today man is the primary agent in transporting insects from one land to another. Further research is required to determine accurately to what extent insects are distributed by nature across the ocean’ (Holzapfel and Harrell, 1968: 150).
The island volcano of Krakatau has become a shrine of dispersalist biogeography. MacArthur and Wilson (1967: 43) refer to ‘the famous recolonization episode of the Krakatau Islands’ where ‘repopulation proceeded rapidly’ after ‘the entire flora and fauna were destroyed’ by volcanic eruption. No consideration is given to the possibility that some of the island's biota may have survived the eruption. This is precisely the thesis developed by Backer (1929) in his book ‘The Problem of Krakatao as seen by a botanist’. Backer concluded his work with three terse statements (p. 289): ‘1. It is not at all proven that by the eruption of 1883 all vegetable life on Krakatao was destroyed. 2. Even if this could be proven, we know with the exception of the littoral flora — nothing at all about the manner in which the new vegetation has appeared. Only guesses without scientific value have been made, but no reliable observations nor experiments. 3. Therefore the Krakatao problem can neither now nor in the future either be posed or solved and is of no importance at all for Botanical Science.’ Which throws a new light on MacArthur and Wilson's (1967) ‘dynamic equilibrium model’ partially based on the orthodox interpretation of Krakatau.
Islands in the Pacific Ocean basin are seen as the proofs of long-distance dispersal: ‘The particular importance of insular zoogeography is that it permits the unambiguous demonstration of the dispersal powers of animals. In the eastern Pacific (east of the Andesite line) all islands and archipelagos are nothing but the tops of volcanoes that have arisen from the largely undisturbed ocean bottom. In view of this unequivocal geology, it is evident that all animal and plant dispersal must have been transoceanic. The distances involved in some of these colonizations are truly miraculous’ (Mayr and Phelps, 1967: 299). Earlier this century it was de rigeur to erect lost continents and sunken land masses in Pacific Basin biogeography (Meyrick, 1929; Pilsbury, 1900). Reaction was not long in coming. Zimmerman (1938) regarded lost Pacific continents as ‘absurd’ and Meyrick's (1929: 156) ‘a former larger extended land-area, Palaeonesia’ was seen to be ‘as mythical as the lost continent of Mu’ (p. 14). ‘Reckless landbridge builders of an earlier period’ are dismissed by Mayr (1953: 7) who goes on to state: ‘Today geologists are virtually unanimous in stating that the Pacfic is an old and undisturbed ocean basin.’ Stabilist geological interpretations may have been the order of the day in the 1950's and 1960's but they are no longer. Some current geological work strongly page 101 suggests that we are moving away from a stable towards a highly mobile conception of the Pacific. Hughes (1975: 37) postulates ‘that cordilleran North America had separated from eastern Asia during the Mesozoic, and that cordilleran North America because attached to cratonic North America during the Cenozoic,’ thus introducing the idea of ‘a Mesozoic opening of the North Pacific Ocean’. If this view is accepted then as Nelson (1975: 501) noted ‘… the Hawaiian Islands were not “oceanic” in their beginnings and are probably not “oceanic” even today’ and it is possible that ‘… the modern Hawaiian biota has Mesozoic roots’.
Meanwhile all is not quiet in the South Pacific. Nur and Avraham (1977a, 1977b) speculate ‘… that a large continental mass existed once in what is today's Pacific Ocean… . This mass … could have been part of the Pangea Super Continent adjacent to Australia and Antarctica. The breakup of this continent into fragments and their drift resulted in continental collision in South America, North America, Alaska, Kamchatka, Japan and East Asia. Furthermore, the submerged platforms in the Pacific Ocean such as the Ontong Java, the Shatsky Rise, and the Manikiki Plateau may be remnants of Pacifica.’ The old, vertical mobilist Pacific geology is being replaced by the new concept of lateral mobilism in the Pacfic.
Recent geological work has important implications for dispersalist island biogeography. If the Hawaiian Islands (Nelson, 1975) and many other islands as well (see e.g. Holden and Dietz, 1972, on the Galapagos Islands, and Shields, 1976, on island age) developed as part of Mesozoic and later geological change, and if their present biotas have ancient roots, then obviously distances and dispersal routes, if we continued to invoke them (need we?) to these islands were different in the past. Some islands, for example the Canary Islands (Dietz and Sproll, 1970) and the Indonesian Island (Audley-Charles et al., 1972), may have been microcontinental areas within the boundaries of the Gondwana-Laurasia super continents. Within the above conceptions of island origin and development the MacArthur- Wilson theory of island biogeography, with its elegant graphs and formulae, becomes redundant. This mathematical theory is based on concepts of Darwinian biogeography; upon uncritically accepted assumptions of colonising flights, long-distance dispersal, centres of origin and stabilist geography. ‘That such factors as distance from source area, ecological richness, and “saturation” should be expressed as a series of mathematical models (as offered by MacArthur and Wilson) is a natural culmination of ideas advanced by Darwin and Wallace and extended by such workers as Ernst Mayr and P. J. Darlington, Jr’ (Carlquist, 1974: 2). This is not to say that Darwin and subsequent dispersalists are wrong; only to question whether the assumptions upon which they have built are necessarly correct. It has been shown above, particularly with reference to Krakatau, that this need not be so.page 102
Biotas of many islands and island groups are often stated to be disharmonious (e.g. Carlquist, 1974). The concepts of harmony and disharmony of floras and faunas in conservative biogeography are naturally based on the centre of origin/dispersal apriorism: ‘… a harmonic flora or fauna contains a spread of forms with poor to excellent dispersal ability, whereas waif biotas will result from only the more easily dispersed end of the spectrum’ (Carlquist, 1974: 6). Both Skottsberg (1925-1956) and Van Steenis (1964) have questioned and rejected, on the basis of many arguments, the received Darwinian doctrine of dishamony. Van Steenis (1964: 86) showed ‘that there are no general features of island floras which differ essentially from continental floras’. Miraculous dispersal events, compilations of general statistical validity (sic) and tables of dispersal spectrums notwithstanding Skottsberg's (1925: 27) criticism still has general application: ‘It is a current idea that the statistical composition of an insular flora is a proof of its oceanic character. Such floras have been called fragmentary. But the same character may result from isolation through transgression and disappearance of land… .’ The manner in which characteristic ‘oceanic islands’ may have acquired their biotas within the context of geological mobilism is suggested by Holden and Dietz (1972) for the Galapagos Islands and Croizat (1958a) in general.10 Ball (1974) has commented on the naiviety of those who infer a direct relationship between geological age and age of the occupying biota.
Biogeography and the New Geology
‘It is evident that not a single aspect of the ocean-floor spreading hypothesis can stand up to criticism. This hypothesis is based on a hasty generalization of certain data whose significance has been monstrously overestimated. It is replete with distortions of actual phenomena of nature and with raw statements. It brought to the earth sciences an alien, rough schematization permeated by total ignorance of the actual properties of the medium.’
(Beloussov, 1970, 505)
‘Theories utilizing only movements by continental plates to explain the disjunct relationships of organisms are too simplistic and, until greatly refined, must be considered highly speculative, as is the case with many biogeographic ideas. I would suggest that authors trying to explain animal distribution using continental drift models do so cautiously, for a necessary full geologic verification for the concept does not yet exist.’
(Howden, 1974: 2500)
‘The implication that biogeographers should rationalize their data so as to conform with current geological opinion (McDowall, 1973: 91-92) is a viewpoint with which I disagree, especially as geologists are by no means in agreement with page 103 each other. It is the triumph of Croizat (1958, 1962), a biogeographer much misunderstood by most recent workers, that he has stressed the independence and validity of biogeographical data.’
(Ball, 1974: 32)
Nowhere is the nature of orthodox biogeography more clearly exposed than in the ease with which dispersalists have abandoned the stable continents flagship and clambered aboard the plate tectonic/continental drift bandwagon. It is ironic, as well as an indictment of conventional zoogeographic and phytogeographic approaches, that the drift school's most formidable opponents, the Meyerhoffs, in their 1972 paper, cite with approbation the biogeographic work of Simpson and Axelrod, in support of stable continents. Simpson (1940b: 757) asserted that the hypothesis ‘… of Wegener, seems to me and to a consensus of geologists ill supported and improbable’. In his 1976 testimonial. ‘The Compleat Palaeontologist?’ Simpson has shifted into reverse gear, because of course science has now ‘proved’ that Gondwanaland, etc., existed: ‘Much of theoretical biogeography involves the ways in which taxa spread, especially when their subsequent distribution is disjunct. Drift now provides a ready mechanism for disjunction by the separation of continents once united… . Thus plate tectonics is leading and will surely lead further to enrichment both in knowledge and the several principles of biogeography’ (p. 11). Axelrod (1963: 3262) claimed that ‘… the distribution of ancient forests, and the climates that they indicate, appears to be consistent with continental stability since at least the Carboniferous.’ In reply Hamilton (1964: 1666) appealed to ‘The impressive paleobotanical evidence for continental drift …’ but this evidence was denied: ‘Hamilton's opinion that there is “impressive paleobotanical evidence for continental drift” … fit readily into a picture of latitudinally and altitudinally controlled climate consistent with stability’ (Axelrod, 1964: 1669). But conventional geology was about to take a new turn. So for those to whom biogeography is enslaved by geology ‘The recent discovery of new facts which demonstrate beyond reasonable doubt that the crust of the earth is mobile, demands that biologists look again at their explanations of some old problems’ (Axelrod, 1972: 15). Those who regard centres of origin/dispersal frameworks tailored to fit a particular Gondwanic reconstruction — ‘There have been far greater opportunities for migration in the Southern Hemisphere than most biogeographers accepted as recently as a decade ago’ (Raven, 1975: 380), and ‘We must reconcile ourselves to a situation where, until at least mid-Cretaceous times, widespread overland migration throughout the Southern Hemisphere was readily possible …’ (Schuster, 1976: 131) — as the new biogeographic synthesis could well consider what Wegener (1929: 111) wrote: ‘This, along with the facts given above, shows only that two separate migration routes led away from South America: one towards New Zealand probably via western page 104 Antarctica, and the other towards Australia, probably via eastern Antarctica.’ But we don't read Wegener, do we, for he, along with Rosa and Croizat, belongs to the ‘lunatic fringe’.
A major problem for the ‘new’ drift biogeographers is that there is more than one way of reconstructing Gondwanaland. For instance the southern East Indies can have alternative Laurasian or Gondwana locations (see Hughes, 1975: fig. 2; Audley-Charles et al., 1972; Ridd, 1971). Moulding dispersal avenues to one particular reconstruction, for instance the orthodox reassembly with East Indies and South-East Asia in a Laurasian location as in Schuster (1976), causes a great many difficulties for the story changes if we accept an alternative view. And what if Hughes (1975), and Nur and Avraham (1977) are correct? What if Meyerhoff and Meyerhoff (1972) are right and continents are stable? What happens to our new synthesis then?
Croizat is the only biogeographer who has consistently and repeatedly stressed the independence of biogeography from other disciplines. And through this independence geology assumes a meaningful role within the context of vicariance biogeography. No one geological model is accepted a priori and the biotic data trimmed to fit. Rather, biogeographical models are developed in their own right on the basis of the biological data and then examined against a variety of geological hypotheses (see especially Croizat, 1964: 174-175, and Croizat, 1960: 1790: ‘It is my understanding that a student of dispersal, whether of plants or animals or both stands under no obligation to indorse one or the other geophysical theory of earth-making… .’
Conclusion: What is Biogeography?
‘… as between facts and manners of thinking — that is, ideas — facts are at bottom less material than ideas. Indeed, we understand, or misunderstand, the facts we see with the eye, naked or assisted by the most powerful of the microscopes, in the precise measure we have on the score of their portents right or wrong preliminary ideas.’
(Croizat, 1972: 160)
The controversy that has developed in the field of biogeography over the rejection/rehabilitation of Leon Croizat's work is not a dispute about verifiable or falsifiable data but one about the concepts through which these data are to be interpreted. Orthodox biogeographers hold that the distributional patterns exhibited by the world's biota are explicable in terms of taxa arising in a centre of origin followed by dispersal, i.e. as organisms evolve they disperse across the surface of the globe. Vicariance biogeographers, presenting a radical alternative to this traditional view, claim that these patterns are explicable in terms of the fragmentation of ancestral biotas and development in situ in response to tectonic change since the Mesozoic.page 105
The nature of biogeography as a science is also a major point of contention. Fleming's (1962: 107) position is clear. ‘In the very inexact science of biogeography, such hypotheses cannot yet be directly proved and in Charles Darwin's words “the doctrine must sink or swim according as it groups and explains phenomena”.’ Vicariance biogeography as developed in the United States (e.g. Ball, 1975; Rosen, 1975) does not see biogeography as an inexact science nor is science seen as providing proof or certainty. Biogeography is seen as a science that generates questions within a predictive, testable and falsifiable framework.
General questions raised go far beyond what significance is to be attributed to migratory insect flights. They drive at the basic commitments through which we view the world. The current controversy about biogeography raises not only the question — ‘What is biogeography?’ but the broader problem of ‘What is science?’ Both questions can never be asked too often of the biological polity. For myself, after considerable reading in the backwaters of ‘biogeography’. I feel like flotsam and jetsam tossed up on New Zealand shores.
‘The Lord St. Alban would say to some philosophers — “Gentlemen, nature is a labyrinth, in which the very haste you move with, will make you lose your way.”’
— Bacon, Apopthegms
(a) The relationship between biogeography and taxonomy is too complex to discuss in a paper of this nature. For a variety of viewpoints on this subject see Ball (1975), McDowall (1973) and Rosen (1975).
(b) Croizat uses the term dispersal throughout his work but not in the conventional sense:—‘The formula: dispersal = form-making + translation in space is indeed correct in general. However during a period of immobilism it becomes: dispersal = form-making by elimination of the factor of translation in space (migration). During a period of mobilism it turns into: dispersal = translation in space by elimination of the factor of form-making. Of course, neither immobilism or mobilism are ever absolute, but the mere fact that vicariant form-making is the rule of life tells us that immobilism is after all by far more important as a factor of evolution over space, in time than mobilism’ (1964: 212). A sound grasp of the concepts page 106 of immobilism and mobilism is essential, if Croizat's work is to be understood: ‘The greatest single error popularly accepted against fundamentally sound biogeographic thinking is in taking for granted, e.g. that Galinsoga, Taraxacum, etc. do actively “emigrate” by “means” which often are difficult to identify; therefore, distribution must be casual in principle. Galinsoga and Taraxacum spp. did themselves arise by normal processes of form-making (recombination of characters effected in isolation within the bosom of an ancestral plexus, etc.) before ever starting their career as loose weeds. Sooner or later, their wandering will stop, too, and within their bosom new form-making will stir is isolation, etc. In sum, the evolution of plant (and animal) life is a constant interplay of immobilism and mobilism but, of the two, the former is by far more important than the latter in point of form-making, therefore ultimately in regard of evolution in space over time by form. Advocates of mobilism a outrance (that is, virtually the majority of the “phytogeographers” and “zoogeographers” of this hour) should ponder the following: (1) It is true that Taraxacum proves for mobilism; (2) It is quite as true, however, that the “cloud forest”, the great “tropical forest”, etc., finally almost the entirety of avian, especially passeriform, life do vouch for immobilism. The essence of a genuine science of dispersal (panbiogeography!) is in harmonizing mobilism and immobilism within a rational scheme of thinking’ (1965: 635-636).
|1.||The centres of origin concept has never been satisfactorily defended and Cain's criticisms still stand at this hour. Turrill (1964: 213) notes ‘… that the criteria suggested are of very varied importance and none can give conclusive results.’ Yet most biogeographers persist in using this dubious concept wasting much print and creating many fruitless arguments. See further Croizat et al. (1974).|
|2.||Both Wallace's biogeography and subsequent interpretations of it are somewhat enigmatic. MacKenna (1975: 350) refers to Wallace as ‘… a proponent of dispersal via land continuity if possible. His ideas contrast with what might be called the Darwinian fascination with theoretical chance dispersal.’ Actually Wallace (1869: 161) is on record as stating: ‘It has been objected to Mr Darwin's theory of Oceanic Islands having never been connected with the mainland, — that this would imply that their animal population was a matter of chance; it has been termed the “flotsam and jetsam theory” and it has been maintained that nature does not work by the “chapter of chance”. But in the case which I have here described, we have the most positive evidence that such has been the mode of peopling the islands.’ Wallace clearly supported chance dispersal with regard to true ‘oceanic’ islands and landbridges for mammals (1880: 72) but was confused by the case of New Zealand (see his work as a whole).|
|3.||Continental drift interpretations of biogeographical phenomena are of course nothing new, despite the affirmation of Raven and Axelrod (1975: 420) to the contrary: ‘Until the late 1960's most attempts to interpret the global distribution of plants and animals were based upon the assumption that the relative positions of continents and islands had remained unchanged since their formation.’ There is a huge literature, chiefly French, German and Italian, dating back to the early years of this century interpreting biogeography within the context of continental drift: see the bibliography in Wegener (1929); and the often overlooked papers by Brehm (1936), Jeannel (1930s on, reviewed in his 1961 monograph), Sewell (1956) and Wolfson (1948, 1955).|
|4.||Darlington (1947: 343) was astute enough to recognise this: ‘That many groups of insects arose in the Old World tropics (nearly equivalent to eastern Gondwana), perhaps before the Tertiary invaded Asia and radiated there, and then spread through the whole north temperate zone is a good working hypothesis — but not necessarily Wegenerian.’|
|5.||Earlier New Zealand biogeographers had recognised biotic elements; see Fleming (1963a) for a review.|
|6.||The conceptual confusion amongst the dispersalist biogeographers who have embraced continental drift is astounding. For instance Raven (1972: 251) tells us that: ‘All three continents (i.e. Antarctica, Australia and South America) were occupied by a page 107 continuous cool temperate forest …’ subject to ‘… gradual disruption … by the movements of the continents …’, which implies vicariance, but in 1975 (see the main text) he returns to migration routes. It is worth noting Edmund's (1975: 251) restrained evaluation: ‘The number of biogeographers who confidently drew dispersal routes on fixed continent maps ten or more years ago and now just as confidently draw dispersal of the same organisms on continental drift maps must cause us to seriously question the procedures of biogeographers’, and Croizat's (1960: 1685-86) iconoclastic candour: ‘It is plain that biogeography, geology, geophysics and the like only then may hope to come to an understanding when the scientific polity at large shall stop mistaking “phytozoogeography” for a genuine science. This by now evident fake… . It is an evident fake. Entirely lacking methods and principles, misbegotten by Darwin and Wallace within the frames of a “theory of evolution” heedless of time and space, further stultified by Matthew, etc., this fake distorts the critical powers of those who believe in it.’|
|7.||Skinks traditionally travel via the “Flotsam and Jetsam Steamship Company” (Towns, 1974). It is interesting to note that the scinc'd genus Scincella (Greer, 1974: Fig. 39) displays the classic East Asia-eastern North American disjunction known also for bryophytes (Scholfield and Crum, 1972), and numerous cerambycid beetles and angiosperms (Linsley, 1963). ‘Dispersal is one for plants and animals …’ (Croizat, 1964: 566).|
|8.||In all fairness Fleming (1962, 1975) has recognised the dangers inherent in interpreting fossil evidence but his caution is not applied, in practice, to his narrative biogeography of New Zealand.|
|9.||Turrill (1959: 218-219) has proffered the following sensible comments on plant dispersal: ‘The evidence for long distance transport over oceans, extensive deserts, etc., is indirect or meagre… . The two natural agencies whose efficacy over very long distances is in dispute are wind and birds… . Birds are said generally to travel on long distance migrations with empty alimentary systems and with clean feet and feathers.’|
|10.||For the Galapagos Islands: ‘The Galapagos Islands contain many endemic birds and bizarre animals which have required millions of years for their evolution in isolation. By our model, the modern Galapagos Islands may have inherited faunas from a whole series of ancestral “Galapagos Islands” which existed over a span of 40 m.y. Presumably the animals would have little difficulty negotiating the short span of water to a new volcanic island as an older extinct volcanic island drifted eastwards and subsided beneath the sea …’ (Holden and Dietz, 1972: 269) and in general: ‘Concluding the distribution of birds of the waters is in no sense whatsoever less analyzable than that of the rest of creation, and easily ranks on the contrary as one of the most instructive and interesting. It so does, because the birds of the waters are, generally speaking, old in point of origins, not only, but are competent to hold in their grasp even specks of land lost at sea hardly fit to sustain life of other description. If anything were ever left of a whole continent the chance is that its last remnant in the shape of an oceanic rock would still be tenanted by breeding birds of the sea, perhaps a lizard, a bug and a few enduring weeds’ (Croizat, 1958a, Vol. l: 722).|