摘要:

A general review of the patterns of species richness of insular mammals (Lomolino, 1984a) indicated that richness is determined by interactive as well as additive effects of factors affecting immigration and extinction. The present paper reports that species composition of insular mammals is also influenced by such additive and interactive effects. Therefore, insular incidence should be high for those species whose (or on those islands where) (immigration rates) are high relative to extinction rates. The model presented in this paper predicts that species have high incidence on islands if low immigration rates (poor immigrators and/or distant islands) are compensated by low extinction rates (good survivors and/or large islands), or high extinction rates are compensated for by high immigration rates. Therefore, poor immigrators may be frequent inhabitants of distant islands if their extinction rates are compensatorily low (large islands and/or low resource requirements). Conversely, extinction‐prone species (large, specialist carnivores) may be frequent inhabitants of small islands if their immigration rates are compensatorily high (near islands and/or good immigrators). These ‘compensatory effects’ were well evidenced by the mammalian faunas of the islands in the Thousand Islands Region, New York, and Lake Michigan (U.S.A.). ‘Compensatory effects’ are also evidenced by mammals of other archipelagos, as well as by birds inhabiting real and habitat islands. These results are consistent with the fundamental assumption of the equilibrium theory of island biogeography, i.e. insular community structure is the result of recurrent (rather than unique) immigrations and extinctions. Accordingly, I suggest that the concept of a fixed critical minimum area for isolated populations may be meaningless unless immigrations are unimportant with respect to the fauna under study. Finally, apparently anomalous or stochastic distribution patterns of insular species may readily be explained by the deterministic model presented here which incorporates the interactive as well as additive effects of immigration and extinctions on insular community

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1986.tb01746.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

Three of the six species of shrew in Finland,Sorex araneus, S. caecutiens, and S. minutus, are common on the mainland and widespread on islands in lakes. The islands range from 0.01 to 500 ha in area, and from 10 to 3000 m in isolation (distance from the mainland). The species‐area relationship, the lack of importance of habitat diversity, the increasing frequency of unoccupied small islands with isolation, and direct observations of small populations, all suggest that populations on small islands have a high extinction rate. Demographic stochasticity is the main cause of extinctions in the superior competitor,S. araneus, which occurs consistently on islands greater than 2 ha. The small species,S. caecutiens and S. minutus, are more sensitive to environmental stochasticity than isS. araneus, and are inferior to it in interspecific competition; these factors probably contribute to the absence of the small species from many islands tens of hectares in area. Frequent colonization of islands less than 500 m from the mainland is indicated by large numbers of shrews trapped from tiny islets where breeding is not possible, by increasing epigenetic divergence of island populations with isolation, and by observations of dispersal to and colonization of islands. Dispersal ability decreases with decreasing individual size, which may partly explain the absence of the small shrews from many relatively large islands. The shrew populations persist in a dynamic equilibrium on the islands. Epigenetic morphological variation is a useful tool in ecological studies of island population

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1986.tb01747.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

For the mammalian faunas of 24 landbridge islands in the Gulf of Maine (0.003–279 km2in size), area accounts for 86% of variance in species richness. The slope,z, of the species‐area curve is 0.247. For the seven largest islands (>10km2), the non‐equilibrium hypothesis of relaxation following saturation in the post‐Pleistocene is suggested by (1) elevated slope of the species‐area curve (0.353), (2) correlation of species richness with island age (r=‐ 0.81) and water depth to mainland (r= ‐0.70), (3) highly non‐random nested subsets of species ranked by island area, and (4) discontinuity with the extremely depauperate faunas of oceanic islands of the eastern North Atlantic. The alternative hypothesis of a dynamic equilibrium determined by recurrent immigration and extinction is supported by (1) documented turnover in 16 species, (2) correlation of species‐area residuals with distance (r= ‐ 0.90), (3) distribution dependent upon vagility with reduction or absence of hibernators and other poor dispersers, (4) low levels of endemism, and (5) congruence of community structure with that of mainland fauna for both trophic level and body size.I conclude that while some insular populations may be relictual, the faunal composition of most of these islands is dependent on recurrent colonization, much of which takes place over ice bridges. However, true equilibrium is perturbed by climatic shifts, range expansions, an

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1986.tb01748.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

The nested subset hypothesis was formulated to describe and explain patterns in the community structure of insular mammal faunas which are in the state of ‘relaxation’. The hypothesis states that the species comprising a depauperate fauna should constitute a proper subset of those in richer faunas, and that an archipelago of such faunas arranged by species richness should present a nested series. The non‐randomness of this pattern is evaluated for montane mammals in the American Southwest using Monte Carlo simulations under two sets of conditions. First, we constructed model archipelagos with the observed distribution of species richnesses, drawing individual species at random (without replacement) from the species pool (RANDOM0). Secondly, we constructed model archipelagos having the observed distribution of species richnesses, but weighted the selection of species by their actual frequencies of occurrence (RANDOM1). The degree of nestedness in the model archipelagos was then used to assess the non‐randomness of the observed structure. Actual Southwestern mammal faunas have a far more nested structure than model archipelagos produced by either RANDOM0 or RANDOM1, and there is virtually zero probability that observed structure is represented in the distribution of scores from either simulation run. Similar analyses were conducted on other archipelagos to determine the generality of this relationship and to identify variables putatively responsible for its production. Mammal faunas of large islands off the coast of Maine, U.S.A., studied by Crowell (1986) also comprise nested subsets, as do those inhabiting islands off the coast of Baja California, Mexico, studied by Lawlor (1983). Significantly, when the Baja archipelago is divided into landbridge islands (which are presumed to be relaxing to lower species level) and oceanic islands (where species number is limited by successful overwater dispersal), only the former show significant nestedness under the more stringent conditions of RANDOM1. These results and theoretical considerations suggest that selective extinction of species may be chiefly responsible for the nestedness in natural archipelagos. Our conclusions have obvious implications for the design of natural preserves (e.g. SLOSS): several small fragments of a single biota can be expected to support nested subsets of the species originally present or that would likely be retained in a single large preserve. Even more sobering are arguments raised which suggest that the faunas of preserves established in different habitats within the same biome might be expected to converge in composition via selective ext

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1986.tb01749.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

The relationship between non‐volant mammalian species richness and area in 24 western North American national parks is examined. The exponential and the power function models are concluded to be the ‘best’ models and account for nearly an identical proportion of the total variance (˜ 69%). Two principal hypotheses, the urea per se and the habitat diversity hypotheses, have been proposed to explain the species‐area relationship. Support exists for both hypotheses based upon partial correlation analysis of non‐volant mammalian species richness with area, elevational range, latitude, number of vegetative cover types and index of vegetative cover diversity. I conclude that areaper seand habitat diversity defined as environmental heterogeneity are the best predictors of non‐volant mammalian species richness in western North American national parks. I also conclude that vegetative cover diversity is a poor predictor of mammalian species richness in western North American national parks. Several problems with assessing the area per se and habitat diversity hypotheses are noted. These are: (1) the definition of the term ‘habitat’; (2) the predictions of these two hypotheses may not be mutually exclusive; and (3) area and habitat diversity tend to be intercorrelated. The slope (z) of the power function is equal to 0.12. The hypothesis that variation in the slope of the power function for nature reserves worldwide is a result of the comparative sizes of the nature reserves cannot be excluded. There has been considerable discussion in recent years about the conservation implications of the species‐area relationship. Much of this discussion has been concerned with whether a single large reserve contains more species than several small reserves (SLOSS). The answer to SLOSS is heavily dependent upon the objectives of a reserve, the autecology of the species, and the ecological independence of the reserves. It is suggested that particular attention be given to area and elevation when designi

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1986.tb01750.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

Insular faunas of terrestrial mammals and bats are examined on a worldwide basis to test the adequacy of equilibrium and historical legacy models as explanations for species‐area relationships. Species numbers of bats on islands conform to predictions from equilibrium theory, whereby recurrent immigrations and extinctions influence species richness. By contrast, species numbers of terrestrial mammals on islands result from a historical legacy of very low immigration rates on oceanic islands (the faunas are colonization‐limited) and by the fragmentation of once contiguous continental faunas to form relictual populations, which subsequently undergo extinctions, on landbridge islands (the faunas are extinction‐limited). This explanation is supported by several lines of evidence: (1)zvalues (slopes of species‐area curves) are lower for non‐volant mammals on oceanic islands than for those on landbridge islands, but are the opposite for bats; (2)zvalues for non‐volant mammals are lower than those for bats on oceanic islands, but are higher than those for bats on landbridge islands; and (3) landbridge island faunas are attenuated mainland faunas, whereas those on oceanic islands are ecologically incomplete. No support is found for alternative hypotheses to explain low species‐area slopes for terrestrial mammals on oc

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1986.tb01751.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

Four categories of islands in SE Asia may be identified on the basis of their histories of landbridge connections. Those islands on the shallow, continental Sunda Shelf were joined to the Asian mainland by a broad landbridge during the late Pleistocene; other islands were connected to the Sunda Shelf by a middle Pleistocene landbridge; some were parts of larger oceanic islands; and others remained as isolated oceanic islands. The limits of late Pleistocene islands, defined by the 120 m bathymetric line, are highly concordant with the limits of faunal regions. Faunal variation among non‐volant mammals is high between faunal regions and low within the faunal regions; endemism of faunal regions characteristically exceeds 70%. Small and geologically young oceanic islands are depauperate; larger and older islands are more species‐rich. The number of endemic species is correlated with island area; however, continental shelf islands less than 125 000 km2do not have endemic species, whereas isolated oceanic islands as small as 47 km2often have endemic species. Geologically old oceanic islands have many endemic species, whereas young oceanic islands have few endemic species. Colonization across sea channels that were 5–25 km wide during the Pleistocene has been low, with a rate of about 1–2/500000 years. Comparison of species‐area curves for mainland areas, late Pleistocene islands, and middle Pleistocene islands indicates that extinction occurs rapidly when landbridge islands are first isolated, with the extent of extinction dependent upon island size; extinction then slows to an average rate of 1–2%/10 000 years. The great majority of the non‐volant Philippine mammals arrived from the Sunda Shelf, the geographically closest of the possible source areas. Speciation within the Philippines has contributed substantially to species richness, perhaps exceeding colonization by a factor of two or more as a contributor to species number. Colonization, extinction and speciation rates differ among taxonomic groups, with murid rodents being most successful and carnivores least successful. In order for any model of island biogeography to be widely applicable to insular faunas, the model must include speciation as a major variable. It is suggested that insular mammalian faunas typically are not in equilibrium, because geological and climatic changes can occur as rapidly as colonization a

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1986.tb01752.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

The timing and causes of extinctions of West Indian land mammals during three time intervals covering the last 20000 years (late Pleistocene and early Holocene, Amerindian, and post‐Columbian) are discussed in detail. Late Pleistocene extinctions are attributed to climatic change and the post‐glacial rise in sea level, whereas most late Holocene extinctions are probably human caused, resulting from predation, habitat destruction and introduction of exotic species. Extinctions have dramatically altered the composition of the non‐volant mammal fauna, but have had a lesser impact on bats. Of the 76 recognized species of living and extinct non‐volant mammals in the West Indies, 67 species (88%) have gone extinct since the late Pleistocene, whereas only eight of the 59 species of bats (14%) have disappeared during this same time interval. A larger percentage of Antillean bat species (24%) have suffered localized extinction on certain islands, particularly obligate cave‐dwelling forms. These local extinctions occurred primarily on small islands, and probably resulted from changes in cave microclimates and flooding of low‐lying caves by rising sea levels.The majority of West Indian bats and all of the edentates, primates and rodents are Neotropical in origin. The South American fossil record indicates that most West Indian terrestrial mammals did not evolve until the early Miocene or thereafter. The Caribbean islands had assumed essentially their modern position and configuration by the Miocene, thus leaving overwater dispersal as the primary mechanism by which these endemic South American mammal groups reached the islands. The primitive insectivores,SolenodonandNesophontes, are derived from Early Tertiary forms in North America that may have reached the islands through vicariance by way of a proto‐Antillean archipelago. Many of the bats are either conspecific or congeneric with mainland taxa, suggesting that most species reached the islands by overwater dispersal during the Late Cenozoic, primarily from Central and South America.Two hypothetical immigration rates are calculated for West Indian land mammals, one assuming the earliest colonization in the late Eocene and the other based on an early Miocene origin. The known Late Quaternary and living Antillean land mammal fauna was derived from approximately 50 separate colonization events (13 for non‐volant mammals and 37 for bats) giving immigration rates of one species per 800000 years since the late Eocene, or one species per 400000 years since the early Miocene. Immigration rates for bats are approximately three times greater than those for non‐volant mammals throughout the Tertiary and eight times greater in the Pleistocene, presumably reflecting their greater dispersal abilities. These immigration rates should be considered rough values, owing to deficiencies in the fossil record, especially the absence of pre‐Pleistocene fossils. Extinction rates calculated for the last 20 000 years demonstrate that an average of one species of mammal went extinct every 267 years during that time period. Since the arrival of man in the West Indies some 4500 years ago, 37 species of non‐volant mammals have disappeared giving the rapid extinction rate of one species every 122 years. Island area‐species diversity curves are plotted for both the current and late Pleistocene mammal faunas. All Caribbean islands with a reasonably complete fossil record have more species in the late Pleistocene and Holocene than in the living fauna. The living non‐volant mammals of the West Indies do not constitute a natural fauna, but are an impoverished subset of species that managed to escape the extinctions that decimated the remainder of the fauna. Historical or theoretical biogeographic analyses of Antillean mammals that fail to incorporate extinct forms will be unlikely to elici

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1986.tb01753.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

Island populations are of interest for their differentiation as well as their species diversity; some of the earliest biological interest in islands was concerned with the number of ‘endemics’ thereon. There is dispute about the long‐term evolutionary importance of island forms, but they are rich sources of data for studying the under‐exploited interface of genetics, ecology and physiology. Differentiation of island populations may arise from genetic change after isolation, or from the chance collection of alleles carried by the colonizing group itself. The general reduction of genetic variance in island populations compared to continental forms of the same species suggests that founder events have played a major role in the formation of most island forms. However, there is ample evidence of adaptation in island populations despite this lower variation; this is relevant when using island biology as a base for the deriving of rules for genetic conse

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1986.tb01754.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

More than two decades after its publication, MacArthur and Wilson's equilibrium model of insular biogeography continues to provide the conceptual foundation for investigating the distribution of species on islands and the composition of insular biotas. During this period, studies of the distributions of mammals among insular habitats have tested, modified, and extended MacArthur and Wilson's simple formalism to enhance greatly our understanding of the complexities of biogeographic patterns and processes. The papers in this symposium summarize many of the past contributions of mammalian biogeographers and introduce important new data and ideas. The diversity of biological characteristics and associated distributional patterns exhibited by mammals has facilitated this endeavour. Some insular mammalian faunas appear to represent approximate equilibria between opposing rates of contemporary colonization and extinction. Other faunas are currently decreasing in diversity because of extinctions, owing either to natural habitat fragmentation that has occurred since the Pleistocene or to human activities within the last few centuries. Still other faunas have been increasing in diversity (at least until recent human impacts) because limiting rates of origination, both colonization and speciation, have been extremely low. The questions and analyses of island biogeography can also be applied to continents with comparable overall results: the distributions of continental faunas reflect the consequences of similar processes of colonization, speciation and extinction. Analyses of insular distributions show unequivocally that probabilities of extinction, colonization and speciation are highly deterministic and vary in predictable ways among different taxa and archipelagos. These findings have important implications for applying the theory and data of insular biogeography to the pressing practical problems of designing natural reserves to preserve native species.

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1986.tb01755.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY