The Theory of Island Biogeography. Robert H. Article · Info & Metrics · eLetters · PDF. Loading The first page of the PDF of this article appears above. The Theory of Island. Biogeography. Extinction balances. Immigration. Assumptions: Increasing isolation decreases immigration rate. Increasing size decreases. The Theory of Island Biogeography. Series:Princeton Landmarks Pages i-iv. Download PDF. Free Access The Importance of Islands. Pages Get Access .
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The Theory of Island Biogeography Revisited This page intentionally left blank The Theory of Island Biogeography Re. Island Biogeography Theory: Emerging Patterns and Human Effects MacArthur and Wilson () developed the theory of island biogeography (next section). The Theory of Island Biogeography Revisited Your use of this PDF, the BioOne Web site, and all posted and associated content indicates your acceptance.
MacArthur and Edward O. MacArthur and Wilson's equilibrium theory represented a radical change in biogeographic thought. Prior to their work, investigators had focused on historical problems concerning relationships between floras and faunas of islands and continents. As indicated by the following quote of J. Hooker: "There are only two possible hypotheses to account for the stocking of an oceanic island with plants from a continent: either seeds were carried across the ocean by current, or birds, or similar agencies; or the islands once formed part of the continent, and the plants spread over intermediate land that has since disappeared" Joseph Dalton Hooker, , much of the emphasis within island biogeography was placed within debates about the historical connections between regions and whether island endemics were stranded relicts paleoendemics or in situ evolutionary products neoendemics.
Hence, much of the work was concerned with idiographic questions such as where a particular taxonomic group of organisms originated and how, as result of subsequent dispersal, speciation, and extinction in particular regions, its diversity and distribution changed. Prior to , the dominant theme of island biogeography was referred as static theory of island Dexter, According to the static theory, insular community resulted from immigration and extinction events and species number was determined by the limited number of niches available on each island Lack, However, the pres island biogeographers did not have restrictively static vey of island life, ignorant of all short-term natural dynamics, but it is true that their focus was on the big time-space questioning of origins and relationships.
All this was changed with the publication of MacArthur and Wilson's dynamic equilibrium model of island biogeography, not so much because it overturned a dominant paradigmatic structure among island biologists, but rather because in postulating a simple, general, process-based theory, MacArthur and Wilson opened up an entirely new research program-equivalent to opening a 9 marvelous new suite of laboratories complete with all the equipment and materials any number of research teams could wish for Lomolino, By starting with the essential processes at work, MacArthur and Wilson deliberately departed from the classical historical approach and were able to pose radically new kind of questions.
They searched for general patterns across different taxa, in the hope that such patterns would have general ecological explanations rather than idiographic and historical ones. Although they knew their theory was simplifying reality, they viewed this as the route to generating testable general hypotheses at the intersection of population and community ecology Lomolino, Prior to ETIB, the static theory of island hypothesizes that island community structures remain relatively constant over geological time.
The only mechanism for biological change was the gradual evolutionary process of speciation. Few successful colonization events would occur due to a limited number of ecological niches on the island Lack, Once these niches are completely filled, no space and resources are available for new immigrants, and they may not become successfully established on the island.
The ETIB refuses the static theory, indicating that island communities exhibit a dynamic equilibrium between species colonization and extinction, or species turnover. Perhaps MacArthur and Wilson's innovation was to recognize the common themes that underlie these observations the species-area relationship, the species-isolation relationship, and species turnover and to propose a single, unifying theory to account for them. Species number tends to increase with increasing area, regardless of the taxonomic group or type of ecosystem being considered.
This relationship, however, is not linear; richness increases less rapidly for larger islands. The Swedish ecologist Arrhenius , was the first to propose a mathematical generalization of this fundamental pattern or relationship between species number and area.
Assuming, that the decline in species richness results from a decline in dispersal rates with isolation, the form of the species-isolation relationship should be a consequence of dispersal curves for the pool of species. Therefore, for a variety of taxa and ecosystem, species richness should decline as a negative exponential or sigmoidal function of isolation.
Figure 3: The graph representing the relationship between species richness S and Island isolation I Lomolino, However, the species-isolation relationship remains less clearly established than the species- area relation.
The measure of isolation or assessing the isolation of island is very difficult in the study of species-isolation relationship. These islands are located in the Sunda straits between the Indonesian islands of Sumatra and Borneo. Violet volcanic eruption destroyed the original island of Krakatau in , leaving several remnant islands devoid of life.
Recolonization apparently form the nearby islands of Java and Sumatra was rapid; by , a tropical rainforest; supporting numerous species of plants, birds and other organism was developing.
MacArthur and Wilson noted that the number of bird species on Rankata and Sertung increased rapidly until about , but, after that the total number of species remained relatively constant, despite changes in the composition of the avifauna suggested that; 'continual turnover might be typical of insular biotas'. Such turnover might be particularly high when organisms need to cross only modest barriers to reach small islands Lomolino, They proposed that the number of species inhabiting an island represents a dynamic equilibrium between opposing rates of immigration and extinction.
The equilibrium is termed "dynamic" because immigration and extinction are held to be recurrent, opposing process, maintaining a relatively stable species number despite ongoing changes in species composition.
The equilibrium model can be presented graphically by plotting immigration and extinction rates as a function of the number of species present on an island.
The number of species S can range from zero to hypothetical maximum, P, the number in the pool of species that is available to colonize the island from a nearby continent or other source are. Starting as the island is empty. The immigration rate defined as the rate of arrival of propagule of species not already present on the island must decline from some maximum value when the island is empty, to zero when the island contains all the species in the pool and there are no more new species to arrive.
As the number of resident species grows, there remain fewer new species on the mainland to colonize the island. Conversely, the extinction rate defined as the rate of loss of existing insular species should increase from zero when 13 Figure 4: A simple model depicting equilibrium between immigration and extinction process there is no species present on the island to become extinct, to some maximum value when all the species in the mainland pool are inhabiting the island Lomolino, At some number of species of species between zero and P, the lines representing the immigration and extinction rate cross.
This point represents a stable is perturbed from this value, it should at least theoretically always return. Its elegantly simple graphical presentation made the essential elements of the model accessible to a wide audience, including persons with minimal mathematical training.
Moreover, the equilibrium theory not only introduced stimulating ideas, also helped to bridge the gap between traditional biogeography and ecology. It predicts qualitative trends increase or decrease of number of species and turn over rates with island size and isolation. Interspecific differences and interactions among species: The theory ignores the individual identity and characteristics of a particular species. New species immigrates and existing one dies out more or less random, and only the approximate number of species remains the same.
It is thus very much a macro-ecological model, focused on the emergent statistical properties of the system. Interdependence of immigration and extinction: The theory treats these two processes are independent. However, many evidences from the study of various islands like Krakatau suggest that these are generally interdependent process.
In a similar manner, area may also affect the processes, because larger islands may intercept more potential colonists.
Biogeographically meaningful measures of isolation: It may be difficult to identify the source of island biota. Species inhabiting a island may be derived from several sources, including over-water dispersal from continents and other island, past connection with other landmasses, and due to in situ speciation. Thus, the meaningful measures of isolation is difficult, whether it be regarded as the measure of the resemblance of the biota to the mainland or is be regarded as the measure of distance between the island and mainland.
Biogeographically meaningful measures of island area: Total island area provides only a general and indirect measure of the capacity of island to support the species. Even for the same island the carrying capacity vary for different species, depending upon their habitat requirements. Larger islands tend to have higher mountains, more aquatic habitat, and so on, as well as larger areas of most of the vegetation types found on small islands.
Consequently, some of the increase in species diversity with 15 the island size may be owing to the addition of specialist whose habitat requirements are met only on large islands. So, a more elaborate model should be needed to incorporate all these variables. The importance of Speciation: The theory ignores speciation.
However, MacArthur and Wilson explicitly recognize that speciation becomes of increasing importance on very large and isolated islands on which immigration rate is too low to fill the potentially available niche spaces. Disturbance in ecological to geological time scales: Many insular biotas may not be in equilibrium between opposing processes of immigration and extinction.
Rather, the species may increase or decrease over evolutionary time, or with major environmental disturbances such as hurricanes and volcanic eruptions. This is particularly likely when immigration occurs on approximately the same time scale as speciation that is, at a slow pace relative to the geological and climatic events that create, change, and destroys islands.
Here, insular communities may never reach or only fleeting reach equilibrium Lomolino, The initial objective of the ETIB was to gain a better understanding of island ecosytem and their dynamic process. But, as the studies continued, many ecologist, biogeographers, conservation biologist discovered a parallel relation between oceanic islands and fragments habitats on continental landmasses.
The human activities such as, habitat destruction, deforestation, urbanization etc. These remaining patches of these natural habitats may be perceived as habitat islands. From the similarities between habitat islands and actual oceanic islands, biogeographer utilizes the ETIB as a guideline to preserve the biodiversity in these patches Whittaker, However, some geographers has criticized these use of the ETIB in conservation practices of habitat islands, as the habitat islands differ significantly from that of the oceanic islands.
Hence, the scale and degree of insularity are critical components while making such comparisons. For these reasons, in addition to theories concerning oceanic island biogeography, issues such as minimum viable population and area, along with the meta-population dynamics must be evaluated when determining the most effective 16 continental reserve design.
The evaluation of Minimum viable population and the meta- population dynamics is very important in the process of reserve design. Meta-population dynamic theory is utilized to find the most effective and efficient strategies for continental reserve design, and has allowed for a better understanding of population ecology. Quarterly Review of Biology — The geographical distribution of cold-blooded vertebrates concluded. Zoogeography: The Geographic Distribution of Animals.
New York: Wiley.
The Theory of Island Biogeography Revisited
Marshall, L. Land mammals and the Great American Interchange. American Scientist — Matthew, W. Climate and evolution. Annals of the New York Academy of Science — MacArthur, R. An equilibrium theory of insular zoogeography. Evolution — The Theory of Island Biogeography. Simberloff, D. Experimental zoogeography of islands: defaunation and monitoring techniques. Ecology — Experimental zoogeography of islands: a two-year record of colonization.
Simpson, G. Wilson, E. Adaptive shift and dispersal in a tropical ant fauna.
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The challenge from related species. In The Genetics of Colonizing Species, ed. Baker and G. Stebbins, 7— New York: Academic Press. Lomolino, James H.
Brown, and Dov F. While fascinating accounts in their own right, studies of the historical development of scientific theories e. In the following section we present a brief history of island theory, in general, and summarize foundational insights that were available to scientists by the middle decades of the twentieth century in their attempts to explain patterns in geographic variation among insular biotas. In the final sections of this chapter we observe that, like other disciplines in contemporary biogeography, evolution, and ecology, island theory may again be entering an exciting and perhaps transformative period of advance through consilience and reintegration.
Toward this end, we conclude with a case study on biogeography, ecology, and evolution of insular mammals to illustrate an approach toward integration of island biogeography, which may ultimately lead to a more comprehensive and insightful understanding of the ecological and evolutionary development of insular biotas.
Encyclopedia of patterns. Island research has a distinguished history of providing insights that have either fundamentally transformed existing fields of science, or spawned new ones.
Thus, the early naturalists of the Age of European Explorations—visionaries whom today we recognize as the founders of the fields of biogeography, evolution and ecology—set out to describe the diversity and the geographic and temporal variation of life across an expanding spectrum of domains from the local and short-term scales to global and geological evolutionary ones.
Certainly the most distinctive types of newly discovered biotas, and of unrivaled importance to development of theories in biogeography, evolution, and ecology, were those inhabiting isolated islands.
The seminal works of Darwin and Wallace are legendary in this respect, but these nineteenth-century naturalists were far from the first to appreciate the heuristic value of studying insular biotas see summaries in Berry , Wagner and Funk , Grant , Whittaker and Fernandez-Palacios Resolution — He described the general tendency for isolated biotas to be less diverse than those on the mainland, and for the diversity of plants to increase with island area, availability of resources, variety of habitats, and heat energy from the sun.
Thus, two fundamental patterns which island theory attempts to explain— the species-isolation and species-area relationships—along with basic explanations for those patterns precursors of area per se and habitat diversity hypotheses, and species-energy theory; Hutchinson , Preston , Williams, , MacArthur and Wilson , Brown , Wright , Currie , Ricklefs and Lovette , Hawkins et al.
Charles Darwin, Alfred Russel Wallace, Joseph Dalton Hooker and many other naturalists of the late eighteenth and early nineteenth centuries would continue to add to the already voluminous accounts and explanations for the diversity and geography of island life.
As we now well know, their efforts to explain this immense and ever-expanding encyclopedia of patterns would shake the very foundations of established doctrine and eventually lead to identification of the fundamental, dynamic processes influencing the diversity and geography of nature. Dynamics of nature global to regional scales. The Age of European Exploration and, indeed, the first globalization of the natural sciences, provided scientists with far more than just a fascinating and continually expanding catalogue of the marvels of nature.
The Strategy of Colonization Pages Invasibility and the Variable Niche Pages Stepping Stones and Biotic Exchange Pages Evolutionary Changes Following Colonization Pages Prospect Pages Glossary Pages References Pages Index Pages General note: By using the comment function on degruyter. A respectful treatment of one another is important to us.Rather, the species may increase or decrease over evolutionary time, or with major environmental disturbances such as hurricanes and volcanic eruptions.
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The Theory of Island Biogeography
Wilson and Simberloff confirmed that there was an inverse relationship between the number of species on an island and the distance to the source region as predicted in The Theory of Island Biogeography.
Habitat islands: These are essentially all forms of insular system that do not qualify as being 'real islands'. The people living in the islands are all dependent on local resources either directly traditional use or indirectly ecotourism revenue. The theory predicts other things, too.
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