Conclusions

Metapopulation biology and spatial ecology have provided a new framework for both population and conservation biology. Spatial locations of populations and the interactions among local populations have as great an effect as the traditional parameters of birth and death rates, age structures, and interspecific interactions. Although a metapopulation was originally just a "population of populations" (Levins 1970), many of Levins' simplifying assumptions have been relaxed in modern models. As we have seen, the persistence of the metapopulation is highly influenced by: (i) the number of patches; (ii) the size and quality of the patches; and (iii) the connectivity between the patches. Spatially explicit models attempt to encompass these variables.

We have not specifically discussed the topic of corridors between patches. The usefulness of corridors to metapopulation persistence has been widely discussed. The general idea is that, since movements between populations have the potential to stabilize both the local population and the metapopulation, a corridor between habitat patches would increase connectivity and facilitate these movements. Yet in spite of intuitive appeal and theoretical support, the benefits of corridors remain a controversial topic in metapopulation and conservation biology. Although corridors have not yet been proven irrefutably to be beneficial to wild populations, Laurance and Laurance (2003) concluded that the preponderance of available evidence is positive. They recommended that corridors be regarded as beneficial in fragmented landscapes unless specific local evidence suggests otherwise.

The metapopulation approach has challenged the dogma that populations only exist in locations where they are optimally adapted. Rather, we know that local populations go extinct on even the best-quality habitats, and that so-called sink populations hang on in areas of marginal habitat. Furthermore, most natural populations are small enough to be subject to stochastic extinctions. Metapopulations, in which populations in different patches have independent growth and decline dynamics, may therefore be necessary for the long-term persistence of the regional population (Hanski 1999). Foppen et at. (2000) have even demonstrated that sink populations can be essential to the preservation of the populations found in larger patches.

Within a decade of the publication of MacArthur and Wilson's theory of island biogeography it dominated conservation biology to the extent that "rules" of refuge design were based on it. In the 1990s there occurred a shift, and now metapopulation theory has replaced island biogeography as the major theoretical basis for conservation biology, although its applications to specific situations should not be undertaken lightly (Doak and Mills 1994). Metapopulation theory may be replaced by some other paradigm in the future. But the overall message is clear. Spatial dynamics matter.

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