Chapter Synthesis

The emergence of modern conservation biology as a scientific discipline began with concerns about the genetics of small and declining populations. Problems associated with population bottlenecks, genetic drift, and inbreeding rose in prominence concurrent with increasingly sophisticated molecular techniques for genetic assessment. This confluence of growing concern and increasingly precise methods to assess and measure genetic parameters was a strong contributing factor in the preeminence genetic paradigms gained in the early development and definition of conservation biology.

The rise and fall of island biogeography, as well as the ongoing reevaluation of classical genetic concerns associated with small populations, illustrates a danger inherent in scientific theories that arise during crises—the use of broad generalizations to address complex and specific problems is likely to lead to profound disillusionment. Metapopulation theory faces the same danger, and so must continue to grow and mature in its grasp of the complexities of real populations, or suffer the same fate.

Many species now exist as metapopulations because human activity has fragmented their habitats. By definition, every declining population will reach some critical threshold in its loss of habitat when simple, additive habitat loss becomes compounded by habitat fragmentation and patch isolation (Andrén 1994). When this happens, we have perhaps added a new "metapopulation" as a potential research target that may advance our understanding of our new paradigm. But the use of a sophisticated name for the demographic effects of our relentless shredding of the natural world will be no comfort to the species that receives metapopulation status, and no surety that the new mantle it wears will help it to persist. Unless individuals in the metapopulation have the dispersal abilities to move from patch to patch in an increasingly broken landscape, its subunits will not be examples of enhanced spatial demographics and "rescue effects." They will only too soon become another statistic of contemporary extinction.

We perceive now that rates of dispersal, immigration, and emigration, although hard to measure and long overshadowed by our fascination with population birth and death rates, may hold the keys to conservation. Our knowledge of how well species disperse, and when and where, may become the means through which we understand not only the dynamics of metapopulations, but also whether or not any species can long endure the new paradigm we have created for it. Today, even the existence and apparent survival of metapopulations in fragmented landscapes may be deceptive. Contemporary metapopulations may be far from equilibrium because the landscape has changed so quickly (Hanski 1997). Some current "metapopulations" may already be on the road to extinction. Their conservation will increasingly depend not only on our knowledge of metapopulation dynamics, but also on our understanding of habitat heterogeneity and ecological scale in their population processes.

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