Metapopulations and Wildlife Conservation. - book reviews

Ecology, Sept, 1997 by Mary M. Peacock

Habitat loss and fragmentation have become the dominant concern in conservation biology. The fragmentation of once continuous habitat often results in reduced population size, loss of genetic variation, and increased susceptibility to demographic and environmental stochasticity. Habitat fragmentation may lead to increased extinction risk for individual populations and species. The metapopulation concept has been embraced as a means for understanding the dynamics of spatially subdivided populations. From a management perspective, the utility of the metapopulation concept lies in effective reserve design.

Before we can design reserves based upon metapopulation ideas, the following questions need to be answered: (1) what types of metapopulations exist and, more importantly, what types have a high probability of persisting; (2) what are the population dynamics of these various metapopulation types and do they vary for species with differing life histories; and (3) can we collect the appropriate data to model accurately spatial dynamics for individual species? Unfortunately, there are few long term studies on naturally occurring metapopulations from which to draw clear conclusions. As a result, the effect of habitat spatial structure on population dynamics remains undetermined for most species and metapopulation theory remains largely untested.

Despite the gap between metapopulation theory and our understanding of population dynamics in fragmented habitats, the metapopulation concept has already shaped our thinking about connectivity among habitat fragments. The authors in this volume outline the types of questions we should be asking before implementing metapopulation ideas for management purposes. The emphasis is not on testing theory, given limitations of existing data and the time to collect additional data, but taking the general notion of connectivity among habitat patches and overlaying the complexity of species life histories and land management politics.

McCullough (Chapter 1) reviews early theoretical work and discusses the formidable challenges facing the conservation biology community in ameliorating the effects of habitat fragmentation. Gilpin (Chapter 2) and Noon and McKelvey (Chapter 7) discuss various spatially explicit modeling approaches. Gilpin suggests that preliminary models be used to guide further data collection and model refinement. Price and Gilpin (Chapter 10) use this approach in designing a reserve for Stephen's kangaroo rats. This chapter and Beier's chapter on cougar conservation (Chapter 14) illustrate the problems typically faced in formulating habitat conservation plans for endangered species, i.e., lack of data and political and economic pressure to produce a plan. Beier presents a sobering look at our ability to conduct thorough studies and implement reserve designs in the face of human encroachment. Gutierrez and Harrison (Chapter 8) point out that the precision of metapopulation models depends upon collecting the appropriate temporal and spatial data. These data are often difficult to collect given the time scale and spatial dynamics of metapopulations.

Wiens (Chapter 4) and Lidicker, Jr., and Koenig (Chapter 5) go beyond the general idea of corridors. These chapters address corridor size, shape, edge effects, and habitat mosaics in the context of single and multiple species management. Hedrick (Chapter 3) argues that we have very little information about the impact of metapopulation dynamics on population genetic parameters (inbreeding depression, effective population size, loss of genetic variation and reduced evolutionary potential) and encourages additional research.

Sjorgren-Gulve and Ray (Chapter 6) model the dynamics of the Swedish pool frog metapopulation. They present a complex but realistic patch occupancy model that includes local environmental heterogeneity. This chapter illustrates the importance of collecting the appropriate demographic and environmental data. Sjorgren-Gulve and Ray assert that effective management of metapopulations will depend upon using real-world complexity in modeling efforts.

Detailed demographic and environmental data are often difficult to gather, especially in the case of endangered species. In the many case studies presented here (Stith et al., Chapter 9; Harwood et al., Chapter 11; York et al., Chapter 12; Craighead and Vyse, Chapter 14; Bleich et al., Chapter 15; McCullough et al., Chapter 16), the authors use data available (e.g., genetics, current and historical population censuses) to try to identify metapopulations and examine population dynamics. In all cases the authors draw reasonable conclusions with the data they have.

I found this volume interesting and useful, primarily because of the realistic approach to management and reserve design that most of the authors took. The metapopulation concept (habitat spatial structure and connectivity among habitat patches) has great potential for management of species in fragmented landscapes. The take home message is that there is no panacea and decisions will have to be made on a case-by-case basis. However, the metapopulation concept has influenced our thinking and forced us to focus on what questions we should be asking.