7 - Spatial structure and population vulnerability  pp. 125-140

Spatial structure and population vulnerability

By Michael E. Gilpin

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Population extinction can result from many factors. Even though most cases are hidden from observers, its processes can be viewed in different ways. The other chapters of this book focus on single features of species biology that contribute to species extinction. Superficially, this chapter treats yet another factor: the extension of the spatial stage on which the extinction drama is played. Nonetheless, space is something different. It affects and is, in turn, affected by the other aspects of species biology that contribute to extinction.

The spatial extension of ecological systems, which considers the actual locations of organisms in the landscape, is not routinely incorporated into theoretical formulations of population genetics, demography, population dynamics, and community ecology. Our theories typically present variables such as N's and p's that summarize, with a single number, the ecological and genetical states of a system over some conceptually delimited region of physical space. That is, N is a count of all the animals in this space; it does not tell where they are, or how they are clumped or otherwise associated. Similarly, p represents a gene frequency in a ‘population’ of organisms, but the region over which this estimate is valid is not normally specified.

This reluctance to address questions of spatial extension results from at least two important considerations.