A general model of site-dependent population regulation: population-level regulation without individual-level interactions

Authors

  • Mark A. McPeek,

  • Nicholas L. Rodenhouse,

  • Richard T. Holmes,

  • Thomas W. Sherry


M. A. McPeek and R. T. Holmes (correspondence), Dept of Biological Sciences, Dartmouth College, Hanover, NH 03755, USA (richard.t.holmes@dartmouth.edu). – N. L. Rodenhouse, Dept of Biological Sciences, Wellesley College, Wellesley, MA 02181, USA. – T. W. Sherry, Dept of Ecology and Evolutionary Biology, Tulane Univ., New Orleans, LA 70118, USA.

Abstract

In this paper, we use a modeling approach to explore the population regulatory consequences of individual choices for where to breed in heterogeneous environments. In contrast to standard models, we focus on individuals that interact only indirectly through their choices of breeding sites (i.e., individuals preempt the occupation of a breeding site by others when they choose to breed there). We consider the consequences of individuals choosing breeding sites either randomly or sequentially from best to worst. Our analysis shows that average per-capita fecundity of the population is independent of the number of occupied breeding sites if individuals choose sites at random and that variation in average per-capita fecundity increases as population size declines. In contrast, if individuals choose breeding sites sequentially from highest to lowest quality, then as population size increases average per-capita fecundity declines and variation in average per-capita fecundity increases. Consequently, aggregate population-level demographic rates can change in ways that generate population regulation, even when change in population size does not change the demographic performance of any individual on any particular breeding site. However, such regulation occurs only when individuals make adaptive choices of where to breed. Because variation in average per-capita fecundity decreases when population size declines, populations regulated in a site-dependent manner should be much less susceptible to the vicissitudes of small population size than those which choose breeding sites at random.

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