Detecting Regulation in Patchily Distributed Animal Populations

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Abstract
A model for an insect herbivore in a patchy environment is used to illustrate difficulties in detecting density-dependent regulatory processes from temporal series of life-table data that ignore within-generation heterogeneity. In a deterministic world there is no problem:spatial and other patterns of density dependence acting on populations within generations translate directly to density dependence acting on total population between generations. The introduction of stochastic variation can change this clear-cut picture, although random variations in net reproductive rate have little effect. In particular, variability in the parameters governing spatial distribution and within-patch survival can lead to spatial density dependence being overlooked using the conventional techinique of plotting mortality against population size from generation to generation. This outcome is made more likely if relatively few generations are available and only a small subset of the total patches are sampled. Future life-table studies should aim: not only to cover as many generations as possible, but also to take account of spatial and other forms of within-generation variability in survival.