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Ecology (Brooklyn, NY)


The nature and extent of population regulation remains a principal unanswered question for many types of organisms, despite extensive research. In this paper, we provide a new synthesis of theoretical and empirical evidence that elucidates and extends a mechanism of population regulation for species whose individuals preemptively use sites that differ in suitability. The sites may be territories, refuges from predation, oviposition sites, etc. The mechanism, which we call site dependence, is not an alternative to density dependence; rather, site dependence is one of several mechanisms that potentially generate the negative feedback required for regulation. Site dependence has two major features: (1) environmentally caused heterogeneity among sites in suitability for reproduction and/or survival; and (2) preemptive site occupancy, with the tendency for individuals to move to sites of higher quality as they become available. Simulation modeling shows that these two features, acting in concert, generate negative feedback when progressively less suitable sites are used as population size increases, reducing average demographic rates for the population as a whole. Further, when population size decreases, only sites of high suitability are occupied, resulting in higher average demographic rates and, thus, population growth. The modeling results demonstrate that this site‐dependent mechanism can generate negative feedback at all population sizes in the absence of local crowding effects, and that this feedback is capable of regulating population size tightly. Operation of site dependence does not rely on the particular type of environmental factor(s) ultimately limiting population size, e.g., food, nest sites, predators, parasites, abiotic factors, or a combination of these. Furthermore, site dependence operates in saturated or unsaturated habitats and over a broad range of spatial scales for species that disperse widely relative to site diameter. A review of relevant field studies assessing the assumptions of the mechanism and its regulatory potential suggests that site dependence may provide a general explanation for population regulation in a wide variety of species.