Limitation and Regulation of Ecological Populations: a Meta-analysis ofTipula paludosaField Data

Whether the size of an animal population is environmentally limited or regulated by density dependent negative feedback mechanisms is of ecological interest. Proponents of limitation theory have issued a set of specific challenges which are addressed in this paper using field data for the insect Tipula paludosa. This species is known to be subject to population crashes caused by adverse environmental conditions and assumed to be limited. We re-examine published data in support of this hypothesis and show that there is also evidence of negative feedback between generations. Meta-analyses of annual count data from individual fields, and regional surveys provide further evidence of negative feedback and it is concluded that population regulation occurs at both local and regional scales. Evidence from other studies is used to propose that cannibalism is the causative mechanism. Since similar negative feedback responses were apparent under both normal and environmentally limiting conditions when populations crash, a single population model that could simulate the differing regional dynamics observed from the annual surveys was produced. We conclude that the range of annual fluctuations observed in T. paludosa populations is the outcome of both limiting and regulating processes, confirming from field observations that these are not exclusive mechanisms.