Limitation and Regulation of Ecological Populations:a Meta-analysis of Tipula paludosa Field Data

Abstract

Whether the size of an animal population is environmentally limited or regulatedby density dependent negative feedback mechanisms is of ecological interest. Proponents oflimitation theory have issued a set of specific challenges which are addressed in this paperusing 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 alsoevidence of negative feedback between generations. Meta-analyses of annual count data fromindividual fields, and regional surveys provide further evidence of negative feedback and itis concluded that population regulation occurs at both local and regional scales. Evidencefrom other studies is used to propose that cannibalism is the causative mechanism. Sincesimilar negative feedback responses were apparent under both normal and environmentallylimiting conditions when populations crash, a single population model that could simulatethe differing regional dynamics observed from the annual surveys was produced. We concludethat the range of annual fluctuations observed in T. paludosa populations is the outcome ofboth limiting and regulating processes, confirming from field observations that these are notexclusive mechanisms.