Detecting the causes of population cycles by analysis of R‐functions: the spruce needle‐miner, <i>Epinotia tedella</i> , and its parasitoids in Danish spruce plantations

Abstract

Explaining the causes of regular multi annual oscillations (cycles) in animal populations has been a major problem for ecology, partly due to a lack of methodological rigor. In this paper we show how the analysis of R‐functions, the functional relationship between the per capita rate of change of a species and components of its environment, can be used to detect the causes of population cycles. Analysis of the R‐functions enables one to separate cycles due to negative feedback between species (endogenous causes) from those forced by one‐way effects (exogenous causes). We illustrate the approach by reference to the spruce needle‐miner inhabiting Danish spruce plantations, and conclude that population cycles in this insect are probably caused by interactions with two species of parasitic hymenoptera.