A GENERAL-THEORY OF ENVIRONMENTAL NOISE IN ECOLOGICAL FOOD WEBS

We examine the effects of environmental noise on populations that are parts of simple two-species food webs. We assume that the species are strongly interacting and that one or the other population is affected by the noise signal. Further assuming that a stable equilibrium with p ositive population densities exists, we are able to perform a complete frequency analysis of the system. If only one of the populations is s ubject to noise, the relative noise response by both populations is fu lly determined by the sign of a single element of the Jacobian matrix. The analysis is readily extended to cases when both species are affec ted by noise or when the food web has more than two species. The gener al conclusion about relative responses to noise is then less unambiguo us, but the power spectra describing the frequency composition of the population variabilities are nevertheless completely determined. These results are entirely independent on the exact nature of the interacti on (i.e., predation, competition, mutualism) between the populations. The results show that the interpretation of the ''color'' of ecologica l time series (i.e., the frequency composition of population variabili ty over time) may be complicated by species interactions. The propagat ion of noise signals through food webs and the importance of web struc ture for the expected response of all parts of the web to such signals is a challenging field for future studies.