Host–parasitoid associations in patchy environments
- 1 March 1990
- journal article
- Published by Springer Science and Business Media LLC in Nature
- Vol. 344 (6262), 150-153
- https://doi.org/10.1038/344150a0
Abstract
Studies of insect host-parasitoid interactions have contributed much to the consensus that spatial patchiness is important in the regulation of natural populations. A variety of theoretical models predict that host and parasitoid populations, although unstable in the absence of environmental heterogeneity, may persist at roughly steady overall densities in a patchy environment owing to variation in levels of parasitism from patch to patch. Observed patterns of parasitism, however, have a variety of forms (with variation in attack rates among patches depending directly or indirectly on host density, or showing variation uncorrelated with host density). There is some confusion about the dynamical consequences of these different forms. Here we first show how the dynamical effects of all these forms of environmental heterogeneity can be assessed by a common criterion. This 'CV2 greater than 1 rule' states that the overall population densities will remain roughly steady from generation to generation if the coefficient of variation squared (CV2) of the density of searching parasitoids in the vicinity of each host exceeds approximately unity. By partitioning CV2 into components, we show that both direct and inverse patterns of dependence on host density, and density-independent patterns, all contribute to population regulation in the same way. Second, we show how a maximum-likelihood method can be applied to the kind of field data that are usually available (that is, percentage parasitism versus local host density) to estimate the components of CV2. This analysis indicates that heterogeneity is large enough to stabilize dynamics in 9 of 34 published studies, and that density-independent heterogeneity is the main factor in most cases.Keywords
This publication has 31 references indexed in Scilit:
- Environmental Variability, Migration, and Persistence in Host-Parasitoid SystemsThe American Naturalist, 1988
- Parasitoid Competition and the Dynamics of Host-Parasitoid ModelsThe American Naturalist, 1988
- Spatial Density Dependence in ParasitoidsAnnual Review of Entomology, 1988
- The Frequency of Density Dependence in Insect Host‐Parasitoid SystemsEcology, 1987
- Distribution of Progeny in Two Ineffective Parasites of a Gall Midge (Diptera: Cecidomyiidae)Environmental Entomology, 1986
- Aggregation of Risk: Relationships Among Host-Parasitoid ModelsThe American Naturalist, 1986
- Parasitoid Foraging: Should Parasitism be Density Dependent?Journal of Animal Ecology, 1985
- Aggregation in field parasitoid populations: foraging time allocation by a population of Diadegma (Hymenoptera, Ichneumonidae)Ecological Entomology, 1983
- Patterns of parasitism by insect parasitoids in patchy environmentsEcological Entomology, 1982
- Aggregation of Predators and Insect Parasites and its Effect on StabilityJournal of Animal Ecology, 1974