Functional and numerical responses do not always indicate the most effective predator for biological control: an analysis of two predators in a two-prey system
Article first published online: 13 JUN 2002
Journal of Applied Ecology
Volume 39, Issue 3, pages 455–468, June 2002
How to Cite
Lester, P. J. and Harmsen, R. (2002), Functional and numerical responses do not always indicate the most effective predator for biological control: an analysis of two predators in a two-prey system. Journal of Applied Ecology, 39: 455–468. doi: 10.1046/j.1365-2664.2002.00733.x
- Issue published online: 13 JUN 2002
- Article first published online: 13 JUN 2002
- Received 25 June 2001; final copyreceived 11 March 2002
- alternative prey;
- generalist predators;
- intraguild effects
- 1Functional and numerical responses are key components in the selection of predators for biological control. We examined the relevance of these responses for predicting the effectiveness of generalist predators, taking into account effects of alternative prey and multiple predators. Our system involved two acarine predators of two prey species on apple. Responses were measured on leaf discs in the laboratory, and predictions assessed on small potted apple trees. In particular, we tested three hypotheses.
- 2Hypothesis I: the species with the higher predatory responses will be more effective in limiting prey populations. Neither predator had a consistently higher functional response, which depended on prey stage and species. Amblyseius fallacis had a (approximately two times) higher ovipositional response than Typhlodromus pyri. We therefore hypothesized that A. fallacis would be more effective in controlling prey. No evidence was found to support this hypothesis.
- 3Hypothesis II: alternative prey reduce the functional response of predators to target prey. Alternative prey did or did not reduce the functional response to target prey, depending on the predator, stage and species of alternative prey. The only consistent trend for both predators was that the predation of Panonychus ulmi deutonymphs was reduced when Tetranychus urticae was present.
- 4Hypothesis III: the predator species with the highest mean ovipositional response will out-compete the other predator species. The number of predators observed in the mixed predator treatments depended on the prey composition. Although A. fallacis had a higher ovipositional response, it was never more abundant. Intraguild predation probably played a role in determining predator abundance, although prey composition altered intraguild effects.
- 5These results highlight the complex nature of predator and prey interactions. Because of these interactions, functional and numerical assays on single predator–single prey systems in simplified laboratory environments do not allow predictions of the growth of mixed populations in realistic habitats, or of the effectiveness of predators as biological control agents in the field.