Testing intraguild predation theory in a field system: does numerical dominance shift along a gradient of productivity?
Article first published online: 19 AUG 2003
Volume 6, Issue 10, pages 929–935, October 2003
How to Cite
Borer, E. T., Briggs, C. J., Murdoch, W. W. and Swarbrick, S. L. (2003), Testing intraguild predation theory in a field system: does numerical dominance shift along a gradient of productivity?. Ecology Letters, 6: 929–935. doi: 10.1046/j.1461-0248.2003.00515.x
- Issue published online: 19 AUG 2003
- Article first published online: 19 AUG 2003
- Editor, M. Hochberg Manuscript received 1 July 2003 First decision made 11 July 2003 Manuscript accepted 17 July 2003
- Aphytis melinus;
- California red scale;
- community theory;
- Encarsia perniciosi;
- food web;
- trophic interactions
Although ecological theory exists to predict dynamics in communities with intraguild predation (IGP), few empirical tests have examined this theory. IGP theory, in particular, predicts that when two competitors interact via IGP, with increasing resource productivity: (1) the IG predator will increase in abundance as the IG prey declines, and (2) increasing dominance of the IG predator will cause resource density to increase. Here, we provide a first test of these predictions in a field community consisting of a scale insect and its two specialist parasitoids, Aphytis melinus (the IG predator) and Encarsia perniciosi (the IG prey). The shared resource, California red scale, is a pest of citrus, and its productivity varies across a threefold range among citrus cultivars. We examined both absolute and relative densities of parasitoids along this natural gradient of scale productivity in three citrus cultivars (orange, grapefruit and lemon). Although both parasitoid species were found in all three cultivars, their abundances reflected those predicted by IGP theory: the IG prey species dominated at low productivity and the IG predator dominated at high productivity. This relationship was caused by an increase in Aphytis density with productivity. In addition, the density of scale increased with the dominance of the IG predator. These results from a field system demonstrate the important dynamic outcomes for food webs with IGP.