Niche engineering reveals complementary resource use

Background/Question/Methods

Greater resource use by diverse communities might result from species occupying complementary niches. Identifying the underlying basis of complementary resource use is often difficult, however, due to the difficulty in relating trait differences between species to their use of complementary resources. Here, we overcame this obstacle by exploring interrelations among habitat complexity, niche complementarity, and biodiversity effects in a community of aphid predators foraging on Brassica oleracea plants. Diverse communities of these predators kill far more aphids than any single predator species, consistent with space-use complementarity leading to emergent diversity effects. The aphids and their predators often co-occur with Plutella xylostella caterpillars, however, which could dampen spatial niche separation among predators by chewing holes in leaves. In turn, reduced niche differences might reduce the benefits of predator diversity for aphid suppression seen on plants with intact leaves. To examine this possibility, we exploited engineering of the foraging environment by caterpillars as a tool to dampen niche divergence among predator species, and thereby reveal any relationship between space-use differences and consumer-diversity effects.

Results/Conclusions

On leaves undamaged by caterpillars, edge- and center-foraging predators combined to kill more prey than any single predator species could by itself. These emergent diversity effects, however, disappeared on plants damaged by caterpillar larvae. Caterpillar chew-holes brought edge micro-habitats to the center of leaves, such that all predator species could attack aphids anywhere on the plant. With spatial niche differences diminished, there were no benefits of predator diversity, as the most voracious single predator species killed the most aphids. Thus, caterpillar herbivory determined whether the combined impacts of multiple predator species reflected complementarity or species’ individual effects. Our study provides direct evidence for a causative relationship between niche differentiation and increased resource consumption by diverse communities. Ecological engineers revealed this relationship by homogenizing the foraging environment and dampening niche separation among consumers.