PARENT SESSION
Oral Session # 26: Agro-Ecology II.
Presiding: K Gross
Tuesday, August 5. 1:30 PM to 5:00 PM, SITCC Meeting Room 100.
Predator diversity and the biological control of agricultural pests: A test of the host-plant heterogeneity hypothesis.
Aquilino, Kristin*,1, Cardinale, Bradley1, Ives, Anthony1, 1 University of Wisconsin-Madison, Madison, Wisconsin, USA
ABSTRACT- Recent theoretical and experimental evidence suggests that consumer diversity may influence how efficiently limited resources are captured through resource partitioning and/or changes in species interactions. Resource partitioning and species interactions are known to be sensitive to habitat diversity; yet few studies have examined the potential for diversity effects of consumers on resources to change between homogeneous and heterogeneous environments. We used a dual replacement series experimental design to simultaneously manipulate the species richness of predators (consumer diversity - Harmonia axyridis, Coleomagilla maculata, and Nabis) of the pea aphid Acyrthosiphon pisum (the resource) in laboratory microcosms having one or three host plant species (habitat heterogeneity - Medicago sativa, Trifolium pratense, and Vicia faba). We then compared how predator richness influenced aphid consumption in plant monocultures and polycultures. We found no interaction between predator and host plant richness on the consumption of aphids (F1,100 = 0.01, P=0.92). There were, however, main effects of both predator diversity and habitat heterogeneity treatments. Consumption of aphids was significantly higher (by 21%) in microcosms containing three predator species versus those having an equal density of just one predator species (F1,100 = 4.46, P=0.04). This was due to either reduced intraspecific competition in the more diverse assemblages and/or interspecific facilitation between predator species. The consumption of aphids was also significantly reduced in plant polycultures (by 31%) compared to monocultures having equal plant density (F1,100 = 4.60, P=0.03). These results were driven by a reduction in predator efficiency on the host plant Vicia faba, and were potentially exacerbated by aphids moving to Vicia faba in polycultures. Our study demonstrates that diversity at multiple trophic levels may simultaneously impact the capture of limiting resources. Furthermore, in our study, the diversity of trophic levels acted independently as some theory has predicted.
Key words: ecosystem functioning, natural enemies hypothesis, biodiversity, species richness