We investigated the numerical response by coccinellids to aphid density within individual alfalfa fields and among geographically separated alfalfa fields. When patterns of aphid and predator abundance were analyzed on the basis of variation within individual fields during the growing season, there was an aggregative numerical response by Hippodamia convergens but not by other Coccinellidae. There was a reproductive numerical response by most coccinellids. When patterns of coccinellid and aphid abundance were compared for geographically separated fields there was no evidence of an aggregative or reproductive numerical response by any species. Variables describing the composition and structure of the landscape surrounding alfalfa fields and the vegetation within fields entered into stepwise regression models for coccinellid abundance in geographically separated fields more frequently than aphid abundance did. We conclude that features of the landscape play an important role in determining coccinellid abundance and distribution in space, and determine the size and species composition of the pool of coccinellids available to colonize alfalfa fields.
Species 1: Coleoptera Coccinellidae
Species 2: Homoptera Aphididae
Keywords: predator-prey interaction
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