How the aphids got their spots: predation drives self-organization of aphid colonies in a patchy habitat

Authors


Miroslav Kummel, Environmental Program, Colorado College, 14 E Cache la Poudre, Colorado Springs, CO 80903, USA. E-mail: mkummel@coloradocollege.edu

Abstract

Using a 30 day time series of aphid Aphis helianthi and coccinellid counts on 107 mapped racemes of Yucca glauca, we demonstrate progressive, predation-induced self-organization of aphid colonies on individual racemes into extremely low and extremely high population sizes. This was driven by a two-attractor structure of density dependence that developed only in the presence of coccinellid predators. Foraging movements of the coccinellids among plants produced a power law relationship (average power = 0.142) between aphid and coccinellid numbers. This resulted in increased predation pressure on mid-size colonies and decreased predation pressure on small and large populations. A field-parameterized mathematical model predicts a two-attractor structure in broad agreement with our observations. The overall system was integrated by the influence of the largest aphid populations, which determined the total number of coccinellids present, and thus the predation pressure throughout the system. Our study provides clear evidence of predator-driven self-organization of prey populations in a patchy environment.

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