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Summary: Covariation and composition of arthropod species across plant
genotypes of evening primrose, Oenothera biennis
Marc T. J. Johnson and Anurag A. Agrawal
M. T. J. Johnson (mtj5@duke.edu), Dept of Ecology and Evolutionary Biology, Univ. of Toronto, Toronto, Canada, ON M5S 3B2.
Present address for MTJJ: Dept of Biology, Duke University, Durham, NC 27708, USA. Á A. A. Agrawal, Dept of Ecology and
Evolutionary Biology, Corson Hall, Cornell Univ., Ithaca, NY 14853, USA.
Genetic variation in plants has broad implications for both the ecology and evolution of species interactions. We
addressed how a diverse community of arthropod species covary in abundance among plant genotypes of a
native herbaceous plant (Oenothera biennis), and if these effects scale-up to shape the composition, diversity, and
total abundance of arthropods over the entire lifetime of plants (two years). In a field experiment, we replicated
14 plant genotypes of O. biennis across five field habitats and studied the arthropod communities that naturally
colonized plants. Genetic variation in O. biennis affected the abundance of 45% of the eleven common species
in 2002, and 75% of sixteen common species in 2003. We examined the strength of correlations in mean
abundance of arthropod species among plant genotypes and found that species responded independently to
variation among genotypes in the first year of the study, whereas species formed positively covarying clusters of
taxa in the second year (rmean 00.35). The strength of these correlations did not consistently correspond to
either taxonomy or functional attributes of the different species. The effects of plant genetic variation on the
abundance and covariation of multiple arthropod species was associated with cascading effects on higher levels of
community organization, as plant genotype and habitat interacted to affect the species composition, diversity,
and total abundance of arthropods in both 2002 and 2003, though the specific effects varied across years. Our
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