Proximity to agriculture alters abundance and community composition of wild sunflower mutualists and antagonists

Abstract

Anthropogenic modifications of the landscape, such as agriculture, are widespread globally and can reduce native biodiversity and homogenize communities by decreasing variation in species composition across sites. Partitioning anthropogenic impacts among species that have positive versus negative effects on plants may improve our ability to forecast the ecological and evolutionary consequences of these alterations in communities. Here, we manipulated the distance of populations of a wild sunflower species (Helianthus annuus texanus) to fields of its domesticated relative (crop sunflowers, H. annuus) and contrasted subsequent shifts in the abundance and community composition of mutualists (pollinators) and antagonists (seed predators, folivores) of H. a. texanus. With some exceptions, populations of H. a. texanus near crop sunflowers supported higher numbers of pollinators than those far from crop sunflowers. In contrast, in the majority of cases, populations of H. a. texanus supported more seed predators when located far from crop sunflowers. Folivore damage to plants was greater far from crop sunflowers, and was never greater near crop sunflowers. Contrary to the prediction that proximity to agriculture homogenizes community composition, we found β-diversity of pollinators (species turnover between populations) was greater near crop sunflowers. Our results demonstrate that mutualists and antagonists of a wild plant species respond differently to the proximity of a related crop species, indicating the potential for both altered population dynamics and complex selection pressures on wild species in agricultural landscapes. © 2013 Chamberlain et al.