, Volume 25, Issue 1, pp 69-78
Date: 20 Oct 2009

Measuring edge contrast using biotic criteria helps define edge effects on the density of an invasive plant

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Habitat edges can alter population dynamics, influence community structure, determine the success of conservation efforts, and facilitate the spread of invasive species. Despite recognition that edges influence the nature and strength of ecological interactions, edges are generally characterized using abiotic measures that likely capture habitat quality for only the focal taxa, and ignore the potential for biotic interactions to explain edge effects. Here we describe the association between edges and the density of an invasive shrub, Lonicera maackii, and infer the functional role of edges by using multiple criteria to weight edge contrast. We define edge contrast using both an abiotic criterion in which contrast is weighted by differences in light availability, and a biotic criterion in which edge contrast is weighted by the association between edges and the abundance of the American Robin (Turdus migratorius), an important avian seed disperser. Biotically defining edge contrast significantly improved model fit in all cases, demonstrating that the large-scale distribution of an invasive shrub is best predicted using both abiotic and biotic edge characterization. More generally, our work suggests that weighting edge contrast using key biological interactions in addition to abiotic criteria may be a promising way to understand the multiple pathways by which edges influence the distribution and abundance of organisms.