Edge effects on ground beetles at the woodlot-field interface are short-range and asymmetrical

Abstract

Boundaries between woodlots and agricultural habitats are numerous in temperate agricultural landscapes and influence ecological processes in both woodlots and agricultural habitats. 2 We aimed to determine how far the species assemblage of ground beetles in woodlot and open habitats was influenced by the presence of the woodlot-field boundary. 3 We studied the distribution of ground beetles on both sides of the boundaries of four woodlots along transects of pitfall traps (n = 140). The depth of edge influence (i.e. the distance from the boundary at which the presence of the boundary has no more significant influence) on the species assemblage of ground beetles in each woodlot and in each agricultural habitat was determined with nonlinear canonical analysis of principal coordinates, an ordination method that is followed by nonlinear regression of the principal coordinates on distance from the boundary. 4 The depth of edge influence on the species assemblages of ground beetles was asymmetrical relative to the boundary: it was generally higher and had higher variability in open habitats (14.4 ± 12.3 m) than in woodlots (4.9 ± 2.3 m). Species assemblages of ground beetles in edges were a mix between both adjacent species assemblages. Edge effects in woodlots were deeper in the woodlots exhibiting a deeper penetration of open habitat species. Symmetrically, edge effects in open habitat were deeper in the open habitats with a deeper diffusion of forest species into the open habitat. 5 Forest ground beetles were not threatened by edge effects. Rather, edge effects are likely to benefit agriculture, mostly through the dispersal of predatory forest species into agricultural fields.