Differential response of selected taxa to landscape context and agricultural intensification

Understanding the dynamics of biodiversity in changing agricultural landscapes is a goal for nature conservation and agricultural policies. Agriculture operates at several spatio-temporal levels from field to landscape, and induces differential response of communities according to their ecological traits. Reactions of several taxa to landscape and agricultural changes was conducted along landscape gradients in northern Brittany (France) gathering 14 sites. Landscapes ranged from fine grained areas, with a large proportion of permanent grasslands, wood and hedgerows, to coarse grained ones dominated by crops. Response of communities were either loss of species along the gradient (as for Diptera Chironomidae and Empididae), replacement (Coleoptera Carabidae) and no change in species composition (small mammals). In this paper, we present why these taxa react in such different ways according to their life history traits, their mobility patterns and to which parameters of landscape structure or agriculture intensification they are sensitive. Density of hedgerow networks, and permeability of individual hedgerows determine the spatial distribution of adults Diptera according to their flying ability. Mean body size of carabid beetles significantly decreases along the gradient of agricultural intensification, small species adapted to disturbance replacing large ones that are characteristic of stable habitats. The same small mammal species are found all along the two gradients, but their relative abundance is linked to the importance of crops versus more stable habitats in the landscape. We concluded that species survival in those fine grained agricultural landscapes depends on processes operating at the site scale and defining habitat quality, and processes operating at the landscape and/or metapopulation scale such as landscape modifications in connectivity and habitat availability. (C) 2003 Elsevier Science B.V. All rights reserved.