Scale dependency of insect assemblages in response to landscape pattern

Patches and their boundaries are sensitive to the scale at which they are viewed. The response of species to patchiness may depend on the resolution and on the extent by which the spatial pattern is perceived. The goal of this paper is to identify the scale at which forest spatial pattern causes changes in species richness and abundances of Dipteran and Homopteran species as a whole, and further on their distinctive ecological functional groups. Using remotely-sensed optical imagery, we described the landscape structure surrounding sampling sites. We used two approaches to deal with the problem of the scale of observation: 1) variation of extent using a multiscale analysis, and 2) comparison of two satellite sensors with different spatial resolutions (SPOT: 20 x 20 m, and Landsat TM: 30 x 30 m). The relationship between entomological data and landscape descriptors at different spatial scales was tested with the Mantel test, redundancy analysis and stepwise multiple linear regression. Relative abundances of Homopteran species were affected by landscape patterns at finer scales than in Diptera. The strength of response to landscape was different for each Dipteran functional group. The multiscale analysis also enabled the optimal scale (6.25 ha) of landscape pattern, accounting for 62% of the variation in Homopteran richness, to be identified. As a practical application, Homopteran richness was mapped by extrapolation of the regression function to the pixels of the image. Multiscale analysis provides an alternative view of fragmentation effects, which are traditionally studied through the patch-based approach, and highlights the importance of scale in ecological processes. The detection of optimal scales and the use of satellite images enable maps of important biotic indicators to be drawn up.