Response of Soil Fauna to Landscape Heterogeneity: Determining Optimal Scales for Biodiversity Modeling G. CHUST, ∗ †§ J. L. PRETUS, ∗ D. DUCROT,† A. BED ` OS,‡ AND L. DEHARVENG‡ ∗ Departament d’Ecologia, Facultat de Biologia, Universitat de Barcelona; Diagonal 645, 08028 Barcelona, Spain †Centre d’Etudes Spatiales de la Biosph` ere, Centre National d’Etudes Spatiales, 18, Avenue Edouard Belin, 31055 Toulouse Cedex, France ‡Laboratoire d’Entomologie, ESA8043 du Centre National de la Recherche Scientifique, Mus´ eum National d’Histoire naturelle, 45 rue Buffon, 75005 Paris, France Abstract: The concept of scale is inherent to ecological processes that occur over landscapes. To address this issue, we examined the response of soil fauna (Collembola) to landscape heterogeneity at different spatial scales. We derived spatial features from satellite images of the Massif of Arize in the French Pyrenees. We developed a multiscale approach to test the effect of scale of the landscape pattern on species abundance and biodiversity, with a Mantel test and stepwise multiple linear regression analysis, respectively. We distinguished the effect of the “regional” habitat (landscape descriptors) on soil fauna, which is a spatially explicit concept, and that of the “local” habitat (topography and forest type). We carried out a variance-partitioning analysis of species composition and richness to assess the relative contribution of regional and local habitat. The effect of the spatial structure on species abundance was especially strong at a well-defined scale of 48 ha. The surrounding environment that primarily structured the soil fauna assemblages was vegetation cover, measured as the mean of a radiometric vegetation index. Our results show that regional habitat can play an important role in structuring species composition, which is frequently hidden when the scale component is not taken into consideration. Further, we modeled endemic Collembolan richness based on a combination of landscape features at two spatial scales (2.25 ha and 292 ha). The landscape descriptors accounted for 72% of endemic richness variance, although within that variation 41% is shared with local habitat and spatial terms. We used the linear regression model to extrapolate endemism scores over the landscape. Such spatial models could be powerful tools for the selection and delimitation of high-biodiversity areas in conservation policies. Respuesta de la Fauna del Suelo a la Heterogeneidad del Paisaje: Determinaci´ on de Escalas ´ Optimas para el Modelado de Biodiversidad Resumen: El concepto de escala es inherente a los procesos ecol´ ogicos que ocurren en el paisaje. Para abordar este tema, examinamos la respuesta de la fauna del suelo (Collembola) a la heterogeneidad del paisaje en difer- entes escalas espaciales. Derivamos caracter´ ısticas espaciales de im´ agenes de sat´ elite del Massif de Arize, en los Pirineos Franceses. Desarrollamos una aproximaci´ on multi-escala para probar el efecto de la escala del patr´ on del paisaje sobre la abundancia de especies y la biodiversidad utilizando una prueba Mantel y an´ alisis de re- gresi´ on linear m´ ultiple, respectivamente. Distinguimos el efecto del h´ abitat “regional” (descriptores del paisaje), que es un concepto espacialmente expl´ ıcito, y el del h´ abitat “local” (topograf´ ıa y tipo de bosque) sobre la fauna del suelo. Realizamos un an´ alisis de partici´ on de varianza de la composici´ on y riqueza de especies para eval- uar la contribuci´ on relativa del h´ abitat regional y local. El efecto de la estructura espacial sobre la abundancia de especies fue especialmente fuerte en una escala bien definida de 48 ha. El ambiente circundante que pri- mariamente estructur´ o los ensambles de fauna del suelo fue la cobertura vegetal, medida como la media de un ´ ındice radiom´ etrico de vegetaci´ on. Nuestros resultados muestran que el h´ abitat regional puede jugar un papel importante en la estructuraci´ on de la composici´ on de especies, que frecuentemente es escondido cuando el §Address for correspondence: Laboratoire Evolution et Diversit´ e Biologique, CNRS/UPS UPS Toulouse III, bˆ atiment IVR3, F31062 Toulouse, France, email chust@cict.fr Paper submitted November 16, 2001; revised manuscript accepted April 30, 2003. 1712 Conservation Biology, Pages 1712–1723 Volume 17, No. 6, December 2003