Spatial structure of community of darkling beetles (Coleoptera: Tenebrionidae) in the Negev Highlands, Israel

The distribution of niches in resource space of darkling beetles of Negev desert, Israel were studied using discriminant analysis. Seventeen environmental variables (substrate structure and vegetation) were measured at 375 plots within 15 grids. The first three discriminant axes account for 77% of the variance and reflect a soil structure gradient from sand to clay (the first axis), a gradient of increasing productivity (the second axis), and a type of vegetation architecture (the third axis). Abundance and biomass of tenebrionids increased linearly along the first, the second and the third axes. Species richness and diversity had a slanting parabola shape along the substrate axis and increased along the productivity axis. There were two distinct spatial guilds of tenebrionid species. One guild was composed by species that preferred sandygravel soils, and another guild consisted of species that preferred clay soils. Niche overlapping of the "sandy-gravel" species was lower than that of the "clay" species. Niches of the "sandy-gravel" species were randomly distributed in the resource space. Those of the "clay" species formed a tight cluster with most niches placed in the center of the space, representing the centrifugal type of organization. The conformity of the guild structure with the different types of organization was supported by comparisons between empirical data and stochastic models. The border between these two guilds matches with proposed earlier bioaeographical boundary (Ramon-Zohar line).