Mammalian species richness and morphological complexity along an elevational gradient in the arid south-west

Aim We examined the relationship between species richness and morphological complexity of terrestrial mammal communities along an elevational gradient . Location The gradient is in the Sonoran Desert in Southern California and e xtends from a sand dune habitat near sea level to coniferous forest ending at >2600 m. Methods Morphological diversity, characterized by both size and shape of co existing mammal species, was estimated within and between sites from projec tions of variables on principal components axes. Similarities among species were calculated as Euclidean distances. To tease apart size and shape, we constructed two principal component analyses: one based on log-transformed original measurements, the other on log-transformed proportional shape vari ables. To test whether species number accounted for the morphological diver sity at each site we designed two null models. The models generated were ra ndom communities generated from the forty-two-species pool. Indices of morp hological diversity for real communities were compared with the results of 500 simulations of each null model. Results Species richness varied along the gradient, peaking in the mid-elev ation agave ocotillo habitat. Morphological diversity of shapes and sizes c orrelated strongly with species richness. Locomotor, tooth, and skull trait s were all important in distinguishing among species. Main conclusions Two important patterns emerged: (1) diversity of both size s and of shapes of species within communities correlated positively with sp ecies number, and both sets of variables behaved similarly across this grad ient; (2) the most species rich sites were not composed of specialists on t hese best places, but rather, a community of species derived from overlappi ng faunal groups.