Lizard community structure along environmental gradients.

1. How the total number of individuals in a community is divided among its species is governed by both the distribution of species along landscape-scale environmental gradients and by local resource partitioning. In vertebrate ectotherms, abiotic environmental conditions may constrain geographic distributions more strongly than local population densities due to thermal constraints on resource acquisition and due to behavioural thermoregulation. 2. We investigate whether local density and species richness are decoupled for lizard communities within the Southwest US by comparing 18 species-abundance distributions. 3. While species richness decreases strongly with decreasing temperature, there is no significant relationship between temperature or resource availability (net primary productivity) and the total number of individuals within a community. Consequently, in more species-rich communities species have lower mean abundances. 4. This suggestion that lizard species richness is not a function of an area's capacity to support more individuals questions for this group species diversity theories based on this assumption.