Local community diversity is a function of both regional-scale processes (speciation, extinction) that determine the size of colonizing species pools and local-scale processes (competition, predation) that limit community membership. Recently, research has focused on spatial population processes occurring at the mesoscale, including mass effects, source-sink, and colonization-extinction dynamics of metapopulations, that link such local- and regional-scale processes. The population processes of these metacommunities jointly influence the diversity of local communities and are sensitive to the composition and spatial geometry of different habitat types across landscape mosaics. Indeed, the surrounding landscape can influence the diversity of local communities in ways that may not be predicted by local- and regional-scale factors alone. As such, the spatial relationships of different landscape features at the mesoscale represent essential determinants of local community diversity, and provide the context necessary for a more thorough understanding of community organization. One complication, however, is that there are many landscape features found within the vast spatial and temporal extent of the mesoscale, and community organization may need to be examined through many different spatial contexts.
Results/Conclusions
We used a hierarchical approach to describe how spatial relationships of landscape features calculated at different spatial extents determine the composition of 59 local communities of lizards occupying Shinnery Oak sand-dune habitats within the Mescalero Sands ecosystem of New Mexico. We evaluated characteristics of lizard species’ distributions, including coherence, species turnover and range boundary clumping, to distinguish among idealized patterns of metacommunity structure. We observed a nested subsets pattern of diversity with clumped species loss, which indicates these lizard species co-occur in discrete communities with groups of species replacing each other along a latent environmental gradient. We then used regression tree analyses to quantify associations between site scores from the primary ordination axis (reciprocal averaging) and the spatial geometry of different landscape features calculated at 20, 100, and 1000 hectare spatial extents. Ordination scores for sites and therefore metacommunity structure were primarily dependent on the number and geographic arrangement of different landcover types. We observed scale-dependence, however, in the specific landcover types and spatial relationships among them that best explained variation in ordination scores across sites. From these observations, we therefore conclude that multiple spatial contexts are needed to comprehensively understand community structure in this lizard assemblage.