Community complexity: Stratifying monitoring schemes within a desert sand dune landscape

Abstract

Landscapes of desert sand dunes are sometimes viewed as biologically and ecologically homogeneous, yet they can be deceptively complex. We analysed temporal and spatial patterns of species occurrence across a desert dune landscape to clarify the utility of a priori community divisions and how those designations facilitate evaluations of whether conservation objectives are being met, and whether adaptive management approaches are necessary. There was a high degree of community concordance within each of the taxonomic groups considered here; where significant patterns in community structure for one taxonomic group occurred, they were paralleled by other taxa in the same areas. Community divisions were identified that provided population sources for species such as federally threatened Coachella Valley fringe-toed lizards, Uma inornata, and endangered Coachella Valley milkvetch, Astragalus lentiginosus var coachellae, while adjacent communities appeared to be population sinks. Despite similarities in appearance and species occurrences, the eolian sand community of the Coachella Valley is a complex matrix of subdivisions, each with different relative species abundances, and different local population responses to changing resources. This degree of demographic asynchrony may provide a level of protection from regional extinction events. Recognizing community subdivisions allows monitoring sampling frames to be stratified and analyses be focused on habitats with similar population drivers, responses and constraints, therefore reducing statistical variance and increasing the power to detect departures from predicted population trends.