| The shift to multiple species conservation plans has not been accompanied by methods to evaluate these efforts, nor to provide managers information to employ adaptive management. Here I develop a framework to evaluate hypotheses for species associations within natural communities. These models link species to environmental parameters, shifting the focus of monitoring to environmental drivers of species occurrence and abundance, supplying managers with direct information as to how to employ adaptive management. Key to this framework is being able to distinguish natural population dynamics from a downward trajectory of a species at risk of extinction. For many species in arid environments, rainfall drives population changes. This is the case for Coachella Valley fringe-toed lizards, Uma inornata. A regression model using rainfall and diet to explain lizard population dynamics resulted in an R2 of 0.956, p<0.0001. Departures from the rainfall-diet-population model may signal a need for management actions. The Coachella Valley is a complex matrix of natural community divisions, each with different species abundances, and population responses to changing resources. Recognizing natural community divisions allows sampling frames to be stratified and analyses to be focused on habitats with similar population drivers, responses, and constraints, thus reducing statistical variance and increasing the power to detect departures from predicted population dynamics. Responses of two anthropogenic stressors were examined: edge effects and impacts from an exotic plant invasion. The only species examined that demonstrated a negative response to habitat edges was the flat-tailed horned lizard, Phrynosoma mcallii. Three potential hypotheses were explored to explain this edge response: (1) invasions of exotic ant species reducing native ant abundance; (2) road avoidance and road associated mortalities; and, (3) predation from avian predators whose occurrence was augmented by resources available in the adjacent suburban habitat. The data supported the predation and road mortality hypotheses. The exotic plant, Brassica tournefortii, also had a limited effect on the community, with negative impacts to native annual plant reproduction and sand stabilization. Understanding cause and effect relationships of environmental stressors allows land managers to focus their efforts on components of the environment at greatest risk and where the greatest positive response from intervention will likely occur. |
