Boundary processes between a desert sand dune community and an encroaching suburban landscape

Abstract

In contrast to the body of work in more mesic habitats, few studies have examined boundary processes between natural and anthropogenic desert landscapes. Our research examined processes occurring at boundaries between a desert sand dune community and an encroaching suburban habitat. We measured responses to an anthropogenic boundary by species from multiple trophic levels, and incorporated measures of habitat suitability, temporal variation, and spatial scales. At an edge versus core habitat scale the only aeolian sand species that demonstrated an unambiguous negative response to the anthropogenic habitat edges was the flat-tailed horned lizard (Phrynosoma mcallii). Conversely loggerhead shrikes (Lanius ludovicianus)demonstrated a positive response to that edge. At a finer scale, species that exhibited a response to a habitat edge within the first 250 m included the horned lizards along with desert kangaroo rats (Dipodomys deserti). The latter species' response was confined to 25 m from the edge. For the flat-tailed horned lizard, edge effects were measured up to 150 m from the habitat boundary. Three potential causal hypotheses were explored for explaining the edge effect on horned lizards: 1) potential invasions of exotic ant species Barrows, C. W., et al. 2reducing potential prey for the lizards; 2) road avoidance and road associated mortalities; and, 3) predation from a suite of avian predators whose occurrence and abundance may be augmented by resources available in the suburban habitat. We rejected exotic ant hypothesis due to the absence of exotic ants within the boundary region, and because native ant species (prey for horned lizards) did not show an edge effect. Our data supported the predation hypothesis and road mortality hypotheses. Mechanisms for regulating population dynamics of desert species are often "bottom-up," stochastic processes driven by precipitation. The juxtaposition of an anthropogenic edge appears to have created a shift to a "top-down," predator mediated dynamic for these lizards.

Modeling Landscape‐scale Erosion Potential Related to Vehicle Disturbances Along the USA–Mexico Border

“…The disturbance maps and erosion potential models indicate that two areas with considerable disturbances and erosion potential happen to be designated critical habitat areas for the federally listed endangered Sonoran pronghorn and threatened flat‐tailed horned lizard (Figures and ). Aside from contributing to compaction and erosion, OHV use can potentially affect flat‐tailed horned lizard populations through direct road mortality, the reduction of shrub cover that otherwise protects flat‐tailed horned lizard from predators, and the reduction of annual plants that support invertebrate food sources (Luckenbach & Bury, , Barrows et al ., , Grant & Doherty, ). Sonoran pronghorn are sensitive to noises and other factors related to human presence (Wilson et al ., ); as a result, areas of BMGR, Cabeza Prieta NWR, and Organ Pipe Cactus National Monument are closed off to public access during fawning season (Wilson et al ., ).…”

Population Dynamics of a Threatened Sand Dune Lizard

“…In a related example elsewhere on the Thousand Palms Preserve, the same 2 avian predators were implicated in a decline of flattailed horned lizards, Phrynosoma mcallii, (Barrows et al, 2006). A population model was used to demonstrate that the predators were responsible for a decline of the horned lizards that was in excess of an otherwise modeled/predicted population decline.…”

The impacts of roads and other infrastructure on mammal and bird populations: A meta-analysis

“…Therefore, we highlight the importance of broadening the analysis to other taxonomic groups, such as herpetofauna, plants and invertebrates (e.g. Przybylski, 1979;Angold, 1997;Auerbach et al, 1997;Haskell, 2000;Shine et al, 2004;Barrows et al, 2006). Further research on these taxonomic groups would add up to the current models presented in this study, contributing to eventually produce a model that would provide an accurate estimate of the effects of infrastructure development on biodiversity.…”