COS 120-8
Impacts of an invasive mustard on an threatened sand dune lizard
Desert sand dunes are among the harshest environments on earth. They also provide habitat for a diverse array of plants and animals that have evolved unique adaptations enabling them to exist and thrive despite the challenges sand dunes present. Such a hot, dry, wind-blown and sand-scoured landscape would seem immune from invasive species, yet Sahara mustard, Brassica tournefortii, has spread throughout the hot arid regions of North America, becoming especially abundant on and surrounding aeolian sand communities. Previous research has demonstrated that this mustard dramatically reduces native sand dune annual plant, and native arthropod abundance and species richness, but impacts higher within food webs have not yet been documented. Here I present data and analyses from a long-term study on the threatened Coachella Valley fringe-toed lizard, Uma inornata, a species now restricted to less than 5% of its original range, with remaining populations fragmented on a handful of protected reserves. Using abundance data collected over 100, 0.1 ha plots distributed across a gradient of mustard densities, I was able to partition demographic shifts attributed to the mustard from rainfall, the otherwise primary driver of population dynamics.
Results/Conclusions
I was able to identify reductions in lizard population growth, λ, independent of rainfall effects, on sites with higher Sahara mustard densities. Mechanistically, Sahara mustard has impacted the amount, character, and composition of detritus that blows onto the dunes and which is the food web foundation for the diversity of species occurring on, and in many cases restricted to these dunes. In this case the replacement of a diverse array of native annual plants with a near-monotypic stand of another, invasive annual plant, has resulted in a trophic cascade of effects. The need to control the mustard is acute; however developing targeted methods for killing or otherwise removing the mustard without collateral damage to native species presents a substantial management challenge.