Mechanisms driving avoidance of non-native plants by lizards.
Abstract
Introduced plant species modify the environment and alter ecological interactions in communities, often to the detriment of native fauna, but the causes driving negative effects on fauna are rarely examined. We used native Australian scincid lizards Carlia munda and Carlia pectoralis and the introduced weed rubber vine Cryptostegia grandiflora as a model system to determine the possible underlying mechanisms driving habitat selection by native fauna in an environment invaded by weeds. Lizards were allowed to select between rubber vine and native eucalypt leaf litter in semi-natural enclosures. To determine the mechanisms of habitat preference, we examined differences in temperature, prey (arthropod) availability and composition, and leaf shape of naturally occurring rubber vine and native vegetation. Lizards discriminated between leaf litter types: 85% of Carlia pectoralis and 80% of Carlia munda chose native leaf litter over rubber vine, clearly indicating a preference for native habitat. In the field, rubber vine leaf litter was cooler at the surface than native leaf litter, and during peak lizard activity was below the temperature range of Carlia. Rubber vine also contained significantly fewer arthropod taxa and a significantly different composition of arthropod taxa, with fewer preferred prey items of Carlia than native vegetation. Finally, rubber vine leaves were significantly shorter than native leaves and the lizards themselves. The shape of rubber vine leaves was different from that of the lizards, potentially making the lizards more obvious on rubber vine litter. This may increase the susceptibility of the lizards to detection by predators. Synthesis and applications. In comparison with native habitat, rubber vine provided a suboptimal environment for litter-dwelling lizards because of the lower ambient temperatures, reduced availability of prey and a reduction in camouflage from predators (dissimilar leaf and lizard shapes). Our study has identified three possible mechanisms by which an introduced plant species can alter the availability of resources in an environment, making it less attractive to native fauna. Our results highlight the importance of understanding how alien plants alter the environment and further emphasize the critical need for management of plants that replace native habitat with a suboptimal environment.