RESEARCH:  Impacts of Biological Invasions

Identifying the direct and indirect impacts of invaders is essential for prioritizing conservation efforts. One particularly damaging species is the Argentine ant (Linepithema humile). In addition to being widespread urban and agricultural pests, Argentine ants eliminate most native ants in areas they invade. This loss of an entire assemblage of species has numerous community-wide effects. For example, as part of a long-term survey of reptile and amphibian communities throughout southern California initiated by Ted Case and Robert Fisher, we determined that there was a striking lack of spatial overlap between coastal horned lizards (Phrynosoma coronatum) and Argentine ants. Through an examination of horned lizard diet in the field, coupled with laboratory prey preference and growth rate experiments, we have been able to measure the indirect effects of Argentine ants on horned lizard populations through changes in prey availability. Presently, we are finishing a 4-year radio-telemetry project on horned lizards to further examine the mechanisms responsible for their decline.  While habitat loss was thought to be the primary reason behind the decline of coastal horned lizards, we were able to determine that the invasion of Argentine ants is further causing the decline of this threatened vertebrate in its remaining habitat. Argentine ants also cause changes in the densities of other arthropods including species that may be important pollinators, seed dispersers, or predators of damaging homopterous pests. I plan to continue studying the community-wide impacts of invasions, particularly the direct and indirect effects of ant invaders on vertebrate and invertebrate communities.

An aspect of invasion biology that has only recently begun to be appreciated is that interactions among a variety of invasive species may lead to greater impacts. Particularly, the modification of habitat by one exotic species may facilitate the invasion of other species that otherwise would not have been able to successfully establish or spread. In California, this dynamic is well illustrated by ice plant (Carpobrotus edulis). Ice plant creates thick mats that trap moisture in areas it invades. My preliminary work shows that the abundance of exotic arthropods is much higher in areas dominated by ice plant, and invasive species such as Argentine ants use these areas to penetrate into surrounding areas of native vegetation. Invasive ants in the United States provide another system to examine how previous invasions may pave the way for future ones. For example, the recent establishment of the red imported fire ant (Solenopsis invicta) in coastal California will provide unique opportunities to examine interactions between the two most damaging ant invaders in the United States, Argentine ants and red imported fire ants.

Public Outreach

An important, yet often overlooked, aspect of biology is the direct integration of research with policy, management, and the public. By directly interacting with the public through lectures and the popular press, scientists can reinforce the importance of their work and the value of basic science overall. In the course of my work on biological invasions, I have appeared on CNN, Good Morning America and various national and local television and radio programs. In addition, our work has been highlighted in many local and national newspapers (such as the Los Angeles Times, New York Times, Science Times, and the Orange County Register) and popular magazines including National Geographic, Discover (top 100 stories of 1997 issue), National Wildlife International, and UCSD Perspectives.

• Mechanisms of success in biological invasions
• Patterns and mechanisms of nestmate recognition in social insects
• How different animal taxa respond to habitat fragmentation