Meeting Abstract
In an era of global warming, ecological communities are increasingly influenced by species invasions and shifting species ranges. To predict and mitigate potential negative impacts, it is important to understand how interactions with natural enemies can impact the distribution and abundance of species in motion. Shifting geographic ranges may allow hosts either to escape from natural enemies, such as parasites, parasitoids and predators, or to experience biotic resistance from novel resident enemies in their new range. In addition, whether the losses or gains of natural enemies during a range shift will affect the population abundance of a species in motion will depend on its abiotic tolerances. Here, I present two case studies examining the influence of natural enemies on host species following a range shift. In the first study, I examine the abundance and diversity of parasites of a large marine snail, Kellet’s whelk (Kelletia kelletii), throughout its historical and expanded range in coastal California. Expanded-range populations of Kellet’s whelk experienced substantially lower parasite abundance and diversity than the historical-range populations, perhaps due to the limitations resulting from complex parasite life cycles and a major biogeographical boundary. In the second study, I examine the abundance and diversity of parasitoids and pathogens of the light brown apple moth (Epiphyas postvittana), a highly polyphagous leafroller that recently invaded California from Australia. Although this leafroller continues to increase its range in coastal California, an initial increase in abundance in San Francisco and Santa Cruz has been followed by a subsequent decline. Constraints imposed by both abiotic factors and natural enemies are considered in the unusual decline of this exotic pest in California.
