|Callaham, Jr., M|
Submitted to: Biological Invasions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/20/2005
Publication Date: 9/1/2006
Citation: Hendrix, P., Baker, G., Callaham, Jr., M., Damoff, G., Fragoso, C., Gonzalzez, G., James, S., Lachnicht Weyers, S.L., Winsome, T., Zou, X.M. 2006. Invasion of exotic earthworms into ecosystems inhabited by native earthworms. Biological Invasions. 8:1287-1300. Interpretive Summary: Human industrial activities are leading to an increase of invasions by exotic earthworms into habitats occupied by native species. Although not as well studied as plant or insect invasions, invasive earthworms have caused significant changes in ecosystem dynamics that may have a negative impact on ecosystem functioning and future sustainability. Case studies of exotic earthworm invasions into native earthworm-dominated habitats are examined in this report to develop an understanding of factors that have lead to the proliferation of exotic species. It was found that disturbance is a factor that enhances the ability of exotics to invade native ecosystems but that disturbance may not be a prerequisite to invasion. Native species may resist competitive pressures from exotic species depending on physical, chemical and biological characteristics of individual habitats. It appears that exotic earthworms are capable of exploiting resources not fully utilized by native species. As understanding of factors leading to invasion grows, so does our awareness of impacts on ecosystem function. With this information land managers, researchers, policy makers, and industrial service providers can establish guidelines to prevent or remedy the threat of invasive earthworm species and possible negative effects on ecosystem function and sustainability.
Technical Abstract: The most conspicuous biological invasions in terrestrial ecosystems have been by exotic plants, insects and vertebrates. Invasions by exotic earthworms, although not as well studied, may be increasing with global commerce in agriculture, waste management and bioremediation. A number of cases have been documented in which invasive earthworms have caused significant changes in soil profiles, nutrient and organic matter dynamics, other soil organisms or plant communities. Most of these cases are in areas that have been disturbed (e.g., agricultural systems) or were previously devoid of earthworms (e.g., north of Pleistocene glacial margins). It is not clear that such effects are common in ecosystems inhabited by native earthworms, especially where soils are undisturbed. We explore the idea that indigenous earthworm fauna and/or characteristics of their native habitats may resist invasion by exotic earthworms and thereby reduce the impact of exotic species on soil processes. We will review data and case studies from temperate and tropical regions in order to test this idea. Specifically, we will address the following questions: Is disturbance a prerequisite to invasion by exotic earthworms? What are the mechanisms by which exotic earthworms may succeed or fail to invade habitats occupied by native earthworms? Potential mechanisms could include 1) intensity of propagule pressure (how frequently and at what densities have exotic species been introduced and has there been adequate time for proliferation?); 2) degree of habitat matching (once introduced, are exotic species faced with unsuitable habitat conditions, unavailable resources, or unsuited feeding strategies?); and 3) degree of biotic resistance (after introduction into an otherwise suitable habitat, are exotic species exposed to biological barriers such as predation or parasitism, "unfamiliar" microflora, or effective competition by resident native species?). Once established, do exotic species co-exist with native species, or are the natives eventually excluded? Do exotic species impact soil processes differently in the presence or absence of native species?