Implications of Climate Change for Earthworm Distributions

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Possible interactions between global change and earthworm invasions are of considerable interest (Bohlen et al. 2004, Frelich et al. 2006). First, the distributions of invasive earthworms worldwide could be altered with changes in land use and climate. Land transformation provides more opportunities for invasion, and, conversely, invasions enhance and drive land transformation (Hobbs 2000). For example, deforestation and other human disturbances could create more habitats suitable for occupation by introduced species. Climate change has the potential to modify impacts of invasive species by affecting their sources, pathways, and destinations (Sutherst 2000). Furthermore, with a warming climate, the demarcation lines of earthworm distributions might advance poleward and to higher elevations, where few or no earthworms occur owing to continental and alpine glaciations. Some European lumbricid species (e.g., Dendrobaena octaedra and Eisenia nordenskioldi) already occur near the Arctic Circle in Russia (Tiunov et al. 2006) and could be expected to advance more rapidly northward into thawing permafrost. Even at lower latitudes altered temperature and precipitation patterns could have more localized effects such as restriction of temperate-adapted lumbricids in tropical areas or expansion of the ranges of regional peregrines such as pheretimoid species in East Asia. Warming at high elevations might be a particular problem for biodiversity conservation; high endemism in mountainous areas could be threatened by invading earthworms (e.g., Pop & Pop 2006). Second, the impacts of earthworms on global change are likely to be complex. In the short term, especially in areas previously devoid of earthworms, invasive earthworms may increase the decomposition of soil organic matter and release more CO2 into the atmosphere (Potthoff et al. 2001, Speratti & Whalen 2008), and in some cases also more N2O (Rizhiya et al. 2007). In the longer term, earthworm activities may increase sequestration of organic carbon in soil via protection from decomposition within waterstable aggregates resulting from earthworm castings (Bossuyt et al. 2005, Martin 1991). Finally, it is interesting to speculate on possible changes in the pool of candidate invasive earthworm species that could result from changing climate, altered land use patterns, and expanding global commerce. In addition to the possible expansion of regional peregrines noted above, rapid adaptations (phenotypic and genetic) among known invasive species should be considered as possible mechanisms that could accelerate their spread into new habitats (Terhivuo & Saura 2006). Conversely, introduced species with narrower temperature or moisture tolerances may become more restricted in distribution under warmer or dryer conditions induced by climate change.