Introduction of Exotic Earthworms

in the Boreal Forest of Western Canada

Erin K. Cameron, Dr. Erin M. Bayne, Dr. David W. Coltman, and Dr. M. Jill Clapperton

CW 405, Biological Sciences Centre, University of Alberta, Edmonton, Alberta, Canada, T6G 2E9

Recreational and industrial development is expanding rapidly in the boreal forest of western Canada.  Concerns exist that such activity is facilitating the introduction and spread of non-native species such as exotic earthworms.  The mechanisms by which earthworms are introduced and spread in forested systems are not well understood.  Given the poor innate dispersal abilities of earthworms, we propose four major introduction mechanisms: 1) Direct introduction by humans via abandonment of fishing bait; 2) indirect dispersal by humans via vehicle traffic; 3) transport via waterways; or 4) “natural dispersal” via vertebrate predators.  To test the plausibility of these various hypotheses, we sampled earthworms in forest stands near boat launches, linear features (roads & seismic lines), forest interiors, and remote shore lines of lakes in the boreal forest of northern Alberta, Canada.  Boat launches and roads had a significantly higher probability of earthworm occurrence compared with the other locations.  Species commonly used as fishing bait occurred more often near boat launches than near roads alone.  These results suggest that both vehicle transport and bait abandonment are the major mechanisms of earthworm introduction in Alberta’s boreal.  The consequences of these introductions remain unclear, but suggest that reduced road construction and regulations prohibiting the discarding of bait need to be considered to slow earthworm invasions.

Because the number of individuals introduced and the number of introduction events is emerging as the most consistent predictor of the establishment success of invasive species (Lockwood et al. 2005), we are using genetics to determine whether Dendrobaena octaedra populations are established by single or multiple introduction events.  We sequenced the mitochondrial cytochrome oxidase subunit I of Dendrobaena octaedra individuals collected at the locations described above. This information is allowing us to test several predictions about the results expected under different introduction scenarios: 1) if all populations originate from a single source and single invader, one genotype should be detected across the range; 2) if populations originate from a single invader from multiple sources, populations should each contain a unique genotype; and 3) if populations are founded by multiple invaders, either from single or multiple sources, multiple genotypes should be detected in each population (Bohonak et al. 2001).  Results indicate that populations may be established by single invaders or multiple invaders.  As well, the likelihood of multiple introduction events appears to be greater in areas with greater human activity.  If this result is borne out by our continuing research, it would suggest that measures should be taken to reduce human activities associated with greater earthworm introduction rates in Alberta’s boreal.