Tuesday, August 5, 2008
Exhibit Hall CD, Midwest Airlines Center
Background/Question/Methods Invasive species are a top cause for species endangerment worldwide, pose serious threats to native plant and animal communities, and reduce the diversity of native species especially in forests. Studies from Northern States document that exotic earthworm species have invaded forests altering decomposition and nutrient cycling. Further, invasive earthworms may facilitate the expansion of invasive plant species such as Microstegium. To date, little work has been done to determine the threats these earthworms pose to native plant communities in the Southeastern USA. We set out to survey earthworm and plant communities in forest fragments around Roanoke, VA. Our specific goals were to determine (1) if invasive earthworms were present, (2) whether patterns of earthworm abundance would indicate likely methods of release, and (3) if invasive earthworm abundance was correlated with exotic plant abundance or levels of human disturbance. In the early fall of 2007, we surveyed vegetation using strip transects and earthworms using mustard water extraction methods in 7 sites. These sites ranged from small suburban fragments (<10 ha) to large nature reserves (5,100 ha).
Results/Conclusions Invasive earthworms are indeed common in the area; we found 430 individuals from 7 different species. Abundance did not differ between sites near to and distant from waterways, indicating that discarded fishing bait is unlikely the sole source of release. Nearly all the invasive earthworms (96 percent) were found in small fragments less than 10 ha rather than in large fragments greater than 100 ha suggesting that proximity to human development is an important factor in invasive earthworm population dynamics. Invasive earthworm abundance was highly correlated with invasive plant species richness and abundance. Our next step is to examine causal relationships between invasive earthworms and native plant diversity.
