Community assembly of earthworms in previously glaciated regions of North America

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Julieanne Montaquila, Yuntong Sun and Caroline Kim, Colgate University, Hamilton, NY, Timothy S. McCay, Biology and Environmental Studies, Colgate University, Hamilton, NY

Background/Question/Methods
Exotic earthworms, including European lumbricids and Asian megascolecids, negatively affect ecosystems of northern North America at many levels, from the soil to the plant community composition. These effects vary based on earthworm functional group. With this imminent threat to North American ecosystems, especially those in previously glaciated regions that developed without earthworms, understanding how earthworm communities assemble is vital to conservation. We conducted a study using raw data from 21 published field studies in the United States and Canada to better understand the pattern in and drivers of earthworm community structure. We gathered data on the earthworm species found at each of 945 sites, along with geographic coordinates and environmental variables. We analyzed sites for nestedness, and correlated habitat and environmental traits with the maximally-packed nested matrix to assess potential drivers of community structure. We also analyzed the nestedness of the matrix organized by earthworm functional group.
Results/Conclusions
Earthworm assemblages at these sites in previously-glaciated North America were significantly nested. Latitude and sample year were correlated with site nestedness. Northernmost sites included the least diverse and most nested assemblages; whereas assemblages in the south were the most diverse and inclusive. Sites studied more recently were more diverse and inclusive than sites studied a long time ago. Functional groups were also significantly nested. The epigeic functional group was most centrally nested, and Dendrobaena octaedra was the species most often found alone. The nested pattern, from least to most inclusive, was as follows: epigeic > epi-endogeic > anecic > endogeic. This pattern suggests a successional trajectory and facilitative relationship among species. Further research on earthworm community assembly will help scientists better understand the invasive dynamics of earthworms into North America, how earthworms will impact these ecosystems, and how to better manage the progressing earthworm invasion.