Below ground competition among invading detritivores

Authors: CHANG, CHIH-HAN - Johns Hopkins University; SLAVECZ, KATALIN - Johns Hopkins University; FILLEY, TIMOTHY - Purdue University; Buyer, Jeffrey; BERNARD, MICHAEL - Johns Hopkins University; PITZ, SCOTT - Johns Hopkins University

Submitted to: Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/6/2015
Publication Date: 1/29/2016
Citation: Chang, C., Slavecz, K., Filley, T., Buyer, J.S., Bernard, M.J., Pitz, S.L. 2016. Below ground competition among invading detritivores. Ecology. 97:160-170. doi: 10.1890/15-0551.1.

Interpretive Summary: Earthworms play several important roles in soil ecology. They decompose surface litter, move organic matter from the surface down into the soil, digest and decompose soil organic matter, and create tunnels that alter soil porosity. There are many earthworm species in North American soils, both native and invasive, and it is not known how, or even if, they compete with each other. In this study both field observations and laboratory experiments were used to analyze the competition between native and non-native earthworm species. We found that two earthworm species directly compete for leaf litter and that, in the presence of one species, the other species altered its feeding behavior. We also found that certain species could feed on a wider variety of organic materials than other species, which could provide a competitive advantage when food was a limiting resource. These results will be useful to soil ecologists and may lead to strategies for managing earthworms and other soil biota in improving sustainability of agroecosystems.

Technical Abstract: The factors regulating soil animal communities are poorly understood. Current theory favors niche complementarity and facilitation over competition as the primary forms of non-trophic interspecific interaction in soil fauna. However, competition frequently has been suggested as an important community-structuring factor in earthworms, ecosystem engineers that influence belowground processes. To date, direct evidence of competition in earthworms is lacking due to the difficulty inherent in identifying a limiting resource for saprophagous animals. In the present study, we offer the first direct evidence of interspecific competition for food in this dominant soil detritivore group by combining field observations with laboratory mesocosm experiments using 13C and 15N double-enriched leaf litter to track consumption patterns. In our experiments, the Asian invasive species, Amynthas hilgendorfi, was a dominant competitor for leaf litter against two European species currently invading the temperate deciduous forests in North America. This competitive advantage may account for recent invasion success of A. hilgendorfi in forests with established populations of European species, and we hypothesize that specific phenological differences play an important role in determining the outcome of the belowground competition. In contrast, Eisenoides lonnbergi, a common native species in Eastern United States, occupied a unique trophic position with limited interactions with other species, which may contribute to its persistence in habitats dominated by invasive species. Furthermore, our results supported neither the hypothesis that facilitation occurs between species of different functional groups, nor the hypothesis that species in the same group exhibit functional equivalency in C and N translocation in the soil. We propose that species identity is a more powerful approach to understand earthworm invasion and its impacts on belowground processes.