The structure and dynamics of communities are influenced by a variety of trophic and non-trophic interactions. Recent literature has highlighted the role of ecosystem engineers in many communities. Earthworms act as ecosystem engineers through their burrowing activities, and are also a prey item for many animals, including salamanders. Many terrestrial salamanders spend large portions of their time underground; underground habitat availability likely affects salamander interactions and provides overwinter refuges. However, to my knowledge, no researcher has tested the hypothesis that these salamanders utilize and benefit from burrows created by earthworms. However, indirect effects resulting from competition between earthworms and micro-invertebrates, may also affect salamanders because micro-invertebrates are an important food source for salamanders. To examine the influence of earthworms on salamander behavior and survival via indirect and ecosystem engineering effects, I conducted a series of mesocosm experiments using semi-natural enclosures. I used the common non-native earthworm, Lumbricus terrestris, as my ecosystem engineer. Because of their large size, adults of L. terrestris are unlikely to be consumed by adults of the salamanders, Plethodon cinereus and P. glutinosus, used in these experiments. This allowed me to examine the indirect effects (through both biotic and abiotic pathways) of an earthworm on the salamanders, as opposed to the direct effects caused by the consumption of earthworms by salamanders. Results/Conclusions
The behavior (i.e., cover object use) of P. cinereus, but not P. glutinosus, was influenced by the presence of earthworms. I found that individuals of P. cinereus used earthworm burrows 50% of the time given the opportunity, indicating that habitat creation by earthworms may be important for this species. Earthworms also significantly reduced the amount of leaf litter and the number of microinvertebrates in the mesocosms, suggesting that earthworms affect P. cinereus through both ecosystem engineering and indirect pathways. In addition, I found that the importance of the non-trophic pathway between earthworms and salamanders might vary by season, but that the refuge provided by earthworm burrows increases overwinter survival. Finally, I found that the ecosystem engineering activities of earthworms provided a refuge for P. cinereus allowing them to avoid a common predator, Thamnophis sirtalis. By providing underground habitat for P. cinereus, the most abundant vertebrate in many eastern forests, earthworms may have a large impact on aboveground faunal communities.
