Earthworms, Slugs, and Salamanders: Community Interactions in a Massachusetts Forest

Earthworms (Order: Opisthopora) have several important ecological interactions with eastern red-backed salamanders (Plethodon cinereus). For the salamanders, earthworms can be nutrient-rich, easy-to-digest prey, or ecosystem engineers of burrows. Indirectly, earthworms can be competition for other microinvertebrate prey species that salamanders prefer to eat. Red-backed salamanders are thought to be a critical player in forest food-webs and possible ecosystem indicator, as they are highly abundant, mid-level consumers that are very sensitive to their abiotic environment. These factors make understanding the interactions between earthworms and salamanders valuable for broader understanding of forest communities. To better understand the earthworm community present at a long-term salamander research site, I tested several earthworm sampling methods in Great Hill Forest on the campus of Bridgewater State University, including mustard vermifuge, hand sampling, and worm grunting. Overall, these methods produced few earthworms; however, dry conditions at the time of sampling may have impacted their success. While sampling, I observed that slugs were numerous. Literature suggests that slugs can also fill the same ecosystem engineer role as earthworms, constructing burrows which salamanders can use. Given this, I conducted several post-hoc analyses to compare slug abundance to both abiotic and salamander abundances and density in order to better understand the distribution of slugs, earthworms, and salamanders in Great Hill Forest. With different distribution patterns, these interactions could play a role in the favorability of particular forest microhabitats for Red-backed salamanders. Red-backed salamanders are thought to be an indicator species of northeastern North American forests, and understanding the interactions of the salamanders, worms, and slugs will allow us to better predict factors that may limit salamander abundance, like possibly forest type.