Spatial Distribution Analysis of Invasive Pheretimoid Earthworms in West Liberty University’s Campus Woods.

Abstract

The United States is currently amidst a wave of invasion by East Asian pheretimoid earthworms. Multiple genera, genus Amynthas in particular, are widespread invaders with powerful ecosystem engineering capabilities and an expanding range. Invasive populations can reach extreme densities and fluctuate heavily on weekly-to-yearly timeframes compared to other earthworms. Despite their impacts, pheretimoid genera are poorly understood, under-researched, and uncontrolled. A deeper understanding of population dynamics and their mechanisms may allow effective management practices to be developed.  The research was conducted in the summer of 2023 in a forest stand at West Liberty University, a known invaded site. Spatial Analysis by Distance Indices (SADIE) was used to analyze weekly distributions of pheretimoids, showing aggregated distributions in 5 of 7 weeks of surveying, 2 of which were statistically significant (P value < 0.05). Linear regression showed no recorded environmental variables were statistically significant (P value < 0.05) in more than 1 out of 7 weeks and were inconsistent in their impact. Population density was reduced during this survey compared to previous years, likely weakening significance due to sample size. Distributions still showed aggregation, suggesting clustering behavior is the norm for pheretimoid worms even at low population sizes. As regression couldn’t adequately explain clustering patterns, more environmental variables and new data analysis techniques may be needed for future work to determine the underlying mechanisms for pheretimoids.