Evaluation of Earthworm Populations in Managed Ecosystems in Northern Arkansas.
Ashley Rashe and Mary Savin. University of Arkansas, HCR 64 Box 2165A, Shell Knob, MO 65747, United States of America
Native and non-native earthworms exist worldwide in the soil under vegetation that may be native or exotic. The ecology of organisms that co-evolve within an ecosystem is likely to be distinct from that involving organisms recently introduced to an area. Populations in northern Arkansas were measured to provide a current estimate of earthworm identities, distributions, and level of diversity in different ecosystems. We expected to find that under native vegetation, earthworm populations would be predominantly native. Conversely, the disturbance of introducing non-native vegetation may benefit non-native worms. Field plots, including toxic and non-toxic endophyte-infected fescue, forest, restored grasslands and prairies, residential garden, and a pond edge were sampled in the spring of 2006. Sampling methods included a physical approach of digging and sorting by hand or electroshocking. Electroshocking and the dig and hand-sort resulted in average population sizes that were not markedly different, and when grouping ecosystem types as “grass” versus “not grass” there was no difference by ecosystem type. Dig and sort resulted in higher average numbers in the grass ecosystem group than electroshocking, which yielded higher average numbers in “not grass.” Overall, average abundances were higher under native vegetation. Among exotic earthworm species, Lumbricus rubellus, an epigeic worm, was the most abundant earthworm identified,followed by Apporectodea species (which are mainly endogeic). Native earthworms identified included Diplocardia species. No anecic worms were identified in any sample. This research contains preliminary data and more quantitative studies are being conducted. However, this research shows that both native and non-native earthworms are present in northern Arkansas and suggests that native vegetation may support high abundances of earthworms. If we can differentiate worm populations among ecosystems, then we can improve studies investigating how worms alter nutrient availability.