Invasive Asian Earthworms Negatively Impact Keystone Terrestrial Salamanders

Area of Science:

• Ecology
• Invasive Species Biology
• Herpetology

Background:

• Asian pheretimoid earthworms (Amynthas, Metaphire spp.) are invasive in North American forests.
• These earthworms consume forest detritus, impacting habitat for native biota, including the Eastern Red-backed Salamander (Plethodon cinereus).
• Previous research linked leaf litter loss to earthworm invasion and salamander declines, but direct interactions remain understudied.

Purpose of the Study:

• To investigate the direct interactions between invasive Asian pheretimoid earthworms and Plethodon cinereus.
• To test the hypothesis that earthworms exclude salamanders from high-quality microhabitats, reduce foraging efficiency, and negatively affect fitness.
• To assess the impact of earthworm invasion on salamander abundance and body condition in invaded versus non-invaded sites.

Main Methods:

• Laboratory trials assessing salamander microhabitat use and foraging in the presence of earthworms.
• Field experiment comparing salamander and earthworm co-occurrence under cover objects in invaded and non-invaded Ohio forests.
• Statistical analysis of earthworm abundance and its association with salamander abundance and body condition.

Main Results:

• In lab trials, salamanders used lower-quality microhabitats and consumed fewer prey when earthworms were present.
• Field observations showed significantly less overlap between salamanders and earthworms under cover objects than expected.
• Earthworm abundance negatively correlated with juvenile and male salamander abundance, but not female abundance.
• No significant effect of invasion on salamander body condition was detected.

Conclusions:

• Invasive earthworms physically exclude Eastern Red-backed Salamanders from critical cover objects.
• This exclusion, coupled with habitat degradation, likely hinders juvenile and male salamander performance.
• Reduced access to resources and increased risks may lead to decreased recruitment and population declines in invaded areas.