Behavioral responses of a native salamander to native and invasive earthworms

Abstract

Invasive species may positively affect native organisms by providing habitat, serving as prey, or acting as an ecological substitute for a beneficial native species. I examined whether the behavioral responses to invasive earthworms of Plethodon cinereus, a woodland salamander native to eastern North America, were influenced by co-occurrence with native earthworms. Co-occurrence with native earthworms varies throughout North America because earthworms were extirpated from the northern portion of the continent during the Wisconsin Glacial Episode. Non-native earthworms have invaded most of North America, including once-glaciated areas. I compared responses to earthworms by P. cinereus from (1) historically glaciated areas with no co-occurrence (for ~7 ky) with native or invasive earthworms, (2) historically glaciated areas with recent co-occurrence (~10 years) with invasive earthworms, but no historical co-occurrence (for ~7 ky) with native earthworms, or (3) unglaciated areas with recent and historical co-occurrence with invasive and native earthworms. Salamanders from different areas did not differentiate between native (Eisenoides carolinensis or Diplocardia sp.) and invasive earthworms (Lumbricus terrestris) as prey or differentiate between their burrows. Salamander burrow use and time to first burrow use were influenced by recent or historical co-occurrence with earthworms, respectively. Salamanders with historical range overlap with native earthworms had shorter latencies to attack and handling times, and were more likely to consume earthworms. As globalization increases the frequency and impact of invasive species in native systems, we should consider the multiple ways in which invasive species interact with native communities and potential geographic variation in the responses of native organisms to invasives.