Habitat, predation, and coexistence between invasive and native crayfishes: prioritizing lakes for invasion prevention

Conditions fostering coexistence of native species with invasive species have received little attention in invasion biology, especially for closely related invasive and native species. We used long-term datasets on multiple replicate invasions to define conditions under which native virile crayfish (Orconectes virilis) can coexist with invasive rusty crayfish (O. rusticus). We examined multiple drivers of coexistence involving habitat use and predation at between-lake and within-lake scales to derive predictions that could guide prioritization efforts to prevent future introductions of rusty crayfish and mitigate impacts of existing invasions. Lakes in which native species persisted for many years had significantly less cobble and sand habitats, and significantly more vegetated habitats compared to lakes from which native crayfish have been displaced. In the presence of rusty crayfish, virile crayfish alter their habitat use to vegetated habitats relative to habitat use in the absence of rusty crayfish. Such vegetated habitats had greater plant standing crop, plant species richness, and sediment percent organic matter compared to vegetated sites occupied by rusty crayfish. Our results suggest that low abundance of cobble habitat and altered habitat use allows native crayfish to coexist with the rusty crayfish invader. At the within-lake scale, virile crayfish persist by escaping predation in the vegetated habitats, despite suboptimal abiotic conditions. By understanding these abiotic and biotic conditions that promote coexistence, managers could enhance native crayfish persistence by targeting high cobble lakes for efforts to prevent the introduction of invasive crayfish, and targeting vegetated habitats for protection in already invaded lakes.