ECOLOGICAL RELEASE AND NAÏVETÉ SHAPE PREY CONSUMPTION IN A RAPIDLY EXPANDING INVASIVE PREDATOR

Abstract

Invasive predators face novel eco-evolutionary pressures yet processes governing shifts in prey consumption and associated trophic benefits that promote invasion success remain poorly understood. Ecological release from competitors and enemies, combined with predator and prey naïveté, is likely to shape predator–prey interactions and prey consumption by invasive predators. Thus, we predicted ecological release and increasing naivete along invasion pathways will yield broader, more flexible diets at leading edges, intermediate diets in established regions, and narrower diets in native ranges. Thus, to test this prediction, we screened 543 intestinal samples using DNA metabarcoding to understand how and why diet diversity and composition shift along an invasion pathway for a successful generalist predator, the barred owl (Strix varia), spanning its native range in Minnesota and Wisconsin, established invasive range in Oregon and Washington, and the leading invasion edge in California. Barred owls consumed 135 species across 67 families and 12 classes. The diversity of prey families consumed doubled in both the established invasion (Hill-Shannon Diversity (H) = 22.8) and leading edge (H = 23.4) stages compared to the native stage (H = 10.5). Diet composition varied among invasion stages but not seasonally, with owls consuming a greater proportion of mammals and reptiles in their native range, amphibians in the established areas, and birds and invertebrates in leading edges. Biogeographic variation in prey availability did not appear to influence the diversity or composition of prey consumed. We suggest naïveté shapes prey consumption in range-expanding predators, leading to diets composed of nutritionally poor prey where naïveté is high. Flexibility in nutritional requirements allows predators to overcome nutritional deficiencies, promoting invasion success.