LAUSR

Comparison of highly successful and less successful invasive species can highlight traits that are associated with invasion success, and indicate the associated risk of further establishment or invasion from novel species. We compared variation in δ13C and δ15N, or isotopic niche, in the tissues of matched pairs of highly successful and less successful (respectively) freshwater and marine aquatic invasive species: violet tunicate Botrylloides violaceus and golden star tunicate Botryllus schlosseri from the northwest Atlantic coast; spiny waterflea Bythotrephes longimanus and fishhook waterflea Cercopagis pengoi from the Great Lakes basin; and Pacific oyster Crassostrea gigas and eastern oyster Crassostrea virginica from the northeast Pacific coast. Individual (δ13C and δ15N) and population (Bayesian ellipses of δ13C and δ15N) level comparisons of isotopic niche revealed, in most cases, greater niche breadth in the more successful species of tunicate but the less successful species of waterflea and oyster. Comparison with the literature suggested that a broad dietary niche is less crucial for widespread distribution of aquatic invasive invertebrates than it is for vertebrates (i.e., fishes). Inconsistency in the association between isotopic niche breadth and invasion success could be due to a greater influence of habitat suitability on variation in invertebrate diets. These findings challenge the common assumption that a broader niche promotes invasion success, and thus, have implications for invasive species risk assessment, management, and our understanding of species spread and distribution.