Establishment of Anolis sagrei on Bermuda represents a novel ecological threat to Critically Endangered Bermuda skinks (Plestiodon longirostris)

Abstract

Bermuda is an isolated, oceanic island with only one endemic terrestrial vertebrate, the Critically Endangered Bermuda skink (Plestiodon longirostris; Squamata, Scincidae). Major declines in P. longirostris populations have been caused primarily by habitat loss and mortality via invasive species (e.g., predation from birds and cats) and human waste products (e.g., trapped in discarded bottles). However, biotic interactions and interspecific competition with invasive lizards have also been identified as potentially detrimental to P. longisrostris populations. Here, we provide the first occurrence records of a highly invasive lizard, the Cuban brown anole (Anolis sagrei), on Bermuda. We assess the brown anole’s diet, habitat use, morphology, and island-wide distribution for comparison to the native skink, P. longirostris. Results of this study indicate that A. sagrei in Bermuda are highly terrestrial (>60% of all lizards observed on the ground vs. in trees) and forage primarily on terrestrial invertebrates. These data indicate substantial ecological overlap with the exclusively-terrestrial P. longirostris. This is in contrast to the other established non-native lizards on Bermuda, which are principally arboreal and have successfully coexisted with P. longirostris for >60 years. At present, the geographic distributions of A. sagrei and P. longirostris do not overlap. However, all extant skink populations are within several kilometers of brown anole populations (with the nearest being <0.5 km). The extensive overlap in ecological niche between the Bermuda skink and the invasive brown anole will likely present a serious conservation threat if contact is made. This study is exceptional in providing clear in situ ecological data which predict a conservation threat of an established invasive species to a Critically Endangered island endemic prior to coexistence. Continued monitoring of this situation as P. longirostris and A. sagrei inevitably come into contact will allow these a priori hypotheses of conservation risk via ecological overlap to be tested.