Invasive black rats menacing endangered lizards

Abstract

Despite the pernicious impacts that invasive black rats Rattus rattus have on island ecosystems, little is known about their effect upon insular reptiles, which are a highly vulnerable but pivotal element of island biota. To bring to light these effects, we evaluated the threat posed by R. rattus on the critically endangered Canarian spotted lizard Gallotia intermedia by analyzing its frequency of occurrence on rat feces, estimating rat abundance and density, and correlating these parameters with previous lizard censuses. We genetically detected that 14.96% of all rat feces contained G. intermedia, with 27.27% of individual R. rattus consuming this lizard. Rat density varied from 0.740 ± 0.474 to 2.183 ± 1.137 rats/ha and was correlated with larger declines of G. intermedia between past censuses and those of 2019. These results confirm for the first time that R. rattus consumes and impacts this endemic and endangered lizard species. From a broader perspective, this is one of the first studies detecting rat impact on a large-sized reptile, which calls for further attention to the interaction between invasive rats and a highly vulnerable but essential component of island ecosystems.