Management of invasive iguanas mitigates deleterious impacts on an imperiled tortoise.

Invasive species are a major driver in the global decline of biodiversity. Invasive herpetofauna cause ecological harm through different mechanisms that vary in scope and severity, and Florida boasts more established nonnative herpetofauna species than any other region in the world. There, black spiny-tailed iguanas (Ctenosaura similis) are one of several large invasive reptiles known to occupy the burrows of the imperiled, native gopher tortoise (Gopherus polyphemus) and may even exclude tortoises from their burrows. To test the hypothesis that iguanas exclude tortoises from their burrows and evaluate effectiveness of iguana management, we conducted a field study on Gasparilla Island, Florida, USA. We used a burrow scope to estimate occupancy of each species within tortoise burrows at sites with and without sustained iguana removal efforts and modelled co-occurrence patterns between the two species. We used two-species occupancy analyses to test three predictions relating to gopher tortoise burrow use; 1) that tortoise occupancy within burrows would be lower given the presence of iguanas, 2) that iguana occupancy would be positively associated and tortoise occupancy would be negatively associated with the presence of iguana sidetunnels within a tortoise burrow, and 3) that iguana occupancy would be lower and tortoise occupancy would be higher at sites with ongoing iguana removal. Our results support the hypothesis that gopher tortoises are less likely to utilize burrows that are or have been utilized by black spiny-tailed iguanas. We estimated the probability of tortoise occupancy conditional on iguana presence to be 63% lower than tortoise occupancy conditional on iguana absence. Our results also show that sustained iguana removal is likely effective at reducing iguana occupancy of tortoise burrows, as the probability of iguana occupancy was 72% lower where iguanas are actively managed. [ABSTRACT FROM AUTHOR]