For the efficient management and eradication of invasive species, it is crucial both to understand the mechanisms of range expansion and to estimate past and future distributional area from presence or absence data. Anolis carolinensis, an arboreal lizard native to the Americas, is designated as one of Japan's 100 worst invasive alien species. A. carolinensis preys on insects endemic to the Ogasawara Islands and is responsible for significant decreases in their populations. A. carolinensis invaded Anijima island in 2013, and an eradication project by the Ministry of Environment was established to preserve the native insects and the surrounding ecosystem.
Using trapping data collected from emergency control efforts for A. carolinensis on Anijima island from 2013-2015, we sought to address three research goals: (1) Determine the environmental preferences of A. carolinensis; (2) Predict the past distributional area of A. carolinensis on Anijima Island in order to estimate the initial invasion site; (3) Predict the future distributional area of A. carolinensis on Anijima island. We created a distribution expansion model using a Bayesian framework that simultaneously estimates environmental and diffusion parameters. Using the estimated model, we conducted stochastic simulation to predict past and future distributional area of A. carolinensis on Anijima island.
The expected value of expanding distance of A. carolinensis in 1 year was estimated to be 165.07m (95% CI: 126.25-217.20m). We estimated that A. carolinensis prefers vegetated areas to more bare environments such as those along the coast, but this preference was not clear for Anijima Island, where dry shrub forest is ubiquitous. Based on the results of the estimation of past distribution, we suggest there may be multiple initial invasion sites in the southern area of Anijima island. The simulation study indicated that the distributional area of A. carolinensis will be over 90% of the whole Anijima island in 2021.
The quantitative findings of this study could be support to the management of invasive species. When aiming at eradication of A. carolinensis, it is desirable to apply trapping effort in the range including the distributional area predicted in this study.