Where will they come from, when did they go? Squamate extirpations and recoveries in Singapore

The island nation of Singapore has experienced large-scale habitat loss over the last two centuries, accompanied by unprecedented defaunation. Nevertheless, the remnant forests have seen some recovery in the last 100 years and some species that had previously become extirpated have recolonised and re-established, particularly birds, mammals, and butterflies. Most locally extirpated squamates, being less able to recolonize islands, can only be reintroduced through human-mediated conservation translocation. Some of Singapore’s several extirpated squamate species may be more suitable for reintroduction than others. However, there is a lack of objective tools for selecting candidate species for reintroduction. In this paper, we explore the novel application of a mathematical extinction model (MODGEE) to select squamate species for potential reintroduction to Singapore. The extirpation timeline identifies two periods of heightened extirpation rates (around the 1900s and the 2000s). Extirpation rates of 17% (95% CI [1 to 31%]) estimated in squamates were comparatively lower than those previously estimated for birds in Singapore, implying that squamates may be more resilient to habitat degradation. The model identifies three species of squamates that were extirpated recently and would thus experience the least “ecological memory loss” and be better able to reintegrate into a recovering landscape. We identify the southern green-eyed gecko, Gekko hulk, as the best candidate for conservation translocation into Singapore from stock populations in Peninsular Malaysia.