Population increase and changes in behavior and morphology in the Critically Endangered Redonda ground lizard (Pholidoscelis atratus) following the successful removal of alien rats and goats.

Colin M Donihue,Shanna Challenger,Jennifer C Daltry,Anthony Herrel

doi:10.1111/1749-4877.12500

Abstract

Redonda is a small volcanic Caribbean island that is home to at least 4 endemic lizard species, including the Critically Endangered ground lizard (Pholidoscelis atratus). Black rats (Rattus rattus) and domestic goats (Capra hircus) were introduced to the island at some time after its discovery by Europeans in the late 1500s. They had a devastating effect on the island, resulting in the loss of nearly all trees and most of the ground vegetation. Point count surveys of P. atratus in 2012 indicated low densities, and the invasive rats were observed hunting and preying on the lizards. Both populations of rats and goats were successfully removed in 2017 as part of an ecological restoration program, and native vegetation and invertebrate populations have increased rapidly since. Population surveys in 2017, 2018, and 2019 show the lizard population has increased by more than sixfold. In 2017, as rats and goats were being removed, we evaluated the morphology and escape behavior of this species and repeated these measurements 1 year later. We observed that P. atratus had become bolder, with a reduced flight distance. We also detected changes in limb morphology related to locomotion and suggest possible explanations that will need to be further investigated in the future. These results show how the removal of invasive species can rapidly affect lizard population recovery and behavior, potentially restoring island ecosystems to their pre‐human interference dynamics.

Highlights

Invasive alien species are a global scourge, responsible for driving multiple species to extinction, imperiling fragile ecosystems, and causing billions of dollars in economic damage (Parmesan 2006; Simberloff et al 2013)
Controlling for differences in body size, we found a significant difference in head shape in male P. atratus
Following the removal of goats and rats in 2017, we saw a substantial increase in the relative density of P. atratus on Redonda

Summary

INTRODUCTION

Invasive alien species are a global scourge, responsible for driving multiple species to extinction, imperiling fragile ecosystems, and causing billions of dollars in economic damage (Parmesan 2006; Simberloff et al 2013). Redonda has largely remained uninhabited by humans except between 1860 and the 1920s, when the island was mined for seabird guano by the American Phosphate Company Much like they have done elsewhere in the world, the rats (Pascal et al 2004; Daltry 2006; Harper & Bunbury 2015) and goats (Coblentz 1978; Campbell & Donlan 2005; Chynoweth et al 2013) contributed to the deforestation and desertification of Redonda, and are blamed for the extinction of the endemic skink (Copeoglossum redondae; Hedges & Conn 2012) and iguana, as well as the extirpation of the Antiguan burrowing owl (Athene cunicularia amaura; Bell & Daltry 2012) on the island. We explored whether changes in predation pressure and vegetation regrowth had an impact on the morphology of the lizards, as previous studies have shown rapid changes in morphology following major alterations to the environment of lizards following translocation or catastrophic events (Herrel et al 2008; Donihue et al 2018)

MATERIALS AND METHODS

RESULTS

DISCUSSION