Reintroducing species when threats still exist: assessing the suitability of contemporary landscapes for island endemics

Abstract

Reintroducing species into landscapes with persistent threats is a conservation challenge. Although historic threats may not be eliminated, they should be understood in the context of contemporary landscapes. Regenerating landscapes often contain newly emergent habitat, creating opportunities for reintroductions. The Endangered St Croix ground lizard Pholidoscelis polops was extirpated from the main island of St Croix, U.S. Virgin Islands, as a result of habitat conversion to agriculture and predation by the small Indian mongoose Herpestes auropunctatus. The species survived on two small cays and was later translocated to two islands. Since the 1950s, new land-cover types have emerged on St Croix, creating a matrix of suitable habitat throughout the island. Here we examined whether the new habitat is sufficient for a successful reintroduction of the St Croix ground lizard, utilizing three complementary approaches. Firstly, we compared a map from 1750 to the current landscape of St Croix and found statistical similarity of land-cover types. Secondly, we determined habitat suitability based on a binomial mixture population model developed as part of the programme monitoring the largest extant population of the St Croix ground lizard. We estimated the habitat to be sufficient for > 142,000 lizards to inhabit St Croix. Thirdly, we prioritized potential reintroduction sites and planned for reintroductions to take place during 2020–2023. Our case study demonstrates how changing landscapes alter the spatial configuration of threats to species, which can create opportunities for reintroduction. Presuming that areas of degraded habitat may never again be habitable could fail to consider how regenerating landscapes can support species recovery. When contemporary landscapes are taken into account, opportunities for reintroducing threatened species can emerge.

Birds in the Diet of Invasive Boa imperator on St. Croix, U. S. Virgin Islands

“…On Aruba, introduced B. constrictor (Bushar et al 2015) initially fed largely on native birds and mammals and have shifted to feed more heavily on “urban subsidies” like domestic chickens and non-native birds, although they still consume native prey (Quick et al 2005; Reinert et al 2021). Because the native species assemblage on St. Croix was depleted by post-1500 colonial agriculture (97% of large forests clear cut by 1950; Angeli and Fitzgerald 2021), non-native species such as mongeese, rats, mice, cats and chickens may be subsidizing the B. imperator population on St. Croix. It is also possible that B. imperator predation on mongeese and rodents on St. Croix might release native birds and lizards from predation pressure from these invasive species, with potential benefits for some native species, as was seen on Aruba (Goessling et al 2015) and has been anecdotally reported on St. Croix.…”