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Title: Population status and conservation of the critically endangered Bermuda skink
Author: Turner, Heléna Summers
ISNI:       0000 0004 9357 1493
Awarding Body: University of Kent
Current Institution: University of Kent
Date of Award: 2018
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Global biodiversity is currently facing the sixth mass extinction with species disappearing at a rate 100 times background levels - mostly driven by anthropogenic pressures. Island species are often evolutionarily distinctive and are highly vulnerable to novel disturbances due to having small geographic ranges. The isolation of Bermuda has led to the evolution of a unique ecosystem with many endemic species. However, native species across Bermuda have become especially vulnerable ever since human colonisation, due to habitat loss and destruction, and predation and competition by several introduced species. The Bermuda skink (Plestiodon longirostris) was once widespread and commonly found along stone walls and cedar groves across Bermuda. By 1965, the population had become extremely fragmented and was declining across Bermuda and its offshore islands. This thesis investigates the threats to the Bermuda skink, listed as Critically Endangered by the International Union for the Conservation of Nature. Surveys were conducted between 2015 and 2017 across Bermuda to (1) estimate population parameters such as abundance, capture and survival probabilities; (2) estimate occupancy, colonisation, extinction and detection rates; (3) determine if skink sub-populations are morphologically different; and (4) compare the body condition between sub-populations that may provide warning signs of issues in the environment such as changes in the level of competition, predation or available habitat. Additionally, recommendations are provided for the conservation management and recovery of this species. From capture-mark-recapture surveys and subsequent robust design modelling, it was found that the two largest populations fluctuated in size at both sites over the three-year survey period, and are imminently threatened by increasing anthropogenic activities, invasive species, and habitat loss in Bermuda. Using dynamic occupancy modelling across Bermuda, skinks were detected at 13 locations. The probability of detection was higher on island sites and with the presence of seabirds, prickly pears and coastal habitat. However, skinks were unlikely to be detected at sites with cat and rat predators. We demonstrate that morphological diversification has occurred, possibly in response to isolation and changes to habitat and predator levels over time, especially on these small offshore islands. Finally, our study showed that trends in body condition differed between sub-populations with the two largest sub-populations – on Castle and Southampton Islands – having higher body condition compared to other populations. Overall, body condition has declined significantly over the past 15 – 20 years. After more than 50 years of study of the skinks, there is sufficient evidence to identify the reasons for their population decline. Although future studies may be needed to monitor populations, long-term the ongoing threats these populations face should be mitigated to help prevent extinction.
Supervisor: Griffiths, Richard Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QH75 Conservation (Biology)