Could brown bears (Ursus arctos) have survived in Ireland during the Last Glacial Maximum?

Claire L Risley,Samuel T Turvey,Saoirse A Leonard

doi:10.1098/rsbl.2013.0281

Claire L Risley, Samuel T Turvey + Show 1 more

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https://doi.org/10.1098/rsbl.2013.0281

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Abstract

Brown bears are recorded from Ireland during both the Late Pleistocene and early–mid Holocene. Although most of the Irish landmass was covered by an ice sheet during the Last Glacial Maximum (LGM), Irish brown bears are known to have hybridized with polar bears during the Late Pleistocene, and it is suggested that the Irish brown bear population did not become extinct but instead persisted in situ through the LGM in a southwestern ice-free refugium. We use historical population modelling to demonstrate that brown bears are highly unlikely to have survived through the LGM in Ireland under any combination of life-history parameters shown by living bear populations, but instead would have rapidly become extinct following advance of the British–Irish ice sheet, and probably recolonized Ireland during the end-Pleistocene Woodgrange Interstadial from a closely related nearby source population. The time available for brown bear–polar bear hybridization was therefore restricted to narrow periods at the beginning or end of the LGM. Brown bears would have been extremely vulnerable to extinction in Quaternary habitat refugia and required areas substantially larger than southwestern Ireland to survive adverse glacial conditions.

Highlights

The origin of Ireland’s modern terrestrial vertebrate fauna is the subject of ongoing debate [1,2,3]
A small habitat refugium in southwestern Ireland probably remained ice-free throughout the Last Glacial Maximum (LGM) [5], suggesting that some cold-adapted terrestrial lineages may instead have persisted in situ across the Late Pleistocene–Holocene
Sensitivity analysis showed that interbirth interval and female mortality rate have greatest impact on population persistence; there is little difference in these parameters between barren-ground and coastal brown bear populations, due to higher levels of intraspecific competition in more productive environments [22], suggesting that our models were not compromised by preferential use of barren-ground life-history data

Summary

Introduction

The origin of Ireland’s modern terrestrial vertebrate fauna is the subject of ongoing debate [1,2,3]. Many modern Irish animal groups are known to have become locally extirpated during this extreme climatic interval and recolonized during the subsequent Woodgrange Interstadial (end-Pleistocene) or early Holocene, probably via transient landbridges or anthropogenic introduction [3,4]. A small habitat refugium in southwestern Ireland probably remained ice-free throughout the LGM [5], suggesting that some cold-adapted terrestrial lineages may instead have persisted in situ across the Late Pleistocene–Holocene.

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