Optimising assisted colonisation of a Critically Endangered turtle using mechanistic models

Nicola Mitchell (1), Sophie Arnall (2), Matthew Hipsey (3), Jana Colletti (4), Gerald Kuchling (5), Hasnein bin Tareque (6), Michael Kearney(7)

1 School of Animal Biology, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, nicola.mitchell@uwa.edu.au

2 School of Animal Biology, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, arnal01@student.uwa.edu.au

3 School of Earth and Environment, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, matt.hipsey@uwa.edu.au

4 School of Earth and Environment, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, jana.zanellacolletti@uwa.edu.au

5 Department of Parks and Wildlife, PO Box 459, Wanneroo WA 6946, gerald.kuchling@dpaw.wa.edu.au

6 School of Earth and Environment, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, a.m.hasnein@gmail.com

7 School of BioSciences, The University of Melbourne, Parkville Campus, Victoria 3010, m.kearney@unimelb.edu.au

Species distribution models based on correlations between environmental and occurrence data have limited application when a species has a naturally restricted range. This is a pressing concern for many species subject to assisted colonisation initiatives, as identifying new habitats where translocations could occur is crucial to decision making. In contrast to correlative models, mechanistically based distribution models hold considerable promise for identifying regions where the abiotic requirements of a species would be met under a changing climate. Here we demonstrate the integration of two types of mechanistic models: one an eco-hydrological model of an ephemeral wetland, and the other a dynamic energy budget model that partitions the energy assimilated by an individual into growth and reproduction. This has allowed the assessment of the longer-term viability of wild populations of the Critically Endangered Western Swamp Turtle (Psuedemydura umbrina) from south-western Australia, and has supported the case for assisted colonisation. This species is one of the world’s rarest reptiles and has experienced a drying climate over the past half-century, and consequently increasingly shorter hydroperiods. Our coupled model highlights the interaction between hydric and thermal constraints on foraging opportunities for the turtles, which in turn drive key demographic parameters such as age at maturity and lifetime reproductive output. When these models are applied as screening tools to identify suitable regions for assisted colonisation,they can be forced by a range of possible future climates and can capture the consequences of different climates on growth, reproduction and body condition.

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