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Modelling koala density using incidental koala sightings in South East Queensland, Australia (1997-2013)
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  • Ravi Dissanayake,
  • Emanuele Giorgi,
  • Mark Stevenson,
  • Rachel Allavena,
  • Joerg Henning
Ravi Dissanayake
The University of Queensland
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Emanuele Giorgi
Lancaster University Lancaster Medical School
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Mark Stevenson
University of Melbourne Faculty of Veterinary and Agricultural Sciences
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Rachel Allavena
The University of Queensland Faculty of Natural Resources Agriculture and Veterinary Science
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Joerg Henning
The University of Queensland Faculty of Natural Resources Agriculture and Veterinary Science
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Abstract

The koala, Phascolarctos cinereus, is an iconic Australian wildlife species, but faces rapid decline in South-East Queensland (SEQLD). For conservation planning, estimating koala populations is crucial. Systematic surveys are the most common approach to estimate koala populations, but such surveys are restricted to small geographic areas, they are costly and conducted infrequently. Public interest and participation in the collection of koala sightings is increasing in popularity, but such data is generally not used for population estimation. We used incidental sightings of koalas reported by members of the public from 1997-2013 in SEQLD to estimate the yearly spatio-temporal koala sightings density. For this, a spatio-temporal point process model was developed accounting for observed koala density, spatio-temporal detection bias and clustering. The density of koalas varied throughout the study period due to the heterogeneous nature of koala habitat in SEQLD, with density estimates ranging between 0.005 to 8.9 koalas per km2. The percentage of land areas with very low sightings densities (0-0.25 koalas per km2) remained similar throughout the study period representing in average (SD) 68.3% (0.06) of the total study area. However, land areas with more koalas per km2 showed larger annual variations, with koala mean (SD) densities of 0.25-0.5, 0.5-1, 1-2, 2-5 and > 5 koalas per km2 representing 16.8% (0.21), 13.8% (0.25), 0.7% (0.20), 0.3% (0.13), and 0.2% (0.1) of the study area in South-East Queensland, respectively.We did find that clustering of koala sightings was not prominently different between the mating and non-mating seasons of koalas. While acknowledging the limitations associated sightings data, we developed a statistical model that addressed the spatio-temporal bias associated with observed koala sightings and provided long-term relative koala density estimates for one of the largest koala populations of Australia.

Peer review status:IN REVISION

29 Sep 2020Submitted to Ecology and Evolution
01 Oct 2020Submission Checks Completed
01 Oct 2020Assigned to Editor
20 Oct 2020Reviewer(s) Assigned
10 Nov 2020Review(s) Completed, Editorial Evaluation Pending
13 Nov 2020Editorial Decision: Revise Minor
21 Mar 20211st Revision Received
23 Mar 2021Submission Checks Completed
23 Mar 2021Assigned to Editor
23 Mar 2021Review(s) Completed, Editorial Evaluation Pending
23 Mar 2021Reviewer(s) Assigned
16 Apr 2021Editorial Decision: Revise Minor