Roughing it: terrain is crucial in identifying novel translocation sites for the vulnerable brush-tailed rock-wallaby (Petrogale pencillata)

Translocations—the movement of species from one place to another—are likely to become more common as conservation attempts to protect small isolated populations from threats posed by extreme events such as bushfires. The recent Australian mega-fires burnt almost 40% of the habitat of the brush-tailed rock-wallaby (Petrogale pencillata), a threatened species whose distribution is already restricted, primarily due to predation by invasive species. This chronic threat of over-predation, coupled with the possible extinction of the genetically distinct southern population (approx. 40 individuals in the wild), makes this species a candidate for a conservation translocation. Here, we use species distribution models to identify translocation sites for the brush-tailed rock-wallaby. Our models exhibited high predictive accuracy, and show that terrain roughness, a surrogate for predator refugia, is the most important variable. Tasmania, which currently has no rock-wallabies, showed high suitability and is fox-free, making it a promising candidate site. We outline our argument for the trial translocation of rock-wallaby to Maria Island, located off Tasmania's eastern coast. This research offers a transparent assessment of the translocation potential of a threatened species, which can be adapted to other taxa and systems.


Dear Mr Morris
On behalf of the Editors, we are pleased to inform you that your Manuscript RSOS-201603 "Roughing it: terrain is crucial in identifying novel translocation sites for the vulnerable brushtailed rock-wallaby (Petrogale pencillata)." has been accepted for publication in Royal Society Open Science subject to minor revision in accordance with the referees' reports. Please find the referees' comments along with any feedback from the Editors below my signature.
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Kind regards, Andrew Dunn Royal Society Open Science Editorial Office Royal Society Open Science openscience@royalsociety.org on behalf of Prof Pete Smith (Subject Editor) openscience@royalsociety.org Associate Editor Comments to Author: The referees recommend your paper be modified slightly, and provide helpful suggestions. Please can you amend your work to include these suggestions, and return a revision with a pointby-point response -full details of what you need to include are provided at the end of the decision letter. Congratulations! Reviewer comments to Author: Reviewer: 1 Comments to the Author(s) This is a nicely constructed paper which provides a good model for others wishing to use species distribution models for conservation planning. While the conclusions in this case are unsurprising, they do further refine understanding of the habitat of the Brush-tailed rockwallaby, and the discussion on potential for introduction to areas outside the current distribution to provide protection from affects of climate change is topical. I have only a few minor editorial comments and suggestions: Line 67 -should be wallaby's, not wallabies.
Lines 107-108 -more information is needed on why these two climatic variables [minimum temperature in the coldest month, and annual mean precipitation] were selected from the large pool of potential climate variables. Line 133 -Sup xxx -to be completed Line 232 -apostrophe misplaced. Line 233 -'score' should be plural -there are 2, one for each background. Line 245 -delete 'with' Line 279 -sentence needs recasting as it currently suggests that a dietary assessment from Tasmania exists for the rock-wallaby. The dietary assessment referred to took place at three sites in NSW. Line 287-288 -need to more directly link your expression 'the habitat and climate argument' to the second criterion for assisted migration -the potential to move -assuming that is what is meant. Line 304 -delete 'outside their recipient site', it just repeats the information contributed by 'areas to which they were introduced'. Line 314 -insert 'in' after 'increase'. Line 320 -sentence beginning with 'It' needs work -'offers', larger area of potential ? Line 351 -delete 'that' or change 'as' to 'is'. Line 352 -the terrain in the Grampians is extremely rough and broken. I don't see that rockwallabies would be more exposed to predators there than at other occupied sites. Line 354 -recast to 'being less accessible to people.' References -need a careful check, for example the surname Burbidge is missing from number 19 Reviewer: 2 Comments to the Author(s) The authors describe a study where they used species distribution modeling to define areas to which the brush-tailed rock wallaby could be introduced since its original habitat is being diminished as a consequence of climate change effects.
In general, the manuscript is very well and clearly written, the methods are well justified and described adequately, and the results and conclusions inferred are robust. I see no major concern with the scientific content of the paper.
The study is case-specific and concerns the immediate conservation of a specific species for a specific reason. As such, I feel that the authors could have the potential to reach a more targeted audience through offering the manuscript for publication to a more conservation-oriented paper, like Conservation Biology where it could function as an interesting case-example for similar conservation projects. However, with a bit of effort and considering the open access policy of RSOS, I am sure that the paper has potential to reach readers most interested in this type of case study. The most novel aspect of their paper is the use of terrain characteristics in addition to habitat and climate variables, for modelling the suitable area for the species. As such, it offers a valuable example of how the scientific process can be used for informing practical conservation planning. I have only a few minor comments, most of which relate to being a bit more specific with the concepts under the rather wide conservation translocation umbrella.
Minor comments: line 24: could you be more specific on what kind of translocation you refer to? Translocation is an umbrella concept and includes very many different methods. Please refer to the IUCN: https://www.iucn.org/content/guidelines-reintroductions-and-other-conservationtranslocations A translocation can be unintentional (cf. invasive species) or conducted because of conservation concern (=conservation translocation). I believe you a referring to a conservation introduction, and within that, assisted migration. Throughout the manuscript, please consider where you need to specify these terms more precisely. line 40. Ditto. This definition is not specific enough, please refer to the IUCN guidelines: "Conservation translocation is the intentional movement and release of a living organism where the primary objective is a conservation benefit." line 210: visual --> visualize? 271-274: Again, please be specific with the definitions. Assisted migration is not only characterised by release outside historic distribution (that would be the definition of any introduction), but additionally, and importantly, because of conservation concerns, often caused by climate change. Please refer to IUCN and or Hällfors et al. 2014 who define it even slightly more specifically: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0102979 320-322: please revise this sentence, there is some mistake in the beginning Caption of Fig. 3: The first sentence/title of the figure is too long.

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Decision letter (RSOS-201603.R1)
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Dear Mr Morris,
It is a pleasure to accept your manuscript entitled "Roughing it: terrain is crucial in identifying novel translocation sites for the vulnerable brush-tailed rock-wallaby (Petrogale pencillata)." in its current form for publication in Royal Society Open Science.
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Thank you for your fine contribution. On behalf of the Editors of Royal Society Open Science, we look forward to your continued contributions to the Journal. identify potential sites for a myriad of species, from mussels (Margaritifera margaritifera) [10] to 53 European bison (Bison bonasus) [11]. In plants, areas which were predicted by SDMs to have higher 54 suitability resulted in higher germination success post-translocation [12].

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Notwithstanding these benefits, the reliability of SDMs is often compromised by their assumption 57 that species are in equilibrium with their habitat, and the exclusion of factors such as dispersal 58 limitations (though this has been incorporated in newer models, see Zurell et al. [13] for further 59 details), and biotic interactions that may vary spatially and temporally. As a result, SDMs are not always suitable for extrapolation into new conditions [14]. These problems are particularly acute 61 when predicting future distributions, which necessitates both spatial and temporal extrapolation.  [33]. These variables were also chosen to avoid overprediction in colder and wetter 200 climes (e.g., Tasmania). The correlation between these variables was inspected using Spearman's 201 rank correlation, as collinearity is a common problem in SDM construction [47], although Maxent is 202 less influenced by this than are other algorithms [37].

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Maxent models were parametrized with only hinge features allowed, and a beta-value of 2.5, 205 allowing a partly non-linear fit [36,48] that would be best suited to generalising to new areas. Hinge 206 features can model complex relationships (e.g. inverted U-shape) and have strong predictive 207 accuracy [49]. As rock-wallabies are difficult to detect [50] prevalence was set as 0.3. Models were k-208 fold cross-validated (k=10) and this k-fold-sampling was repeated ten times to ensure a robust and 209 stable model-selection metric. All of the best models derived from each k-fold sampling were then 210 ensembled and weighted using area under the receiver operating curve (AUC). AUC, in a Maxent 211 context, is a measure of a model's ability to discriminate between presence and the background 212 points [37]. True Skill Statistic (TSS), which is a measure of accuracy developed specifically for SDMs, 213 was also calculated [51]. All models were fitted, evaluated and ensembled using the sdm package 214 [52]. A single Maxent model, with the same settings as above, was also created and tested using the 215 limiting function in the Rmaxent package [53], to visualise the limiting predictors of rock-wallabies 216 spatially.

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The six predictors showed minimal intercorrelation, with the greatest being between the minimum 219 temperature in July and the mean annual precipitation (Spearman rank coefficient, SRC = 0.53). The 220 largest negative correlation was between terrain roughness and minimum temperature in July (SRC 221 = -0.44). Terrain roughness was the most important predictor-by a substantial margin-in correctly 222 identifying suitable areas (Fig 2(a)), whilst aspect was the least. The method of background selection 223 did not affect the importance ranking of the predictors, but it did affect the response curves ( Fig   224  2(b)). The response curves of percentage woodland and the minimum temperature in July changed The model did not predict many areas of high suitability far from areas the rock-wallaby currently 247 occupies (Fig 3(a)). The exceptions to this were the Yarra Ranges (Latitude ~ 37.5°S, Longitude ~ 248 146°E), the Central Queensland Sandstone Belt (Latitude ~ 25°S, Longitude ~ 148°E), and Tasmania.

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In fact, a large portion of eastern Tasmania was considered suitable. The choice of background 250 affected the magnitude of the suitability, with the IBRA background predicted higher suitabilities 251 than the SE background, but overall, the two alternative background-sampling approaches showed 252 no major discrepancies (Fig 3(b)).   (Fig. 2 (b)), in the west (Fig. 3(c)), supporting previous 318 findings [33]. Although not considered here, climate change could increase the suitability of 319 Tasmania even further as the island is expected to experience warmer temperatures, a 2.9°C 320 increase in mean annual temperature by 2100 under a high emissions scenario, and unchanged 321 mean annual precipitation state-wide, but with differences at the regional and seasonal level [66].

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To allay concerns of unwanted negative consequences of a translocation, a trial translocation to an 324 offshore island, such as Maria Island off eastern Tasmania (Fig 3(a) Fig. 2(a)), as it likely captures the characteristics of inaccessible habitat better than either elevation 347 or slope alone. The greater importance of mean annual precipitation in comparison to minimum 348 temperature supports previous findings [33] and suggests the importance of an availability of 349 refuges in which to shelter, if a translocation to Tasmania were to take place. The importance of 350 terrain roughness, which is likely a proxy for protection from predation, and rainfall (Fig 2(a)), have 351 been previously noted as the most influential factors dictating macropod populations [50,[71][72][73].

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The percentage of woodland cover was more important than the percentage of grassland cover,

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indicating the beneficial role that habitat complexity may play in rock-wallaby occurrence, though 355 this might be affected by our exclusion of cleared land from the grassland calculations. Aspect was of 356 little importance in predicting habitat suitability at this scale, but seems to be of greater importance 357 at finer resolutions [22,24]. The relevance of scale in the choice of predictors for rock-wallaby 358 habitat has been highlighted in detail before [24], and confidence in our choice of predictors is 359 supported by the suitability projected for the Grampians. Fig. 3 Ultimately, the undertaking of an assisted migration for the brush-tailed rock-wallaby does not 374 depend solely on the predicted suitability of an area. It must not only be beneficial for the species, 375 present a limited threat of invasive potential, and be logistically feasible; it must also be accepted 376 and wanted by society [75]. Therefore, the future of the rock-wallaby will not depend on the AUC of 377 an SDM, but to a large part also on the decision making of the Australian people in the context of the 378 trade-offs of twenty-first century conservation management.

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Ethics. No human or animal subjects were included in this study. Therefore, no ethical approvals 381 were required.

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Competing interests. The authors declare no competing interests.

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Funding. This work was funded by Australian Research Council grants FL160100101 to B. W. B.

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Acknowledgements. The authors are grateful to all the people who collected and collated the data 390 used in this research, especially the occurrence data. We acknowledge the traditional owners of the 391 land on which this data was collection.