The ecology of an arboreal rainforest gecko: Saltuarius cornutus

Gourret, Arnaud (2016) The ecology of an arboreal rainforest gecko: Saltuarius cornutus. Masters (Research) thesis, James Cook University.

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Global temperatures have increased by 0.6°C and are expected to continue rising between 1.4°C and 5.8°C over the next century. In addition to this, recent studies also predict changes in seasonality as well as a higher incidence and rise in intensity of in extreme disturbance events. This unprecedented rate of change in environmental conditions resulting in a loss of biodiversity worldwide raises new questions in conservation: How does one determine a species vulnerability to a changing climate?

Given that their physiology is driven by environmental temperatures, ectotherms are likely to be strongly and directly affected by changes in climate. As a result of their evolutionary history under warm and aseasonal climates, tropical species, in particular, are sensitive to the slightest changes in temperatures. Leaf-tailed geckos (Saltuarius cornutus) are cryptic, arboreal geckos occurring in the Wet Tropics rainforests of North Queensland, Australia. I aimed in this study to refine estimates of population size and describe the thermoregulatory ecology of these animals in an attempt to partially measure their exposure to changing environmental conditions.

Due to their cryptic nature and very efficient camouflage, leaf-tailed geckos are very difficult to detect during surveys. As a result, numbers of geckos actually counted are variable and may be inaccurate. As these geckos are arboreal, the main factor affecting their detection is visibility through the canopy. Consequently, in my first chapter I measured the variation in detection probability in relation to canopy height. This, in turn, allowed me to reduce detection bias, and to model occupancy and abundance at various elevations. In contrast to previous estimates, these models revealed a much more homogeneous distribution across the region, and an even occupancy of leaf-tailed geckos in rainforest habitats at different elevations. In addition, it is likely that a large portion of the population remains undetected in the higher levels of the rainforest canopy, so estimates of abundance are also higher than those made using raw counts.

In the second chapter of this study I aimed to examine some of the behavioral patterns associated with movement and body temperature regulation in these geckos. To do this, I attached thermally sensitive radio transmitters to the animals and remotely recorded their locations and experienced temperatures. In addition to this, I also set up thermal data loggers to monitor air temperature available in the canopy. I found what appeared to be active thermoregulatory behavior. Leaf-tailed geckos seldom moved, and diurnally, were often found in the emergent canopy. Experienced temperatures were significantly higher than surrounding air temperatures, suggesting the animals actively sought warm microhabitats as diurnal retreats. In addition, they remained warmer than air in the evening, suggesting they used tree temperatures to remain warmer than ambient for much of the day, in both winter and summer. Also, the canopy's strongly stratified thermal environments offered cooler and more stable conditions near the ground, where the geckos could potentially find shelter from temperature extremes in future.

In conclusion, the results of this study paint a positive picture with regards to the conservation status of this species. Both parts of the project suggest that these geckos use the canopy's upper levels. Accounting for detection bias in models predicting occupancy and abundance models reinforced the idea that these animals were widespread and abundant in rainforest habitats throughout the region. The results of my behavioral study coincided with this, suggesting geckos preferred the emergent canopy, especially as they seek warmer diurnal retreats, but also at night. This tendency to thermoregulate, the availability of shelter only a few meters below their present canopy use, and a widespread distribution suggest leaf-tailed geckos populations may have behavioral and habitat options for mitigating the effects of climate change.

Item ID: 51779
Item Type: Thesis (Masters (Research))
Keywords: arboreal geckos, climate change, cryptic geckos, ectotherms, geckos, leaf-tailed geckos, population size, Saltuarius cornutus, thermoregulatory ecology, tropical rainforests, Wet Tropics of Queensland
Date Deposited: 14 Dec 2017 02:34
FoR Codes: 05 ENVIRONMENTAL SCIENCES > 0502 Environmental Science and Management > 050202 Conservation and Biodiversity @ 100%
SEO Codes: 96 ENVIRONMENT > 9605 Ecosystem Assessment and Management > 960505 Ecosystem Assessment and Management of Forest and Woodlands Environments @ 100%
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