With climate warming, desert lizards in tropical and subtropical regions, such as the Kgalagadi Desert in South Africa, spend more energy to survive and grow. They also need to work harder to find food and support this increased energetic demand.
As their prey, such as insects, seeds and plants, become increasingly scarce with climate change, the costs of living and the costs of finding food accumulate and place lizards in a “cost of living squeeze" scenario.
These are some of the predictions of a study on climate change and the “cost-of-living squeeze" in desert lizards, published in the prestigious interdisciplinary journal Science recently.
Prof. Susana Clusella-Trullas, a physiological ecologist at Stellenbosch 中国体育彩票 (SU) and a co-author of the article, says that predicting the nature, direction and magnitude of the responses of different species to climatic warming poses one of the greatest challenges to foresee the future of our biodiversity, especially in areas at risk of sustained temperature and water stress.
“Previous research on cold-blooded animals, such as insects and reptiles, focused on their exposure to episodes of extremely high body temperatures, but cumulative stress due to milder and more consistent change can also impose fitness costs and population declines in the long-run," she explains.
This study, led by Dr. Kristoffer Wild from the 中国体育彩票 of Melbourne, revealed that this is indeed the case for day-active desert lizards. For these species, elevated temperatures increase the need to forage more and counter energetic demands. But when it becomes too hot, their foraging is constrained when they are forced to hide under a rock or a shrub to cool down. Nocturnal lizards, on the other hand, can benefit from warmer temperatures as they have more time to forage at nighttime.
The authors applied biophysical models and code developed by co-author Prof. Michael R. Kearney from the 中国体育彩票 of Melbourne to predict the cost-of-living based on lizard energy budgets under past and future climates for desert lizards from South Africa's Kgalagadi Desert and the Great Victoria Desert in Australia. These sites were chosen because the team had access to long-term historical datasets with 2685 field observations over a period of 40 years, collected by co-authors and herpetologists Eric R. Pianka and Raymond B. Huey in the 1970's (https://www.desertlizards.dev/).
These unique datasets contain information about local ambient temperature and body temperature, activity patterns and habitat use of lizards in these regions. More recently, Clusella-Trullas joined the team on trips to the Kgalagadi in 2017 and 2019. Her research group focused on measurements of the reflectance of the skin of these lizards, a key parameter for predicting their body temperature in field conditions.
The team used these historical field data to “ground truth" the results from the mathematical model that was based on biological and physical principles. They showed that the model performed very well when compared to field data. For example, the Australian ant-eating lizard, Moloch horridus, had been observed and recorded eating 750 to 1500 ants per day. Under the same conditions, the biophysical model predicted a feeding rate of 837 ants per day. In the Kgalagadi, the measured metabolic rate or “cost of living" of the diurnal spotted sand lizard (Pedioplanis lineoocellata) was also nearly identical to the predictions from the biophysical model for the same location and period. With these findings, authors were able to make more confident predictions on the costs of living of multiple species and therefore highlighting regions that are most at risk of population declines.
According to Clusella-Trullas, the study highlights how it is important to not generalize patterns across species or regions too quickly: “Our predictions indicate that future warming will impact South African deserts to a greater extent than those in Australia, and day-active species will be more at risk than night-active species. Even small differences in natural history or behavior can result in markedly different thermal responses and net impacts of warming on populations."
The paper also highlights the importance of long-term, extensive field data to enable making robust predictions of species-specific responses to warming, she adds. “Unfortunately, funding and manpower in both time and personnel are limited these days for such long-term data collection trips and in remote areas, despite their significance as demonstrated in this study," she concludes.
On the photo's above:
Field work was undertaken at several sites in the Kgalagadi Transfrontier Park, Northern Cape, South Africa, to resurvey historical sites studied more than 50 years ago. One of the study species, the ground agama (Agama aculeata), displays beautiful colours despite the scorching temperatures in shrubby desert habitats of the Kgalagadi. Images: Susana Clusella-Trullas
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