Exposure to climate change drives stability or collapse of desert mammal and bird populations
E.A. Riddell, K.J. Iknayan, L. Hargrove, S. Tremor, J.L. Patton, R. Ramirez, B.O. Wolf, S.R. Beissinger
Summarized by Anna Geldert
What data were used? Researchers compared climate change responses in desert species, including 34 small mammal species and 135 bird species. Surveys were conducted at 151 sites throughout the Mojave Desert, concentrated mostly in Death Valley National Park, Mojave National Preserve, and Joshua Tree National Park (California, USA). Modern observations were compared to historical observations by Joseph Grinnell and colleagues in the early 20th century to assess change over time.
Methods: The authors used a dynamic multi-species occupancy model to determine how the proportion of sites that a species occupied changed over time. In summary, this approach assessed the probability of detecting a species at different time periods, and used this data to determine the change in occupancy (likelihood of a species occupying a site), change in species richness (number of species at a site), colonization probability (likelihood of expanding to new sites), and persistence (long-term survival of a species at a site) probability. This model also factored in the impacts of climate change and habitat loss. The authors also estimated the degree of exposure (or how greatly an organism is affected by climatic changes) in small mammals and birds by simulating the “cooling costs” of each species. Cooling costs represent the water required for evaporative cooling to maintain a stable body temperature and were based on the species’ behavior, morphology, and microhabitat conditions.
Results: Overall, modern bird species declined in occupancy when compared to historical records, while small mammal occupancy remained relatively consistent. The model estimated that the occupancy of 29% of bird species decreased, 70% were unchanged, and only 1% increased. Meanwhile, only 9% of small mammals saw an occupancy decrease, while 79% stayed constant and 12% increased. Similarly, bird species richness decreased at 90.1% of sites and only 3.3% of sites for small mammals. The authors also found that bird populations experienced higher exposure to climate change than small mammals. The exposure model estimated that cooling costs were approximately 3.3 times higher in birds than they were in mammals, with this number projected to increase to 3.8 times by 2080. Finally, the level of adaptation and specialization among species of both groups had little influence on changes in cooling costs, suggesting that microhabitat conditions and their behavioral ability to “buffer” against climatic changes had a much greater impact.
Why is this study important? This study counters the traditional approach of assessing impacts from climate change, which often assumes that exposure within an ecosystem is uniform across all species. This study revealed that in the same locations birds were more severely impacted by climate change than small mammals, as shown by the lower occupancy probability, lower species richness, and higher cooling costs in birds. Additionally, this study highlighted the importance of microhabitat buffering potential, which may be a driving factor as to why small mammals were sheltered in their burrows during the day from the worst of the impacts of heat, while birds were not.
The big picture: As the impacts of climate change on animal populations progress, desert communities remain especially vulnerable. In order to minimize these impacts, it is important to understand how ecosystems respond to climate changes. This study suggests that impacts should be considered at the population level, rather than the community level, as species responses varied greatly even within the same ecosystem. Furthermore, the results suggest that microhabitat buffering is especially important in reducing impacts from climate change, and should be given greater attention in conservation efforts and future studies.
Citation: Riddell, E. A., Iknayan, K. J., Hargrove, L., Tremor, S., Patton, J. L., Ramirez, R., … Beissinger, S. R. (2021). Exposure to climate change drives stability or collapse of desert mammal and bird communities. Science, 371(6529), 633–636. https://doi.org/10.1126/science.abd4605