As visual evidence of climate change continues to shed light on a huge problem in the world, scientists studying at several National Science Foundation (NSF) Long-Term Ecological Research (LTER) sites are partly addressing the problem. problem by examining changes in the diversity and abundance of small mammals to understand their vulnerabilities to climate change.
Long-term regional monitoring can improve detection of biodiversity declines associated with climate change by combining information from both temporal and spatial dimensions. In the drylands of North America, future climate predictions include a nearly 100 percent chance of a decadal drought, the impacts of which will be magnified by ongoing global warming. Drylands are regions constrained by water scarcity and are essential for understanding how climate change affects biodiversity, as they cover 45 percent of the earth’s surface.
In a study published today in Global Change Biology titled “Decline in rodent abundance and diversity follows regional climate variability in the drylands of North America“, a group of scientists are trying to understand long-term changes in the diversity and abundance of small mammals and identify species that may be most sensitive to our drier, less predictable climate.
“Over the past 100 years in the southwestern United States, our climate has become drier and more variable, with increasing differences in drought index from year to year.” said Jennifer Rudgers, professor of biology at the University of New Mexico, senior author. and director and principal investigator of the Sevilleta Long Term Ecological Research (SEV LTER) Program in New Mexico. “Increasing climate variability is an aspect of climate change that has not been studied as extensively as changes in average temperature such as the climate becoming, on average, warmer or drier. Yet most climate predictions for the future include the prediction of increasing variability. ”
As part of the study, scientists analyzed abundance data from 22 rodent species in grassland, scrub, ecotone, and forest ecosystems in the southwestern United States as part of a time series (1995-2006 and 2004-2013) representing the Pacific phases. Decadal oscillation (PDO). PDO influences drought in southwestern North America, where rodents are diverse and important consumers.
The study, which took place at LTER sites from the northern Chihuahuan Desert to the southern Great Plains of western North America, combined 12 datasets on eight ecosystem types to examine the models. temporal diversity, composition and abundance of rodent species at the regional scale.
“Long-term observations that occur during periods with varying climates have allowed us to look for non-linear relationships between mammalian abundance and climatic variables,” Rudgers explained. “Non-linearities give signals about the sensitivity of species to climate variability. Because our climate is quite variable, we could capitalize on this inherent variability to detect past patterns that can predict the future. “
A key element that impacted the study was the Pacific Decadal Oscillation (PDO) and the role it plays in climate change. PDO is a climatic phenomenon that occurs when the sea surface waters in the northern Pacific Ocean fluctuate in temperature. This is an often decades-long oscillation that affects precipitation in the southwestern desert. When the surface temperatures of the Pacific Ocean along the west coast of North America are warm, the southwestern United States is generally in a phase of drought. When surface waters are cool, they tend to be wetter in the southwest.
“Because we had long-term small mammal abundance datasets (almost 20 years of data), we were able to separate our dataset into two time periods that each covered a phase of AOP: one wetter and earlier period in the mid-1990s-early 2000s and a drier, later period (2004-2013), ”said Rudgers. “This allowed us to explore how the climatic sensitivities of small mammals have changed over time, in concert with different phases of AOP.”
Using a climate sensitivity function approach developed by the team, scientists were able to comb through long-term observations that occurred during periods with varying climates to look for non-linear relationships between the abundance of mammals and climatic variables.
“We detected regional trends in our New Mexico, Colorado, and Arizona data sets,” Rudgers said. “Regionally, the diversity of rodent species has declined by 20 to 35 percent, with greater losses in the subsequent period. The abundance has also declined regionally, but only recently, with losses of 5 percent of the animals we have captured and released.
However, Rudgers noted that these declines in diversity varied across ecosystem types and locations. “The greatest declines in diversity have occurred in three types of ecosystems: the juniper pine forests and creosote shrub areas of the Sevilleta National Wildlife Refuge in New Mexico and the mixed shrub areas of salt bush on the Shortgrass Steppe LTER site in Colorado.
“The declines in abundance that we observed and the sensitivity of mammals to climatic variables were highly dependent on the ecosystem and location that we studied,” said Rudgers. “Thus, sensitivity to climate change was not at all consistent across a species’ range. In fact, the identities of winning and losing species differed between ecosystems for 70 percent of the taxa. This means that we need to take the local environment into consideration when making predictions about species vulnerabilities. “