Study warns of the impact of extreme droughts on Chilean wildlife

Research published in the journal Ecology, of the Ecological Society of America, analyzed 12 years of records from a population of degus in central Chile, revealing that these endemic rodents managed to withstand nearly a decade of megadrought but disappeared locally following the extreme drought of 2019. The study, which involved Annemarie van der Marel, a postdoctoral researcher at the Institute of Ecology and Biodiversity (IEB), highlights the vulnerability of species to climatic events that exceed the resilience limits of ecosystems.

For nearly a decade, a population of common degus (Octodon degus) inhabiting Rinconada de Maipú, in Chile's Metropolitan Region, managed to survive the prolonged megadrought that affected central Chile. Despite declining rainfall and vegetation productivity, these small rodents maintained positive population growth throughout much of the study period. However, in 2019, something happened that abruptly changed their fate. That year, rainfall was exceptionally scarce, and vegetation production fell to critical levels. The lack of food affected both the animals' survival and the recruitment of new individuals into the population. In 2020, researchers stopped recording degus at the study site despite continued trapping efforts, and no individuals were detected during additional surveys conducted in 2021.

These findings are documented in the study “The Effects of an Extreme Drought Led to the Local Extinction of a Social Rodent,” which analyzed data collected between 2009 and 2020 using capture-mark-recapture techniques. The research revealed that the population did not experience a gradual decline throughout the megadrought. Instead, it persisted for years under adverse environmental conditions until the extreme drought of 2019 caused a critical reduction in available resources.

“What happened in 2019 was that there was virtually no rain throughout the entire year. Normally, even during the drought, there was some winter rainfall that allowed plants to grow and provided food for the degus. But that year, the plants didn't grow, and there was practically no food,” explains Annemarie van der Marel, a biologist and postdoctoral researcher at the IEB.

The findings reveal that a population's ability to withstand unfavorable environmental conditions for years does not necessarily guarantee its survival when faced with an exceptionally intense climatic event. The study was made possible by 15 years of records collected at the Germán Greve Silva Experimental Station in Rinconada de Maipú. Originally, these data were gathered as part of research into the social organization of degus—a species that also engages in communal care of its young—conducted by a team led by Dr. Luis Ebensperger of the Pontifical Catholic University of Chile and Dr. Loren Hayes of the University of Tennessee at Chattanooga.

Subsequently, collaboration with Annemarie van der Marel of the IEB and researchers from Universidad Mayor, the University of Florida, and NOAA (National Oceanic and Atmospheric Administration) made it possible to analyze population changes associated with the megadrought, underscoring the value of long-term ecological studies in understanding extreme events. Funding for this long-term research effort was secured through successive FONDECYT and NSF grants, as well as a FONDAP grant.

Although the common degu is classified as a species of Least Concern by the International Union for Conservation of Nature (IUCN), the status of many of its populations in Chile remains unknown. For van der Marel, one of the main challenges is understanding why some populations manage to survive extreme climatic conditions while others disappear. Factors such as vegetation, food availability, and social organization may help explain these differences.

Food Scarcity as a Decisive Factor

The common degu is a rodent endemic to Chile that primarily inhabits semi-arid environments. Degus are diurnal and social animals that live in groups and use underground burrows as shelter. During the day, they venture out to forage before returning to their burrows to rest and seek protection. Their diet depends largely on available vegetation, particularly green annual herbs that grow during the wetter months of the year.

One of the study's main findings was that gross primary productivity—an indicator of the amount of plant matter produced through photosynthesis—was the environmental factor that best explained variations in the species' survival and recruitment rates. This means that when vegetation declines, food availability also decreases, potentially affecting both adult survival and the recruitment of new individuals into the population through births or immigration.

This relationship is particularly important given the species' reproductive characteristics. “The most important thing is having food available during winter, because that's when reproduction begins. Females have a gestation period of almost three months, which is a very long time for a rodent. Then, once the pups are born, they need enough food to produce milk,” van der Marel explains.

Degus reproduce mainly during the austral winter, with their young born between late August and early September, coinciding with the period of greatest vegetation availability. They are also a relatively short-lived species, as most adults do not survive into their second year. This means that the constant recruitment of new individuals is essential for sustaining their populations.

Why Did Some Populations Survive While Others Disappeared?

Although the study documented the local disappearance of degus in Rinconada de Maipú, this does not mean that the species has become extinct in Chile or that all its populations responded to the megadrought in the same way. In fact, one of the questions that subsequently emerged was why other groups of degus had managed to survive in relatively nearby areas. Following the disappearance of the study population, researchers began searching for new sites where they could continue their observations. They eventually identified another population less than ten kilometers from the original study site.

For Annemarie van der Marel, this finding raises questions about the role that specific habitat characteristics may play. “We found a new population less than ten kilometers from where the local extinction occurred. So why did one population survive while another, so close by, disappear? Everything suggests that the characteristics of the local ecosystem may have played a role,” she says.

One of the differences observed was the presence of trees and shrubs at the new site, whereas the location where the population disappeared had limited shrub cover, at approximately 14%. This vegetation could provide alternative food sources during periods of scarcity, as well as shade and protection from predators.

Degus have several strategies for coping with adverse environmental conditions. During summer, when green herbs become less available, they can expand their foraging ranges and consume other plant resources, such as leaves, seeds, and parts of shrubs. They also adjust their feeding schedules to avoid the hottest hours of the day and seek refuge in their burrows.

In addition, they possess physiological adaptations that help them conserve energy in hot conditions, including mechanisms for conserving water and energy and the ability to recycle nutrients through coprophagy (the reingestion of feces). However, these adaptations may prove insufficient when resource availability falls to extreme levels.

When Resilience Is No Longer Enough

The research demonstrated that the ability to withstand adverse environmental conditions does not guarantee a population's capacity to recover. Although the degus endured much of the megadrought, the dramatic decline in vegetation in 2019 led to a drop in survival and recruitment rates, followed by a population collapse.

This phenomenon is associated with an ecological tipping point, at which environmental conditions cross a critical threshold and trigger abrupt changes. The study highlights how prolonged droughts can increase species' vulnerability, while extreme events can accelerate their local disappearance—a particularly significant risk in the context of climate change.