A long drought did not produce a steady decline
A 12-year study of common degus in central Chile offers a stark view of how climate extremes can push wildlife beyond a threshold. The population endured nearly a decade of megadrought, maintaining positive growth through much of that period, before an exceptional drought in 2019 was followed by its local disappearance from the study site.
The work, published in the journal Ecology, examined a population of the endemic rodent Octodon degus at Rinconada de Maipú in Chile’s Metropolitan Region. Its central finding is not simply that dry conditions are harmful. Rather, the population persisted under years of deteriorating conditions until an especially severe event coincided with a critical drop in resources.
That distinction matters for understanding ecological risk. A population can appear resilient during prolonged environmental stress, yet still be vulnerable to a further extreme that reduces food and survival below a recoverable level.
Twelve years of field records
Researchers analyzed data collected between 2009 and 2020 using capture-mark-recapture methods. This approach allowed them to follow population patterns over time rather than relying on a single survey or a short-term snapshot.
Central Chile experienced a prolonged megadrought during the study period. Rainfall declined and vegetation productivity fell, but the degu population continued to show positive population growth for much of the record. The study therefore did not identify a simple year-by-year collapse across the entire drought.
The turning point came in 2019. Rainfall was exceptionally scarce, and vegetation production dropped to critical levels. The report says the shortage of food affected both survival and recruitment, meaning the addition of new individuals into the population. By 2020, researchers no longer recorded degus at the site despite continued trapping. Additional surveys in 2021 also detected no individuals.
The researchers describe the outcome as a local extinction, or local disappearance, of this population. It does not mean the species has disappeared from Chile. Common degus are endemic to the country and inhabit semiarid ecosystems, while this study concerns the population at one central Chile location.
Resilience has limits
The study’s most consequential lesson is about thresholds. Years of megadrought did not automatically translate into a continuously shrinking population. The animals endured adverse conditions for a substantial period. But the drought of 2019 appears to have reduced available resources far enough to overwhelm that resilience.
In ecological terms, this makes the timing and intensity of weather events as important as their long-term average. A species or population may tolerate repeated stress until an unusually severe episode affects several necessities at once, such as vegetation productivity, food availability, survival and reproduction.
The degu record also cautions against interpreting temporary persistence as evidence that a population is secure. Continued observations during a long drought can show that animals are still present and growing, while masking proximity to a point at which additional stress creates a rapid shift.
What the researchers observed
- The research analyzed 12 years of records from 2009 through 2020.
- The central Chile population persisted through much of a prolonged megadrought.
- Exceptionally scarce rainfall in 2019 coincided with critically low vegetation production.
- The study links reduced food availability to lower survival and reduced recruitment.
- No degus were recorded at the site in 2020, and subsequent surveys in 2021 found none.
The pattern is especially notable because it was abrupt rather than gradual. The authors report that the population did not decline steadily throughout the megadrought. Instead, it remained present under challenging conditions before the 2019 extreme drought changed the trajectory.
Why local records are valuable
Long-running population records are essential for detecting this kind of non-linear change. A shorter study begun during the megadrought might have found a population that was coping with dry conditions. A survey conducted only after 2019 might have documented absence without revealing the lengthy period of persistence that preceded it.
By combining repeated captures over more than a decade, the researchers were able to connect the population’s trajectory to changing environmental conditions. The study does not claim that drought automatically determines the fate of every degu population or every semiarid species. It instead documents a specific population’s experience and identifies the extreme drought of 2019 as the point at which conditions exceeded its apparent resilience.
That evidence is relevant beyond one rodent species because climate impacts are often discussed through gradual averages: average temperature, average rainfall or average productivity. The degu study highlights a different risk: the individual extreme event that arrives after an ecosystem has already spent years under stress.
A warning about compounding climate pressure
For wildlife managers and researchers, the result argues for monitoring both long-term trends and rare extremes. A prolonged drought can erode the margin that enables a population to recover from poor seasons. When another unusually dry year follows, the effects on food, survival and recruitment may combine quickly.
The local disappearance at Rinconada de Maipú does not erase the species from its wider range. But it provides a concrete, field-based example of how resilience can fail abruptly. The central message from the 12-year record is that persistence through a megadrought should not be mistaken for immunity to a more severe climatic shock.
This article is based on reporting by Phys.org. Read the original article.
Originally published on phys.org
