The desert tortoise, a hardy resident of the U.S. Southwest, may have met its match in climate change, authors of a new paper write. Unlike creatures such as insects, rodents or birds, tortoises display "impressive longevity," the authors write. Their slow development and long lifespan, however, makes it difficult to conduct studies on how environmental conditions such as climate change may or may not impact their ability to thrive. The study's results, unfortunately, don't bode well for these long-lived desert dwellers. According to the long-term study, under future climate model predictions, the survival of this threatened species looks pretty iffy in its increasingly hostile, dry desert environment.
The researchers got an early start on collecting their data: starting in 1978, they began to monitor threatened Agassiz’s desert tortoises living in a 1-square mile plot just Joshua Tree National Park in California. Throughout the years, they would check up on the tortoises, using the method of capture-mark-recapture to see which individuals had passed on and which were still around. In 2012, they decided it was at last time to analyze their results and see how the tortoises had fared over the years.
From 1978 until 1996, they found, things were looking pretty good for the tortoises. Their population was high and stable. But from 1997 onward, things took a downward turn when a drought began and continued until 2002. Many turtles died, and populations began to shrink. According to computer models, mortality coincided with lack of rain in the winter.
After 2002, the population never fully recovered. Those that perished likely experienced very unpleasant final days, as the team writes, "The postures and positions of a majority of dead tortoises found in 2012 were consistent with death by dehydration and starvation." Those that hadn't succumbed to death by drought appeared to have been predated on by coyotes--which usually eat mammals--leading the team to fear that those carnivores are now developing a taste for turtle flesh under the more stressful environmental circumstances.
The conclusions are pretty dire: "If drought duration and frequency increase, they will likely have wider and more significant impacts on Agassiz’s desert tortoise survivorship, particularly in the low Sonoran Desert portion of their range in California, and it will be difficult or impossible for resource managers to mitigate their effects."
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