The sloths came from the lowlands of the South Caribbean of Costa Rica and from the highlands of the country. The highlands in Costa Rica are typically 3-9°C cooler than the corresponding lowland forests, and this difference is important in the study.
Although climate change is predicted to have a substantial effect on the energetic requirements of organisms, the longer-term implications are often unclear. Sloths are limited by the rate at which they can acquire energy and are unable to regulate core body temperature (Tb) to the extent seen in most mammals. Therefore, the metabolic impacts of climate change on sloths are expected to be profound.
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“Sloths are inherently limited by their slow metabolism and unique inability to regulate body temperature effectively, unlike most mammals. Our research shows that sloths, particularly in high-altitude regions, may not be able to survive the significant increases in temperature forecast for 2100.”
Dr. Rebecca Cliffe
For All Readers - AI Explainer
Why are sloths particularly vulnerable to the impacts of climate change?
Sloths are particularly vulnerable to climate change because their ability to acquire energy is limited, and they cannot regulate their core body temperature as effectively as most mammals. As a result, changes in ambient temperatures due to climate change are expected to have profound effects on their metabolism and overall survival.
What was the methodology used to study sloth metabolism in relation to temperature?
The researchers used indirect calorimetry to measure oxygen consumption (VO2) and core body temperature (Tb) of highland and lowland two-fingered sloths when exposed to various ambient temperatures (18 °C to 34 °C). They also recorded changes in Tb and posture over several days in response to natural fluctuations in temperature.
How do highland and lowland sloths respond to increasing temperatures?
Highland and lowland sloths exhibit different metabolic responses to rising temperatures. Lowland sloths invoke metabolic depression when temperatures exceed their thermally-active zone (TAZ), whereas highland sloths show an increase in resting metabolic rate (RMR) under the same conditions. This difference indicates that lowland sloths may have a greater ability to cope with temperature increases compared to their highland counterparts.
What are the projected impacts of climate change on sloths by the year 2100?
By 2100, climate models predict a 2–6 °C increase in average daily air temperatures in the South and Central American rainforests. As temperatures rise, both highland and lowland sloths are expected to experience increased metabolic rates. However, high-altitude sloths, lacking the metabolic and geographic plasticity of lowland sloths, may find it increasingly difficult to survive in a warming climate.
What challenges do sloths face regarding energy expenditure and intake?
Sloths face significant challenges in balancing energy expenditure with energy intake. Due to their slow digestive rates and constantly full stomachs, they have intrinsic limitations on food intake. Estimates show that digesta passage time for sloths can range from 150 to 1,200 hours, which is much slower than similar-sized arboreal folivores. This slow digestion makes it biologically implausible for sloths to increase their energy intake at a rate that matches their increased energy expenditure caused by rising temperatures.
What further research is needed to understand the metabolic response of sloths to climate change?
Further research is needed to fully understand how sloths’ metabolic responses to temperature changes might vary. The current models are rudimentary and do not account for error and uncertainty. Future studies should focus on the specific mechanisms behind sloths’ metabolism and their ability to adapt to rising temperatures, as well as how these factors might affect their survival in a changing climate.
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