World’s slowest mammal sloth faces extinction risk due to deteriorating energy balance

Climate change is having a detrimental effect on the metabolism and behavior of organisms. While some animals can survive under varying degrees of temperature variations, owing to genetic adaption, physiological and behavioral plasticity, for some it becomes implausible.

One such species is sloths, which have an unusually low and variable body temperature (Tb). They utilize postural adjustments in order to exploit favourable microclimates within the canopy and thereby regulate Tb.

Researchers have noted that sloths have a slow metabolism and limited ability to regulate body temperature. These things might make them unsuitable to survive in a warming world, especially for populations living in high-altitude regions.

Sloths’ limited energy reserves and adaptability make them vulnerable to climate change

As per a report by PeerJ Publishing sloths have little energy at their disposal, and are presumed to exist within a narrow and finely-tuned energy budget. In this case, minimal energy expenditure is tied to minimal energy intake.

Since sloths have limited ability to disperse, the report notes that even minor climate changes could have significant metabolic effects. These changes in climatic conditions could even threaten the survival of the sloth population.

The report further highlights that the lowland-dwelling sloth genus Bradypus can invoke temporary metabolic depression when responding to high temperatures.

With this flexibility in physiology, sloths can lower their body temperature and energy use. They can do this by reducing the amount of body heat from their bodies.

On top of that, the study notes that sloths inhabit both highland and lowland tropical forests. However, their metabolic response to changes in ambient temperatures still remains unknown.

“We hypothesised that this increase in insulation would reduce the thermal conductance of high-altitude sloths and should, theoretically, result in them having a higher overall body temperature and, consequently, a higher metabolic rate than sloths from low-altitude regions.

This, combined with their lack of geographical plasticity, may leave high-altitude populations in a vulnerable position when faced with a warming climate, especially given that atmospheric warming in highland forests is amplified relative to the lowlands” the report said.

The impact of rising temperatures on sloths’ energy demands and survival

The report also mentions that as ambient temperatures change, the energetic demands on animals also change. “The thermoneutral zone (TNZ) is the range of ambient temperatures within which a homeothermic animal does not need to expend extra energy to maintain its core body temperature (Tb). For the majority of homeotherms, this typically means that, as Ta’s rise above the TNZ, energetically costly mechanisms are instigated in order for Tb to remain stable”.

It added that ectotherms experience an exponential increase in metabolic rate with absolute temperature. This happens due to an increase in the rates of biochemical and enzymatic reactions.

The study notes that this is one of the primary reasons why climate change can invoke large metabolic costs. It also highlights that species living in the tropics are much less resilient to fluctuations in temperature.

Sloths , with their slow metabolism and limited ability to disperse, are particularly vulnerable to climate change. Even small temperature increases can disrupt their delicate balance of energy intake and expenditure.

As climate change intensifies, their habitats could shrink, and food sources may become scarcer, threatening the long-term survival of these unique creatures.