Resting Time as an Ecological Constraint on Primate Biogeography

The act of resting is not often treated as an aspect of animal behavior that directly impacts survival, and is more frequently perceived as time that could be used for other activities. While this is true of some resting time, animals do need a certain amount, known as enforced resting time, to perform necessary biological processes such as regulating body temperature (thermoregulation) and digesting food. In turn, the amount of resting time an animal requires can affect where it is able to live. In order to demonstrate this, Korstjens et al. (2010) performed an analysis of climate and common animal behavioral data. The team of scientists chose to focus on primates for this analysis because they are frequently studied, and have a wide range of dietary specializations and geographic distributions. The scientists compared observation data on primate resting times with dietary needs as well as social groupings and climate data. They found that while the percent of the day a primate spent resting was significantly affected by social group size, annual temperature variation, and the percentage of leaves in the primates diet, only temperature variation and percentage of leaves significantly affected enforced resting time. In addition, the researchers found that the minimum amount of enforced resting time a primate required affected it’s geographical location. These discoveries bring new insight to

models that predict how a species will fair with the oncoming climate change.—Emily Cole

Korstjens and her partners chose data sets for this analysis based on several parameters. The data had to include observations on resting time, diet, and group size, and had to have been carried out over 8 months or for multiple seasons. If a data set failed to meet these requirements it was not used. The scientists then compared these data to several climatic variables, including average annual rainfall, average annual temperature, variation from month to month of rainfall, and monthly variation of temperature. These data were either gathered by the same scientist who made the primate observations, a colleague or, in the absence of these, through the Willmott and Matsuuras climate model<!–[if supportFields]> XE “climate model” <![endif]–><!–[if supportFields]><![endif]–>.
The scientists found three parameters that significantly affected resting time. Dietary needs, specifically the amount of leaves consumed, were one. Primates who’s diet was made up of more than 33% leaves (folivores) needed far more resting time than those who consumed fewer leaves, presumably to aid in digestion. The monthly variation of temperature was also found to have a significant effect, especially on folivores, with higher variation leading toward more resting time probably because more thermoregulation was required. It was also hypothesized that temperature could affect the quality of the foliage consumed by the primates, thus heightening it’s impact. The size of the social group the primates participated in also significantly affected resting time, however the researchers argued on theoretical grounds that this only affected uncommitted resting time and not the enforced resting time of interest.
From the data, the researchers were able to extrapolate an equation that predicted the minimum amount of enforced resting time a generic primate would require based on monthly temperature variation, the constraints placed on this by mean annual temperature, and the amount of leaves in the primates diet. Using their equation, the researchers found that the predicted resting time was significantly higher for areas in which primates were absent, than for areas in which they were present. This implies that resting time does influence geographic distribution. This is most likely because places that require too much enforced resting time draw time away from other vital activities, such as foraging. The researchers found that almost any area that required more than 33% of the day for rest was uninhabited and inferred this to represent the maximum enforced resting time, above which it would difficult for a species to sustain itself.
Using their new-found equation, the researchers went on to predict the enforced resting times for primates that would be needed in scenarios of climate change where the mean temperature would rise by 2 °C or 4 °C. They found that nonfolivore distributions would remain relatively unaffected in the 2 °C scenario, while African folivore distributions would be largely affected in either case. South American folivore distributions, however, would remain largely unaffected in the 2 °C scenario as well. The scientists hypothesized that this was due to the fact that South American primates are largely arboreal, while their African counter-parts are often at least semi-terrestrial.
The findings imply that enforced resting time plays a key component in both the survival and distribution of a species. As such, this paper presents yet more important aspects to consider when predicting the effect climate change will have on animal behavior and, ultimately, biodiversity<!–[if supportFields]> XE “biodiversity” <![endif]–><!–[if supportFields]><![endif]–>.

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