Thermal constraints on activity scheduling and habitat choice in baboons

Hill, Russell A.

doi:10.1002/ajpa.20264

Cited by 88 publications

(109 citation statements)

References 37 publications

(49 reference statements)

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“…We hypothesize that the baboons shift from a strategy of seeking more food and more water to one of avoiding heat, minimizing energy expenditure and water needs, and avoiding exposure to water that is increasingly of poor quality as well as being scarce. A behavioral response of this sort has been reported for chacma baboons during the long days of southern African summers (Hill, 2006), and the present findings demonstrate a parallel physiological response. Such 'strategy switching' may be more general than previously appreciated.…”

Section: Environmental Conditions and Fgc Variabilitysupporting

confidence: 83%

Coping with a challenging environment: Effects of seasonal variability and reproductive status on glucocorticoid concentrations of female baboons (Papio cynocephalus)

Gesquiere

Khan

Shek

et al. 2008

Hormones and Behavior

105

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Environmental stressors impact physiology and behavior in many species of animals. These effects are partly mediated through changing concentrations of glucocorticoids, which also vary with reproductive state and social conditions. Prior research has focused largely on seasonal breeders, but the close temporal linkage between season and reproductive state in these species hinders ability to disentangle environmental effects from those of the animal's reproductive status. Here we assessed the effects of environmental challenges on the fecal glucocorticoid (fGC) levels of non-seasonal breeders, female baboons (Papio cynocephalus) of Amboseli, Kenya. Amboseli is characterized by a long dry season, during which food and water become scarce, and by extreme temperatures above 40°C in the shade during some months of the year. We found that after accounting for female reproductive status and individual variability, females exhibited higher fGC levels during the dry season than during the wet season. Further, during the wet season, fGC levels were higher in months of high average daily maximum temperatures. During the dry season, fGC levels were elevated both in hotter months and in months during which the baboons spent a relatively high proportion of time feeding. In spite of these stressors, female baboons reproduce during all months of the year in Amboseli, unlike most other mammals in this environment. This may be attributable to their extreme adaptability, specifically their diversified diet, and their ability to modify their behavior, including their activity profiles.

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Section: Environmental Conditions and Fgc Variabilitysupporting

confidence: 83%

Coping with a challenging environment: Effects of seasonal variability and reproductive status on glucocorticoid concentrations of female baboons (Papio cynocephalus)

Gesquiere

Khan

Shek

et al. 2008

Hormones and Behavior

105

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show abstract

“…Our evidence for dramatic variability is consistent with water as a strong selective pressure in human evolution (1,2). However, thermoregulatory and dietary constraints function at microhabitat scales (64), and many hominin fossil sites-including Olduvai Gorge (9)-are associated with ephemeral or saline water sources (65). Our reconstructions of precipitation and lake-chemistry indicate that, even during maximum lake expansion, lake waters at Olduvai Gorge were likely not potable (12).…”

Section: Interpretations and Discussionmentioning

confidence: 90%

Water, plants, and early human habitats in eastern Africa

Magill

Ashley

Freeman

2012

Proc. Natl. Acad. Sci. U.S.A.

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Water and its influence on plants likely exerted strong adaptive pressures in human evolution. Understanding relationships among water, plants, and early humans is limited both by incomplete terrestrial records of environmental change and by indirect proxy data for water availability. Here we present a continuous record of stable hydrogen-isotope compositions (expressed as δD values) for lipid biomarkers preserved in lake sediments from an early Pleistocene archaeological site in eastern Africa-Olduvai Gorge. We convert sedimentary leaf-and algal-lipid δD values into estimates for ancient source-water δD values by accounting for biochemical, physiological, and environmental influences on isotopic fractionation via published water-lipid enrichment factors for living plants, algae, and recent sediments. Reconstructed precipitation and lakewater δD values, respectively, are consistent with modern isotopic hydrology and reveal that dramatic fluctuations in water availability accompanied ecosystem changes. Drier conditions, indicated by less negative δD values, occur in association with stable carbon-isotopic evidence for open, C 4 -dominated grassland ecosystems. Wetter conditions, indicated by lower δD values, are associated with expanded woody cover across the ancient landscape. Estimates for ancient precipitation amounts, based on reconstructed precipitation δD values, range between approximately 250 and 700 mm·y −1 and are consistent with modern precipitation data for eastern Africa. We conclude that freshwater availability exerted a substantial influence on eastern African ecosystems and, by extension, was central to early human proliferation during periods of rapid climate change.paleohydrology | plant waxes | carbon isotopes

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“…However, activity is strongly influenced by shade attraction in times of high temperature and solar radiation in this species (see ref. 24 for a review). The skin of baboons has an unusually high density of sweat glands (25), and sweating seems an important aspect of thermoregulation (23).…”

Section: Discussionmentioning

confidence: 99%

Avoidance of overheating and selection for both hair loss and bipedality in hominins

Ruxton

Wilkinson

2011

Proc. Natl. Acad. Sci. U.S.A.

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Two frequently debated aspects of hominin evolution are the development of upright bipedal stance and reduction in body hair. It has long been argued, on the basis of heat-balance models, that thermoregulation might have been important in the evolution of both of these traits. Previous models were based on a stationary individual standing in direct sunlight; here we extend this approach to consider a walking hominin, having argued that walking is more thermally challenging than remaining still. Further, stationary activities may be more compatible with shade seeking than activities (such as foraging) involving travel across the landscape. Our model predictions suggest that upright stance probably evolved for nonthermoregulatory reasons. However, the thermoregulatory explanation for hair loss was supported. Specifically, we postulate progressive hair loss being selected and this allowing individuals to be active in hot, open environments initially around dusk and dawn without overheating. Then, as our ancestors' hair loss increased and sweating ability improved over evolutionary time, the fraction of the day when they could remain active in such environments extended. Our model suggests that only when hair loss and sweating ability reach near-modern human levels could hominins have been active in the heat of the day in hot, open environments.T wo frequently debated aspects of hominin evolution are the development of upright stance and the reduction in body hair. Indeed, a good case can be made that upright stance was "the first novelty of our lineage" (1), and lack of hair is one of the visually most obvious aspects of modern humans compared with other similar-sized mammals (2). One line of reasoning posits that thermoregulation may have been important in the evolutionary development of both of these traits. Highly supportive of such discussions has been a series of papers by Wheeler that used simple heat-balance models to quantify the potential effects of such adaptations (3-10). Recently, we presented a revised version of Wheeler's model to explore thermoregulatory aspects of putative endurance running in extinct hominids (11). The key modification in our revised model was a change from a stationary individual, as considered by Wheeler, to a moving one. Movement both adds to the thermal challenge on an individual by increasing their metabolically generated heat production and allows greater heat loss to the air by forced convection. Here we apply a further development of this model to the issues in which Wheeler was originally interested: bipedalism and hair loss.We believe that consideration of a walking individual should be particularly informative, because it is easier to envisage ecological reasons why an individual would be required to walk through areas that offer no shade compared with situations where an individual would stand still for long periods in direct sunlight. Vision is likely to have been an important sense in both food finding (e.g., searching for and pursuing mobile animal prey) and predator...

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Thermal constraints on activity scheduling and habitat choice in baboons

Cited by 88 publications

References 37 publications

Coping with a challenging environment: Effects of seasonal variability and reproductive status on glucocorticoid concentrations of female baboons (Papio cynocephalus)

Coping with a challenging environment: Effects of seasonal variability and reproductive status on glucocorticoid concentrations of female baboons (Papio cynocephalus)

Water, plants, and early human habitats in eastern Africa

Avoidance of overheating and selection for both hair loss and bipedality in hominins

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