Elephant movement patterns in relation to surface water demonstrate that they are a water-dependent species. Thus, there has been interest in using surface water management to mitigate problems associated with localized elephant overabundance. However, the physiological mechanisms underlying the elephant's water dependence remain unclear. Although thermoregulation is likely an important driver, the relationship between thermoregulation, water use and climate has not been quantified. We measured skin surface temperature of and cutaneous water loss from 13 elephants (seven African, 3768±642 kg; six Asian, 3834±498 kg) and determined the contribution of evaporative cooling to their thermal and water budgets across a range of air temperatures (8–33°C). We also measured respiratory evaporative water loss and resting metabolic heat production on a subset of elephants (N=7). The rate of cutaneous evaporative water loss ranged between 0.31 and 8.9 g min−1 m−2 for Asian elephants and 0.26 and 6.5 g min−1 m−2 for African elephants. Simulated thermal and water budgets using climate data from Port Elizabeth, South Africa, and Okaukuejo, Namibia, suggested that the 24-h evaporative cooling water debt incurred in warm climates can be more than 4.5 times that incurred in mesic climates. This study confirms elephants are obligate evaporative coolers but suggests that classification of elephants as water dependent is insufficient given the importance of climate in determining the magnitude of this dependence. These data highlight the potential for a physiological modeling approach to predicting the utility of surface water management for specific populations.
R.C.D. conceived of the question and design, carried out the measurements, analyzed the data and wrote the manuscript. D.W., N.W. and K.J. contributed to the design of the study, made possible the execution of the study by providing access to and training of the animals in this study, and provided feedback on the manuscript. T.M.W. contributed to the design, assisted with the execution and contributed to the writing of the manuscript.
Supplementary material available online at http://jeb.biologists.org/cgi/content/full/216/15/2939/DC1
No competing interests declared.
This work was supported with a Wings World Quest grant to T.M.W., a grant from The Society for Integrative and Comparative Biology to R.C.D., and several grants from the Department of Ecology and Evolutionary Biology at UC Santa Cruz to R.C.D.
LIST OF SYMBOLS AND ABBREVIATIONS
- area (m2)
- foot thickness (m)
- cutaneous evaporative water loss (g min−1 m−2)
- raw rate of cutaneous evaporative water loss (g min−1 m−2)
- flow rate for calibration experiments (l min−1)
- convection coefficient (W m−2 °C−1)
- thermal conductivity (W m−1 °C−1)
- gas constant for water vapor (J K−1 kg−1)
- restricted maximum likelihood analysis
- respiratory evaporative water loss (l day−1)
- air temperature (°C)
- floor temperature (°C)
- skin surface temperature (°C)
- STPD-corrected flow rate of air (l min−1)
- water vapor pressure saturation deficit (kPa)
- emissivity of skin (decimal fraction)
- water vapor pressure (Pa)
- Stephan–Boltzmann constant (W m−2 K−4)
- © 2013. Published by The Company of Biologists Ltd