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Rising temperatures have important consequences for somatic growth, but observed relationships between temperature and growth can vary in both magnitude and direction. The key to understanding such variation is knowing how temperature affects both the amount of energy available for growth and the efficiency with which surplus energy is assimilated into the body. We tested the hypothesis that patterns of temperature-dependent growth are driven by differential sensitivities of energy intake and expenditure to temperature. Larvae of California grunion Leuresthes tenuis were reared across a range of temperatures and 2 levels of food availability. Energy intake was measured from feeding rate, and energy expenditure was evaluated by measuring respiration and excretion rates. When food was abundant, both intake and expenditure increased with temperature, but intake increased more rapidly. These results suggest that high temperatures should lead to faster growth, and these predictions were confirmed by a separate experiment. In contrast, when food was restricted, the increase in energetic demand with temperature outpaced energy intake, suggesting a dwindling surplus of energy at high temperatures. This predicted reversal of the effects of temperature on growth was also confirmed experimentally. Finally, we compared patterns of energetics and growth to test the effects of temperature on food assimilation efficiency. When food was unlimited, assimilation efficiency decreased rapidly with temperature. When food was restricted, assimilation efficiency remained relatively high. Overall, our results emphasize the value of a bioenergetic perspective for illuminating why and how growth rates are likely to change in a warming ocean.
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Wild Bornean orangutan ( Pongo pygmaeus wurmbii ) feeding rates and the Marginal Value Theorem
Abstract The Marginal Value Theorem (MVT) is an integral supplement to Optimal Foraging Theory (OFT) as it seeks to explain an animal's decision of when to leave a patch when food is still available. MVT predicts that a forager capable of depleting a patch, in a habitat where food is patchily distributed, will leave the patch when the intake rate within it decreases to the average intake rate for the habitat. MVT relies on the critical assumption that the feeding rate in the patch will decrease over time. We tested this assumption using feeding data from a population of wild Bornean orangutans (Pongo pygmaeus wurmbii) from Gunung Palung National Park. We hypothesized that the feeding rate within orangutan food patches would decrease over time. Data included feeding bouts from continuous focal follows between 2014 and 2016. We recorded the average feeding rate over each tertile of the bout, as well as the first, midpoint, and last feeding rates collected. We did not find evidence of a decrease between first and last feeding rates (Linear Mixed Effects Model,n = 63), between a mid‐point and last rate (Linear Mixed Effects Model,n = 63), between the tertiles (Linear Mixed Effects Model,n = 63), nor a decrease in feeding rate overall (Linear Mixed Effects Model,n = 146). These findings, thus, do not support the MVT assumption of decreased patch feeding rates over time in this large generalist frugivore.
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- Award ID(s):
- 1638823
- PAR ID:
- 10457015
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- American Journal of Primatology
- Volume:
- 82
- Issue:
- 10
- ISSN:
- 0275-2565
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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