Tri-Axial Dynamic Acceleration as a Proxy for Animal Energy Expenditure; Should We Be Summing Values or Calculating the Vector?

Emily L. C. Shepard,Lewis G. Halsey,Antonia Cardew,Iwan Griffiths,Rory Wilson,Lama Qasem,Alexis Wilson,Adrian C. Gleiss

doi:10.1371/journal.pone.0031187

Emily L. C. Shepard, Lewis G. Halsey

Open Access

https://doi.org/10.1371/journal.pone.0031187

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Abstract

Dynamic body acceleration (DBA) has been used as a proxy for energy expenditure in logger-equipped animals, with researchers summing the acceleration (overall dynamic body acceleration - ODBA) from the three orthogonal axes of devices. The vector of the dynamic body acceleration (VeDBA) may be a better proxy so this study compared ODBA and VeDBA as proxies for rate of oxygen consumption using humans and 6 other species. Twenty-one humans on a treadmill ran at different speeds while equipped with two loggers, one in a straight orientation and the other skewed, while rate of oxygen consumption () was recorded. Similar data were obtained from animals but using only one (straight) logger. In humans, both ODBA and VeDBA were good proxies for with all r2 values exceeding 0.88, although ODBA accounted for slightly but significantly more of the variation in than did VeDBA (P<0.03). There were no significant differences between ODBA and VeDBA in terms of the change in estimated by the acceleration data in a simulated situation of the logger being mounted straight but then becoming skewed (P = 0.744). In the animal study, ODBA and VeDBA were again good proxies for with all r2 values exceeding 0.70 although, again, ODBA accounted for slightly, but significantly, more of the variation in than did VeDBA (P<0.03). The simultaneous contraction of muscles, inserted variously for limb stability, may produce muscle oxygen use that at least partially equates with summing components to derive DBA. Thus, a vectorial summation to derive DBA cannot be assumed to be the more ‘correct’ calculation. However, although within the limitations of our simple study, ODBA appears a marginally better proxy for . In the unusual situation where researchers are unable to guarantee at least reasonably consistent device orientation, they should use VeDBA as a proxy for .

Highlights

The broad interest in animal optimal foraging [1] underpins the central concept that creatures should behave in such a way as to maximize their inclusive fitness by maximizing their net rate of energy intake [see 2,3]
A direct test of the predictive power of overall dynamic body acceleration (ODBA) and vector of the dynamic body acceleration (VeDBA) is required, yet Gleiss, Wilson et al [24] note that no studies have explicitly sought to determine whether ODBA or VeDBA is a better predictor of metabolic rate and whether the outcome of such a test might be influenced by logger orientation on the animal
How much higher ODBA is than VeDBA will depend, inter alia, on the type of motion recorded which, in turn depends on animal type, gait and tag location

Summary

Introduction

The broad interest in animal optimal foraging [1] underpins the central concept that creatures should behave in such a way as to maximize their inclusive fitness by maximizing their net rate of energy intake [see 2,3]. Understanding optimality in foraging is only one example that demonstrates the importance of being able to determine energy expenditure but it, like many other biological processes, is best informed by energy expenditure at a fine-scale temporal resolution, something that is notably rare in published studies with some exceptions [9,10,11,12]. This situation stems from a paucity of appropriate methods for determining the power use of wild animals. See Halsey [25] and references therein for further details

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