The Ecology of Exercise: Mechanisms Underlying Individual Variation in Behavior, Activity, and Performance: An Introduction to Symposium

Abstract

Wild animals often engage in intense physical activity while performing tasks vital for their survival and reproduction associated with foraging, avoiding predators, fighting, providing parental care, and migrating. In this theme issue we consider how viewing these tasks as "exercise"-analogous to that performed by human athletes-may help provide insight into the mechanisms underlying individual variation in these types of behaviors and the importance of physical activity in an ecological context. In this article and throughout this issue, we focus on four key questions relevant to the study of behavioral ecology that may be addressed by studying wild animal behavior from the perspective of exercise physiology: (1) How hard do individual animals work in response to ecological (or evolutionary) demands?; (2) Do lab-based studies of activity provide good models for understanding activity in free-living animals and individual variation in traits?; (3) Can animals work too hard during "routine" activities?; and (4) Can paradigms of "exercise" and "training" be applied to free-living animals? Attempts to address these issues are currently being facilitated by rapid technological developments associated with physiological measurements and the remote tracking of wild animals, to provide mechanistic insights into the behavior of free-ranging animals at spatial and temporal scales that were previously impossible. We further suggest that viewing the behaviors of non-human animals in terms of the physical exercise performed will allow us to fully take advantage of these technological advances, draw from knowledge and conceptual frameworks already in use by human exercise physiologists, and identify key traits that constrain performance and generate variation in performance among individuals. It is our hope that, by highlighting mechanisms of behavior and performance, the articles in this issue will spur on further synergies between physiologists and ecologists, to take advantage of emerging cross-disciplinary perspectives and technologies.

Fig. 1

The potential costs of various behaviors associated with high levels of physical activity, inspired by Piersma (2011) and Peterson et al. (1990). The dark curve represents the sustainable level of energy throughput to support activity over a given time frame. At shorter temporal scales, increased energy can be spent on activity without incurring additional physiological costs. Activities that use amounts of energy above this line will potentially incur additional physiological costs (as indicated at the bottom of the figure) with potential implications for individual fitness. Individuals may minimise costs by either: (1) reducing the energetic costs of each behavior, by decreasing the frequency of each behavior or increase the efficiency with which it is performed; (2) adjusting physiological traits to attenuate the negative effects of operating above a sustainable level for various amounts of time (e.g., through training-induced plasticity). The width of the arrow associated with each type of behavior approximates the time scale over which each can occur; the elevation along the y-axis (in combination with the brackets along the y-axis) approximates the energy required for each behavior. Similarly, the width of the arrow associated with each physiological cost roughly indicates the temporal scale and activity types most likely to elicit each effect. At the top of the figure, types of human exercise (associated with running, specifically) are indicated that may be viewed as analogous to the non-human animal behaviors that elicit various intensities of activity at various temporal scales. Note that human exercise labels do not strictly align with the temporal labels along the x-axes.