Energetics of a super-predator: the cheetah

The race for survival is common to all living organisms: when it comes to predator-prey interactions, this involves predators developing more effective means to catch prey whilst their prey counteracts with new evasion tactics. Energy is a primary limiting resource in most natural systems. To understand how energy budgets compel certain species to inhabit specific environments, it is necessary to identify a species that displays extreme energy requirements. Within mammals, large predators often experience high energy costs while hunting and it is suggested that this may restrict their ecological niches, obliging them to inhabit only areas with abundant food sources and minimal competition. However, no study has yet attempted to measure energy expenditure in a large carnivore while simultaneously monitoring interactions between competitors and prey. With the greatest power output for their size of any mammal and the greatest speed reached on land, cheetahs (Acinonyx jubatus) are positioned at an apex in the topography of evolutionary adaptation. Does such an evolutionary peak come with a cost? Research suggests cheetahs are severely restricted in their abilities to acquire and utilise energy. In the current study, we will measure energy expenditure in free-ranging cheetahs to determine which behaviours or circumstances cause particular energetic constraints. Cheetahs are built for speed, accelerating from 0 to 30 kph in three strides and reaching a maximum speed of about 110 kph in 4 seconds. At full speed, the cheetah is running at about three strides per second and the respiratory rate climbs from 60 to 150 breaths per minute. Cheetahs can only maintain this for a few hundred metres before exhaustion. Such a high-speed foraging strategy imposes severe limits on all other aspects of their lives, leaving them vulnerable to starvation, or to reproductive failure due to lack of energy. This is because their predation tactics are energetically costly, and, being 'built for speed' rather than strength, they are easily driven off their prey by more robust rival species. Consequently, cheetahs are suggested to be at an 'energetic edge', with the viability both of individual animals and populations depending on how close individuals approach the evolutionary limits of energy supply and demand. An understanding of their energetic tactics will therefore help provide insights as to how energetic constraints can shape the evolution of these super-predators. Energy use will be measured using the doubly labelled water technique [1] whilst field observations will be made of activities and of incidents where rival species steal prey or interact with cheetahs in other ways that may affect their energy balances. In addition, multi-channel data loggers -'daily diaries' - will be attached to the cheetahs using collars for up to 80 days at a time. These devices provide data on detailed movement in three dimensions [2] at a very fine resolution (32 Hz). Interpretation of the resulting electronic traces recorded will reveal the time spent on various activities such as resting, feeding, walking and running. The data will also be used to calculate a proxy of energy expenditure, known as 'overall dynamic body acceleration'. This will complement the energetics data and provide a fine-scale record of continuous activity. Thus, individual activities and their associated energy costs will be elucidated to paint a complete picture of the animals' energy budgets. The study will provide valuable information as to how carnivores in general manage their energy budgets. It will also demonstrate how the measurement of physiological characteristics can help determine the long-term viability of rare and threatened species. Thus we shall be providing insights into how energetic constraints can shape species' viability. [1] Speakman, J.R. Doubly Labelled Water. 1997. Chapman and Hall. [2] Wilson, R.P. et al. 2008 Endang. Species. Res. 3:1-15