|
Vigilance, in the field of behavioural ecology, refers to an animal’s examination of its surroundings in order to heighten awareness of predator presence. Vigilance is an important behaviour during foraging as animals must often venture away from the safety of shelter to find food. However being vigilant comes at the expense of time spent feeding so there is a trade-off between the two. The length of time animals devote to vigilance is dependent on many factors including predation risk and hunger. Vigilance is often observed in animals that forage in groups, such as yellow-eyed juncos (''Junco phaeonutus'') and meerkats (''Suricata suricatta''). Foraging in groups dilutes an individual’s risk of predation, and allows them to reduce their own vigilance while the vigilance of the group is maintained.〔Davies, N.B., Krebs, J.R. & West, S.A. (2012) An Introduction to Behavioural Ecology 4th edn, Wiley-Blackwell, Oxford, UK〕 Alarm signals may be used to alert the group to the presence of predators. Groups of some species have at least one individual on sentry duty who looks out for predators on a perch while the rest of the group forages.〔 == Feeding and predation risk trade-off == Vigilance and feeding (both searching for and handling food) are generally mutually exclusive activities, leading to foragers facing a trade-off between energy intake and safety from predation. As time allocated to scanning reduces the time spent feeding, vigilant individuals must devote more time on foraging to obtain the required food intake.〔Illius, A.W. & Fitzgibbon, C. (1994) Costs of vigilance in foraging ungulates. Animal Behaviour 47: 481-484〕 This impedes on other activities in their time budget such as mating and prolongs their exposure to predation as foraging occurs away from shelter.〔 When foraging time is limited, vigilant animals are left with a reduced energy intake.〔 Optimality models can be used to predict foraging decisions of an animal based on costs (predation risk, starvation) and benefits (safety, food), which are also affected by physiology such as hunger levels.〔 Grey squirrels (''Sciurus carolinensis'') alter their behaviour according to the relative costs and benefits when foraging in the open.〔Lima, S.L., Valone, T.J. & Caraco, T. (1985) Foraging-efficiency – predation-risk trade-off in the grey squirrel. Animal Behaviour 33: 155-165〕 Small food items are consumed immediately to maximise energy intake, as they require little handling time so the cost of predation risk is low.〔 Large items that require a long handling time, and hence time exposed to predators, are carried back to the safety of a tree to minimise predation risk.〔 Although there is an energetic cost to transporting food, large food items have a high contribution to nutrient intake so the cost outweighs the benefits.〔 The overall predation risk is a function of the abundance, activity and ability of predators to detect the forager, as well as the likelihood that the forager can escape the predator if it is not vigilant.〔Brown, J.S. (1999) Vigilance, patch use and habitat selection: foraging under predation risk. Evolutionary Ecology Research 1: 49-71〕 Animals prioritise vigilance over feeding when the predation risk is high. For example, yellow-eyed juncos spend more time scanning for predators when a potential predator, a Harris's hawk (''Parabuteo unicinctus''), is present compared to when the hawk is absent.〔Caraco, T., Martindale, S. & Pulliam, H.R. (1980) Avian flocking in the presence of a predator. Nature 285: 400-401〕 Another factor that influences vigilance is the benefit that is expected from foraging in the absence of predation.〔 This is dependent on the quality of the food as well as the energetic state of the individual. If there is much to be gained from feeding, foragers may forgo vigilance. Similarly, if hungry animals have a higher chance of dying from starvation than from predation, it is more beneficial to sacrifice vigilance to fulfill their energy requirements. When three-spined sticklebacks (''Gasterosteus aculeatus'') are deprived of food, they prefer to feed in locations with a high density of water fleas.〔Milinski, M. & Heller, R. (1978) Influence of a predator on the optimal foraging behaviour of sticklebacks (''Gasterosteus aculeatus''). Nature 275: 642-644〕 The cost to this choice is that the sticklebacks must concentrate on picking out the prey due to the 'predator confusion effect' where many moving targets make it difficult for predators to pick out individual prey.〔 This choice means that the sticklebacks are less able to scan for predators however the risk of starvation is relatively higher than the risk of predation.〔 Similarly, juncos that have been deprived of food exhibit lower levels of vigilance, instead focusing on rapid feeding which is a behaviour incompatible with scanning.〔Lima, S.L. (1995) Back to the basics of anti-predatory vigilance: the group-size effect. Animal Behaviour 49: 11-20〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Vigilance (Behavioural Ecology)」の詳細全文を読む スポンサード リンク
|