PDF《wolf》

Kotler 2004). For example, prey may have to avoid the richest resource patches when trading-off energy gains for safety (Lima &

Dill 1990;

Lima 1998). Bison (Bison bison L.) have been observed to decrease their selection of optimal food items in response to predation risk, resulting in lower rates of energy gains (Fortin &

Fortin 2009). Prey also uses vigilance to avoid being sur- prised by a predator, a behaviour that tends to decrease foraging rate (Lendrem 1983;

Brown 1999). In general, the level of anti-predator behaviour should increase with the risk of mortality, the prey'

s energy state, and its ?t- ness, and decrease as its marginal value of energy rises (Brown 1999;

Brown &

Kotler 2004). The co-evolution of predators and prey may result in prey developing chronic anti-predator responses (Schmitz, Krivan &

Ovadia 2004). Because of the high costs of anti-predator behaviours, a speci?c chronic response may not always maximize ?tness, and it may be bene?cial for the prey to adjust its level of anti-pred- ator behaviour based on its current perception of the threat level. A prey should exhibit its strongest anti- predator behaviour in brief and infrequent high-risk situ- ations, whereas allocation of anti-predator effort to high-risk situations should decrease as they become more frequent or lengthy (Lima &

Bednekoff 1999;

Creel et al. 2008). Chronic and ephemeral behavioural responses should ultimately be dictated by factors such as the mobility of predators, their hunting mode (Schmitz, Kri- van &

Ovadia 2004) and the prey escape tactics (Wir- sing, Cameron &

Heithaus 2010). An optimal prey response may not simply use either chronic or ephemeral anti-predator behaviours, but may use a combination of both. Such a combination of anti-predator responses can then be used to characterize a prey'

s '

landscape of fear'

, in which '

hills'

and '

valleys'

are de?ned by the predation risk and related in particular to spatial patterns in habi- tat features (Laundré, Hernández &

Ripple 2010). Given the possibility of chronic and ephemeral behavioural responses to risk, the landscape of fear could vary broadly, from static to highly dynamic according to the spatial and temporal scales of the prey'

s perception of risk. A comprehensive assessment of the impact of pre- dators should therefore involve the quanti?cation of a prey'

s perceptual range (or the range within which signs of predators can trigger a response), together with the time that the perceived changes in threat last (Lima &

Dill 1990;

Lima &

Zollner 1996). Several studies have examined the impact of the pres- ence of predators at ?ne temporal and spatial scales. For example, elk tend to leave food-rich grasslands and moved into the protective cover of wooded areas when wolves were present in the same drainage on the same day (Creel et al. 2005). They also increase their movement rate when wolves are within

5 km from its location during the previous

4 h (Prof?tt et al. 2009), a response that may vary with the presence of calves, group size and season (Liley &

Creel 2008). Elk become more vigilant when wolves are present within

3 km from their location (Liley &

Creel 2008). Likewise, zebra (Equus quagga B.) display intense vigilance when lions (Panthera leo L.) are within

2 km (P eriquet et al. 2012), and individuals become less abundant on grasslands during the night if lions have also been present during the past