Plasticity and Personality

Behavioral ecology has traditionally used what is known as the optimality approach to study animal behavior. This approach is typically used to predict the optimal expression of a behavioral trait for the average individual in a population given any constraints that may limit the expression of that trait (Davies et al. 2012). For example, in order to minimize the probability of being depredated, individuals can invest in anti-predator vigilance. However, individuals are limited in how much time they can invest in vigilance, because time is a limited resource and individuals must also engage in other time consuming behaviors such as foraging. The trade-off between the costs and benefits of increased time invested in vigilance leads to individuals accruing the maximum net-benefit from vigilance at some intermediate level of expression, and this level of expression is considered optimal. The optimality approach has been successfully used to predict mean behaviors in populations but not variation among individuals. However, individuals often show consistent differences in behavior over time or across contexts, a phenomenon referred to as animal personality. This is represented statistically by a significant proportion (i.e., repeatability, r) of the total variation in behavior occurring between individuals [i.e., Vbetween individuals/(Vbetween individuals + Vwithin individuals)], and suggests that individuals may differ from the optimum or mean behavior at the population level. For example, female Ural owls (Strix uralensis) aggressively defend their nests, and while the intensity of nest defense varies depending on brood size or environmental factors like food availability, an

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