Early exposure to nonlethal predation risk by size-selective predators increases somatic growth and decreases size at adulthood in three-spined sticklebacks.

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Abstract

Predation has an important influence on life history traits in many organisms, especially when they are young. When cues of trout were present, juvenile sticklebacks grew faster. The increase in body size as a result of exposure to cues of predators was adaptive because larger individuals were more likely to survive predation. However, sticklebacks that had been exposed to cues of predators were smaller at adulthood. This result is consistent with some life history theory. However, these results prompt an alternative hypothesis, which is that the decreased size at adulthood reflects a deferred cost of early rapid growth. Compared to males, females were more likely to survive predation, but female size at adulthood was more affected by cues of predators than male size at adulthood, suggesting that size at adulthood might be more important to male fitness than to female fitness.

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Ecological consequences of the trade-off between growth and mortality rates mediated by foraging activity.

E Werner, B Anholt (1993)

Animals are frequently faced with trade-offs created by the fact that both resource acquisition and risk of mortality increase with activity, for example, with foraging speed or time spent foraging. We develop models predicting adaptive responses for both foraging speed and proportion of time active when individual growth rate and mortality risk are functions of these variables. Using the criterion that animals should minimize the ratio of mortality to growth rates, we show that, when both growth and mortality rates are linear with activity levels, the latter should be either maximal or minimal depending on resource level. If growth rate is a decelerating function of activity, then speed or time active should decrease with increases in resources, handling time, or the effect of activity on mortality rate. By contrast, if mortality rate unrelated to activity increases, then activity rate also should increase. We also develop predictions for cases in which time horizon is critical using a dynamic programming framework. The general patterns of predicted activity responses are similar to the time-invariant analytical solutions, but foraging speed is reduced relative to the analytical solutions when time remaining is long or when accumulated reserves are high. This effect is ameliorated when accumulated reserves (size) increase resource capture efficiency or reduce mortality risk. If resources decline with time (e.g., because of competition) optimal foraging speeds are also higher than predicted by the analytical solutions. We discuss the relation of our predictions to previous models and the available empirical evidence. The majority of available data appear to be consistent with our models, and in some cases quantitative comparisons are quite close. Finally, we discuss the implications of our results for ontogenetic changes in behavior and for population- and community-level phenomena, particularly the role of activity responses in competitive interactions and indirect effects and patterns of coexistence among competitors.

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Growth-mortality tradeoffs and 'personality traits' in animals.

Judy A. Stamps (2007)

Consistent individual differences in boldness, reactivity, aggressiveness, and other 'personality traits' in animals are stable within individuals but vary across individuals, for reasons which are currently obscure. Here, I suggest that consistent individual differences in growth rates encourage consistent individual differences in behavior patterns that contribute to growth-mortality tradeoffs. This hypothesis predicts that behavior patterns that increase both growth and mortality rates (e.g. foraging under predation risk, aggressive defense of feeding territories) will be positively correlated with one another across individuals, that selection for high growth rates will increase mean levels of potentially risky behavior across populations, and that within populations, faster-growing individuals will take more risks in foraging contexts than slower-growing individuals. Tentative empirical support for these predictions suggests that a growth-mortality perspective may help explain some of the consistent individual differences in behavioral traits that have been reported in fish, amphibians, reptiles, and other animals with indeterminate growth.