Andrew Sih

Costs and limits of phenotypic plasticity

The costs and limits of phenotypic plasticity are thought to have important ecological and evolutionary consequences, yet they are not as well understood as the benefits of plasticity. At least nine ideas exist regarding how plasticity may be costly or limited, but these have rarely been discussed together. The most commonly discussed cost is that of maintaining the sensory and regulatory machinery needed for plasticity, which may require energy and material expenses. A frequently considered limit to the benefit of plasticity is that the environmental cues guiding plastic development can be unreliable. Such costs and limits have recently been included in theoretical models and, perhaps more importantly, relevant empirical studies now have emerged. Despite the current interest in costs and limits of plasticity, several lines of reasoning suggest that they might be difficult to demonstrate.

Behavioral Syndromes: An Integrative Overview

A behavioral syndrome is a suite of correlated behaviors expressed either within a given behavioral context (e.g., correlations between foraging behaviors in different habitats) or across different contexts (e.g., correlations among feeding, antipredator, mating, aggressive, and dispersal behaviors). For example, some individuals (and genotypes) might be generally more aggressive, more active or bold, while others are generally less aggressive, active or bold. This phenomenon has been studied in detail in humans, some primates, laboratory rodents, and some domesticated animals, but has rarely been studied in other organisms, and rarely examined from an evolutionary or ecological perspective. Here, we present an integrative overview on the potential importance of behavioral syndromes in evolution and ecology. A central idea is that behavioral correlations generate tradeoffs; for example, an aggressive genotype might do well in situations where high aggression is favored, but might be inappropriately aggressive in situations where low aggression is favored (and vice versa for a low aggression genotype). Behavioral syndromes can thereby result in maladaptive behavior in some contexts, and potentially maintain individual variation in behavior in a variable environment. We suggest terminology and methods for studying behavioral syndromes, review examples, discuss evolutionary and proximate approaches for understanding behavioral syndromes, note insights from human personality research, and outline some potentially important ecological implications. Overall, we suggest that behavioral syndromes could play a useful role as an integrative bridge between genetics, experience, neuroendocrine mechanisms, evolution, and ecology.

Emergent impacts of multiple predators on prey

Although almost all prey live with many types of predator, most experimental studies of predation have examined the effects of only one predator at a time. Recent work has revealed new insights into the emergent impacts of multiple predators on prey and experimental studies have identified statistical methods for evaluating them. These studies suggest two main types of emergent effect-risk reduction caused by predator-predator interactions and risk enhancement caused by conflicting prey responses to multiple predators. Some theory and generalities are beginning to emerge concerning the conditions that tend to produce these two outcomes.

Antipredator Defenses and the Persistence of Amphibian Larvae With Fishes

Communities of larval amphibians in fishless habitats often differ strikingly from those in habitats with fish. We surveyed larvae of 15 amphibian species to determine if presence or absence of specific defenses against fish was correlated with breeding habitat. Each species was tested for two key defenses: unpalatability and chemically mediated predator avoidance. In eight of nine cases, larvae of species that often encounter fish had at least one of these defenses. In contrast, larvae of seven species that breed in fishless pools consistently lacked defenses against fish. Lack of appropriate defenses appears to be a primary reason why temporary pool species cannot successfully coexist with predatory fishes in permanent habitats. Palatability and responses to chemical cues from fish often differed among closely related taxa and were correlated strongly with frequency of encounter with fish. Thus, natural selection rather than phylogeny best explains interspecific variation in antipredator defen- ses. Our data show that members of at least two orders and four families of amphibians use chemical cues to reduce predation risk from predatory fish.

Evolution and behavioural responses to human‐induced rapid environmental change

Almost all organisms live in environments that have been altered, to some degree, by human activities. Because behaviour mediates interactions between an individual and its environment, the ability of organisms to behave appropriately under these new conditions is crucial for determining their immediate success or failure in these modified environments. While hundreds of species are suffering dramatically from these environmental changes, others, such as urbanized and pest species, are doing better than ever. Our goal is to provide insights into explaining such variation. We first summarize the responses of some species to novel situations, including novel risks and resources, habitat loss/fragmentation, pollutants and climate change. Using a sensory ecology approach, we present a mechanistic framework for predicting variation in behavioural responses to environmental change, drawing from models of decision‐making processes and an understanding of the selective background against which they evolved. Where immediate behavioural responses are inadequate, learning or evolutionary adaptation may prove useful, although these mechanisms are also constrained by evolutionary history. Although predicting the responses of species to environmental change is difficult, we highlight the need for a better understanding of the role of evolutionary history in shaping individuals’ responses to their environment and provide suggestion for future work.

Prey Uncertainty and the Balancing of Antipredator and Feeding Needs

Predation risk often varies in space and time. To respond adaptively to fluctuations in risk, prey must sample to gain information on the current presence or absence of predators. Bayesian statistical decision theory provides a framework for modeling the effects of prey uncertainty about predation risk on prey behavior. The model predicts that due to prey uncertainty, prey should often stay in refuge long after predators have left an area. Prey behavioral time lags should depend on the quality of prey information about predation risk and on the costs and benefits of refuge use. Under biologically reasonable conditions (e.g., if prey escape success is low), uncertainty can cause prey to always stay in refuge even though predators are only occasionally present. Although many studies have examined prey responses to predator addition, few studies have quantified prey responses to predator removal. Observations on the responses of juvenile aquatic bugs, Notonecta hoffmani, to the experimental addition and removal of cannibalistic adults showed that, as predicted by theory, prey behavioral time lags were longer when predator density was higher, prey were less hungry, and prey had lower escape ability.

FORAGING STRATEGIES AND THE AVOIDANCE OF PREDATION BY AN AQUATIC INSECT, NOTONECTA HOFFMANNI'

Field and laboratory experiments demonstrated that the degree to which an aquatic insect, Notonecta hoffmanni, shows avoidance behavior towards an important predator is propor- tional to the magnitude of the risk of predation. Laboratory experiments showed that I, II, and III instar juvenile N. hoffmanni can suffer significant mortality due to predation from adult N. hoffmanni whereas IV and V instars suffered no mortality from adults. In particular, the relative risk of predation from adults was I > II > III > IV = V - no risk. Based on these data I predicted that I, II, and III instars should avoid adults whereas IV and V instars should not, and that the relative degree of avoidance should be I > II > III > IV = V = no avoidance. Two measures of predator avoidance were documented: alterations in the use of space, and reductions in movement. In both the laboratory and the field the effects of adults on the behavior of juvenile notonectids were determined by comparing the juveniles behavior when adults were experimentally removed to that in controls where adults were present. Alterations in spatial patterns were as predicted, i.e., in both the laboratory and the field only I, II, and III instars avoided adults by altering their use of space, and the degree to which spatial patterns were altered was highly correlated with the relative risk of predation. In the laboratory, reductions in movement were also as predicted, i.e., only I, II, and III instars reduced their movement in the presence of adults and the reduction in movement was highly correlated with the risk of predation. However, in the field, only I and III instars avoided adults by moving less; i.e., II instars did not conform to expectations. Accordingly, in the field the correlation between the reduction in movement and the risk of predation was positive but not signif- icant. In the laboratory, the effects of adults on juvenile feeding rates were also documented. Because I and II instars avoided adults by altering their spatial and movement patterns, they suffered a cost in reduced feeding rates. Unexpectedly, III instars altered their feeding behaviors but suffered no reduction in feeding rates. Partial correlation analysis showed that a decrease in the juveniles use of the central region of water bodies (where prey were four times more dense) resulted in a significant decrease in their feeding rates, but that a reduction in their movement had no such effect. I then discuss the effects on the predictions of optimal foraging theory of some common mecha- nisms by which notonectids avoid their predators. Because the degree of avoidance is related to the risk of predation I also discuss the possibility that feeding behavior represents an adaptive compromise between the conflicting demands of feeding efficiently and avoiding predators. Finally, because the avoidance of predation reduces both the feeding rate of predators on foragers and of foragers on prey, I examine the effects of such reductions on population interactions among predators, foragers, and prey.

Sexual conflict and the evolutionary ecology of mating patterns: water striders as a model system.

Two core ideas in the study of mating systems and sexual selection are (1) the existence of a conflict between the sexes over mating decisions, and (2) that variation in ecological conditions drives the evolution of adaptive mating strategies and the diversification of mating systems. A recent burst of experimental studies of mating behavior and sexual selection in water striders has focused on the interaction of these ideas and led to new insights into the evolutionary ecology of mating systems and sexual selection.

Patch Size, Pollinator Behavior, and Pollinator Limitation in Catnip

We examined the effects of the patch size of catnip, Nepeta cataria, on pollinator visitation rates and pollinator limitation. The most important floral visitors were honey bees (Apis mellifera), solitary bees (Halictidae), and bumble bees (Bombus spp.). Our first goal was to see how spatial variation in patch size affected the rate at which individual flowers received pollinator visits (visitation rate). Visitation rate was higher in larger patches for honey bees and bumble bees, but lower for solitary bees. Patch size explained 74-83% of the variation in visitation rate. Intraspecific isolation also had an effect: isolated patches received relatively few visits. Visitation rate depended both on visitor abundance and on the proportion of flowers entered during one visit. All three visitor types wee more abundant in larger patches, i.e., flowers showed mutual attraction of pollinators. Relative to a visit to a small patch, during a visit to a large patch, honey bees visited more flowers but a lower proportion of flowers; solitary bees visited fewer flowers and thus a lower proportion of flowers; and bumble bees visited not only more flowers but a higher proportion of flowers as well. Thus within patches, flowers competed for visits from honey bees and solitary bees but showed facilitation regarding bumble bee visits. Our second goal was to relate patch size and visitation rates to immediate pollinator limitation. Comparisons of the percent of capsules setting seed (fruit set) of open-pollinated, hand-pollinated, and bagged flowers were used to evaluate pollinator limitation. The ranking of fruit set was: hand-pollinated > open-pollinated > bagged. Patch size did not affect fruit set in hand-pollinated or bagged flowers; however, for open-pollinated flowers, fruit set was lower in smaller patches. patch size explained 63% of the variation in pollinator limitation. The effect of patch size comes through its effects on visitation rates. A multiple regression model using visitation rates of the three types of visitors as independent variables explained 67% of the variation in pollinator limitation.

Chapter 5 Insights for Behavioral Ecology from Behavioral Syndromes

Publisher Summary This chapter provides insights for behavioral ecology from behavioral syndromes. A behavioral syndrome involves behavioral consistency, both within and between individuals. Within-individual consistency occurs when individuals behave in a consistent way through time or across situations, that is, individuals have a behavioral type. Between-individual consistency occurs when individuals differ in their behavioral type, which would be reflected statistically as a behavioral correlation among individuals. The chapter also deals with understanding variation in behavioral syndromes. Simply examining changes in the distribution of behaviors is a useful first step to understand the causes of variable correlations. Morphological mechanisms (like organ size or brain structures) that can only change slowly are good candidates for explaining the stable behavioral types and a stable behavioral syndrome. One proximate source that could anchor a behavioral type involves physiological mechanisms associated with variation in growth rate. The quantitative methods used for examining multiple behavioral tendencies are also presented.