To feed or flee: early life-history behavioural strategies of juvenile lake sturgeon (Acipenser fulvescens) during risk-sensitive foraging

Balancing foraging opportunities with predation risk can promote complex behavioural strategies in juvenile fishes, particularly in northern temperate environments with short growing seasons. To test how predation experience may influence foraging effort and risk assessment of juvenile lake sturgeon (Acipenser fulvescens Rafinesque, 1817), flight response and substrate preference behavioural measurements were taken during critical life periods of early exogenous feeding (∼60 days post fertilization (dpf)) and pre-winter (∼160 dpf). Lake sturgeon were placed in arenas with partial cover and exposed white plastic bottom. Chemical alarm cue (AC) was introduced to predator naïve individuals in the presence or absence of food over the exposed portion of the arena to simulate risk sensitive foraging over diurnal and seasonal periods. The same protocol was run on predator-experienced individuals, which were classically conditioned to predator cue (PC) prior to the trials. Whole-body cortisol measures were also taken to determine the physiological response to predation experience. Results suggest a propensity to forage in spite of predation risk during the naïve ∼60 dpf trials and highlight context-specific anti-predator responses of naïve and experienced lake sturgeon. Elevated basal whole-body cortisol levels and reduced body condition (p < 0.05) were observed with increased predator experience.

Risk-sensitive foraging does not explain condition-dependent choices in settling reef fish larvae

The transition from the planktonic larval to the benthic adult stage in reef fishes is perilous, and involves decisions about habitat selection and group membership. These decisions are consequential because they are essentially permanent (many fish rarely leave their initial settlement habitat, at least for the first several days or weeks). In one common Caribbean reef fish, the bluehead wrasse (Thalassoma bifasciatum), settling larvae either join groups or remain solitary. Grouped fish have lower mortality rates but slightly slower growth rates, and fish that are smaller at the time of settlement are less likely to join groups. We hypothesized that the decision of smaller (i.e., lower condition) fish to remain solitary could be explained by risk-sensitive foraging: with less competition, solitary fish may have higher variance in foraging success, so that there is a chance of a high payoff (outweighing the increased mortality risk) despite the lack of a large difference in the average outcome. We tested this by comparing the mean, standard deviation, and maximum number of (a) prey items in stomach contents and (b) post-settlement growth rates (from otolith measurements) of solitary and grouped fish during two settlement pulses on St. Croix, US Virgin Islands. However, we did not find evidence to support our hypothesis, nor any evidence to support the earlier finding that fish in groups have lower average growth rates. Thus we must consider alternative explanations for the tendency of smaller fish to remain solitary, such as the likely costs of searching for and joining groups at the time of settlement. This study reinforces the value of larval and juvenile fish as a testbed for behavioral decisionmaking, because their recent growth history is recorded in their otoliths.

Risk-sensitive foraging strategy of flower visitors in Serjania caracasana

Production of nectar can play a fundamental role in the foraging behaviour of floral visitors through its availability and distribution. The aim of this study was to understand the foraging pattern of floral visitors in Serjania caracasana. The field study observed the strategy of nectar production and the foraging behaviour of the floral visitors of Serjania caracasana, carried out through an experiment that evaluated the amount of nectar produced by flowers, species richness and frequency of visits. The data analysis showed that there is no significant correlation between any of the variables analysed. The unstable nectar between the flowers and the unpredictability during the hours of the day suggest a risk-foraging strategy of risk-prone type of the species of floral visitors. The data from this study suggests that Serjania caracasana has potential to understand the theory of risk-sensitive foraging in relation to its reproductive success.

Mechanistic models must link the field and the lab

In the theory outlined in the target article, an animal forages continuously, making sequential decisions in a world where the amount of food and its uncertainty are fixed, but delays are variable. These assumptions contrast with the risk-sensitive foraging theory and create a problem for comparing the predictions of this model with many laboratory experiments that do not make these assumptions.

Risk, Rational Choice, and Evolution

Decision-theoretic ideas arise in two areas of biology: risk-sensitive foraging, and the theory of evolution in variable environments. The former concerns the actual behavioural choices that organisms make, the latter the ‘choices’ made by natural selection. A natural suggestion is that both sorts of choices can be modelled in terms of expected utility maximization, the standard theory of rational decision in the face of risk. However, this is only true under particular model assumptions; it does not hold in situations involving a combination of aggregate and idiosyncratic risk. Mixed strategies further complicate the relation between rational and biologically optimal risk preferences. This implies a limit on the validity of the organism-as-rational-agent heuristic as a tool for understanding evolved behaviour.