Top predator’s aggressiveness and mesopredator’s risk-aversion additively determine probability of predation

Abstract

Predator–prey interactions strongly affect ecological dynamics. Consistent inter-individual differences in behaviour (individual behavioural types, BTs) of predator and prey (or both) may fundamentally shape their mutual interactions. Several recent studies have shown that it is important to consider the interaction of BTs on both sides of predator–prey interactions. Otherwise, there is a high risk of erroneous inference about the outcome of predation. Until now, however, no study has investigated how BT vs BT interaction affects the predation of mesopredators by top predators, especially when the mesopredator is a low-ranked prey for the top predator. Such knowledge is extremely important if we want to predict the effect of individual BTs on food web dynamics. We have investigated in our laboratory experiments how foraging aggressiveness of the top predator (spider, Philodromus cespitum, Philodromidae) and risk-aversion as a form of shyness of the mesopredator (spider, Philodromus albidus, Philodromidae) determine the probability of predation. The highest explanatory power had the model with additive effects of mesopredator’s risk-aversion and top predator’s foraging aggressiveness. Other models, including those with BT vs BT interaction, had poor explanatory power. It was probably due to the fact that timid top predators are often choosy and do not catch low-ranked prey, while aggressive top predators are opportunists. The risk-averse mesopredators are also more cautious than risk-prone mesopredators regarding their surroundings and can defend themselves faster. Our results therefore fit with the classical hypothesis about trade-off between foraging and safety. Behavioural types of predator and prey jointly determine the mortality of prey. In our laboratory experiments, we investigated how foraging aggressiveness of a top predator spider and the risk-aversion of a mesopredator spider (potential prey) determine the probability of predation. We demonstrated that top predator’s foraging aggressiveness and mesopredator’s risk-aversion determine the probability of mesopredator’s mortality only additively. The mesopredator’s probability of being killed decreased with its risk-aversion and increased with top predator’s foraging aggressiveness. The effect was additive instead of interactive because the mesopredator represents a dangerous prey for the top predator. The timid top predators are also choosy and do not attack dangerous prey, while the aggressive/non-choosy top predators are opportunistic. Further, the risk-averse mesopredators are more cautious regarding their surroundings and can react faster to the presence of a top predator, compared to risk-prone and slowly reacting mesopredators.