Publisher Summary This chapter reviews the present empirical and theoretical work on antipredator decision making. The ways in which predators influence the behavioral decisions made by their prey is now the subject of a large and growing literature. Some notable recent advances include clear demonstrations that antipredatory decision making (1) may influence many aspects of reproductive behavior, (2) has demonstrable long-term consequences for individual fitness, and (3) may influence the nature of ecological systems themselves. There have also been many advances in the theory of antipredator behavior, which should provide a sound conceptual basis for further progress. Attention is needed for further work on the effects that predator and prey have on the other's behavioral decisions. The range of reproductive behaviors influenced by the risk of predation also requires much more investigation. Work on the long-term costs of antipredator decision making needs more empirical documentation and greater taxonomic diversity. Work on the ecological implications of antipredatory decision making has only scratched the surface, especially with regard to population-level effects and species interactions. Theoretical investigations should also play a prominent role in future work.

Stress and Decision Making under the Risk of Predation: Recent Developments from Behavioral, Reproductive, and Ecological Perspectives

Ecosystem services are natural processes that benefit humans. Birds contribute the four types of services recognized by the UN Millennium Ecosystem Assessment-provisioning, regulating, cultural, and supporting services. In this review, we concentrate primarily on supporting services, and to a lesser extent, provisioning and regulating services. As members of ecosystems, birds play many roles, including as predators, pollinators, scavengers, seed dispersers, seed predators, and ecosystem engineers. These ecosystem services fall into two subcategories: those that arise via behavior (like consumption of agricultural pests) and those that arise via bird products (like nests and guano). Characteristics of most birds make them quite special from the perspective of ecosystem services. Because most birds fly, they can respond to irruptive or pulsed resources in ways generally not possible for other vertebrates. Migratory species link ecosystem processes and fluxes that are separated by great distances and times. Although the economic value to humans contributed by most, if not all, of the supporting services has yet to be quantified, we believe they are important to humans. Our goals for this review are 1) to lay the groundwork on these services to facilitate future efforts to estimate their economic value, 2) to highlight gaps in our knowledge, and 3) to point to future directions for additional research.

Ecosystem Services Provided by Birds

We review the concepts and research associated with measuring fear and its consequences for foraging. When foraging, animals should and do demand hazardous duty pay. They assess a foraging cost of predation to compensate for the risk of predation or the risk of catastrophic injury. Similarly, in weighing foraging options, animals tradeoff food and safety. The foraging cost of predation can be modelled, and it can be quantitatively and qualitatively measured using risk titrations. Giving-up densities (GUDs) in depletable food patches and the distribution of foragers across safe and risky feeding opportunities are two frequent experimental tools for titrating food and safety. A growing body of literature shows that: (i) the cost of predation can be big and comprise the forager’s largest foraging cost, (ii) seemingly small changes in habitat or microhabitat characteristics can lead to large changes in the cost of predation, and (iii) a forager’s cost of predation rises with risk of mortality, the forager’s energy state and a decrease in its marginal value of energy. In titrating for the cost of predation, researchers have investigated spatial and temporal variation in risk, scale-dependent variation in risk, and the role of predation risk in a forager’s ecology. A risk titration from a feeding animal often provides a more accurate behavioural indicator of predation risk than direct observations of predator-inflicted mortality. Titrating for fear responses in foragers has some well-established applications and holds promise for novel methodologies, concepts and applications. Future directions for expanding conceptual and empirical tools include: what are the consequences of foraging costs arising from interference behaviours and other sources of catastrophic loss? Are there alternative routes by which organisms can respond to tradeoffs of food and safety? What does an animal’s landscape of fear look like as a spatially explicit map, and how do various environmental factors affect it? Behavioural titrations will help to illuminate these issues and more.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1461-0248.2004.00661.x

Hazardous duty pay and the foraging cost of predation

To balance conXicting demands for food and safety from predation, feeding animals have two useful tools. First, they can vary the amount of time they devote to harvesting patches that vary in predation risk and feeding rates. Second, they can use vigilance to trade-oV food and safety while feeding from a food patch. I present a model for predicting how an optimal forager should jointly use these two tools. Factors inXuencing the use of these tools include encounter rate with predators, predator lethality in the absence of vigilance, eVectiveness of vigilance in reducing predator lethality, the marginal value of energy to the forager and the forager’s survivor’s Wtness. Patch-use behaviours inXuenced by these factors include vigilance level, quitting harvest rate and giving-up density (GUD). All three of these patch-use behaviours should increase in response to an increase in encounter rate with predators, predator lethality and the forager’s survivor’s Wtness, and decrease with an increase in the marginal value of energy. In response to increasing the eVectiveness of vigilance, vigilance should increase and the GUD and quitting harvest rate should decline. The amount of food left by a forager in a depletable food patch, the GUD, provides an empirical link for testing the model’s predictions. Giving-up densities should increase with increasing predation risk, and GUDs should increase with declining food-densityspeciWc harvest rates. DiVerences in GUDs among food patches attributable to diVerences in quitting harvest rates measure the contribution of time allocation to managing diVerences in predation risk. DiVerences in GUDs attributable to diVerences in food-density-speciWc harvest rates measure the contribution of vigilance to managing predation risk.

/pdf/vigilance-patch-use-and-habitat-selection-foraging-under-3map0avosm.pdf

Vigilance, patch use and habitat selection: Foraging under predation risk

Interactions among predators can a have substantial effect on the total impact of the predator complex. We investigated the interaction between foliar-foraging (Coccinella septempunctata) and ground-foraging (Harpalus pennsylvanicus) predators of the pea aphid (Acyrthosiphon pisum) in a series of laboratory and field experiments. The intensity and direction of the interaction were determined by comparing the combined and individual impacts of both predators. In a laboratory mesocosm, the combined predation rate of both predators was nearly double the sum of their individual predation rates. The mechanism for the interaction was the aphid "dropping" behavior elicited by C. septempunctata, which rendered the aphids susceptible to predation by H. pennsylvanicus on the ground. The strength of the synergistic interaction increased with increasing prey density. The interaction between the predators was also demonstrated in both open and closed field cages where the combined impact of the two predators on aphid population growth was significantly greater than the sum of their individual impacts. These results indicate that the importance of ground-foraging predators in agroecosys- tems may need to be reevaluated and that positive interactions between predators must be considered in models predicting the impact of multiple predator complexes.

http://userwww.sfsu.edu/parker/bio840/pdfs/LoseyDenno1998.pdf

Positive predator–predator interactions: enhanced predation rates and synergistic suppression of aphid populations

Predation may have profound effects on the behavior of prey individuals with consequences for population dynamics and community structure. Here, we report on an experiment in which we examine the response of two gerbil species (Gerbillus allenbyi and G. pyramidum) to the presence of a snake predator, the desert diadema snake (Spalerosophus diadema), and to added illumination (a factor associated with increased risk of predation from owls). We measured rodent foraging behavior by the number of seed trays foraged in each microhabitat and amount of seed resources left in patches following exploitation by gerbils (giving-up densities; GUDs). Fewer seed trays foraged and higher GUDs are indicative of higher perceived predatory risk

Michal Strauss

Papers

The influence of snakes on the foraging behavior of gerbils