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

Aim We reviewed the occurrence of Bergmann’s rule in birds (ninety-four species) and mammals (149 species), using only studies where statistical significance of the results was tested. We also tested whether studies using different characters as surrogates of body size have a different tendency to conform to Bergmann’s rule, whether body size and nest type (in birds) have an influence on the tendency to conform to the rule, and whether sedentary birds conform to the rule more than migratory birds. Location Worldwide. Methods We reviewed published data on geographic and temporal variation in body size, using only studies where the statistical significance of the results was tested. We asked how many species conform to the rule out of all species studied in each order and family. Results Over 72% of the birds and 65% of the mammal species follow Bergmann’s rule. An overall tendency to follow the rule occurs also within orders and families. Studies using body mass in mammals show the greatest tendency to adhere to Bergmann’s rule (linear measurements and dental measurements show a weaker tendency); while in birds, studies using body mass and other surrogates (linear measurements and egg size) show a similar tendency. Birds of different body mass categories exhibit a similar tendency to follow Bergmann’s rule, while in mammals the lower body size categories (4–50 and 50– 500 g) show a significantly lower tendency to conform to the rule. Sedentary birds tend to conform to Bergmann’s rule more than migratory species. Nest type does not affect the tendency to conform to Bergmann’s rule. Main conclusions Bergmann’s rule is a valid ecological generalization for birds and mammals.

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On the validity of Bergmann's rule

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.

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

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

The influence of snakes on the foraging behavior of gerbils

Microbial community patterns of potential substrate utilization were examined at eight study sites. Sample microbial communities were from different habitats including constructed and natural salt marshes, a seawater-irrigated agronomic system, and, for a non-saline comparison, a coastal sand dune. Microbial communities were characterized by patterns of sole carbon source (substrate) utilization using Biolog microplates. Sampling sites were characterized based on analysis of soil biotic and physical properties. Relationships among the eight microbial communities based on substrate utilization potential, and among the sampling sites based on biotic and physical characteristics, were similar. Microbial communities from natural salt marshes at two geographically distant locations had similar patterns of potential substrate utilization. The constructed salt marsh community was dissimilar from the other communities (including two from natural salt marshes located in the same salt marsh complex) in potential substrate utilization. Seawater-irrigated agronomic sites were distinct from the other saline soil sites, possibly due to disturbance caused by agronomic practices. Potential substrate utilization of the microbial communities at the agronomic sites was intermediate compared to the other sites, e.g. higher than the constructed marsh but lower than the natural salt marshes. Relationships among the study communities determined by microbial potential substrate utilization and analysis of site characteristics primarily reflected similarity in habitat type, while geographical influences were less important.

Microbial community patterns of potential substrate utilization: a comparison of salt marsh, sand dune, and seawater-irrigated agronomic systems

Standard operative temperatures of two desert rodents, Gerbillus allenbyi and Gerbillus pyramidum: The effects of morphology, microhabitat and environmental factors

Canonical discriminant analyses were used to assess whether four populations of Cape sparrows varied in body size and shape according to predictions from Bergmann's Rule. In accordance with Bergmann's Rule, birds from two hot, arid Namib desert sites (Namib 1 and Namib 2) were smaller than birds from two cool, mesic Transvaal sites. If heat dissipation through extremities (tarsi) is important to reduce water lost from evaporative cooling, birds under hot conditions in dry environments (Namib 2) should have longer tarsi than those in more humid hot environments (Namib 1). Contrary to this, males at Namib 2 had relatively longer wings hut shorter tarsi than at Namib 1, and female relative tarsus length did not vary between desert sites

Wendy Goodfriend

Papers

The influence of snakes on the foraging behavior of gerbils

Microbial community patterns of potential substrate utilization: a comparison of salt marsh, sand dune, and seawater-irrigated agronomic systems

Standard operative temperatures of two desert rodents, Gerbillus allenbyi and Gerbillus pyramidum: The effects of morphology, microhabitat and environmental factors

Ecogeographic variation in body size and shape of Cape sparrows (Passer melanurus) in southern Africa

Shell colour polymorphism of the Negev desert landsnail, Trochoidea seetzeni: the importance of temperature and predation