restricted access I.7 Foraging Behavior
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I.7 Foraging Behavior Joel S. Brown OUTLINE 1. Foraging behaviors, adaptations, and autecology 2. Finding food 3. Handling time 4. To eat or not to eat? 5. Patch use 6. Social foraging 7. Fear and foraging 8. Coadaptations between foraging behaviors and morphology 9. Nutrient foraging in plants A need for energy and resources for survival, growth, and reproduction is a universal property of life. Hence, all organisms must forage. Even plants have noncognitive foraging behaviors. Life exhibits a wonderful diversity of feeding behaviors and associated morphological and physiological adaptations. Food must be found and handled. Letting the food come to the forager (sit and wait) or actively seeking food items (active pursuit) are two tactics for finding food items. Handling a food item may be as simple as absorption (endocytosis by a single cell organism) or a complex choreography of subduing, dismembering, and/or digesting a prey. Diet choice involves foragers deciding which food items to accept or reject. Patch use considers how thoroughly a forager should deplete the food from a spot before giving up and moving to a fresh spot. Foraging often occurs socially because groups permit sharing of information, scrounging, group hunting, task specialization, and, most often, safety in numbers. Predation risk and fear loom large in foraging, as animals balance the conflicting demands of finding food while avoiding becoming food themselves. All of these topics of foraging behavior become central to understanding an organism’s ecology and evolution. GLOSSARY diet choice. The decisions made by foragers regarding which encountered food items to consume and which to reject. The abundances of different food types, their ease of finding and handling, and their value to the forager generally influence the decisions to eat or not to eat. foraging games. The behavioral challenges facing both predator and prey when the prey can perceive and respond to the hunting tactics of the predator, and the predator can perceive and respond to the antipredator tactics of its prey. These can be as straightforward as pursuit-evasion games; or complex sets of decisions summed up by when and where to forage; or levels of prey vigilance and predator boldness. Finally, foraging games such as producer– scrounger games or behaviors involving territoriality and interference may occur between members of the same species. nutrient foraging. The noncognitive foraging behaviors of plants as they adjust allocations to roots and shoots, alter uptake kinetics or growth forms to in- fluence the uptake of water, light, nitrogen, and other nutrients. patch use. The behaviors of foragers regarding how to deplete the food items of a given spot. Most importantly , when should the forager leave an area with food before moving to a fresh area? A forager should leave a depleted food patch when the benefits of continuing to harvest the patch no longer exceed the sum of metabolic, predation, and missed opportunity costs of foraging. social foraging. When feeding occurs as groups of the same or different species. Social foraging may allow for information sharing, producer–scrounger games, group hunting, task specialization, and very often safety in numbers. Safety in numbers occurs through the many eyes, dilution, and confusion effects. 1. FORAGING BEHAVIORS, ADAPTATIONS, AND AUTECOLOGY An animal’s ecology can be summed up as follows: where does it live, what does it eat, and who eats it? For instance, on the sand dunes of Bir Asluj in the Negev Desert of Israel, afternoon winds blow in from the Mediterranean, redistributing the sand and uncovering seeds. At sunset, as the wind abates, Greater Egyptian sand gerbils (Gerbillus pyramidum) emerge from their burrows and move under shrubs or across open spaces to search for seeds. A knowledge of where seeds likely aggregate guides their search paths. With a keen sense of smell, gerbils hone in on patches of seeds or seeds buried under the sand. With its forepaws, the gerbil recovers seeds and lifts them to its mouth, either transporting them in internal cheek pouches or deftly husking them with practiced coordination of forepaws and incisors. While the gerbil seeks food, predators seek the gerbil. A gerbil’s ears and auditory system can detect the low-frequency sounds of a barn owl’s wingbeat. A gerbil’s quick reactions may save it from the strike of a horned viper, and erratic locomotion permits escape from a pursuing red fox. With cheek pouches full, the gerbil returns to its burrow and deposits the seeds underground in its larder, or it may save time by...