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Living in a group. Costs of group living Benefits of group living Predation avoidance Resource acquisition Optimal group size. Costs of group living. Competition for resources Increased risk of parasitism or disease Increased opportunities for reproductive interference or suppression.
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Living in a group • Costs of group living • Benefits of group living • Predation avoidance • Resource acquisition • Optimal group size
Costs of group living • Competition for resources • Increased risk of parasitism or disease • Increased opportunities for reproductive interference or suppression
Competition for food in fieldfares Nestlings die primarily from starvation
Nests treated with insecticide produce much larger chicks Ectoparasitism in cliff swallows
Reproductive interference Brood parasitism, Extra-pair copulations Reproductive suppression
Predation avoidance benefits • Reduce encounter rate with predator • Protected sites • Selfish herd • Reduce success of predator • Vigilance • Dilution • Confusion, predator-predator interference • Mobbing, cooperative defense
As school size of prey increases, capture success decreases Predator confusion
Predator interference “Schreckstoff” Schreckstoff attracts other pike, which increases handling time
Resource access benefits • Passive attraction to limited resource • Active attraction due to joint benefits • Reduce path overlap • Information transfer • information center • producers-scroungers • acquire public information • Group foraging • Communal hunting
Passive attraction Butterflies at a salt deposit
Information transfer in evening bats Leaders “produce”, followers “scrounge”
Spice finch were taught to open lids and were producers. Other birds had to wait to scrounge The producer-scrounger game
Public information • Forager joins group to acquire information about food availability and/or predator risk • By observing foraging success of others in the group, a naïve forager can estimate the quality of a food patch • Starlings left empty patches sooner when foraging with a partner than when foraging alone.
Reduce path overlap Proposed for sparrow flocks in Mojave desert. Never been tested.
Cooperative hunting Permits capture of prey larger than possible by singletons
Group hunting in wild dogs Larger packs kill larger prey, have higher capture success, and travel shorter distances in a hunt, but must share kills with more members of the group