Living in a group
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Transcript of Living in a group
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Living in a group
• Costs of group living
• Benefits of group living– Predation avoidance– Resource acquisition
• Optimal group size
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Costs of group living
• Competition for resources
• Increased risk of parasitism or disease
• Increased opportunities for reproductive interference or suppression
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Competition for food in fieldfares
Nestlings die primarily from starvation
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Ectoparasitism in cliff swallows
Nests treated with insecticideproduce much larger chicks
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Reproductive interference
Brood parasitism,Extra-pair copulations
Reproductive suppression
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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
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Protected sites
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The selfish herd
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Predator dilution
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Vigilance
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More eyes and ears
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Predator confusion
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Predator confusion
As school size of prey increases, capture success decreases
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Predator interference
“Schreckstoff”
Schreckstoff attracts other pike, which increases handling time
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Cooperative defense: mobbing
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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
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Passive attraction
Butterflies at a salt deposit
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Information transfer?
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Information transfer in osprey
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Information transfer in evening bats
Leaders “produce”, followers “scrounge”
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Two pigeons produced, 14 scrounged
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The producer-scrounger game
Spice finch were taughtto open lids and wereproducers. Other birdshad to wait to scrounge
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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.
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Public information
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Reduce path overlap
Proposed for sparrow flocks in Mojave desert. Never been tested.
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Group foraging
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Cooperative hunting
Permits capture of prey largerthan possible by singletons
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Optimal group size
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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
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Optimal size of wild dog foraging groups
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Lion foraging success