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Living in a group

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

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  1. Living in a group • Costs of group living • Benefits of group living • Predation avoidance • Resource acquisition • Optimal group size

  2. Costs of group living • Competition for resources • Increased risk of parasitism or disease • Increased opportunities for reproductive interference or suppression

  3. Competition for food in fieldfares Nestlings die primarily from starvation

  4. Nests treated with insecticide produce much larger chicks Ectoparasitism in cliff swallows

  5. Reproductive interference Brood parasitism, Extra-pair copulations Reproductive suppression

  6. 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

  7. Protected sites

  8. The selfish herd

  9. Predator dilution

  10. Vigilance

  11. More eyes and ears

  12. Predator confusion

  13. As school size of prey increases, capture success decreases Predator confusion

  14. Predator interference “Schreckstoff” Schreckstoff attracts other pike, which increases handling time

  15. Cooperative defense: mobbing

  16. 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

  17. Passive attraction Butterflies at a salt deposit

  18. Information transfer?

  19. Information transfer in osprey

  20. Information transfer in evening bats Leaders “produce”, followers “scrounge”

  21. Two pigeons produced, 14 scrounged

  22. Spice finch were taught to open lids and were producers. Other birds had to wait to scrounge The producer-scrounger game

  23. 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.

  24. Public information

  25. Reduce path overlap Proposed for sparrow flocks in Mojave desert. Never been tested.

  26. Group foraging

  27. Cooperative hunting Permits capture of prey larger than possible by singletons

  28. Optimal group size

  29. 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

  30. Optimal size of wild dog foraging groups

  31. Lion foraging success

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