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BEHAVIORAL ECOLOGY (Biol 607) Fall 2004 Lecture 6: Spacing and Territoriality II Living in Groups TEMPORAL DISTRIBUTION - dimension also important - Are resources ? TERRITORIALITY evolves as resources become > Costs Ex) - Old World passerines, convergent with hummingbirds - nectarivores - defend areas with - Note: undefended areas are lower in quality over the course of the day - no competitor exclusion Ex 2) - Hawai’ian passerines, impressive , closest ancestor Fringillidae - too few resources: - too many resources: - intermediate levels: of defense > cost GROUP LIVING - as with territoriality, various - costs of sociality can be significant: - increased likelihood of - increased competition for: - increased risk of - therefore and must be high: - KEY: must view behaviors that are advantageous to first; and secondarily to the BENEFITS: 1. Protection from Ex) homeotherms up to 117 in cavity in winter (cost: ) - cactus wrens - huddling - largely energetic savings 2. Protection from through various means - : many additional eyes, noses, ears for detection ex) : flocks had lower kill probabilities and greater detection distances - : reduce vulnerability via mass response ex) flocks: lone individuals very vulnerable numbers safer large flocks - birds (also a vigilance aspect to this example) ex 3) - Combination ? (Mollusca) and fish predators less successful hunting groups Clear to group living ! - Selfish Herd: Hamilton Appearance of cooperation to elude predation due to individuals acting competitively (selfishly) - One animal uses another as a shield selecting for the shield to behave similarly aggregations of individuals DRAW - individuals on periphery most vulnerable - direct competition for central (safe) positions - Why take periphery? young and/or subordinate animals ex) snow geese at Funk Lagoon ex) predation observation at Bosque del Apache ex) snail predation on bluegill sunfish nests HANDOUT - solitary nests higher number of snails (snails and bullheads are predators) fewest number of defense chases - central nests lowest number of snails highest number of defense chases - Dilution: overwhelm consumption capacity of local predators evolution of synchrony ex) seabird colonies sea turtles aquatic emergents Ex) mayflies - when more emerge synchronously chances of any 1 individual female surviving increases HANDOUT FORAGING ALSO LEADS TO BENEFITS OF AGGREGATING Ex) Jarmen’s model of social organization in African ungulates Total of 81 mammalian herbivores Artiodactyla - Bovidae: 78 spp Suidae: 3 spp Perissodactyla - rhinos and zebras: 6 spp Proboscidea - elephant - 1 spp Subdivide available resources Note: in Serengeti Park alone 27 species of carnivore! Relationship between foraging ecology and group size FORAGE TYPE SPATIAL DISTRIBUTION TERRITORIALITY or LARGE GROUPS GROUP SIZE