Ecology Lecture 11 - Social Behaviors PDF

Ecology Week 7 Lecture 11 – Social Behaviors  Social Behavior Social Behavior = Any interactions between individuals of the same species Continued group interactions: – Social Groups = prolonged aggregations of indivs of the same species – Family Groups = related i...

Ecology Week 7 Lecture 11 – Social Behaviors  Social Behavior Social Behavior = Any interactions between individuals of the same species Continued group interactions: – Social Groups = prolonged aggregations of indivs of the same species – Family Groups = related indivs; when offspring continue to interact w/ parents into adulthood  Social Groups Living in groups has distinct advantages and obvious disadvantages European goldfinch Sharp-shinned hawk 3 Vigilance 4 Feeding time Foraging time 5  Cost-benefit analysis Should a given social interaction evolve? Can quantify costs and benefits (currency?) – Can categorize interactions: – Each has a donor and a recipient, and positive or negative effects for each. 6 Interactions w/in Species 7  Selfishness Territoriality: defending a patch of resources from other indivs (same or other species) 8 Male Female -Males defend territories with 2-5X the food they need Male Female Mating success Mating success Nectar content Nectar in territories content in territories 10 Male Female Mating success Nectar content in territories 11  Altruism Altruism requires evolution of behaviors that reduce fitness of individuals performing them. – Evolutionary puzzle – why would this evolve? – One answer: kin selection. 12  Kin Selection Inclusive fitness: Fitness of an individual plus fitness of relatives, weighed by relatedness of relatives 13 Relatedness = genetic similarity, quantified as coefficient of relationship (r). 14  Kin Selection Inclusive fitness: Fitness of an individual plus fitness of relatives, weighed by relatedness of relatives Should an altruistic behavior evolve? – Depends on: Cost to donor (C), Benefit to recipient (B) Coefficient of relationship (r) – Hamilton’s Rule: rB>C 15  Altruism through Kin selection Possibly widespread: Indivs often associate in family groups Limited dispersal increases relatedness Indivs often can sense relatedness by chemical/behavioral cues, even w/o prior experience 16 Kin selection altruism Bee-eaters (groups w/ 3-17) 17 -Defend territories with vocalizations -Only instances of adoption were b/n kin (5 of 2230 litters) (Gorrell et al. 2010) 18 Kin selection altruism (2005, Nature 434:69-72) 19 Kin selection selfishness Tiger salamander 20  Insect Societies Eusociality: – Multiple adults living together in a group – Overlapping generations in the group – Cooperation in nest building/ brood care – Division of labor in reproductive and non- reproductive subgroups: Reproductive dominance by one (queen) or few indivs, and sterile castes of daughters (=altruism) Ants, bees, & wasps (Hymenoptera), termites (Isoptera) 21 Haplodiploidy Males: haploid Females: diploid 22 Haplodiploidy Sisters share 75% of genes: 23 Will altruism evolve among unrelated individuals? 24  Reciprocal Altruism Blood meals and vampire bats Video 25 Will cooperation or selfishness evolve more frequently? 26  Game theory Game theory = mathematical models of decision-making among interacting indivs; assesses costs and benefits of a behavior (fight, help, etc) to determine the optimal strategy Evolutionarily Stable Strategy (ESS) = optimal strategy, which will evolve and will not be ‘invaded’ by other strategies 27  Game Theory: Hawks and Doves Consider a ‘game’ with two strategies: Hawk tactic: selfish (always fight over resources, take all of it) Dove tactic: cooperative (never fight, always share evenly) Note: Same species, different tactics! 28  Game Theory: Hawks and Doves B= Benefit, C = Cost Payoff Matrix: – Hawk-Hawk: ½B – C (average) – Hawk-Dove: Hawk = B, Dove = 0 – Dove-Dove: ½B each Average benefit depends on frequency – P = Frequency of hawk-like behavior 29 Average payoff per interaction: C=1/5B 30 Evolutionary stable strategy (ESS) While from societal point of view, all doves is best, it is not an ESS – Can always be invaded by a hawk A society of all hawk tactics is an ESS – Would varying C (cost of attack) change this? 31 Previous: Higher Cost (C): C=1/2B: ESS now? 32 Previous: Higher Cost (C): ESS = now neither is evolutionary stable; mixed strategy 33 34