Fighting rules. Value of resource. Assessment and possible escalation. Degree of escalation depends on resource value. Elephant seal Rep at age 9-12

Transcription

1 Fighting rules Assessment and possible escalation Degree of escalation depends on resource value Value of resource Red deer Rep from ages % reach rep. age 2-4 calves sired per year Fights typically do not have serious injuries Elephant seal Rep at age % reach rep. age Up to 93 pups sired per year but only 9% of males mated Fights typically escalate to injury 1

2 Weapons usually not fatal Fighting is highly ritualized To escalate and fight or not?? There often is not always one optimum behavior in a population what works might depend on what others do. Why don t fights escalate to lethal fights? Hawk-like tactic vs. Dove-like tactic Fight and risk injury Display and don t escalate 2

3 Costs and benefits: Access to resource (V) if you win Fighting incurs costs (C) of injury Outcome of interactions: Hawk and Hawk: Dove and Hawk: Dove and Dove: If: V = 50, C= -100 Opponent Attacker Hawk Dove Hawk Dove 50 + (-100) = = 25 What if all are doves? What if all are hawks? 3

4 So in this scenario, you would expect some sort of mixture of hawks and doves. (A mixed ESS) You can calculate the exact mixture - When: Dove avg. payoff = Hawk avg. payoff Payoffs depend on proportion of hawks and doves Proportion of hawks = h Proportion of doves = (1-h) Hawk avg. payoff: H = -25h + 50(1-h) Dove avg. payoff: D = 0h + 25(1-h) -25h h = 25-25h 50h = 25 h= ½ 50% hawks, 50% doves is the mixed evolutionary stable strategy in this case only 4

5 Evolutionary stable strategy - (ESS) Tactic or combination of tactics (like 50/50 hawks/doves) that resists invasion by individuals using any of the known tactics. Note that an ESS does not have to be a mixed ESS. Assumptions of ESS approach: Reproduction occurs in proportion to fitness gained relative to V and C. (p.117) Random mixing of strategies in pop n Recall this : amount of escalation depends on the value (V) of the resource. V<C is generally seen in nature, but there are cases where V is very high or where low expected future RS p

6 Bully tactic if it meets a dove, acts like a hawk; if it meets a hawk, acts like a dove. If this invaded, new ESS would be 100% Bully Hawk Dove Bully Hawk Dove Bully Can mixed ESS occur in nature? Maintenance of different tactics within populations Ex: Natterjack toads Callers get 80% of matings overall Satellites gain 50% of females attracted by call Males have conditional strategy with 2 tactics Tactics here are flexible - tactic chosen depends on situation, male size Ex: Manipulations with broadcasted calls Predicting tactics 6

7 Mixed ESS or best of a bad job? Satellite males best of a bad job similar to scroungers in text example Best of a bad job Mixed ESS with frequency dependent selection p. 130 Strategy vs Tactic Strategy genetically based. Can be conditional with different tactics ex: conditional strategy ex: size sets the tactic Tactics specific behavior patterns that are part of a strategy, one usually better ex: call when big, satellite when small Alternative tactics But some tactics may be fixed for lifetime Bearded weevils some small males 10% normal size, sneak matings Male bedbugs traumatic insemination, small males alternative Is this mixed ESS or BOBJ? 7

8 Alternative tactics But some tactics may be fixed for lifetime Dung beetles: Morphological development and body size p. 134 Alternative strategies: mixed ESS Different genetic forms that are maintained in a population (more than 1 strategy in pop n) Payoffs would be about equal on average, like a mixed ESS Frequency dependent selection Alternative strategies with mixed ESS Ruffs - male dimorphism three strategies: - Red residents (~30% of males) 90% of copulations, poorer survival Black marginals (floaters, but future residents) (~50%) - White satellite (~20% of males) only 10% of copulations Satellites live longer, free for forage, find off-lek females - Female mimics (1%) p

9 Alternative strategies with mixed ESS Marine isopods 80% are α males that defend harems (20% of size=testes) 4% are β female mimics (50% testes) 15% are γ tiny males with 80% testes Study examining genetic RS found success was equal among types and varied w/# females, # morphs. Alternative strategies with mixed ESS Side-blotched lizard: 3 male strategies Orange high testosterone territory holders Yellow sneaker female mimics at territory edges Blue defend one female, can drive away yellow males but not orange Again, success of each strategy depends on frequency of others Animal personalities? Mixed ESS and best of a bad job show how different behavioral tactics can persist in populations. When are differences in behavior discrete tactics..can there simply be personality differences?...are they genetic? 9

10 Parus major personalities Exploratory behavior consistent and inheritable Two selection lines formed genetic basis How do these differences persist? Personalities and life history traits 10