Lecture 07

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Biological Sciences
Kamini Persaud

Lecture 7: The Evolution of SOCIAL Behaviour (Kin/NON-kin)  Why do some animals live in groups while others do not?  It comes down to benefits versus costs  Benefits: dealing with the physical environment, information, protection, territory defense, predation/hunting  Costs: competition for food & mates, energy and time of dominance interactions, disease, risk of brood parasitism, conspicuousness  COSTS  competition for MATES  Female Aggression Over Matings in Red Deer: they all want to mate with the same male; especially the oestrous female (alpha male)  competition over NESTING SITES;  best nesting sites hard to come by!  You share but you want your offspring to have the resources = so dump the other female’s eggs (ovicide)  Female removing eggs has less laid eggs but has more eggs incubated  Dominance interactions: ENERGETIC COSTS  Takes time + energy to live in a group  A “poor start to life” affects ability to dominate in male Green Swordtails  PG; poor food in beginning  GG; good food all the time  GG tends to show more aggressive behaviour than PG; who show more defensive behaviour!  Parasitic Infection  Greater population means greater risk of infection  In the beginning, as brood size increases then LRS increases but later LRS decreases b/c of increased parasite infections.  BUT...being social has its benefits!  BENEFITS  Dealing/protection with the physical environment; e.g. huddle together and warm each other can make difference of couple degrees. It helps them survive!  Information Centres; reap the same benefits from individual who HAS spent time + energy on gaining info.  Protection from predators; spend less time being vigilant with increased group size! e.g. emit sounds + stand erect when predator is around!  QUESTION: Why does a California Ground Squirrel spend less of their time being vigilant with increased group size?  Hypothesis 1: Dilution effect (safety in numbers; other individuals offer protection by simply existing)  Hypothesis 2: Increased detection (“many eyes”; others offer protection by being vigilant)  Hypothesis 2 is correct since the amount of vigilance is the same regardless of distance between you and your neighbour. Individuals pay attention to...ALARM CALLING!  Cooperative Hunting; obtain food you can’t obtain ALONE. It’s observed when benefits>costs! e.g. small mammals  Summary:  Benefits: 1. dealing with the ph
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