Evolution of Social Behavior
Costs of group living:
1. Increased conspicuousness - crypsis is not an available means of predator avoidance.
2. Increased intraspecific competition for food and mates, especially in cases with
dominance hierarchies.
3. Increased risk of parasitism/diseases (e.g., WNS in Myotis).
4. Increased potential for inbreeding and potential inbreeding depression.
Benefits of group living:
1. Selfish herd phenomenon.
2. Cooperative predator defense is possible.
3. Cooperative hunting is possible.
4. Information sharing and cultural inheritance are possible.
5. Division of labor possible.
Macaca fuscata
Polyandry, polygyny, & male-biased dispersal
Male gametes are cheap relative to female gametes.
This explains why polygyny is so much more common than polyandry.
Mate choice is usually driven by females.
Manifestations of sexual selection are usually seen in males (e.g., antlers).
Polyandry, polygyny, & male-biased dispersal
Male gametes are cheap relative to female gametes.
This may explain the pattern of female philopatry and male dispersal in mammals.
Hamilton et al., (2005. Genetics. 170:409) used genetic data to estimate dispersal
among 5 populations of Microtus arvalis.
Kin selection versus altruism in Urocitellus beldingi
Carnivores and Social Behavior
Most Carnivores are solitary, or asocial.
Ursids are asocial.
Carnivores and Social Behavior
Canis lupus
Lyacon pictus
Vulpes vulpes
Carnivores and Social Behavior
Panthera leo
up to 4 breeding females, several non-breeding females
2 males may or may not be related
females are related and hunt cooperatively.
satellite males belong to no pride, attempt sneak
Carnivores and Social Behavior
Crocuta crocuta
Clans of up to 80, both males and females.
Individuals forage alone.
These groups form to defend kills from lions.
Carnivores and Social Behavior
Meles meles
- They forage alone and are rather omnivorous
- Live in communal dens, called setts.
- A clan of 10’s of animals occupy the setts for generations
- Clans defend a territory and share in burrowing work.
Carnivores and Social Behavior
Helogale parvula
There’s a very complex social system.
Dominant breeding pair and several non-reproductive individuals.
They forage independently.
There is cooperative predator defense.
They give alarm calls and there’s a division of labor.
Resource Dispersion Hypothesis
Common set of starting conditions
- Basic territoriality
- Individuals defend the smallest area that will support them in a bad year.
- Size of the territory depends on dispersion of resources.
- The key is that it’s usually not a bad year and resources are readily available.
- Therefore, a single “territory” may support >1 individual most of the time.
- Most often, benefits to group living outweigh the costs.
A now-ageing paper has summarized support for this that’s been generated over the years.
(Johnson et al. 2002. TREE. 17:563)