Evolution of Social Behavior

Costs of group living:

4. Increased potential for inbreeding and potential inbreeding depression.

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.

Benefits of group living:

1. Selfish herd phenomenon.

3. Cooperative hunting is possible.

5. Division of labor possible.

2. Cooperative predator defense is possible.

Ovibos

4. Information sharing and cultural inheritance are possible. Macaca fuscata

3. Increased risk of parasitism/diseases (e.g., WNS in Myotis).

Polyandry, polygyny, & male-biased dispersal

Male gametes are cheap relative to female gametes.

Manifestations of sexual selection are usually seen in males (e.g., antlers).

This explains why polygyny is so much more common than polyandry.

Mate choice is usually driven by females.

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 dispersalamong 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 BehaviorCanid

sCanis lupus Vulpes vulpes

Lyacon pictus

Carnivores and Social BehaviorFelids

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 copulations

Carnivores and Social BehaviorHyaenids

These groups form to defend kills from lions.

Clans of up to 80, both males and females.

Individuals forage alone.

Crocuta crocuta

Carnivores and Social BehaviorMustelids

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.

Helogale parvula

Carnivores and Social BehaviorHerpestids

There’s a very complex social system.

Dominant breeding pair and several non-reproductive individuals.

They forage independently.

They give alarm calls and there’s a division of labor.

There is cooperative predator defense.

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)