ECOLOGY LEC 6

Behavioural ecology

The study of how behavior affects survival and reproduction (fitness)

Fitness

Evolutionary success; ability to pass on genes to next generation

Actor

The individual performing a behaviour

Recipient

The individual(s) affected by the behaviour

Cost (evolutionary)

Decrease in fitness (reduced survival or reproduction)

Benefit (evolutionary)

Increase in fitness (greater survival or reproduction)

Social behaviour

Interactions among individuals of the same species

Types of social behaviour classification

Cooperative, selfish, altruistic, spiteful

Cooperative behaviour (+/+)

Both actor and recipient benefit

Selfish behaviour (+/-)

Actor benefits, recipient is harmed

Altruistic behaviour (-/+)

Actor is harmed, recipient benefits

Spiteful behaviour (-/-)

Both actor and recipient are harmed

Example of altruism

Alarm calls warning others of predators

Problem with altruism

Reduces individual fitness, so why does it evolve?

Inclusive fitness

Total genetic contribution including own offspring and relatives

Direct fitness

Fitness gained through personal reproduction

Indirect fitness

Fitness gained through helping relatives reproduce

Kin selection

Natural selection favoring behaviours that increase relatives’ reproductive success

Hamilton’s rule

C < rB (altruism evolves if cost < relatedness × benefit)

C (cost)

Loss of reproduction for the actor

r (relatedness)

Proportion of shared genes

B (benefit)

Reproductive gain of the recipient

Relatedness formula

r = (1/2)^n where n = number of links

Parent-offspring relatedness

r = 0.5

Sibling relatedness

r = 0.5

Grandparent-grandchild relatedness

r = 0.25

Interpretation of Hamilton’s rule

If C < rB, altruistic behaviour is favored

Example result (saving sibling, high cost)

Not favored if cost too high

Example result (saving sibling, low risk)

Favored if cost is low enough

Why pikas give alarm calls

Low cost + high relatedness → increases inclusive fitness

Reciprocal altruism

Helping non-relatives with expectation of future return

Conditions for reciprocal altruism

Repeated interactions and stable groups

Group living

Living in social groups instead of alone

Benefits of group living

Cooperative feeding, defense

Costs of group living

Disease spread, competition, reduced reproduction

When group living evolves

When benefits outweigh costs

Cooperative breeding

System where some individuals help others reproduce

Dominance hierarchy

Ranking system controlling reproduction

Why helpers stay (cooperative breeding)

Kin selection and future reproductive benefits

Example: Florida scrub jay

Juveniles help raise siblings

Why male scrub jays stay

May inherit territory

Why female scrub jays leave

Less chance of inheriting territory

Eusocial society

Social system with division of labour and reproductive roles

Examples of eusocial organisms

Ants, bees, termites, naked mole rats

Eusocial structure

One or few breeders, many non-reproductive workers

Benefit of eusociality

High inclusive fitness through helping relatives

Naked mole rat behaviour

Workers help queen instead of reproducing

Why mole rats stay

Harsh environment makes independent survival unlikely

Coercion in eusocial systems

Dominant individual suppresses reproduction of others

Mating systems

Patterns of mating behavior in a species

Monogamy

One male and one female pair

Polygamy

One individual mates with multiple partners

Promiscuity

No lasting mating bonds

Polygyny

One male mates with multiple females

Polyandry

One female mates with multiple males

Example of polyandry

Spotted sandpiper

Why polyandry occurs

Enough resources for one parent, females can produce multiple clutches

Environmental influence on behaviour

Behaviour depends on costs, benefits, and environment

Key idea of behavioural ecology

Behaviour evolves to maximize inclusive fitness

Summary of altruism

Explained by kin selection and inclusive fitness

Summary of group living

Evolves when benefits exceed costs

Summary of behaviour

Shaped by natural selection and environment