LEC 11: Behavioural Ecology

Behavioural Ecology

Definition:
Behavioural ecology studies how organisms interact with their environment through their behaviour.
Although it mainly focuses on animals, the field now includes plants and microbes that also show behaviour — like the research done by Dr. James Cahill on plant behaviour.

Definition of Behaviour

Behaviour is “the internally coordinated responses (actions or interactions) of whole living organisms (individuals or groups) to internal and/or external stimuli” (Laevitis et al. 2009).

This isn’t a universal definition, but it’s the one used in this course.

Variation in Behaviour

• Intraspecific Variation: Behaviour differences within a species.

• Interspecific Variation: Behaviour differences between species.

Adaptive Behaviour

Adaptive behaviours are those that increase an organism’s survival or reproductive success (fitness).
If a behaviour has a genetic basis, it can be favoured by natural selection.

Definition:
Adaptive behaviour = behaviour that increases fitness → selected over generations.
These behaviours depend on both genes and the environment.

Behaviour & Genetics

Natural selection can only act on behaviours that have a genetic component.

Example: Honeybees

• Young bees stay inside to care for brood.

• Older bees forage outside.

• The foraging behaviour is controlled by a single gene for a protein kinase (PKG).

  • More PKG → work outside (foraging)

  • Less PKG → work inside (nursing)
    So, even one gene can drastically change behaviour.

Hamilton’s Four Classes of Social Interaction

Donor: performs the action
Recipient: affected by the action
Fitness: number of offspring compared to others in the population

Behaviour and Natural Selection

Natural selection favours behaviours that increase inclusive fitness — an individual’s total fitness, including their relatives’ survival and reproduction (Hamilton, 1964).
→ When behaviours affect who survives and reproduces, populations evolve.

The Paradox of Altruism

Altruism seems disadvantageous because it reduces the donor’s fitness, but it can still evolve through different mechanisms.

Examples:

• Red squirrels adopting orphaned kin.

• Ground squirrels giving alarm calls to warn relatives.

Why be altruistic?

1. Group selection – helping the group benefits everyone.

2. Manipulation – being tricked into helping (like brood parasitism).

3. Reciprocal altruism – “I help you now, you help me later.”

4. Kin selection – helping relatives increases your inclusive fitness.

Coefficient of Relationship (Rg)

Measures how related two individuals are — the probability they share the same allele by descent.

Hamilton’s Rule for Altruism

Altruism evolves if the benefit to the recipient, weighted by relatedness, is greater than the cost to the donor:

Rg×B>CRg​×B>C

or

Rg×B−C>0Rg​×B−C>0

Selfishness

Definition: Actions that help the donor but harm the recipient.

Example:
Cowbirds lay eggs in other species’ nests (obligate brood parasitism) — others raise their young for them.

From the host’s (e.g., Eastern Phoebe’s) perspective, this looks altruistic, since they waste energy caring for another’s offspring without realizing it.

Selfish Herds

Animals in groups try to stay in the center to avoid predation, leaving the outer individuals more exposed.
→ selfish behaviour that still benefits survival.

Spiteful Behaviour

Both donor and recipient lose fitness.
Example: European badgers leaving kin but spreading disease to non-kin — hurts both.

Cooperation and Sociality

Cooperation usually occurs within species, often between relatives, and involves:

• Sharing resources

• Providing protection

• Helping with care

Social Structures & Evolution of Sociality

Sociality = living and interacting in groups with different levels of cooperation.

Common features:

• Cooperative feeding

• Group defense

• Limited reproduction

Examples of social behaviour:

• Mutual grooming

• Group care of young

• Complex societies (ants, bees)

  • Alloparenting and allonursing

Cooperative Breeders

Live in groups where multiple adults care for offspring.

Behaviours include:

• Defending the young

• Maintaining nests/burrows

• Feeding offspring

Benefits:

• Usually among relatives → increases inclusive fitness

• Encourages reciprocal altruism (“tit for tat”)

• Though rare: ~0.5% of mammals, 8% of birds, plus some insects & fish

Eusociality

Most complex social system. Defined by:

1. Multiple generations living together

2. Cooperative care of young

3. Division between reproductive and non-reproductive castes

Examples:

• Leafcutter ants (Atta) – 7 castes

• Naked mole rats & Damaraland mole rats – 3 castes (queens, breeders, workers)

Functional parallels:

• Big individuals → defense

• Small individuals → foraging/maintenance
  → Convergent evolution in behaviour

Evolution of Eusociality

Driven by:

• Kin selection (high relatedness)

• Ecological constraints (need for defense, burrow maintenance)

• Haplodiploidy (genetic system in ants/bees):

  • Females (diploid) = fertilized eggs

  • Males (haploid) = unfertilized eggs

  • Sisters share 75% genes with each other, but only 50% with brothers → encourages female cooperation