Function and Evolution of Animal Behaviour

Function of Behaviour (Ultimate Level)

Definition: Behaviour is adaptive if it increases survival and/or reproductive output.
Example: Courtship displays increase mating success.

Natural Selection

Definition: Differential survival due to heritable traits suited to the environment.
Example: Peppered moth colour change during industrial revolution.

Sexual Selection

Definition: Selection for traits enhancing reproductive success rather than survival.
Example: Birds-of-paradise elaborate courtship displays to secure mates.

Fecundity Differences

Definition: Species vary in number of offspring they can produce.
Example: Mice = high fecundity; elephants = low fecundity.

Attractiveness as Fitness Component

Definition: Individuals with more mates produce more total offspring.
Example: Brightly coloured males gaining more mating opportunities.

Trade-Offs Between Selective Forces

Definition: Behaviours optimise between conflicting pressures (e.g., survival vs reproduction).
Example: Red-breasted goose nests near snow owls to avoid predators, but goslings vulnerable during first march to water.

Survival-Enhancing Behaviours

Definition: Behaviours that directly reduce mortality.
Example: Hiding or escaping predators.

Reproduction-Enhancing Behaviours

Definition: Behaviours increasing mating success, fecundity, or offspring survival.
Example: Ostrich pair-bonding increases egg survival.

Dysfunctional Behaviour (Group-Level Benefits)

Definition: Behaviour maladaptive to individual but beneficial to group fitness.
Example: Prairie dog sentinel behaviour increases predation risk for scouts.

Fossil Evidence for Behaviour

Definition: Behaviour inferred from fossils, trackways, or morphology.
Example: Question of origins of human speech/vocalisation from incomplete lineage.

Changed Environments & Behavioural Shifts

Definition: Behaviour evolves to match new ecological conditions.
Example: Localised climate change altering reproductive timing.

Changed Selection Pressures

Definition: Predator/competitor behaviour alters future selective environment.
Example: Predator innovation shaping prey escape strategies.

Adaptive Landscape

Definition: Concept of genetic fitness peaks shaped by gene-gene interactions.
Example: Selective breeding to increase desirable traits across generations.

Epistasis

Definition: Expression of one gene depends on other genes present.
Example: Gene repression/activation affecting phenotypic expression.

Divergent Evolution

Definition: Common ancestor → different phenotypes due to different environments.
Example: Darwin’s finches varying in beak morphology.

Convergent Evolution

Definition: Unrelated species evolve similar phenotypes due to similar ecological pressures.
Example: Sharks (fish) and dolphins (mammals) both streamline for aquatic life.

Parsimony in Evolution

Definition: Complex traits evolve using minimal necessary changes.
Example: Small genetic modifications producing major functional shifts.

Pre-Existing Behaviour Hypothesis

Definition: New behaviours evolve from older motor patterns.
Example: Preening movements evolving into courtship displays (peacocks).

Pre-Existing Bias Hypothesis

Definition: Females prefer signals already favoured by sensory biases.
Example: Preference for red chests or larger bowers as mate quality cues.

Adaptive Coevolution

Definition: Traits evolve in tandem as each influences selective environment of the other.
Example: Large primate brains → complex social hierarchies → testes size competition in chimps.

Missing Species Problem

Definition: Gaps in fossil lineage obscure origins of behavioural traits.
Example: Unknown origins of human speech behaviour.

Behaviour Modifying Future Selection

Definition: Behaviour itself changes selective landscape for descendants.
Example: Predator hunting methods shaping prey adaptations over generations.