E6 Further Studies of Behaviour


E.6.1  Describe the social organisation of honey bee colonies and one other non-human example

Honey bees

  • Honey bees (Apis mellifera) live and interact in large colonies (20,000 - 80,000 members) that show eusocial behaviour
  • There is a reproductive division of labour, whereby each type of bee is specialised for a particular task that helps the group as a whole
    • A single queen bee (reproductive female) is responsible for the production of eggs
    • A few drone bees (reproductive males) are responsible for the fertilisation of the eggs
    • The majority of bees are workers (sterile females) and may be subdivided into various castes - foragers, soldiers, etc.

Eusocial Organisation of Honey Bees



  • Baboons (Papio cynocephalus) live and interact in small groups called troops (10 - 20 members) organised according to physical dominance
  • Troops are structured around dominant females who rank as leaders, while males will move in and out of different troops
  • Members of the troop do not share food, each individual is responsible for themselves (no division of labour)
  • Baboons do not have a mating season, so females are readily available and highly promiscuous (will take many male partners)
  • Males will form relationships with females through social activities such as grooming, and may help to defend females and infants

Social Organisation of Baboons and Grooming Behaviour


E.6.2  Outline how natural selection may act at the level of the colony in the case of social organisms

  • Natural selection is a mechanism of evolution that acts on the gene pool of a given population
  • Beneficial alleles (those that promote survival) become more frequent in a population as individuals with those alleles are more likely to achieve reproductive success 
  • Many organisms form social clusters as their survival prospects (and those of offspring) are improved by cooperative group organisation
  • Because colonies are usually comprised of genetically related individuals (family members), behaviours or traits that benefit the colony (such as shared nursing duties) will improve the reproductive fitness of the group, even if it does not directly benefit the individual
  • Such characteristics are more likely to be passed on to subsequent generations and hence become more frequent in the gene pool

E.6.3  Discuss the evolution of altruistic behaviour using two non-human examples

  • Altruism is behaviour which benefits another individual at the cost of the performer
  • It appears to be in opposition to natural selection as it reduces the possibility of the altruistic individual passing on their own genes
  • However it improves the chances of the other individual passing on genes into the same gene pool (this is called inclusive fitness)
  • If the individuals are closely related, altruistic genes will persist in the gene pool and be naturally selected
  • Enhancing the reproductive success of relatives is called kin selection
  • Altruism occurs in social animals and is more common in members of the same species who are closely related

Examples of Altruism:

  • Vampire bats commonly regurgitate blood to share with unlucky or sick roost mates unable to gain independent sustenance
  • Velvet monkeys give alarm calls to warn fellow monkeys of predators, even though doing so draws attention to themselves
  • Termites break a gland in their neck, releasing a sticky substance which protects others from attacking ants at the cost of their life

Hamilton's Rule

E.6.4  Outline two examples of how foraging behaviour optimises food intake, including bluegill fish foraging for Daphnia

  • Foraging is the act of searching for, and finding, food
  • As the availability and abundance of food sources will vary, animals must adapt their feeding behaviours to account for these changes
  • According to the optimal foraging theory, animals will adopt strategies that:
    • Minimise the cost of foraging (i.e. the energy cost involved in capturing and consuming prey)
    • Maximise the benefits to the consumer (i.e. the energy yield of a potential food source)

Bluegill Fish

  • The bluegill fish feeds on the aquatic crustacean Daphnia and has been shown to change its foraging behaviour if prey availability is altered
    • If a feeding population is at high density, bluegill fish will predominantly eat larger Daphnia (high energy payoff at low search cost)
    • If a feeding population is at low density, bluegill fish will eat a range of Daphnia sizes (high search cost outweighs benefit of high energy payoff))
  • The bluegill fish has also been shown to demonstrate different foraging behaviour depending on the availability of types of prey
    • Daphnia lumholtzi has a large helmet and long tail spike, making it more difficult to consume compared to Daphnia pulex
    • When both species are found separately, the bluegill fish will eat both species of Daphnia (although greater amounts of D. pulex)
    • When both species are found together, the bluegill fish will eat D. pulex exclusively (lower cost of foraging optimises food intake)



  • Black-capped chickadees (Poecile atricapillus) feed on insects, mealworms and caterpillars
  • Chickadees have been discovered to leave an area after a specified period of time searching for food without success
  • This is because longer search times are associated with increasingly lower probabilities of finding a sufficient food source
  • The chickadee will balance the energy cost of continued foraging against the potential energy benefit of discovering a food source
  • Through natural selection, the foraging behaviour (time taken searching a specific region) has been modified to optimise food intake

E.6.5  Explain how mate selection can lead to exaggerated traits

  • The success of an organism is not only measured by the number of offspring left behind, but also by the quality of the offspring and their capacity to breed - in other words, their reproductive fitness
  • Features that improve a male's chances of successfully competing with other males for the best mate (mate selection) will become more prevalent within the gene pool via natural selection
  • As exaggerated traits (called ornaments) are more likely to attract female attention and consequently promote successful reproduction, these traits will be selected for, even though they may increase predator attention and diminish the survival prospects of the individual
  • The evolution of these traits in a particular gender has led to the marked sexual dimorphism of certain species
  • Examples of exaggerated traits include the plumage feathers of the peacock and the large antlers on male deer

E.6.6  State that animals show rhythmical variations in activity

Animals often show behaviours that follow rhythmical variation, including:

  • Diurnal (daily) cycles
  • Lunar cycles (monthly)
  • Seasonal changes

E.6.7  Outline two examples illustrating the adaptive value of rhythmical behaviour patterns

Grizzly bears

  • Grizzly bears hibernate during the winter (they undergo a period of inactivity due to metabolic depression)
  • Hibernation conserves energy and is therefore of value during winter months when food availability is low and cost of hunting is high


  • In many species of coral, males and females release their gametes at the exact same time of the year (mass spawning)
  • The advantage of such behaviour is that it increases the chances of the male and female gametes undergoing successful fertilisation
  • Spawning may be triggered by a number of factors, including temperature (seasonal) and moonlight (lunar)