Lecture 10: Social Behaviours

Lecture 10: Social Behaviours

• Social behaviours are individual interactions with mates, offspring, relatives, and unrelated conspecifics.
• These behaviours are shaped by genetic and environmental factors.
• Social behaviours are subject to natural selection.
• Social behaviours are usually associated with mate selection or intraspecific competition for food or territory.
• Social interactions have both costs and benefits.

Benefits of Living in Groups

• Living in groups can increase survival.
• Groups of individuals can more effectively fend off attacks from predators.
• The dilution effect reduces the probability of predation for individuals in a group.
• Increased vigilance, such as that seen in meerkats, also aids survival by allowing the group to be better at detecting threats.
• Grouping can improve foraging success by providing more eyes to locate and consume resources.
• Larger numbers of conspecifics improve the chances of finding food.
• Groups can increase the likelihood of capturing prey.
• Grouping can make it easier to find mates, especially in species that use leks.

Increased Vigilance

• Individuals in groups may decrease the amount of time spent watching for predators, and increase the time spent feeding.
• This is demonstrated by the European goldfinch.

Costs of Living in Groups

• Living in groups increases competition for food.
• Larger groups may be better at finding food, but more individuals mean food must be shared.
• High population densities can increase the spread of disease and parasitism.
• Groups of animals are more conspicuous to predators.
• This is demonstrated by studying parasitism in coral reef fish.

Balancing Costs and Benefits

• Natural selection favours group sizes that balance the costs and benefits for each species.
• Medium-sized groups often have the lowest stress levels due to reduced competition for resources and better ability to fend off other groups/predators.
• Yellow baboons are a good example, with group sizes typically ranging from 20 to 100 individuals.

Many Species Establish Territories

• A territory is an area defended by one or more individuals.
• Territories typically contain resources such as food and limited nest sites.
• Defending a territory may allow for access to greater resources and potentially more mates.
• Roe deer are an example of a species that establishes territories.

Dominance Hierarchies

• When benefits of group living outweigh the benefits of defending a territory, species often form dominance hierarchies, establishing social ranking among individuals.
• Dominance hierarchies are often determined through contests of strength or skill.
• Once established, subsequent disputes are typically resolved by the dominance ranking.

Eusocial Species

• Eusocial species exhibit social interactions to the extreme, displaying several characteristics.
• These include overlapping generations of parents and offspring living together in the same group.
• Cooperation in nest building and brood care is characteristic of these species.
• Reproductive dominance by one or a few individuals, and the presence of sterile individuals, is observed.
• Almost all eusocial species are insects, including termites, bees, wasps, and ants.
• Two mammals are eusocial species: the naked mole rat and the Damaraland mole rat.
• Most individuals in eusocial species do not sexually mature and instead specialize in tasks, known as castes.

Eusociality in Ants, Bees, and Wasps

• Eusociality is common in Hymenopterans (ants, bees, wasps).
• The society is typically dominated by one or more egg-laying females, referred to as queens.
• Fertile females produce a large number of offspring, even potentially more than a million offspring over a 10–15 year period.
• Non-reproductive offspring gather food and care for the young.
• The queen has the same relatedness to sons/daughters (r = 0.5).
• All females have the same genes from their father.
• All females retain 50% probability of shared genes from their mothers (r = 0.75).
• Brother-sister relatedness is r=0.25.

Eusociality in Termites

• Termites are diploid insects that have a different evolutionary history compared to hymenopterans.
• Colonies are dominated by one king and queen and produce sons and daughters via sexual reproduction.
• Offspring act as workers, and can become sexually mature if the king/queen dies.
• Soldiers are members of a second non-reproductive caste.

Eusociality in Mole Rats

• Social mole rats live in colonies of up to 200 individuals.
• Reproduction is managed by a single queen and multiple kings.
• All individuals are diploid.
• Workers are capable of reproduction but are often harassed and stressed by the queen, leading to reduced sex hormones and an inhibition of reproductive drive.

Origins of Eusociality

• Eusociality evolved independently multiple times.
• Haplodiploidy seems to favour eusociality, but some haplodiploid species are not eusocial, and some eusocial species are diploid.
• Eusociality could be due to minimal costs in direct fitness, though this is debatable.

Social Interactions in Plants

• Many species besides animals exhibit social behaviour.
• Even bacteria and protists can sense and react to other individuals via chemical secretions, potentially exhibiting aggressive or friendly interactions.
• Free-living slime molds aggregate to form large fruiting bodies.
• Plants communicate chemically with one another.

Social Responses to Herbivory

• Plants can warn other plants about herbivory.
• E.g., Alder trees are known to warn nearby plants about herbivory when their leaves are consumed and releases chemicals when attacked by herbivores.
• Nearby plants detect these chemicals and increase their defences.
• This behaviour is not necessarily considered a social behaviour as the mechanisms are unknown.

Social Responses to Competition

• Plants can distinguish between relatives and non-relatives.
• When grown near relatives, plants often develop less dense root mass due to less competition.
• When grown near non-relatives, plants often develop a denser root mass, indicating higher levels of competition.

Additional Information

• The lecture's learning objectives include describing how living in groups has costs and benefits, explaining the four types of social interactions in animals, and explaining how eusocial species exhibit social interactions to an extreme.
• A concept check in the lecture asked students to identify how the dilution effect is a benefit of group-living.
• A second concept check asked students to explain how optimal group sizes represent a compromise between the costs and benefits of group living, and provide at least one example.
• Another check asked students to explain why altruism cannot be fully explained by direct fitness alone.

Explore the intricacies of social behaviours in various species, focusing on interactions among mates, offspring, and rivals. Understand how genetic and environmental factors shape these behaviours and their implications for survival and natural selection. This quiz will challenge your knowledge of the benefits and costs associated with living in groups.