Animal personality and social niches

Animal personality due to social niche specialization – Bergmueller & Taborsky, 2010

Definitions

1. Animal Personality – Consistent differences between individuals in the behaviour across time and context
2. Behavioural Consistency – this means that the behaviour of individuals remains stable over time while each individual specifically does not express the full range of behavioural trait values seen in a population. This is seen in intra-individual correlation when subjects are measured repeatedly in the same context. As consistency is a relative measure applying to inter-individual comparisons it has also been known as “differential consistency”
3. Character displacement – A shifting in niche whether it is morphological, ecological, behavioural or physiological traits in individuals of sympatric species caused by competition. This review specifically looked at niche diversification of behavioural phenotypes as a result of competition for the same social or ecological niche by conspecifics.
4. Ecological niche – the conditions and resources needed by an individual or species in order to practice its way of life
5. Social conflict – an interaction among conspecifics reflecting conflicting fitness interests that is typically costly for the involved parties, because individuals act on incompatible goals or interests. Social conflicts result from competition for food or other resources.
6. Social niche – the social conditions an individual needs to practice its way of life. These conditions are shaped by interactions with conspecifics. Usually individuals can choose between different social niche options or social roles when adopting a social niche.
7. Social role – This is the realized behaviour or tactic an individual uses in response to social challenges like competing for food or resources. This is the same as a realized niche in ecological theory. Examples of social roles are dominant/subordinate, and producer/scrounger.
8. Social niche specialization – a consistently different way to behave relative to other individuals in a group resulting from the choice of a particular social role.
   

The evolution of animal personality

• Within a species, individuals usually differ consistently in their responses to environmental and social challenges like how to find food or compete with conspecifics. Additionally consistent individual differences in behaviour are usually correlated across functional contexts, these are known as personalities, and behavioural syndromes.
• In ecological factors, the influence of predation is an important cause of personality variation within populations
• Within species competition for a particular social niche can select for consistent individual differences among conspecifics

The intra-specific ecological niche

• Individuals and species that have similar requirements or niches usually adjust to this by niche differentiation when they occur in the same place or sympatrically. This reduces conflict between individuals that may arise from competition for resources.
• Because of niche differentiation, individuals naturally push each other away from their optimal niche by character displacement
• The ecological niche concept deals with how organisms in a given habitat respond to the distribution of resources and competitors in the area. The mechanisms by which individuals resolve conflict over resources.
• This review proposes that between individual consistency and behavioural diversification in one or multiple behaviours, can reflect individual specialization in different social niches. This reduces conflict over resources amongst conspecifics.

The social environment: a key factor for personality evolution

• Social conflict and the simultaneous presence of different social niche options are the key factors involved in making animal personality
• Social conflict is a prevalent evolutionary force that exists between sexes, parents/offspring, and other examples.
• Conflict increases the interaction costs between parties therefore, mechanisms should try to reduce conflict and should be naturally selected for
• Niche diversification of behavioural phenotypes that interact with one another, also known as social character displacement, is a potential means of reducing the costs that come with conflict, especially conflict over resources.
• The social environment also usually provides multiple solutions to cope with the same problem. And using alternative solutions to problems such as finding food or other resources might further generate diverging social niches like producers and scroungers, bold/shy explorers in dispersal and foraging concepts.
• Different social options for individuals or conspecifics of the same population results from ecological parameters like how resources are distributed across the habitat. Social conditions also affect the social options available as things like hierarchy or variation in resource holding potential can affect how many social niches are available.

Social conflict generating consistent individual differences

• Social conflict can select for the stable coexistence of different behavioural types as shown by evolutionary game theory. This game theory takes into account the fitness of individuals and the interactions between individuals where fitness depends on the strategies used by others.
• Negative frequency dependence means that the rare type in a population has the advantage which can maintain alternative behavioural types in a population as it reduces conflict and associated costs.
• Frequency dependence can either maintain a situation where individuals perform different behaviours with certain probabilities, which means their behaviour is not consistent. Or it can maintain certain proportions of individuals that pursue divergent strategies consistently. The social niche concept predicts that consistent individual differences should be favoured over switching because competition for niches makes switching more costly.
• Slight differences in individual idiosyncrasies (distinctive peculiar traits) can cause variations in pay offs associated with social interactions, thus some individuals adopt an alternative role that may have a higher fitness than constantly engaging in competitive costs.
• Individuals of the same species can reduce the amount of conflict by feeding on different prey items when competition for food is high, this can also be done by reducing social niche overlap. For example, solitary bees that were placed experimentally into a group nest, some individuals became specialized in excavation or nest guarding.
• Social interactions that result from competition can cause a lasting modification to behavioural traits due to social character displacement. Additionally switching to a different niche can require changes in physiology and behaviour of the individual which can be very costly and an individual can be constrained with age to a certain niche if learning is involved.
• In contrast to negative feedback mechanism that favours individuals that reduce costs of conflict by adopting different social roles (through character displacement and negative frequency dependence), a positive feedback mechanism can favour behavioural consistency of individuals because they become specialized which increases benefits and reduces costs of switching. Behavioural divergence and consistency may be a result of these two feedback mechanisms working together.

Social conflict generating behavioural correlations

• Combined traits that work well together can be favoured by correlational selection. When social conflict causes individuals to occupy different environments, then environmental correlations can select for a particular set of trait combinations
• Even if individuals are genetically identical, there are small initial asymmetries that exist between them in state, capability, condition or experience. Therefore the options to deal with conflict depend on an individuals’ intrinsic genetic quality, developmental differences and random effects.
• Selection should favour individuals that specialize by adopting a specific niche which in turn reduces interaction costs and creates consistent individual differences. Choosing a certain option in response to environmental or social challenges will expose individuals to divergent environmental influences, this creates a positive feedback based on experience with a certain role that stabilizes behavioural specialization.
• Cascading effects that follow from social specialization in one context might affect the behavioural options of individuals in multiple environmental and social dimensions.
• Division of labour within a group provides another example for how social roles might favour individuals with different behavioural packages. For example in fish, helpers that were consistently aggressive towards intruders which is a prereq for defending your own territory, showed low levels of natal territory maintenance, but had high levels of exploration behaviour.

Adaptive individual differences caused by developmental plasticity

• Personality traits are produced by an interaction of genetic factors with the environment individuals encounter during different life stages.
• The environment is never perceived the same for different individuals which results in variation among individuals that is permanently screened by selection which feeds back on the genotype structure in a population.
• Selection on phenotypic plasticity affects the evolution of reaction norms (range of phenotypes a genotype produces in a given set of environments) and the ability to learn (allowing an individual to develop an adaptive response to a novel challenge within its lifetime).

Social experience affecting the development of personality

• Social factors can shape personality if experience has lasting effects on the phenotype
• During the early stages of life organisms are flexible and susceptible to environmental influences. Traits that are controlled by the environment can be stabilized later in life through organizational effects of hormones or through reduction of flexibility through learning processes with long lasting effects.
• Results suggest that the shared environment, due to the same family setting, is less important for personality development than the non shared environment. For example with twins, the children they interact with school that are different from the ones at home are more important. I personally don’t get this because children spend more time at home than at school, I thought twins would try to reduce social niche overlap at home because they are so similar, while at school they could technically occupy the same niche as they could be in different environments and not around each other.
• Development niche specialization does not imply that personality prevails unchanged throughout life. However there are major transitions that come as developmental stages or changes in the social environment, which can lead to a reorganization of behaviour.

Alternative social options: animal personality and alternative tactics

• Variation in the personality of animals within populations can come from disruptive selection caused by social interactions. If the divergent behavioural types provide higher fitness prospects than the intermediate. Similarly, consistent individual differences in behaviour like those borne of personality might sometimes correspond to a diversification into specific discrete social roles caused by disruptive selection.
• In terms of resource monopolization which requires higher levels of aggressiveness while social parasitism may require submissiveness, therefore the intermediate type may not be favourable. So disruptive selection can favour the extremes of a certain behavioural type while penalizing the behavioural generalists that are intermediate at doing both types of things.