Social behaviour: costs and benefits Flashcards
group living 1 (38 cards)
Define social behaviour and sociality
Social behaviour
–Broad definition: Behavioural interactions between 2 or more animals, usually of the same species
–Narrow definition: Cooperative interactions extending beyond reproductive and parental behaviour
Sociality
–The tendency to form social groups
Why form social groups?
*For the benefit of the species or group?
*For the benefit of the individual?
Group selection original concepts (~1960’s)
it was thought that individual animals “behave in the interests of their species or social group” but this concept of ‘selflessness’ is questionable – it leaves a society open to exploitation by ‘selfish’ individuals (see games theory next lecture).
Group selection
*Wynne-Edwards (1962) Animal Dispersion in Relation to Social Behavior:
*Concept that natural selection ‘chooses’ between groups, populations or species on the basis of how well their individuals serve the collective unit’s interests.
*Animal populations regulate their size to track fluctuations in limited resources:
*Plenty → populations ‘allowed’ to expand,
*Scarcity → reproduction reduced so that populations do not exceed resources.
Social conventions
*territories, dominance, etc
*regulate access to resources & thus breeding opportunity.
*Individuals selflessly obey conventions,
*to breed or not according to social status.
*Social systems that regulate population better are then selected for………….supposedly………
Group selection: the argument against
*Populations generally track resource levels - OK.
BUT:
*animals adopting social systems to bring this about – controversial.
*Social systems based on interests of population are vulnerable to invasion by selfish individuals who ignore rules.
*Selfish individuals are likely to occur (through immigration, mutation or recombination & outcrossing) .
*Selfish traits have reproductive advantage & spread rapidly.
*A group-selected social system would thus collapse.
(See games theory: next lecture)
Group selection: current thinking
*Group selection may work BUT it is unlikely to be a major evolutionary force under natural conditions.
One main problem in group selection theory
*group selection requires unrealistically low levels of gene flow between groups, & low mutation rates within groups.
*Groups would have to be genetically isolated with little chance of a selfish individuals appearing (via immigration or mutation).
*Generally unlikely to be significant form of selection in natural conditions
*Selection acts at the level of the individual
*Genes that avoid replication for the good of a larger entity (group, society, species) – not favoured (selfish genes, tragedy of the commons; Hardin 1968)
group living, why do individuals ‘join’ groups?
*Relatedness – kin selection – to allow the continuation of your genes
*Heterogeneity and repeated interactions (this & next lecture)
*Costs and benefits to individual (this lecture)
Benefits of group living
Benefits:
*Foraging success
-Groups indicate rich food sources
-Cooperative hunting
-Cooperative defence of resources
-Information sharing
*Reduced predation risk
-Predator dilution
-Synchrony and satiation
-Predator confusion
-Cooperative vigilance
-Cooperative defence
*Energetic advantages
-Social thermoregulation
-Slipstreaming in flight/swimming
*Other
-Cooperative mate displays
-Easier to find mates
-Division of labour
-Enhanced learning of young
Costs of group living
Costs
Dominants in the group have first claim on food and mates resulting in some cases in subordinate starvation, lack of food to provide their offspring or no chance to reproduce
*Foraging success
- Local depletion
- Exploitative competition (food displacement)
- Interference competition (intraspecific aggression)
- Time investment in social behaviours (e.g shows of dominance/ submission)
*Mating success
- Risk of accidental / deceptive investment in others’ offspring
- Risk of inbreeding
- Risk of infanticide/cannibalisation (e.g. When a new lion takes over a pack it may kill the young from the previous alpha, Some male seals cannibalise pups on the breeding colony allowing them to hold territory longer)
*Other
- Stress from competition
- Increased risk of disease and parasite transmission
- Free-riders
Benefits of sociality #1: Exploitation of resources: Food
*feeding efficiency – experienced coordinators lead the hunt
*information sharing (see Barta & Giraldeau 2001, Doligez et al 2002)
* increased competitive ability/capture rates
* cooperative hunting → capture larger prey & defense of prey once captured
*e.g. wolves, hyenas, lions (Packer et al. 1990)
Benefits of sociality #2: Exploitation of resources: Mates
*access to potential mates,
*comparison of mates – mate choice- making informed choices from longer observation
*helpers & coalitions, deferred reproduction
*experience & potential territory inheritance in future
Benefits of sociality #3:Anti-predator effects
e.g. increased vigilance (e.g. Redshanks; Cresswell 1994)
*dilution effects & confusion effects
*selfish-herd effects
*mobbing e.g. crows mobbing eagles
*group defense e.g. musk-oxen
*alarm calling e.g Belding’s Ground Squirrel
(many examples in Alcock/Dugatkin/Nordell & Valone)
Benefits of sociality #4: Energetic advantages
Social thermoregulation e.g. in emperor penguins
slipstreaming e.g. wolves travelling through snow follow the leader who creates a path thus saving their energy
This is also why large birds fly in a V-formation as it provides energetic advantages
e.g. A study by Weimerskirch et al. 2001 on White pelicans (Pelecanus onocrotalus) Placed heart rate monitors on trained birds and recorded video flight formations + wingbeat frequency, along with the location of each bird in formation. They found that birds in formation behind the leader had slower wingbeat frequency and lower heart rate.
Benefits of sociality #5: Enhanced learning
*Young individuals in social groups can learn from adults
*e.g. antipredator information
How do young prairie dogs learn their predators & how to avoid them? A study by Shier & Owings 2007 on Black-tailed prairie dogs (Cynomys ludovicianus)
method
They captured 36 juveniles and carried out a pretraining assessment
Then, conducted a five-week training period for juveniles in 3 conditions:
1.With experienced adult
2.With inexperienced sibling
3.Alone
Post-training tests:
Measured activity, fleeing, vigilance, and calls when released back into wild
Results:
Individuals trained with an experienced adult; showed higher levels of antipredator behaviour and higher survivorship
Costs of living in groups #1: Increased competition for resources
Resulting in local depletion, exploitative competition (displacement) and interference competition (intraspecific aggression)
Food:
- increased chance of starvation as dominant individuals monopolise food.
Reproduction:
- Increased time to first reproduction
(e.g. Blumstein & Armitage 1998)
- reductions in offspring viability
(e.g. Tella et al. 2001)
- chance of not breeding at all - reproductive skew theory
Costs of living in groups #2: Mating success:
*Risk of inbreeding → inbreeding depression
*Risk of misdirected parental care
* brood parasitism, e.g. cliff swallows
*extra-pair copulation in colonial birds
*cross-fostering e.g. grey seals
*Risk to offspring from conspecifics.
Costs of living in groups #3: Increased exposure to parasites & disease
exposure to disease and parasites
e.g. cliff swallows (Brown et al 2001).
*Increased conspicuousness to predators
e.g. Whirligig beetles (Watt & Chapman 1998)
*large groups more likely to be attacked but risk per individual is decreased
*Cost in time spent in social behaviours,
-e.g. submissive behaviours
-and stress from competition
The extent of sociality
*Extent & form of social organisation of a population is regulated by balance of costs & benefits of social interactions for individuals.
*Most animal spp. with 2 sexes are to some extent social, with the minimal social behaviour necessary between sexually reproducing animals being that associated with mating.
*There are some examples where individuals do NOT meet - even to mate e.g. broadcast spawning in lugworms, sea urchins
Economics of sociality
See graph in notes
As with all animal behaviour, must consider economics of benefits and costs
Extreme forms of sociality: the classic studies - related individuals
The evolution of such cooperative social behavior is often a result of kin selection:
*helping related individuals → indirect fitness benefits (‘Hamilton’s rule’)
*see lectures on genetics of behaviour
*Often this occurs where ecological constraints limit which or how many individuals can breed
Eusociality: societies that contain specialised non-reproducing castes that assist the reproductive members of the society.
^ e.g. ants, bees (Haplodiploid: ♂ = haploid ♀ = diploid)
Altruism: cooperative behaviour in which the actor’s fitness is reduced by the behaviour but raises the recipients fitness.
e.g: Alarm calling in Belding’s ground squirrels. Alarm calling individuals face risk of immediate costs ( predation) but may also gain recognition and status for their actions
e.g. Cooperative breeders (such as hyenas)
Extreme forms of sociality: not limited to kin the classic studies - UNrelated individuals
Reciprocal altruism: one individual performs a cooperative act which is ‘repaid’ at a later date by the recipient of the assistance. A means by which cooperative behaviour can evolve even between non-relatives.
This requires a means by which individuals can ‘distinguish’ reciprocators from those who refuse to cooperate by:
*individual recognition
*probabalistic (frequency dependence)
^ e.g. Allo-grooming in many primate species.
Extreme forms of sociality – the classic studies
Attempts at deriving a unified social theory of evolution have focused almost exclusively upon eusocial insects, or cooperatively breeding vertebrates (see Emlen 1997 & Ch 10 in Krebs & Davies) and highly social species.
BUT:
cooperative breeding occurs in only 3% of bird and mammal species.
Highly social species are rare
To understand evolution of sociality need to look at less extreme manifestations of social interactions e.g. conflict reduction.
“Simpler” sociality
*Living in groups leads to conflicts of interest between individuals (see list of costs of group living).
Resulting in aggression e.g.:
- chasing off related individuals - inbreeding avoidance
- aggression between neighbouring female seals to protect pups.
Low sociality - e.g. conflict reduction behaviour as seen in seals. This reduction is not cooperation but can lead to reciprocal altruism
