Process of social evolution - part 2 Flashcards
how can there be a -r ( r < 0 )
when an individual is recently dispersed into population
Hamilton’s rule - variables in c < rb
- c is the offspring cost to the actor.
- b is the offspring gain by the recipient.
- r is relatedness of actor and recipient.
How do interactions in nature impact the terms of Hamilton’s Rule, to tip the balance towards the evolution of altruistic acts and sociality?
- c and b are influenced by ecology and synergistic benefits of sociality
- The expected destabilizing effects of r can be manipulated
explain how c and b are influenced by ecology
costs and benefits will depend on the context of the ecological conditions the individuals are in
explain how c and b are influenced by synergetic benefits of sociality
societies can do things that individuals cannot do.
how can the expected destabilizing effects of r be manipulated
it can be manipulated by the social context to achieve conflict resolution and make sociality more stable
Any ecological factor that ____________________ of an altruistic act for the actor and ________________________ to the recipient will promote sociality.
- decreases the cost (↓c )
- increases the benefit (↑b)
Main categories of ecological factors promoting sociality
- Environmental stress.
- Food supply.
- Nest-site limitation.
- Temporal facilitation.
- Parasitism.
- Predation.
Many good examples of ecological factors promoting sociality come from animals that facultatively participate in ________________
cooperative breeding
define cooperative breeding
temporary/juvenile helpers at a nest of related or unrelated individuals
Greater environmental stress or unpredictability means that social acts will likely _____ and _____.
- ↓c
- ↑b
environmental stress - social group acts like an _______________________.
environmental buffer
environmental stress - without the social buffer
- the environmental harshness is likely to result in high adult and offspring mortality
- reproductive output of solitary life is low to none, so the cost of an altruistic act for the actor is very low
environmental stress - with the social buffer
the reproductive output of those that do get to reproduce (b) is boosted by many individuals harvesting scarce resources
environmental stress - example
- mole rat group size increases with greater variability in rainfall
- they experience greater stress from water shortage
mole rats experience _______________ of reproductively capable individuals when environmental ___________
- more dispersal
- stress is low
mole rats - selection favors ___________________ (more altruism) when
____________________________.
- larger groups sizes
- environmental stress is high
_______________________________________ across different potential nesting sites promotes non-dispersal of offspring.
Variability and unpredictability of food
food supply - costs
The dangers of starvation following dispersal make the cost of staying low (↓c).
food supply benefits
↑b for reproductive individuals from the additional helpers finding scarce food
food supply - example
Seychelles Warbler (type of bird) offspring stay as helpers at their natal nest if territory of group has high quality food resources, and if alternative equal-quality territories are not available
____________ of suitable nesting sites results in ___________________________ and establishes a ____________________________________
- Scarcity
- non-dispersal by offspring
- social group around the natal nest.
nest-site limitation - cost
- c associated with the social act of staying to help rear subsequent generations is lowered
- alternative is effectively homelessness (high risk) and no opportunity to reproduce.
nest-site limitation - benefit
- b is boosted by economies of social foraging and offspring rearing
- boost in offspring rearing may be more substantial than just additive/ non-linear.
nest-site limitation - example
In a species of Mexican paper wasp (Mischocyttarus mexicanus), reproductive females form social nests only when protected nesting sites are limited
Length of __________________ can dictate the _________________, and therefore the opportunity for individuals to ________________, and potentially secure direct reproductive opportunities.
- breading season
- number of broods
- stay at the natal nest
what does a longer breeding season indicate
more time for social groups to form and yield associated benefits
Nesting opportunities may also become increasingly scarce as the season progresses, further favoring staying at the natal nest — ___________________________________________________
potential interactions of nest-site limitation and temporal facilitation
temporal facilitation - example
Some species of facultatively social halictid bees are solitary in more northern populations, and social in more southern populations.
Social parasites ________________________ of other species for their own gain, often in the form of ______________________ of social species.
- exploit the social actions
- exploiting brood rearing
Infiltration of a social parasite is achieved by __________________________ of the social species.
circumventing the guarding behavior
Threat of parasitism may make offspring and/or nest _____________________________.
guarding critical for offspring survival
parasitism - how does this impact costs and benefits
- inability for solitary individual to guard when foraging ↓c for individual that acts as a guard in a social group
- ↑b for reproductives in the social group
Similar to the threat of parasitism, ____________________ pressure ___________________________ for better protection of offspring
- increased predation
- favors group formation
_____________ pressure, and therefore high mortality of offspring reared by solitary parents, __________________ that help within a social group and ___________________.
- High predation
- ↓c for individuals
- adding defense to ↑b
predation - example
- The cooperatively breeding cichlid fish (Neolamprologus pulcher).
- Experimental addition of predators reduces dispersal by helpers, increasing likelihood of social group formation.
define synergistic social actions
When members of a group work together to complete actions that each acting alone simply could not complete
Categories of synergistic benefits of sociality
- Assured fitness returns
- Access to novel resources that require social actions
- Division of labor, defined as a form of behavioral specialization within a social group
Categories of synergistic benefits of sociality - assured fitness returns
even if you die, group membership provides some fitness gains (potentially direct and indirect)
In all but clonal societies, ____________________ to potential offspring creates _____________
- differences in relatedness
- inherent conflict
Ecological and synergistic benefits can tip the balance towards sociality, but ____________________________________.
conflict may remain as a destabilizing force
what can further increase b and stabilize the social structure?
The evolution of reproductive traits and social tactics that increase conflict resolution
define conflict resolution
- Reduction of group resources dedicated to conflict within the society
- OR the increase in group resources dedicated to cooperative offspring production.
Conflict resolution traits and tactics generally _______________________________ for individuals to act on conflict.
reduce the information and opportunity
