Frequency-dependent selection Flashcards
What is frequency dependent selection?
When the fitness of a genotype depends on its frequency within a population, i.e. the same genotype will have a different fitness when common and when rare.
What is frequency dependent selection an example of?
Flexibility fitness
What is positive frequency dependence?
A morph increases in fitness as it increases in frequency.
Explain how positive frequency dependence works using the example species A and B.
As A increases in fitness it becomes more successful, causing the numbers of B to decline. Because B is rare it is unsuccessful, and vice versa.
Define the point of neutrality.
When both species have the same fitness, an equilibrium.
Is the point of neutrality stable in positive frequency dependence? Why, why not?
No - if the equilibrium is disturbed in either direction, for example by genetic drift, it will lead to fixation.
Give an example of positive frequency dependent selection in nature.
Mullerian mimicry in butterflies. The more common their phenotypes are, the more likely (young) predators know not to eat them, thus they become more successful in commonality.
What does ‘geographical locality among the same species’ mean?
Members of the same species that look different depending on location.
What is negative frequency dependence?
When a morph becomes less successful when it is common, i.e. it becomes fitter when it is rare.
Is the point of neutrality in negative frequency dependence stable? Why, Why not?
Yes, because the fitness differential pushes a population back to equilibrium.
Explain how negative frequency dependence is maintained using the example species A.
If species A grows in number this has a detrimental effect on their fitness, thus selection acts to remove individuals from the population until A is at a low frequency where it thrives.
Give an example of negative frequency dependence in nature.
Sex ratios: if sex ratios become imbalanced, the rarer sex will have a greater than average contribution to the next generation in the form of gametes. This will restore parity.
What is meant by an ‘evolutionary sustainable strategy’ (ESS)?
One that is un-invadable. ‘If all members of a population adopt the ESS, no mutant strategy can invade’.
What is ‘game theory’ in the context of evolutionary biology?
A method for describing the constraints of ritualised contests between animals as they compete for resources.
HAWK-DOVE theory is the simplest example of game theory. Describe the role of a) hawk and b) dove.
a) Hawk fights unconventionally without restraint. It only stops if it wins or is seriously injured.
b) Dove only ever threatens and runs away at signs of aggression, thus it is never injured.
