Modes of Selection Flashcards
the modes selection vary in their effect on
average value of a trait
variance of a trait
what are the 3 modes or types of selection?
directional
stabilizing
disruptive
directional selection changes the _______ value of a trait
average
in directional selection, fitness can
increase or decrease
directional selection does not necessarily affect the _____ of a trait, but it can!
variance
a population of cliff swallows underwent a cold snap, causing only the swallows with largest body size to survive and reproduce, this changed the average value and is an example of what type of selection?
directional selection
stabilizing selection reduces the amount of _____ in a trait
variance
in stabilizing selection, what generally happens to the average value of a trait?
it is maintained
in stabilizing selection, what happens to the fitness of individuals with an intermediate value for a trait?
fitness is increased
the narrow distribution of the birthweight of babies is an example of what selection?
stabilizing selection
why are 7 pound babies at the highest average?
ver small and very large babies are more subject to infant/maternal mortality
disruptive selection increases the _____ of a trait
variance
does disruptive selection generally change the average of a trait?
no
what happens to the fitness of the intermediate during disruptive selection?
fitness decreases
disruptive selection may lead to
speciation
in black bellied seed cracker birds, only birds with very large bills or very small bills survived, the intermediate bill type died off, this is an example of which selection?
disruptive selection
