Problems of Small Populations Flashcards
What is minimum viable population size (MVP)?
smallest number of individuals necessary to give high probability of survival for a population
How do humans usually affect populations?
usually accelerate the process of extinction of a population
What do larger populations have greater probability of?
colonizing unoccupied habitat and forming new populations
Why are small populations susceptible to dying out?
- loss of genetic variability
- demographic fluctuations
- environmental fluctuations
What is genetic drift?
chance change in allelic frequency from one generation to the next
Why do smaller populations have decreased genetic variability?
- fewer copies of a rare allele than larger ones
How is expected drop in heterozygosity per generation calculated?
(delta F) = 1/(2Ne) where Ne is
the number of breeding adults
How can the remaining heterozygosity be calculated?
H = 1 - 1/(2Ne)
What can offset genetic drift?
migration
What cannot offset genetic drift?
natural mutation (rates not that high)
What is the 50/500 rule?
isolated populations need to have at least 50 and preferably 500 individuals to maintain variabiliity
What does effective population size (Ne) depend upon?
the number of breeding individuals (unequal sex ratios, individual variation in reproduction output, population fluctuations)
What is a genetic bottleneck?
some environmental or demographic event kills all but a few individuals of a population
What is the founder effect?
a few individuals leave a large population and start a new one
What causes inbreeding depression?
mating among close relatives
What results from inbreeding depression?
- fewer or weak/sterile offspring
- allows expression of harming alleles
What are mechanisms to avoid inbreeding?
dispersal, odors/sensory cues, and morphological and physiological mechanisms in plants
What is outbreeding depression?
mating between separate species, subspecies, and populations
Is outbreeding depression common?
rare in nature but more common in plants (pollination = chance)
What is loss of evolutionary flexibility?
low genetic diversity means fewer phenotypes to respond to environmental change
What is demographic variation?
random fluctuations in birth and death
What can demographic variation lead to?
- deviations from equal sex ratio and to breakdown of social structures
- can be devastating for small populations
What is the allele effect?
unable to find mate due to low population density
What is environmental stochasticity?
random environmental fluctuation
What are examples of environmental sochasticity?
natural disasters, fire, drought, etc
What is more important in increasing likelihood of extinction, environmental or demographic stochasticity?
environmental because it affects all individuals in a population
What happens once a population drops below a certain size?
it enters an extinction vortex
What is an extinction vortex?
a self-reinforcing process in which small populations are increasingly likely to decline toward extinction due to a combination of genetic, demographic, and environmental factors.
