Ch. 6 (Risk of small populations) Flashcards
What are the three main factors that put small populations at greater risk of extinction?
-Reduced genetic variability
-Demographic fluctuations (Due to death and birth rates)
-Environmental Fluctuations (Variability of climate, competition, predation, natural disasters.)
How do you calculate the allelic frequency?
-Allelic frequency (% of the total alleles in the population for a specific gene
Ex.
-1000 individuals x 2 alleles/individuals = 2000 total alleles
-If 100 copies of an allele are present frequency = 100/2000 = 0.05 = 5%
What is heterozygosity? Is there any evidence that it effects fitness?
-A measure of genetic diversity.
-the mean % of loci heterozygous per individual
-the mean % of individuals per locus
-the more heterozygous, the better things do
What other ways can you measure genetic variation?
-Allele frequency = 1000/20000 = 5%
-Relative genotype frequency
What mechanisms of evolution decrease heterozygosity? Which ones increase it? How does population size effect the strength of these mechanisms?
-Genetic Drift: Change in frequency of alleles due to sampling, chance.
-Small pops more affected by this
-An allele with a low frequency is more likely to be lost in a small population than a large one
What mechanisms of evolution can counteract loss of genetic variation? Which one seems to be most important?
-Mutation ( i.e, rate = 1/1000 to 1/10,000 per gene/generation)
-Migration
What factors can decrease the effective population size? How can humans play a role here?
-Unequal sex ratio (as sex ration is skewed, smaller groups contribute to the next generation)
-can occur by chance, overharvest of one sex, or social systems, i.e, males fighting for harems, elephant seals preventing some males from mating.
-Variation in reproductive output (Some individuals contribute more to the next gen, smaller individuals may have fewer offspring than large individuals).
-Pop fluctuations/ bottlenecks (may occur as a response to food, predators, climate, etc).
-Population Structure: If pop is composed of numerous sub-pops that go extinct periodically (metapopulations).
Why is inbreeding generally considered to be harmful? (2 ideas..)
-Dominance Hypothesis: Deleterious alleles usually masked by dominant alleles. (increased homozygosity leads to expression of deleterious recessives).
-Heterozygous Advantage Hypothesis: Genome-wide levels of heterozygosity are the main influence (Increased heterozygosity increase fitness)
What is the minimum Ne to prevent inbreeding depression? What Ne should prevent loss of genetic variation from genetic drift?
-50
-500
-This is called the 50/500 rule, danger in applying this to species without study
What is outbreeding depression? How can mating between individuals from different populations harm a species?
-Lack of compatibility of chromies and enzyme systems inherited from different parents
-may erode local adaptation.
A recovery program for a vole population is in its 4th year. If there are currently 250 breeding males and females (with an approximately equal sex ratio), what would the effective population size of this population be if the population passed through a population bottleneck of 50 individuals 3 years ago, then recovered to 90, then 150 in the years following?
-Slide 110
-Unequal sex ratio (slide 118, 122)
-Bottleneck (125)
Do all endangered species have low heterozygosity?
-No
Why might a population with low heterozygosity now, suffer population declines in the future?
-Could cause inbreeding depression
-affect reproductive success
-Affect ability to fight disease
What does it mean for a species to enter an extinction vortex?
-As a population declines, it is at a higher risk of
-losing genetic variation due to genetic drift
-developing unequal sex ratio
-suffering from inbreeding depression
-Further loss due to demographic or environmental variation
The Florida panther has suffered from inbreeding depression – managers decided to bring cougars from the Rockies to FL to breed with the cougars. Based on what you know- what were the potential benefits and risks associated with this plan?
-This could help increase the Florida puma population, however, the two puma species may have been too different to breed, could cause birth defects or no reproduction, could have caused outbreeding depression.
