9.15. (10/21) Population Genetics & Competition Flashcards
What is p?
frequency of one allele
what is q?
frequency of a second allele
How can we calculate the frequency of genotypes in a population in Hardy Weinberg equilibrium? What does this do?
(p+q)^2 = p^2+2pq+q^2= 1.0
- allowing random mating to happen
What is p+q=1.0?
The Hardy Weinberg Equilibrium for a population
What are the necessary conditions to maintain constant allele frequencies in a population?
- random mating
- no mutations
- large population size b/c we don’t want genetic drift
- no immigration b/c new alleles can be introduced or there can be different frequencies
- equal fitness (no natural selection, probability of surviving and reproducing)
Why do we care about the Hardy-Weinberg principle?
- it is the null model of evolution
- by defining the narrow range of conditions necessary for evolution to be unexpected, the large potential for evolutionary change was demonstrated
What is Ne?
effective population size
What is effective population size?
- the average size of a population in terms of the number of individuals that can contribute genes equally to the next generation
- the actual number of individuals that can equally pass on genes to the next generation
- less than actual population
what are some problems associated with small populations?
- loss of genetic variability
- inbreeding depression
- genetic drift
How is Ne different than N?
Ne is much lower than the census population because
1. fluctuating population sizes through time
2. unequal number of females and males
What is the equation for a Ne of fluctuating population size?
1/Ne= 1/t(1/N0+1/N1+1/Nt-1)
*typically estimated as the harmonic mean of the actual size of each generation
What is the equation for Ne when there is an unequal number of females and males?
N=4NfNm/Nf+Nm
*Nf & Nm are the numbers of females and males in the population
What is Tansley’s classic competition study?
- A.G. Tansley, British
- experimentally demonstrate competition between closely related species and their implications for predicting where organisms occur
- two galium species
- one liked acid, organic-rich, peaty soil the other liked limestone, basic soil
- can the two species germinate on either soil?
- then grew them together
- when grown in mixture, each species overgrew and shaded the other on its preferred soil type
- disadvantage in competition
What has been concluded from Tansley’s experiment?
- the presence/absence of species can be determined by competition with other species
- environment can affect the outcome of the competition
- competition may be felt very broadly throughout the community
What is competition?
use or defense of a resource by one individual that reduces the availability of that resource to other individuals
What is intraspecific competition?
- within species
- what regulates population growth
- reduces resources
- promotes evolutionary change
What is interspecific competition?
- two different species
- depresses populations of both competitors
- may lead to the elimination of one species
- potentially important in determining coexistence
- gives the upper hand to the more efficient species
what resources result in competition?
- open space for sessile organisms
- hiding places and other safe sites
*consumed
*conditions are not
What is Liebig’s Law of the minimum? Why is it wrong?
- one resource/nutrient will become limiting to the growth of individuals in a population
- various nutrients may interact in a synergistic fashion to promote plant growth
What does synergistic mean?
two things working together to produce a combined effect greater than when they are alone
What is self-thinning?
process of ecological succession
* intraspecific competition
What is a phase-space diagram?
- dots move in time
- arrows
- high to low number of individuals, but when low high amount of total biomass (in each individual)
- regardless of starting factors, the end product is the same
What is exploitation competition?
individuals are competing indirectly through their mutual effects on some resource
*common
what is interference competition? What are some examples?
when individuals antagonistically interact with each other to defend a resource
*requires that resources can be profitably defended
*hummingbird exclude
*sponges use poisonous chemicals
** bacteria and fungi release poisonous chemicals
what is allelopathy?
the release of toxic chemicals/flammable oil to decrease the chance of other species settling in the area/ depress the growth of competitors
what is migration?
movements between subpopulations
what is emigration?
leaving a subpopulation
What is immigration?
entering a subpopulation
How do we monitor dispersal?
- mobile organisms must be marked and recaptured
- large areas must be covered in order to ensure an adequate sampling of movements
what is average lifetime dispersal distance?
looking at all the individuals in a population, determining how far they moved in their lifetime, and averaging it
What is lifetime dispersal area?
- estimate
- potential
- take the average dispersal distance, make it the radius of a circle, and calculate its area
what is neighborhood size?
- counting all the individuals that are in the average lifetime dispersal area
- individuals could interact/ mate with others in this area
what is the genetic variability of the collared dove populations in turkey vs the british isles?
- it is lower in turkey
- founder events drove the migrations
what is preserved in the sediments of lakes and peatlands that helps understand range changes in response to climate change? How?
- tree movement record
- Anoxic environments allowed for the accumulation of pollen/leaves/seeds in the basins of the trees that grew in the vicinity
- networks of pollen and macrofossil records (C14 dating) could be used to reconstruct patterns of post-glacial migration
- pollen chemically like rubber (even in rock records)
what is the difference between natural selection and evolution?
natural selection acts on individuals where evolution acts on populations
what does homozygous mean?
what does heterozygous mean?
how do we find the frequency of S and A alleles in a population?
S= (frequency of SS) + 1/2 (frequency of SA
A= (frequency of AA) + 1/2 (frequency of SA)
What is the Hardy-Weinberg principle?
in the absence of evolutionary forces, the allele frequencies in a population remain constant over time
what does the Hardy-Weinberg principle assume?
- random mating
- the probability of any two alleles coming together is determined by their frequency
