Selection and Fitness Flashcards
Type of selection often involving a balance between conflicting selective pressures (often due to trade offs)
Stabilizing selection
This governs reproductive output, has consequences for competitive ability, and also determines what kinds of responses will be deployed to deal with competition
Genotype
Differential reproduction as a result fo heritable variation
Selection
How does selection relate to heritability?
The larger genetic variation is relative to total variation (Vg+Ve), the more effective selection will be. More heritable (closer to 1) = more effective selection
Selection when 2 or more discontinuous phenotypes are fittest (on the ends)
Disruptive selection (diversifying selection)
The fitness of other genotypes that aren’t best are set to this
1-s
What is the value of s always between?
0 (no selection) and 1 (complete mortality)
Reduction in fitness relative to best genotype
Selection coefficient (s)
Effect is modulated depending on population size or density
Density dependent factors
Reproduction at same rate but survive at different rates
Differential survival
These integrate resource availability and competition with population growth
Density dependent factors
Three sets of variables shaping population structure
- # of individual having offspring and # of reproductive offspring
- # of reproducers x # of eggs (upper limit on reproductive output cycle)
- Number of cycles per year and number of female cycles per female lifespan
Selection when individuals at one extreme of the range of phenotypes are the fittest
Directional selection (purifying selection)
Examples of density dependent factors
Supply of food or other resources and Disease
What does changing the 6 factors contributing to fitness change?
Population growth profile
How is death related to reproductive output?
How many died vs how many are produced
6 factors contributing to fitness
- # reproductive females
- # offspring per cycle
- # cycles per unit time
- # cycles per female lifetime
- Death rate of reproductive individuals
- Survival rate of offspring
What causes reproductive output (R) to not be the same for all bearers of a specific genotype?
Environmental effects
Effect is the same regardless of population size or density
Density independent factor
Strength of selection depends on these two things
Heritability (h2) and the degree of difference in fitness among phenotypes
What does fittest mean in survival of the fittest?
The best among known genotype or phenotypes
Examples of density independent factors
Environmental phenomena (drought, long winter, natural disasters, etc)
The sum of viability, mating success, fecundity, gametic viability, and fertilization success
Fitness
Non-random processes through which pre-existing variation is sorted
Differential survival and differential reproduction