Natural Selection Flashcards
What is an adaptation?
A characteristic that enhances survival or reproduction
What makes a characteristic an adaptation vs just a characteristic?
Well suited for that particular environment
How do adaptations cause a population to evolve?
The population becomes better suited to its habitat over many generations
How is pseudocopulation inbee orchids an adaptation?
Looking like female bees and producing pheromones increases the pollination rate of the flowers. Is an adaptation only for reproduction and less so for survival
Are all organisms equally well adapted?
No, different organisms show different levels of adaptation
What is the difference between natural selection and artificial selection?
With natural selection, environmental pressures create selection pressure. With artificial selection, human intervention creates selection pressure
How did cabbage, cauliflower, kohlrabi, kale, brussel sprouts, and broccoli arise from wild mustard?
Artificial selection for particular traits in wild mustard
What is natural selection? 3 definitions
- Differential survival and reproductive success among individuals due to selection pressures from the environment
- Mechanism that allows individuals to respond to their environment by refining adaptations
- Mechanism through which evolution occurs
How does natural selection create differential reproductive success?
Individuals with favourable traits will be more likely to survive and reproduce than individuals with unfavourable traits, leading to an accumulation of that favourable trait in the population
What is fitness?
Average lifetime contribution of individuals of a genotype to the populations after 1 or more generations
What determines fitness for an asexually reproducing species?
Population growth
What determines fitness for a sexually reproducing species?
- Probability of surviving to reproductive maturity
- Average number of offspring produced by the female
- Average number of offspring produced by the male
What happens when one genotype is more fit than another in terms of population growth and the next generation?
The fitter genotype has higher reproductive success. It grows faster so makes up more of the next generation
What did John Endler’s experiments with the guppies show?
Natural selection may consist of differences in reproductive rate instead of survival
When a feature is subject to conflicting selection pressures, which one determines the direction of evolution?
Whichever one is stronger
What is required of a trait to be acted on by natural selection?
It must be heritable
What sort of traits are not subjected to natural selection?
Characteristics acquired during the lifetime of the organism, since they aren’t heritable
Is natural selection random?
No, it occurs in response to environmental pressures and results in adaptations that are beneficial for that environment
Why can’t natural selection fashion perfect organisms?
It is limited by historical constraints and can only edit what is already present
Why are adaptations often compromises?
Conflicting selection pressures
What 3 things lead to natural selection?
- Variation - in the environment and between individuals
- Differential reproduction
- Heredity
What are the 3 basic modes of selection?
Directional, disruptive, stabilizing
What is directional selection?
One extreme is favoured over the other
What happens to the population profile that is undergoing directional selection?
It moves in one direction to that extreme being selected for
What is stabilizing selection?
Intermediate phenotypes are selected for over both extremes
What is disruptive selection?
Both extremes are selected for over the intermediate phenotypes
What can disruptive selection ultimately lead to?
Speciation
What is the fitness of a genotype in asexually reproducing species?
Proportion surviving x average fecundity
What is the absolute fitness of a genotype for an asexually reproducing species?
Per capita growth rate of that genotype
What is the relative fitness of a genotype for an asexually reproducing species?
Comparison between the R values of the genotype of interest and a reference genotype with the highest R value
What is the absolute fitness for a sexually reproducing species?
Number of zygotes produced over a lifetime = probability that an individual survives to reproductive maturity x the expected number of offspring
What are 4 components of selection that affect allele frequencies?
- Viability
- Mating success
- Fecundity
- Fertilization success
What is viability?
The probability that an individual survives to reproductive maturity
What is mating success?
The number of mates obtained by an individual
What is fecundity?
Average number of viable offspring per female
