Topic 7 - Evolution Flashcards
What is variation?
Variation is the differences that exist between individuals
What is intraspecific variation?
Variation within species.
What are the 3 sources of genetic variation?
1) Mutation
2) Meiosis - crossing over of chromatids and independent segregation of chromosomes
3) Random fertilisation of gametes
Outline the process of natural selection (evolution)
1) Individuals of the same species vary because they have different alleles.
2) Predation, disease and competition (selection pressure) create a struggle for survival.
3) Because individuals vary, some are better adapted to the selection pressures than others.
4) There are different levels of survival and reproductive success in a population. Individuals with a phenotype that increases their chance of survival are more likely to survive, reproduce and pass of their genes, than individuals with a different phenotype.
5) A greater proportion of the next generation inherit the beneficial alleles.
6) They, in turn, are more likely to survive, reproduce and pass on their genes.
7) The frequency of the beneficial alleles in the gene pool increases from generation to generation.
What is stabilising selection?
Stabilising selection is where individuals with alleles for characteristics towards the middle of the range are more likely to reproduce.
When does stabilising selection occur?
Occurs when the environment isn’t changing and it reduces the range of possible phenotypes.
What is an example of stabilising selection?
In any mammalian population there’s a range of fur length. In a stable climate having fur at the extremes of this range reduces the chances of surviving as it’s harder to maintain the right body temperature. Animals with alleles for average fur length are the most likely to survive
What is directional selection?
Where individuals with alleles for a single extreme phenotype are more likely to survive and reproduce.
What could directional selection be in response to?
An environmental change.
What is an example of directional selection?
Cheetahs are the fastest animals on land. It’s likely that this characteristics was developed through directional selection as individuals that have alleles for increased speed are more likely to catch prey than slower individuals. So they’re more likely to survive
What is disruptive selection?
Where individuals with alleles for extreme phenotypes at either end of the range are more likely to survive and reproduce.
Why is disruptive selection the opposite of stabilising selection?
Because characteristics towards the middle of the range are lost.
When does disruptive selection occur?
Occurs when the environment favours more than one phenotype.
What is an example of disruptive selection?
In bird populations there’s a range of beak sizes. Birds with large beaks are specialised to eat large seed and birds with small beaks are specialised to eat small seeds. In an environment where the majority of seeds are large or small and very few are medium-sized birds with medium-sized beaks may have a reduced chance of survival as they are unable to eat either large or small seeds effectively. Birds with large or small beaks are most likely to survive
What is speciation?
Speciation is the development of a new species from an existing species.
When does speciation occur?
Occurs when populations of the same species become reproductively isolated.
What is geographical isolation?
Occurs when a physical barrier divides the population of a species causing some individuals to become separated from the main population
What does geographical isolation lead to?
Allopatric speciation
What is sympatric speciation?
When a population becomes reproductively isolated without any physical separation. Random mutations could occur within a population
Why does reproductive isolation occur?
Occurs because changes in alleles and phenotypes in some individuals prevent them from breeding successfully with individuals without these changes.
What 3 changes lead to reproductive isolation?
1) Seasonal changes - individuals from the same population develop different flowering or mating seasons or become sexually active at different times of year.
2) Mechanical changes - changes in genetalia that prevent successful mating.
3) Behavioural changes - a group of individuals develop courtship rituals that aren’t attractive to the main population.
What is genetic drift?
Genetic drift is when chance rather than environmental factors
Why does genetic drift impact smaller populations to a larger extent?
Evolution by genetic drift usually has a greater effect in smaller populations where chance has a greater influence. In larger populations any chance variations in allele frequency tend to even out across the whole population.
What is carrying capacity?
The maximum size of a population of species that an ecosystem can support.
What four factors determine the carrying capcity of an ecosystem?
1) Temperature
2) pH
3) Light
4) Water & humidity
What two things cause the population size to vary?
1) Affect of abiotic factors
2) Interactions between organisms (intraspecific and interspecific)
What are microhabitats?
Each habitat has its own microclimates
What is an ecological niche?
How an organism fits into the environment, where it lives and what it does there.
What is the competitive exclusion principle?
No two species occupy the same niche.
What are the two types of sampling populations?
1) Random - using a frame quadrat or point quadrat
2) Systematic - along a belt transect
What are the three factors to consider when sampling popualtions using quadrats?
1) Size of the quadrat - depends on the size of the plant or animal being sampled and their distribution.
2) Number of sample quadrats - larger the number of sample quadrats the more reliable the results will be.
3) The position of each quadrat - produce statistically significant results, random sampling must be used.
What is the equation for the Lincoln Index?
Lincoln Index = (total number of individuals in first sample x total number of marked individuals in second sample) / number of marked individuals recaptured
