Populations and Evolution Flashcards
Define species
Organisms that can reproduce to produce fertile offspring
Define population
All the organisms of a single species in one place at one time, species can exist as more than one population
Define community
All the organisms of all the species in one place at one time
Define gene pool
All the alleles present in a population
Define allele frequency
How common an allele is in the population
Define evolution
A change in allele frequency over time
Define differential reproductive success
Organisms with a phenotype better adapted to their environment have a selective advantage and are more likely to survive and reproduce
Define speciation
The process of forming a new species
What is the Hardy-Weinberg principle?
A model that predicts the frequency of alleles, genotypes and phenotypes in a population
What does the Hardy-Weinberg principle assume?
- No mutations- No selection- Random mating- Large population (no genetic drift)- Population is genetically isolated- No migration
What does the Hardy-Weinberg principle predict?
That the frequency of alleles of a gene will stay constant over generations
What are the two Hardy-Weinberg equations?
- p + q = 1- p^2 + 2pq + q^2
What is intraspecific variation?
Individuals of the same species have the same genes but different alleles and therefore variation in their phenotype
What is interspecific variation?
Individuals of different species have different genes and live in different environments leading to variation in their phenotypes
What is continuous variation?
- Variation is smooth and continuous- Represented on a line graph- e.g. height and weight
What is discontinuous variation?
- Individuals fall into discrete groups with no intermediates- Bar chart- e.g. blood type- Controlled by a single gene with a few alleles
What are the genetic causes of variation?
- Mutation- Meiosis (crossing over/independent segregation)- Random fertilisation - Inherited
What are the environmental causes of variation?
- Environment affects the phenotype constantly across an organisms lifespan- e.g. accent
How can variation be effected by both the environment and genetics?
- Most variation is a result of both environmental and genetic variation- e.g. height, height is controlled genetically but can be affected by childhood nutrition
What does genetic variation result in?
Evolution
What is speciation?
The process of forming a new species
When does speciation happen?
When populations become reproductively isolated therefore preventing gene flow
What is allopatric speciation?
Geographical isolation provides a geographical selection pressure which results in reproductive isolation preventing gene flow
What is sympatric speciation?
Non geographical selection pressures result in reproductive isolation preventing gene flow
What are the non-geographical isolation mechanisms that cause sympatric speciation?
- Morphological (different shaped genetalia)- Seasonal (reproductively active at different times of the year)- Behavioural (different courtship behaviour)- Hybrid sterility (hybrids of two parents are sterile
Why does speciation happen?
- Variation exists in the population due to mutations- Different selection pressures lead to the directional selection of different phenotypes- Differential reproductive success causes a change in allele frequency over many generations
What is genetic drift?
Change in allele frequency between generations due to random change e.g. random fertilisation
What size population does genetic drift have the biggest effect on?
Smaller populations
What does genetic drift change?
Allele frequency
What does genetic drift cause?
Evolution
Does genetic drift depend on the environment?
No
What does random fertilisation mean?
It is random which allele passes to the zygote
What is evolution?
The change in heritable traits of a population over generations
What are examples of genetic drift?
The bottleneck effect and the founder effect
What happens in disruptive selection?
Both phenotype extremes are more likely to survive and reproduce than the mean phenotype therefore the environment selects for two different phenotypes
What is disruptive selection the opposite of?
Stabilising selection
What does disruptive selection contribute to?
sympatric speciation
What is abundance?
- The number of individuals of a single species in an ecosystem/habitat - Population size
What is distribution?
Where a species is found in an ecosystem/habitat
What effects an organisms distribution and why?
Interspecific competition and predators will affect an organisms distribution because organisms will only exist where they can survive
How does intraspecific competition effect abundance?
Members of the same species occupy the same niche and therefore compete for everything
What is the carrying capacity?
The max stable population an ecosystem can support
What does abundance vary with?
Biotic and abiotic factors
What is a biotic factor?
- Living factor- e.g. food competition
What is an abiotic factor?
- Non-living factor- e.g. water, sunlight, soil, temp
How does interspecific competition effect abundance?
- Competition between species- Abundance of one species effects the abundance of another (predator-prey)
How can niches effect abundance?
Species with a similar niche will compete for resources
Where will the greatest population size be?
In an environment with optimal abiotic factors
What is a niche?
The role that an organism plays in an ecosystem
What is a biotic relationship?
Interspecific relationship e.g. what it eats and what eats it
What are examples of abiotic relationships?
- The shade it creates- The O2 it uses and the CO2 is produces - The use of minerals e.g. nitrates
Why dont two species share a niche?
Because they would compete for everything
Where species have similar niches, what happens?
Interspecific competition
How will the abundance of a species be affected by niches?
Abundance will be effected my interspecific competition therefore the more similar niches there are the greater the competition and the greater the effect on abundance
How will distribution be effected by niches?
Distribution will vary because an organism can only exist where its niche exists
What are transects and quadrats used for?
They are used to survey slow moving or immobile organisms e.g. plants
What are transects an example of?
systematic sampling
What do transects record?
How the distribution of plants species changes in a line
What is a line transect?
- Run a tape measure between two points- Record all species that touch the tape
What is a belt transect?
Use quadrats along the length of the transect
What is an interrupted transect?
Use quadrats at fixed intervals along the transect
What is a frame quadrat and how do you use it?
- Square frame divided into 100 sections- Random sampling to record the abundance of a plant species- Record the number of individuals of each species in the quadrat
What is the species frequency?
How often a species is found in each square
What is percentage cover and when is it used?
- Used if a square is more than 50% covered by a species- Faster- Dont have to count all individuals
Why do we use sampling techniques?
It may be impossible to count all the organisms of a species so we want to do many repeats of different samples to make them representative of a whole habitat/ecosystem so we can use the data collected to estimate the total number of individuals in the ecosystem
What factors go into deciding how many samples you carry out?
- Want the data to be representative- Larger numbers are more reliable- Too many is a waste of time and resources- Enough to carry out statistical tests - Calculating a running mean and then stopping sampling when the mean levels off
Why would you use random sampling?
- Avoid bias
How can you sample randomly?
Divide sampling area into a grid and pick co-ords with a . random number generator
What is an example of non-random sampling?
Systematic sampling where samples are taken at fixed intervals (transects)
What is mark - release - recapture?
A sampling method used to estimate the abundance of a mobile species
What is the equation for mark - release - recapture?
( Total no. caught in 1st sample X Total no. caught in 2nd sample ) / ( no. of marked in the second sample)
What is the method for mark - release - recapture?
- Capture organisms 2. Mark organisms in a way that will not harm them/ affect ability to feed/ increase chance of predation3. Wait long enough for them to mix with population but not too long (birth/death/immigration/emmigration)4. Take second sample using the same method5. Use equation
What is succession?
A series of changes in species composition in a given place over time
What starts succession?
An area is colonised by a pioneer species which changes the environment to make it less hostile e.g. by increasing the nutrients
What does a pioneer species allow for?
Continuous outcompeting by preceding species until a climax community is reached
What happens as succession takes place?
- Soil depth (hummus) increases- Water and nutrient availability increases - Biodiversity increases- Plant height increases- Niches increase - Light intensity at the ground decreases
What is a climax community?
- A stable equilibrium of species- Dominated by a few species- Final stage of succession
What are the four types of succession?
- Primary succession- Secondary succession- Deflected succession- Climax communities
What is primary succession?
- Starts from newly formed land (volcanic rock)- Harsh abiotic conditions (no soil/hummus/little water.little nutrients)- Very slow
What is secondary succession?
- Starts from land where vegetation has been cleared (deforestation/forest fire)- Less harsh abiotic factors (soil exists with some water and nutrients available)- Much faster- Pioneer species can be larger
What is a deflected succession?
- A community that remains stable only because human activity prevents natural succession taking place (mowing/grazing)- Stops succession (full plants cant grow because tips cut off/ cannot out compete low growing grass)- Grassland becomes the climax community
What is a climax community?
- Different ecosystems have different abiotic conditions so they develop different climax communities- Tropical rainforest/temperature deciduous forest
