Genetics, populations, evolution and ecosystems Flashcards
Why may genetic variation arise?
- mutation (sudden change to genes or chromosomes)
- meiosis (new combinations of alleles)
- random fertilisation of gametes (new combinations of alleles which are different to parents)
What are the environmental influences on variation?
- climatic conditions (temperature, rainfall, sunlight)
- soil conditions
- pH
- food availability
What in most cases is variation due to?
In most cases variation is due to combined effects of genetic differences and environmental influences
What is continuous variation?
e.g height, body mass
What is discontinuous variation?
e.g eye colour, blood type
What are selection pressures?
environmental factors that limit population of a species - predation, disease and competition. They determine the frequency of alleles within a gene pool
What is a gene pool?
total number of alleles of all the genes of all the individuals within a particular population at a given time
What factors does evolution by natural selection depend on?
- organisms produce more offspring than can be supported by available supply of food, light, space
- genetic variety within the populations of all species
- variety of phenotypes that selection operates against
What does a larger population lead to in terms of genetic differences?
The larger the population and the more genetically varied the individuals are, the greater the chance that one or more offspring will have a combination of alleles that is advantageous for survival
What is stabilising selection?
preserves the average phenotype (ones around the mean)
What is directional selection?
favours phenotypes that vary in one direction from the mean (selection for extreme phenotype)
What is disruptive selection?
favours individuals with extreme phenotypes rather than those around the mean
What is allelic frequency?
the number of times an allele occurs in a gene pool (affected by selection)
What are the effects of environmental changes on alleles?
Environmental changes affect the probability of an allele being passed on and hence the number of times it occurs in a gene pool
What is speciation?
the evolution of new species from existing ones
What is a species?
group of similar organisms that can breed to produce fertile offspring (members of a species are reproductively separated from another species)
Why does genetic drift take place in small populations?
takes place in small populations because a small population possess a smaller variety of alleles compared to a large population
What is genetic drift?
Small number of alleles in the population thus not an equal chance of each being passed on, those that are passed on will affect the whole population. This means that the population will change very quickly, making it more likely for new species to develop.
What is allopatric speciation? + examples
when two populations become geographically separated by a physical barrier e.g oceans, rivers, mountains, deserts. leads to reproductive separation and formation of different species
What is sympatric speciation? + examples
speciation within a population in the same area becoming reproductively separated e.g seasonal isolation (reproducing a different times of year), temporal isolation (reproduce at different times of day), behavioural isolation (different courtship patterns).
What is a community?
all the populations of different species living and interacting in the same place at the same time
What is an ecosystem?
Interaction between living (biotic) and non-living (abiotic) factors in a given area e.g a lake
What is a population?
group of individuals of one species that occupy the same habitat at the same time and are able to interbreed.
What is a habitat?
where an organism lives and this is characterised by physical conditions
What is an ecological niche?
niche→ all biotic and abiotic conditions of the environment which organisms are adapted to
What is carrying capacity?
maximum population size that can be maintained over a period in a particular habitat
What are the abiotic factors that limit carrying capacity?
- Temperature + pH: anything but optimum can reduce population growth
- Light
- Water: reduced population if low water availability
What are the biotic factors that limit carrying capacity?
- Interspecific competition (between different species for food, light, water)
- Intraspecific competition (within the same species for food, water + breeding sites)
- Predation
What are the 2 methods that can be used to estimate the size of a population?
- Using quadrats and counting no of individuals in each species or percentage cover
- Mark-release-recapture for moving organisms, assumes there is no death, births, migration + marking has no effect
How is population size calculated?
-Population size = sample 1 size x sample 2 size / no of marked in sample 2
What is succession?
variety of processes that occur over time in a species that occupy a certain area
What occurs in primary succession?
progressive colonisation of bare rock/barren terrain by living organisms
First the area is colonised by a pioneer species, making the abiotic factors less hostile for other species to live there
Different species could be present at each stage, changing the environment so it is more suitable for other species, which changes the biodiversity
Then a climax community is reached
What is a climax community?
when a stable state is reached, high biodiversity and high number of new species
What is secondary succession?
recolonisation of an area after an earlier community has been removed or destroyed
What is conservation?
maintenance of biodiversity, between species, genetic diversity + habitats/ecosystems
What does conservation involve?
Involves humans by managing community through stopping succession occurring, to save species that would become extinct by the climax community being established
What does there need to be a balance of to maintain human resources?
between conservation and human needs
