populations Flashcards
A community can be defined as:
All populations (of different species) living and interacting in the same area
An ecosystem can be defined as:
The interaction between a community (the living, biotic part) and the non-living (abiotic) parts of the environment
explain niche
The role that a species plays within its habitat is known as its niche, including:
The biotic interactions of the species (e.g. the organisms it feeds on and the organisms that feed on it)
The abiotic interactions (e.g. how much oxygen and carbon dioxide the species exchanges with the atmosphere)
name some abiotic factors that could effect population size
light availability
water supply
temperature
amount of space available
soil pH
problems with systematically sampling
In systematic sampling the positions of the sampling points are chosen by the person carrying out the sampling
There is a possibility that the person choosing could show bias towards or against certain areas
Individuals may deliberately place the quadrats in areas with the least species as these will be easier and quicker to count
This is unrepresentative of the whole area
The group of biologists could determine the present-day mean percentage cover of grass on the island by:
Using quadrats; [1 mark]
Method of randomly determining position (of quadrats) given; [1 mark]
Eg. a random numbers table / random number generator
Many/multiple/large number/sample of quadrats; [1 mark]
Divide total percentage by number of quadrats/samples/readings; [1 mark]
Features of a climax community include:
The same species are present (over long time) OR there is a stable community (over long time); [1 mark]
Abiotic factors (are more or less) constant (over time); [1 mark]
Populations are stable (overall) OR populations are (more or less) at carrying capacity; [1 mark]
outline mark and release
Capture/collect a sample (of beetles), mark them and release; [1 mark]
Method of marking does not harm the beetles OR make the beetles more visible to predators; [1 mark]
(Release and) leave sufficient time for the (marked) beetles to (randomly) distribute (on island) before collecting a second sample; [1 mark]
maths equation [1 mark]
The conditions required for the results from a mark-release-recapture to be valid include:
Marking (of organisms/beetles) is not removed/worn/rubbed off; [1 mark]
Marking (of organisms/beetles) does not affect survival/predation OR marking does not make (organisms/beetles) more visible to predators; [1 mark]
Sufficient time given for (marked) individuals to mix (within the population) OR sufficient time given for mixing to occur between samples; [1 mark]
Sampling method is the same OR organisms/beetles caught in the same way each time; [1 mark]
Limited/no immigration/emigration/migration (into or out of population); [1 mark]
Limited/no births OR limited/nodeaths OR limited/nobreeding; [1 mark]
explain a graph on predator prey relationships
Mice/prey increase in number when stoats/predators are low in number because there is less predation OR Mice/prey decrease in number when stoats/predators are high in number because there is more predation; [1 mark]
When mouse/prey population is high, stoat/predator population increases because there is less (intraspecific) competition for food; [1 mark]
(There is a) time lag in increase in predators due to time for reproduction; [1 mark]
The population growth of P. aeruginosa when grown with P. fluorescens would differ if it were an anaerobic organism because:
It would not compete for oxygen OR It could tolerate higher CO2 concentrations; [1 mark]
So it could have faster population growth; [1 mark]
There would be less interspecific competition; [1 mark]
The scientists could obtain data on seed dispersal by this tree in the open field by:
Using a line transect; [1 mark]
The scientists would then place quadrats at regular intervals along the transect; [1 mark]
The number OR frequency of seeds can be counted in each quadrat; [1 mark]
The number of quadrats placed must be large enough to make the investigation representative and to remove the effect of anomalies; [1 mark]
The scientists can ensure reliable results by repeating the experiment at different locations from the tree; [1 mark]
[Total: 4 marks]
3 statistical tests in biology
There are 3 statistical tests that are in the specification; the correlation coefficient test which determines if there is a correlation between two variables; the Student’s t-test which determines if there is a significant difference between two means; and the Chi2 test which is used to determine the significance of the difference between observed and expected results.
