populations + succession

define population

all the organisms of one species in one area at one time

define community

all the organisms of ALL species in one area at one time

define habitat

the place an organism lives

define niche

the role of an organism in its ecosystem

define ecosystem

the interaction between all the abiotic and biotic factors

what are the 2 ways in which a population can be estimated?

• randomly placed quadrats/ quadrats placed along a belt transect (for slow moving/ non-motile organisms)

• mark-release-capture method for motile organisms

when is random sampling used?

when you want to work out the average population of an area or compare the average of two areas

when is systematic sampling usually used?

When you want to investigate the change in a communities/population over a distance/area

Describe how you would randomly sample an area to estimate the population of stinging nettles in a field

• Create a grid on the field (or on a map of the field)

• Use a calculator to generate random numbers that are used as coordinates

• Place the quadrate at the intersection of the coordinates

• Estimate the abundance of nettles in the quadrat (e.g. using % cover)

• Repeat many times so that the mean abundance calculated per quadrat is reliable

• Multiple the number of plants per quadrat BY the number of times the quadrat fits into the total are of the field in order to work out the population in the whole field

Describe how you would systematically sample an area to investigate the effect of distance from a river on the population of a specific plant

• Place a transect at 90 degrees to the river

• Place a quadrat at regular intervals along the transect

• Estimate the abundance of the plant in the quadrat (e.g. using % cover)

• Repeat the process with many transects which are parallel to each other

• Plot a graph of distance on the x-axis against population of plant on the y-axis

• Use spearman rank correlation to see if there is a significant correlation between them

How can a quadrat be used to measure percentage cover?

Count the number of small squares that are half or more filled with the plant

Work out what % each square is of the whole quadrat

Then multiply the number of squares half or more filled by the % each square is worth

What are the limitations of using percentage cover as a measure of abundance?

It is quite subjective

What are the advantages of using percentage cover as a measure of abundance?

• It is quick and easy to do.

• You don’t have to be able to identify individual plants

How can a quadrat be used to measure frequency of a plant?

Count the number of plants present in the quadrat

What are the limitations of using frequency as a measure of abundance?

• It is time consuming

• It cannot be used if you cannot identify individual plants

What are the advantages of using frequency as a measure of abundance?

It is an accurate way of measuring abundance

Write the equation for mark-release-recapture

(Number of organisms caught in 1st sample x no of organisms caught in 2nd sample)

DIVIDED BY Number of organisms marked in 2nd sample

Describe how you would use mark-release-recapture to estimate the population of bees in a county in the UK.

• Capture a sample of bees

• Count them

• Mark them in a way which does not affect their ability to survive (e.g. using a fluorescent powder which wouldn’t affect the rate of predation OR recapture)

• Release the bees, allow them to disperse and mix back into the population

• Capture a second sample

• Count the total second sample

• Count the number of marked bees in the second sample

• Use the equation to estimate population size

• Take large samples to improve reliability

What are the assumptions of the mark-release-recapture methodology?

• No births and no deaths occur between the first and second sample

• No emigration or immigration occur between the first and second sample

• The first sample have time to mix fully into the population before taking a second sample

• The mark doesn’t wear off and doesn’t affect the organisms ability to survive

How would a scientist decide how many repeats to carry out if they are doing random sampling to find out the population of a plant in a field?

• Calculate a running mean as they collected each sample

• Enough samples have been collected when the running mean becomes constant

How would a scientist decide how many repeats to carry out if they are using quadrats to randomly sample an area to find out the number of species present

• Plot a graph with number of repeats (quadrats) on the x-axis and total number of species found on the y-axis

• When the line levels off this means that new samples are not finding any new species, so stop collecting samples

How would a scientist decide how long to sample an area if they are random sampling to find out the number of species present in a number of areas

• Sample for a known period of time and record how many species are found

• Repeat for different periods of time

• Select the optimum time beyond which further sampling doesn’t lead to any new species being found

What are abiotic and biotic factors? Give examples of each

• Abiotic factors are non living factors e.g. temperature, pH, oxygen concentration, wind level, humidity, light intensity etc etc

• Biotic factors are living factors e.g. food availability, competition, predation

what is intraspecific competition? what might organisms compete for?

Competition between organisms of the same species

• Food, water, mates

what is interspecific competition? what might organisms compete for?

Competition between organisms of different species

• E.g. Food, water, nesting sites

What is meant by the competitive exclusion principle?

• The fact that no two species can occupy exactly the same niche.

• If two species use the same niche then one species will always outcompete the other

one

Sketch a population growth curve (x-axis = time and y-axis = population size) showing the lag

phase, exponential growth phase, stationary phase and death phase.

Annotate the graph explaining what happens at each of the 4 key stages.

What is the carrying capacity in a population?

The carrying capacity is the maximum population size that an ecosystem can support

Sketch a graph to show how the sizes of a predator and prey population vary over time.

Your graph should show 3 complete cycles

Annotate the graph to explain the changes in population sizes: