B1Jimmy4.2

Front 1

4.2.1 Outline how population size can be affected by natality, immigration, mortality and emigration.

Back 1

If (natality + immigration) > (mortality + emigration) then a population is increasing. These factors determine whether a population is increasing or decreasing.

Front 2

4.2.2 Describe the growth curve of the sigmoid (S-shaped) population.

Back 2

It sets off an exponential function and fluctuates steadily at the top.

Front 3

4.2.3 Explain reasons for the exponential growth phase, the plateau phase and the transitional phase between these two phases.

Back 3

During the Exponential phase the population increases exponentially because the natality rate is higher than the mortality rate. The resources needed by the population such as food and space are abundant, and diseases and predators are rare.
During the Transistional Phase, the birth rate begins to decrease. Natality is still larger than mortality, but the difference between them is slowly decreasing.
During the Pleateau phase, available resources become so low that no further reproduction can take place. Mortality starts to become larger than natality. A species may have reached its Carrying Capacity.

Front 4

4.2.4 Define 'carrying capacity.'

Back 4

The carrying capacity is the number of individuals the environment can normally support.

Front 5

4.2.5 List three factors which set limits to population increase.

Back 5

Resources availability
Disease
Space availability
Predators

Front 6

4.2.6 Define ‘random sample.’

Back 6

A sample where every individual in a population has an equal chance of being chosen.

Front 7

4.2.7 Describe one technique used to estimate the population size of an animal species based on a capture-mark-release-recapture method.

Back 7

One method of estimating the population size of an animal species is the capture-mark-release method.
1. As many individuals of a population are caught. These individuals are marked.
2. The individuals are released back into their environment.
3. After a while, as many individuals of a population are caught in the same area again.
4. The total number is taken note of and the number of those caught which are marked

Front 8

4.2.8 Describe one method of random sampling used to compare the population numbers of two plants species, based on quadrat methods.

Back 8

1. Mark out gridlines along two edges of the area.
2. Use a calculator or tables to generate two random numbers, to use as co-ordinates and place a quadrat on the ground with its corner at these co-ordinates.
3. Count how many individuals there are inside the quadrat of the plant population being studied. Repeat stages 2 and 3 many times as possible.
4. Measure the total size of the area occupied by the population, in square meters.
5. Calculate the mean number of plants per quadrat. Then calculate the estimated population size using equation: population size = (mean number per quadrat x total area) / area of each quadrat.

Front 9

4.2.9 Calculate the mean of a set of values.

Back 9

Mean = Total sum of values / number of values

Front 10

4.2.10 What is standard deviation?

Back 10

Standard deviation is used to summarize the spread of values around the mean and that 68% of the values fall within ±1 standard deviation from the mean.

Front 11

4.2.11 Explain how the standard deviation is useful for comparing the means and the spread of ecological data between two or more population.

Back 11

A small standard deviation indicates that the data is dispersed closely around the mean value. Conversely, a large standard deviation indicates a wider spread around the mean. Details of statistical tests to quantify variations between populations, such as standard error, or details about confidence limits are not required.