Required Practical 12 - investigating a named environmental factor on the distribution of a given species

investigating the effect of an environmental factor on the distribution of a species in a habitat (random sampling) method

Divide two areas into grids/ squares e.g. place 2 tape measures at right angles

generate a pair of coordinates using a random number generator

place a quadrat on coordinate and count number of named species

standardise this e.g. only count it if it is more than half in the quadrat

repeat a large number of times over 20 and calculate the mean per quadrat for both areas

measure environmental factor in each area

why percentage cover may be used rather than frequency

too difficult to count individual organisms/ or too small to count

why random sampling is used

to avoid sampling bias

the importance of a large sample size

minimises the effect of anomalies

ensures sample is representative of the population

how you would decide the number of quadrats that should be used in order to collect representative data

calculate a running mean so when enough quadrats it shows little change

enough to carry out a statistical test

Investigating the effect of a factor on the distribution of a species in a habitat (systematic sampling)

Place a transect line across an area with an environmental gradient e.g. tree to full sun

place quadrats at regular intervals e.g. 1m and record number of organisms of a named species and a named environmental factor e.g. light intensity using a light meter

limitations of using systematic sampling to estimate the population of a species in a filed

not appropriate unless there is an environmental gradient

transects run in one direction but would need to be placed in multiple directions to cover entire field

statistical test used to determine the relationship

correlation coefficient