Changes in the size of populations of animals and plants can show how successful a particular management system has been in providing a good habitat for wildlife.
Can also check for abiotic changes which may affect wildlife.
Abiotic factors are tested in the following ways:
Abiotic Factor How is it Measured?
Light intensity Light meter
Temperature Thermometer or thermistor
pH Soil pH test or electric probe and meter
Oxygen Oxygen probe and meter
Relative Humidity Hydrometer
Levels of ions Soil test or electric probe and meter
Soil moisture or soil humus Soil tests
Organisms are also sampled, can't identify every organism present, so representative samples are taken, either with random or systematic sampling.
Study area is divided into a grid system
Random numbers are used to get coordinates
Each number has an equal chance of being chosen
A sample is taken at each coordinate
Assumes that the coordinates are representative of the whole ecosystem
Ensures that every organism has an equal chance of being sampled, removing any sampling bias.
Area is divided into a grid
Sampling points are located at regular intervals
Many samples should be taken from each grid to increase reliability
Can lead to sampling bias (choosing coordinates where they think there will be more interesting things to sample)
At sampling points, biotic factors can be sampled in the following ways
Technique Method Organisms sampled
Quadrat sampling Mark out area with frame Animals and plants within the area
Transect sampling Study along a marked line Organisms where abiotic changes occur along the transect
Sweep netting Sweep net through water Freshwater organisms or or plants (eg. Grasses) flying insects
Kick sampling Kick stones on river bed Freshwater invertebrates catch with a net downstream
Trapping Pitfall/ longworth/ light traps Crawling insects/ small mammals/flying insects
Square frame, sometimes divided into subsections with string or wire.
Placed on ground at sampling point. Species and their abundance within the quadrat are recorded.
Mean density = total number of individuals counted number of quadrats x area of each quadrat
Percentage cover = estimate of the area within the quadrat that that species covers
Abundance scales = give the relative abundance of a particular species, but can be subjective
Has vertical legs, across which is a horizontal bar with 10 small holes.
Long pins are placed in each hole.
Each time a pin touches a species it's recorded as a 'hit'
Hit values are converted into percentage cover
Useful when vegetation is dense as they can sample at different levels
Used where conditions and organisms change over a distance
Tape is stretched across the habitat
Quadrat samples are taken at regular intervals along the line (systematic sampling)
Reliabilty is improved if more than one transect is used
Line transect = records the organisms that lie underneath the string or tape
Belt transect = a strip 0,5 - 1 meter wide placed along the study area. The species within the belt are recorded. Alternatively quadrat samples are taken at regular intervals along a transect (systematic sampling).
If the transect is short, sampling can be continuous along it's length, if it's too long for that then samples are taken at intervals.