Measuring Biotic and Abiotic Factors in an Ecosystem

Measuring Biotic and Abiotic Factors in an Ecosystem

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Why measure?

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.

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Sampling Techniques

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.

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Random 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.

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Systematic Sampling

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)

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Sampling Techniques

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

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Frame Quadrats

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

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Point Quadrats

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

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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.

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