There should always be a large number of samples (at least 10, and preferably 100) to minimise the chance of picking a skewed sample and to allow for bad measurements or anomalies. One should aim to sample at least 2% of the total area, so if the field area was 500m2, you would need to sample 10 m2 of the area altogether.
Random sampling -Used when you want a representative sample of the whole area under study. Measuring tapes are placed along two sides of the area, like axes of a graph, and random numbers (from tables or a computer) are used as coordinates to choose sampling points in the area. Alternatively, random numbers can be used as polar coordinates (angle and distance) starting from a central point.
Systematic sampling -Used when you choose where to take your samples, because you are investigating a specific pattern in the ecosystem. The most common kind of systematic sample is a transect, where samples are taken along a straight line to see what changes there are along the line. The transect usually follows an environmental gradient, such as down a rocky shore, into a forest or down a mountain side. The transect could be a few metres long or a few 100 km long. In a line transect the organisms touching a piece of string stretched along the transect are recorded. In a belt transect quadrats are placed at intervals along the transect and organisms in each quadrat are counted. The line transect is quick but can be unrepresentative while the belt transect involves more work, but can generate more complete data.
Biosphere The part of the planet Earth where life occurs, including land, sea and air.
Ecosystem A reasonably self-contained area together with all its living organisms, e.g. oak forest,deep sea, sand dune, rocky shore, moorland, hedgerow, garden pond, etc.
Habitat The physical or abiotic part of an ecosystem, i.e. a defined area with specificcharacteristics where the organisms live. Most ecosystems have several habitats.
Microhabitat A localised specific habitat within a larger habitat e.g. under a rotting log, in a rock pool,etc.
Terrestrial An ecosystem on dry land
Aquatic An ecosystem in water
Marine An ecosystem in the sea
Community The living or biotic part of an ecosystem, i.e. all the organisms of all the different species living in one habitat.
Biotic Any living or biological factor.
Abiotic Any non-living or physical factor.
Population The members of the same species living in one habitat.
Species A group of organisms that can successfully interbreed