© SSER Ltd.

Ecological Techniques A variety of universal practical approaches exist for investigating the biotic and abiotic components of ecosystems Field ecologists investigate communities by using random sampling techniques that aim to: eliminate bias reduce the effects of chance minimise errors in obtaining measurements/samples Quadrat and transect sampling are commonly used methods for investigating distribution within plant communities and the more sedentary populations of animals such as those found inhabiting seashores

Quadrats Frame quadrats are wooden or metal frames of known area (e.g m 2, 0.5 m 2, 1.0 m 2 ) and are generally square-shaped Various approaches are used to determine the representation of species within an area: Species population density (number of individuals per square metre) is determined by counting all individuals within a series of randomly placed quadrat frames and calculating the mean Percentage cover is determined subjectively by assessing the extent to which different species occupy subdivided quadrat frames or by the use of point quadrat frames Frequency of occurrence of a species is determined using subdivided quadrats and point quadrat frames

Quadrats Square quadrat frame for determining population densities Subdivided quadrat frame for determining % cover of species Quadrat frames, constructed from wood or metal, are used to investigate the distribution of species

Point Quadrat Frame Metal pins are dropped through each hole in turn and ‘hits’ are recorded No. of hits % Cover = x 100 Total no. of pins

Random Sampling The validity of results obtained from the various sampling methods is dependent upon the adoption of random sampling techniques Strategies for avoiding bias through random sampling utilise a number of approaches – these include random sampling using a grid A grid is created by laying out tapes at right angles to one another to form the axes of the gridded area Pairs of random numbers are used to provide the coordinates for locating quadrats

Tapes are laid out at right angles to one another and form the axes for locating quadrats (the size of the grid depends upon the area being investigated) Pairs of random numbers are generated on a calculator or computer and used as coordinates for the location of quadrats

This quadrat has coordinates X09, Y06

Transects A transect is a line, created with string or a tape, along which systematic sampling is performed Transects are particularly useful for sampling areas where there is a transition of species from one habitat to another as environmental conditions change Transect studies are used to investigate gradients such as zonation on rocky shores and changes in the species diversity across sand dunes A line transect is one in which all individual organisms touching the tape/string are recorded The most commonly used belt transect involves laying a tape through the area of study and sampling the population with quadrats positioned at regular intervals alongside the tape

Belt transect Survey of a Dune System A belt transect was used to investigate the distribution of three species of grass commonly found on sand dunes The transect line stretched from the high water mark to the inland area and 1m x 1m quadrats were used to determine the number of individual plants of each grass species along the profile

Present the results as a bar chart