Frequency - Synthetic Characters
This term refers to the degree of dispersion of individual species in an area, and is usually expressed in terms of percentage. Frequency can be studied by sampling the study area at several places at random or in a desired pattern, so that the site is covered adequately and the names of the species that occur in each sampling unit are recorded. Let us now see how frequency of a species is determined. Consider a species that occurs in five sampling units out of a total of 20 sampling units, and then its frequency (F) is 25%. It is calculated by the following formula:
F = (Number of sampling units in which that species occurred /Total number of sampling units studied) * 100
A species most abundantly spread all over the area will have chance of occurring in all the sampling units, and therefore, its frequency will be 100%. A poorly dispersed species, with large number of individuals aggregated in one place will have a chance of occurrence in only a few sampling units and its frequency value will be low. Thus a high frequency value shows a greater uniformity of its dispersion. Have you noticed that for determining the frequency, the presence or absence of a species in the sampling units is recorded and not the number of individuals of each species, and thus, you should be able to differentiate it from density for which the number of individuals per unit area is recorded. 'Frequency of a species relative to other species in a community is called relative frequency, and is calculated as:
Relative Frequency = (Frequency of a species /Total frequencies of all species) * 100