Density - Population Parameters and Regulation
Density is defined as number of individuals or population biomass per unit of area or volume at any given time. Biomass refers to the total weight of all the organism or of a specific group of organisms in a given area. Density is generally expressed in terms of biomass when the size of individuals in a population is quite variable. This measure of number or biomass of individuals per unit total area is called crude density. However populations do not occupy all the space within the unit area because whole of it is not a suitable habitat.
Each organism occupies only areas that can adequately meet its requirements, resulting in patchy distribution. No matter how uniform a habitat may appear, it is not uniformly habitable, sometimes because of even micro differences in light, moisture, temperature etc. Density, thus measured in terms of the amount of area as habitat or living space is ecological density.