In most ecosystems , the community is made up of many populations, each is consisting of individuals of the same species living in the same habitat at the same time. In population studies of a habitat, we investigate the following:
• the types (species) of organisms that are present;
• the dominant species; and
• the characteristics features of each population.
Types of organisms
This is a qualitative study which lists the various types of populations that are found in habitat. It helps us to work out the relationships that can possibly exist between the various organisms.
Dominant species
In any community, one or a few species are dominant over the others in numbers or size or both. These dominant species often exert a great influence on the habitat and other populations.
Size:
Population size is important as it affects the survival of a given species in a habitat. A small population may easily be wiped out by events such as fires, diseases , unfavourable climatic changes, etc. A large population stands a better chance of surviving dangers and unfavourable conditions. In addition, breeding produces greater variability in a larger population, resulting in an increase in its viguor, and hence its ability to withstand adverse conditions
Density:
Population density is the average number of individuals of a species per unit area of habitat. It can be used to estimate the total number of individuals of a population, i.e. population size, in a habitat in the following way:
Density x Area of habitat = population size
For Any population, there is an optimum density that can be reached in a given habitat under the operating environmental conditions.
Frequency:
The frequency of any species is simply how often the species occurs at different sites in the habitat.
Percentage cover:
Percentage cover is the area of ground covered or occupied by a given species in its habitat.
Distribution :
This refers to the way in which individuals of a particular population Are arranged in a given habitat. Generally, the individuals may be clumped , evenly spaced or randomly spaced.
The clumped distribution is a very common occurrence. Clumping in plants may be due to factors such as favourable soil conditions, germination conditions, and vegetative methods of propagation. In animals , clumped distribution, as seen in herds, offer protection from predators; and in termites it is due to the social structure.
Evenly spaced distribution In plants may occur when individuals of a species produce chemicals that inhibit the growth of other members of its species. Random spacing is very uncommon and can only occur if
• environmental conditions are the same throughout the habitat , and
• individual members of a species do not affect one another
Factors affecting populations
Population in a habitat often show changes especially in size and distribution. These changes are usually due to the following factors:
• migration of organism to other habitats;
• invasion or colonization by new species and
• increase or decrease in birth rates and death rates.
These factors operate during
• seasonal climatic changes ;
• changes in food availability;
• breeding periods; and
•unfavorable natural events such as fires and droughts.
