Population

“Populus” in Latin means people from which the term population has been derived. In 1954, Clarke suggested two kind of population:

1.     Mixed or Poly-specific population: sometimes even called as Community where group of different species constitutes a population.

2.     Mono-specific population: is where grouping of same species constitute a population.

Population characteristics

An organism can never live in absolute isolation therefore, interacts and form groups. Even if an individual lives an isolated life, at some time point it may interacts with other species during his entire life cycle. Thus each species at some time point exist as population. All individuals constituting the population get a chance to reproduce with other group members of same species. Thus, a population can be interpreted as a group of species occupying a particular space at certain time where each species is potentially interbreeding with other members of the group belonging to same species.

Local population

Several demes or sub-populations constitute the organism population termed as local population. The smallest and interbreeding group of animal population is termed as “Deme”. Each interbreeding individual in a local population carries certain genetic combinations and share a common gene pool called as genetic unit of a population. Between different populations the genetic information is exchanged through certain group characteristics called immigration or emigration.

When the local population accumulates genetic variations it leads to genetic differentiation and further support a phenomenon called evolution.

Unitary organism is an eminent single unit of organism such as fish, cat, dog etc. but some organisms are called modular organisms, for instance, some grasses, suckers where many suckers are attached together with their root extensions (just like adventitious roots of one plant will give rise to another plant nearby). The individual and a population have different set of characteristics thus, the group characteristic of a population, “density” is a basic feature highly influencing by the rate of emigration, immigration, mortality and natality. Additionally, dispersal and dispersion as a pattern distribution and age distribution are the secondary characteristics of collective group of individuals constituting population.

Thomas Park, an ecologist, states that statistical functions define group characteristics of a population which are not applicable on unitary unit called organism.