Population: An Overview

Well from the title it must be clear what we are going to talk about in this article. So, let’s hop on and first get the definition of a population in ecological terms.

Population: A population is a group of individuals of a single species living in the same general area.

Members of a population generally rely on the same resources, are influenced by similar environmental factors, and are likely to interact and breed with one another. Here the same general area might refer to a natural boundary like an island or a lake, or they may be arbitrarily defined by the person observing it. Practically population is not a really great indication for research purposes, because it does not give an idea of the space in which they are distributed. Hence, to overcome this shortcoming, the term Population Density came into being. The Population density is the number of individuals per unit area or volume: the number of trees per square kilometer in a forest or the number of bacteria in a sample per milliliter in a test tube. Various methods are used to find the population density, some directly by counting all organisms within the boundaries by brute force, while others by more smart and efficient sampling techniques. Direct counting works for large mammals which live in herds or groups like elephants, while in most cases it becomes impractical due to the vastness of the area. In such cases, sampling techniques are used, for instance they might count the number of trees in several randomly located 100 * 100 m plots, calculate the average density in the plots, and then extend the estimate to the population size in the entire area. These estimates are most accurate when there are many sample plots and when the habitat is fairly uniform over its area.

One great example of such techniques is the Mark Recapture Method. In this, researchers typically begin by capturing a random sample of individuals in a population. They tag each individual and then release it. Then they wait for these individuals to mix back into their original population and then sample a second set of individuals. By comparing the number of common individuals in the first and second sampling we can get an estimate of the organism's population size. Although this method doesn’t account for individuals which have born, died, immigrated, or emigrated during the resampling interval, it gives a really great idea of the sample size into consideration.

Similarly, to understand and analyze populations better another term came into being-Dispersion. Dispersion is the pattern of spacing among individuals within the boundaries of the population. By dispersion we understand their distribution and social interaction amongst themselves. Dispersion is mainly of 3 types: Clumped, Uniform, and Random. As the name suggests, in clumped dispersion individuals are aggregated into patches, like plants or fungi. Insects and salamanders may be clumped under the same log because of the higher humidity there. A uniform pattern of dispersion may result from direct interactions (usually aggressive or competitive) between individuals in the population. Some plants secrete chemicals that inhibit the germination and growth of nearby individuals that could compete for resources. In random dispersion the position of each individual in a population is independent of other individuals. This generally occurs in the absence of strong attractions or repulsions among individuals or where key physical or chemical factors are relatively constant across the study area. Dandelions are great examples for the same.

So, we discussed 2 major components of a population, and there are many more such components of the same which shall be discussed in upcoming articles :)