question_answer 18)

List any three important characteristics of a population and explain. 

Answer:

The three important characteristics of a population are: (i) Birth and death rate (ii) Age structure (iii) Sex ratio (i) The birth rate (natality) of a population refers to the average number of young ones produced by birth, hatching or germination per unit time (usually per year). In the case of humans, it is commonly expressed as the number of births per 1,000 individuals in the population per year. The death rate (mortality) of a population is the average number of individuals that die per unit time (usually per year). In humans, it is commonly expressed as the number of deaths per 1,000 persons in a population per year. (ii) The age structure of a population is the percentage of individuals of different ages such as young, adult and old. Age structure is shown by organisms in which individuals of more than one generation coexist. Only organisms in which all adults produce at about the same time and then die, such as annual plants and many insects, do not have coexisting (overlapping) generations. The ratio of various age groups in a population determines the current reproductive status of the population. It also indicates what may be expected in the future. Bodenheimer was the first ecologist to propose three major age groups in any population. These age groups are pre-reproductive, reproductive and post-reproductive also commonly referred to as ecological ages. (iii) The sex ratio of a population refers to the number of females and males per thousand individuals. There were 933 females per 1,000 males in our country in 2001. In animals, males and females are usually in equal numbers. The number of females in a population is very important as it is often directly related to the number of births. The number of males may be less significant because in many species a single male can mate with several females.