Question

Give four attributes of a population. Explain in detail the process of mutualism.

Answer 1

A population has certain attributes that an individual organism does not possess. Followings are some important attributes of a population:

• Birth and death rates: These rates express the change in number (increase or decrease) of the population. These rates refer to per capita births and death, respectively. A population has both birth and death rates but an individual may have birth and death only, not the birth and death rates.
• Sex ratio: Another attribute characteristic of a population is sex ratio. An individual is either a male or female but a population has a sex ratio i.e. a population has both males and females. For example, if in a population of 1000 individuals, 600 individuals are female and rest of them are males then there is 60:40 sex ratio for females to males.
• Population age: A population at any given time is composed of individuals of different ages: pre-reproductive, reproduction and post-reproductive. The representation of population age is carried out by the construction of age pyramids. An age pyramid is a graphic representation of the population of the proportion of various age group of a population. The shape of the pyramids reflects the growth status of the population. These are three types of age pyramids.

• Population density (N) or population size: The size of the population tells us a lot about its status in the habitat. Change in population size is used to evaluate various ecological processes like an outcome of members of one species with another species, the impact of a predator or the effect of a pesticide application.

Mutualism confers benefits on both the interacting species. It is an obligate association of two organisms often lives together and cannot live separately. Some of the examples of mutualism are:

1. Lichens: It is a mutualistic relationship between a fungus and photosynthesising green algae or cyanobacteria (blue-green algae). Algae (phycobiont) produced food through photosynthesis where fungi (mycobiont) absorb nutrients from the soil.
2. Mycorrhizae: This is a mutualistic relationship between fungi and roots of higher plants. Fungi absorb essential nutrients from the soil while the plant, in turn, provides energy-yielding carbohydrates to the fungi.

• Plant-animal mutualism: Plants need the help of animals for pollination their flowers and dispersing their seeds. Plants often reward in the form of pollen and nectar for pollinators and juicy and nutritious fruits for seed dispersers.