Lesson 1 of 13 · 6 min

Ecology and populations

NCERT §11.1, §11.1.1

Rohan's biology teacher in Pune pins a notice on the board: 'Lake survey, every Saturday this term. Bring a notebook and patience.' Rohan signs up first.

The story this chapter follows: Rohan's Saturday lake survey

Rohan, a Class 12 student in Pune, joins his biology teacher's Saturday survey at a lake near school. Week by week the group counts lotus plants and birds, argues over weeds and a banyan, watches egrets and koels, and reads about starfish, barnacles and fig wasps from other shores. Each Saturday is one part of this chapter.

The lesson in notes

In short

Life can be studied at many levels of organisation: macromolecules, cells, tissues, organs, individuals, populations, communities, ecosystems and biomes.

At every level two kinds of question can be asked. A 'how' question looks for the mechanism (how does a bulbul sing? its voice box and a vibrating bone). A 'why' question looks for the significance (why does it sing? to reach its mate in the breeding season).

Ecology studies how organisms interact with one another and with their physical, abiotic surroundings.

It works at four levels of organisation: organisms, populations, communities and biomes. This chapter stays at the population level.

A population is a group of individuals of one species living in a well defined area, sharing or competing for similar resources, and able to interbreed.

For ecological study, a group produced by asexual reproduction also counts as a population.

Examples: all the cormorants of a wetland, rats in an abandoned house, teak trees in a forest tract, bacteria on a culture plate, lotus plants in a pond.

An individual has to cope with a changed environment, but natural selection works at the level of the population. So population ecology connects ecology with population genetics and evolution.