Populations and communities

When you looked at the pond in Activity 12.1, did you see just one fish? Most likely you saw many of the same kind. A group of fish of the same kind living together in a pond is a population of that fish.

Count a population (Activity 12.2). Divide into four or five groups; each group picks any two organisms, plants or animals. Mark an area of 1 m × 1 m in your school garden, identify four organisms in it, count them, record the numbers in Table 12.2, and put together the data from all the groups.

The book's example finds 20 of one plant and only 5 of another in the same square. So a population is a group of the same type of organism in a habitat at a given time. Remember the three sames: same kind, same place, same time.

Could a habitat hold only one type of organism? Think it through. All of them would need exactly the same things (food, water, space), which would lead to competition and a possible shortage of resources.

In real habitats, different groups live together. A community is made of different populations sharing the same habitat. A pond community has a fish population, a frog population, plant populations, insect populations…

The biotic components of a habitat, its plants, animals and microorganisms, together form the community. They interact and depend on one another to survive.

One kind of dependence is worth knowing in detail. A flower has a stalk, green leafy sepals, coloured petals, and two reproductive parts: carpels (female) and stamens (male). Stamens burst and release yellow, dust-like pollen grains. Wind, water, insects, bats and birds carry the pollen from stamens to carpels, of the same flower or a different one. This is pollination, and fruits and seeds can't form without it.