Monitoring and Maintaining the Environment

The number of individuals of a species in an area.

Where in a habitat a species is found.

Counting every organism is impossible and may damage the habitat.

A square frame that marks off a known area for counting.

To avoid bias, so that the sample is representative of the area.

With a random number generator or random number tables, giving coordinates on a grid.

For plants that cannot be counted as individuals, such as grass or moss.

A line laid across a habitat, along which samples are taken.

When there is a gradient in the environment, to show how the distribution of organisms changes.

Any two of light intensity, soil moisture, pH and temperature.

Collecting small insects by sucking them into a jar without harming them.

Small animals that walk on the ground, such as beetles.

A set of paired statements that leads to the name of an organism.

Add up the values and divide by the number of values.

The more quadrats there are, the less an unusual result affects the mean.

The median, the value below which half of the results fall.

Describe how this method is used to sample the abundance of a plant in a field.

Lay tape measures along two sides to make a grid. Use random numbers as coordinates, place a quadrat at each, count the daisies in it and repeat at least 10 times. Then calculate the mean.

What does this transect show about the distribution of the daisies?

The number of daisies rises with distance from the hedge, from 1 per quadrat next to it to 8 at 10 m. This could be because there is more light and water away from the hedge.

The number of quadrats that would fit in the whole area.

Total area divided by the area of one quadrat.

0.25 square metres.

16.

To estimate the population of animals that move about.

They are counted, marked and released.

So the marked animals can mix with the rest of the population.

The total number caught, and how many of them are marked.

Population = (first sample × second sample) ÷ number of marked animals in the second sample.

A small dot of non-toxic paint on the shell.

No births, deaths or movements between samples, and the marks stay on and are harmless (any two).

Fewer marked animals are found, so the population is overestimated.

A small change in the number counted has a big effect on the estimate.

The quadrats may land on more patches or fewer patches than average.

Use larger samples or more quadrats, and repeat and take the mean.

To estimate fish numbers so that they can set sustainable catches.

Describe what is done at each of steps 1, 2 and 3, and how the population size is found.

1 Catch 20 animals, mark them and release them. 2 Wait for them to mix with the population. 3 Catch another sample, of 30, and count those that are marked, which is 6. Population = 20 × 30 ÷ 6 = 100.

The variety of living organisms in a habitat, or on Earth.

Building, farming, quarrying and draining wetlands (any three).

The clearing of large areas of forest.

The habitats and food of many species are destroyed.

They hold more than half of all species, though they cover a small part of the land.

The passenger pigeon.

Catching fish faster than they can breed.

Fertiliser or sewage running into water, which supplies extra nutrients.

The algae block the light, so they cannot photosynthesise.

Bacteria that decompose the dead plants use up the oxygen in the water.

A species brought by humans to a place where it did not live before.

It competes for food and carries a disease that kills red squirrels.

Nature reserves, captive breeding, habitat restoration, laws (any two).

Breed rare animals so they can be released into the wild.

It bans international trade in endangered species.

Species are interdependent, for example as food or shelter.

Describe how fertiliser from a field can lead to the death of fish in a pond.

Fertiliser runs into the pond and the algae grow fast. They block the light, so the plants die. Bacteria decompose the dead plants and use up the oxygen, so the fish suffocate.