Changes in the environment - caused by various factors such as a lack of a usual food source - may affect the distribution and behaviour of organisms.

Changes in the environment affect the distribution and behaviour of living organisms. For example, humans have been cutting down trees for thousands of years. We do this to clear land for farming and building, and for wood to use as a fuel or building material. This deforestation can have local effects, such as a reduction in food and shelter for animals. It can also have more widespread effects, such as changes in rainfall and temperature. These changes may change the distribution of bird species, for example.

The animation shows how the numbers of predators (ladybirds) and their prey (aphids) can change over time. The graph would look fairly similar for any two populations of predators and prey.

The most common source of air pollution is the combustion of fossil fuels. This usually happens in vehicle engines and power stations. Sulfur dioxide is released if the fuel contains sulfur compounds. This gas contributes to acid rain. Lichens can be used as air pollution indicators, especially of the concentration of sulfur dioxide in the atmosphere.

In places where no lichens are growing, it is often a sign that the air is heavily polluted with sulfur dioxide.

clean -mayfly larva
low- freshwater shrimp
high- water louse
very high- rat-tailed maggot, sludgeworm

Rainfall is measured using a rain gauge. The depth of rain is usually measured daily, for example at the same time every morning.
A simple rain gauge consists of a funnel that empties into bottle. The daily contents of the bottle are poured into a measuring cylinder. This is calibrated so that it reads the depth of rainfall in millimetres.