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Unlock This CourseEvery species lives where its needs are met. If the environment changes, the places where a species can survive change too. Some individuals die, some move away and some arrive from elsewhere. The result is that the distribution of the species (where it is found) changes.
The spec names three environmental changes that matter:
These changes may be seasonal, geographic or caused by human interaction. In this lesson we look at what each change does to the distribution of species.
Key terms:
In the UK, temperature rises in summer and falls in winter. Many birds, such as swallows, spend the summer in the UK and fly south for the winter, when it is colder and food is scarcer. Their distribution changes with the seasons. Some mammals hibernate, so they stay in one place but are not active.
Temperature changes from place to place. It is colder high up a mountain than at the bottom. Trees grow in the warmer lower slopes but not near the freezing summit, so different species are found at different heights.
Temperature also affects other conditions. Warm water holds less dissolved oxygen than cold water. Fish that need a lot of oxygen, such as trout, are found in cool, fast-flowing streams. If a stream warms up, they can no longer live there.
All living things need water. Where water is plentiful you find many species. Where it is scarce, only species adapted to dry conditions survive.
The air is made of gases such as nitrogen, oxygen and carbon dioxide. Humans can change the amounts of the gases and add polluting gases. This changes which species can live in an area.
A good example is sulfur dioxide, a gas released when fossil fuels are burned. Lichens are very sensitive to it. Some types of lichen cannot survive where the air contains a lot of sulfur dioxide, so they are found only in cleaner air. Other types are more tolerant and can live in more polluted places.
Because different lichens survive at different levels of pollution, scientists can look at which lichens are present and judge how clean the air is. Species used in this way are called indicator species.
Key terms:
In the exam you will be given information, such as a table, a graph or a short passage, and asked to evaluate the impact of an environmental change. Follow these steps:
A scientist counts three types of lichen on trees at different distances from a city centre, where more fuel is burned.
Type A: 0 at 1 km, 0 at 5 km, 12 at 10 km.
Type B: 0 at 1 km, 8 at 5 km, 15 at 10 km.
Type C: 6 at 1 km, 9 at 5 km, 10 at 10 km.
Evaluation: The number of Type A and Type B lichens is lower close to the city. Type A is only found 10 km away, so it is the most sensitive to pollution. Type C is found everywhere, so it is the most tolerant. This supports the idea that a change in air quality affects distribution. However, only three distances were counted and no other information is given, so other factors such as light or temperature could differ, and more data would be needed to be certain.
Saying a species "adapts" to the change in a few weeks. Adaptation takes many generations. In the short term, species move away or die. Another mistake is giving a conclusion without using any numbers from the data you were given.
A farmer drains a large wet field so that crops can be grown. Before the field was drained, frogs and many types of wetland plant lived there. After draining, a survey found no frogs and only grasses.
(a) Name the environmental change that has affected the distribution of the species. [1 mark]
(b) Explain why the frogs are no longer found in the field. [2 marks]
(c) The table shows the mean number of lichen species on trees at three distances from a power station that burns coal: 1 km = 2 species; 5 km = 6 species; 10 km = 9 species. Evaluate whether the data show that air pollution affects distribution. [3 marks]
(a) A change in the availability of water (1).
(b) Frogs need water or wet conditions to live and breed (1). With the field drained there was no water left, so the frogs died or moved away (1).
(c) The number of lichen species rises from 2 at 1 km to 9 at 10 km, so fewer species survive close to the power station (1). Lichens are sensitive to sulfur dioxide from burning fuel, so pollution is a likely cause (1). Only three distances were used and other factors may differ, so more data is needed to be sure (1).
In an evaluate question, quote numbers from the table, then say what the evidence does not prove.