Living World 2 – Ecosystems 2

●Watch the video below for a recap from last week’s blog and a reminder what will be covered this week from Mr Littlejohns at HWA who is leading these lessons

Change in ecosystems

Changes will often take place frequently within a ecosystem. These changes can be at a range of scales and can also be due to human or natural causes.
Natural changes – ecosystems can cope with slow natural changes with few harmful effects. Rapid changes have more serious impacts. Eg. drought.
Human changes – Human activity can have serious knock-on effects on an ecosystem. These include:
Adding agricultural fertilisers
Draining ponds
Hedgerow removal

Look at the image below, consider how each of these will lead to the ecosystem changing

Change in an ecosystem
Algae bloom


A major problem with the use of fertilisers occurs when they’re washed off the land by rainwater into rivers and lakes. The resulting increase of nitrate or phosphate in the water encourages algae growth, which forms a bloom over the water surface. This prevents sunlight reaching other water plants, which then die. Bacteria break down the dead plants and use up the oxygen in the water so the lake may be left completely lifeless

Changes to the number of organisms with an ecosystem

Task – Use the diagram to answer the questions

1 If a nearby farmer adds fertiliser to his field and the run off leads to nitrogen being added to the pond what will be the consequences?

2. What will an increase in algae blooms mean in term of the number of decomposers in the pond?

3. Explain what other human activities may lead to a change in the ecosystem of the pond

Within a ecosystem a food web will exist. Each of these organisms within the food web is interdependent, (they rely on another living thing for nutrients) they will not be able to survive without their nutrient source. If there are changes (up or down) to the number of the organisms that they rely on or are eaten by this will have an impact on them. The image below gives an example.

If there are significant changes to the number of organisms with an ecosystems these can have wider impacts on the ecosystem. Watch the youtube clip below to see how wolves can change rivers…..

In the early 1900s, wolves largely vanished from Yellowstone. In their absence, elk — which were no longer hunted by wolves — ate more willows by streams. Without enough food or material to build their dams, beavers also declined. That made the willows’ situation even worse, because willows depend on beaver dams to raise water tables to grow successfully. Adding wolves back into Yellowstone National Park changed this…..

Wolves change rivers

1) List how many ways wolves changed the ecosystem within Yellow Stone National Park
2) Write a paragraph explaining how wolves led to rivers changing

Another example of how ecosystems can change is from sea otters. Watch between 11-20 minutes to find out more. Feel free to watch the whole episode if you would like to.
Blue Planet – Green Seas

Make notes, as you watch – how do sea otters improve the ecosystem? Click the arrow to compare your notes afterwards.

They eat sea urchins and other invertebrates that graze on giant kelp.  Without sea otters, these grazing animals can destroy kelp forests and consequently the wide diversity of animals that depend upon kelp habitat for survival.  Additionally, kelp forests protect coastlines from storm surge and absorb vast amounts of harmful carbon dioxide from the atmosphere.

Apply your knowledge – Exam Question

Attempt the following exam question “Using a named example, explain how change can have short-term and long-term effects on an ecosystem” (6 marks) You may need to submit this question to your class teacher.

The images below may help you structure your answer. HINT – Make sure you plan your answer before you start writing.

Some activities and images used have been resourced from GCSE Geography AQA -Simon Ross, Nicholas Rowles, David Holmes, Bob Digby. Published by Oxford.