Question 1
Paper 2Hard16 marksA research group collected the following illustrative monitoring data for one defined region of the Amazon rainforest. The forest area in 1980 is the original area for this region.
| Year | Area of forest remaining / km² | Mean annual rainfall / mm |
|---|---|---|
| 1980 | 100 000 | 1600 |
| 2000 | 90 000 | 1510 |
| 2020 | 80 000 | 1400 |
The group also investigated ecosystem stability in aquatic mesocosms. Each mesocosm was a sealed glass vessel containing freshwater plants and microorganisms. Four vessels were used for each plant-cover treatment. The initial total abundance index was 100 in all vessels. All other conditions were kept the same. Light was reduced to half its starting level for three days and then restored. The table shows the mean total abundance index.
| Plant cover | Before disturbance | At end of disturbance | 14 days after light was restored |
|---|---|---|---|
| 25% | 100 | 64 | 82 |
| 75% | 100 | 80 | 96 |
In this investigation, greater stability is defined as a smaller decrease in abundance during the disturbance and a value closer to the initial abundance 14 days after the disturbance.
Calculate the percentage decrease in forest area between 1980 and 2020. Describe the change in mean annual rainfall over the same period. Show your working.
Explain how continued deforestation could make the Amazon rainforest a possible tipping point in ecosystem stability.
Using the stated definition of stability, compare the stability of the two mesocosm treatments.
Assess how far the monitoring data and the mesocosm results support the claim that continued deforestation could destabilize the Amazon rainforest. Use evidence from both data sets, explain one advantage of the mesocosm design and identify one limitation when applying the model to the Amazon.