Question
Forest fires are very common in the Amazon forest. A study was performed to see the relationship between forest fragmentation, fire and management
a. Describe one method that could have been used to estimate the population size of a given tree in a forest after fire damage had occurred. [3]
b. Outline how the edge effect can affect diversity in forests. [3]
The number of plants in two fields of approximately the same size was counted.
c. Compare and contrast the richness and the evenness of the two fields. [2]
▶️Answer/Explanation
a. One method to estimate population size after forest fire → Quadrat sampling with extrapolation
- Place random quadrats (e.g., 1 m²) in different areas of the forest.
- Count the number of trees of the species inside each quadrat.
- Calculate average per quadrat, then multiply by total forest area (÷ area of one quadrat). This gives a population estimate after the fire.
b. How edge effect affects diversity in forests
- Edge effect occurs at boundaries of forest and open land.
- Microclimate changes at edges: more wind, sunlight, dryness.
- Leads to lower biodiversity: some species avoid edges, predators increase, or new species invade.
c. Compare richness and evenness of Field 1 and Field 2
| Term | Field 1 | Field 2 |
|---|---|---|
| Richness (number of species) | Same – both fields have 3 species | Same – both fields have 3 species |
| Evenness (relative abundance) | High – numbers of all species are fairly close | Low – buttercup dominates heavily |
So, both have equal richness, but Field 1 has higher evenness.
Question
a. Define indicator species. [1]
b. Indicator species may be affected by biomagnification. Discuss biomagnification using a named example of a pollutant. [3]
c. Determine whether islands are open or closed ecosystems. [1]
▶️Answer/Explanation
a. Define indicator species. [1]
An indicator species is an organism whose presence, absence, or abundance reflects specific environmental conditions, such as pollution levels or habitat quality.
b. Indicator species may be affected by biomagnification. Discuss biomagnification using a named example of a pollutant. [3]
- Biomagnification is the process where the concentration of a toxic substance increases at each level of a food chain.
- For example, mercury released into water bodies accumulates in small organisms like plankton.
- As larger animals like fish or birds (e.g., ospreys) eat many contaminated organisms, mercury concentration builds up to harmful levels, affecting indicator species and ecosystems.
c. Determine whether islands are open or closed ecosystems. [1]
Islands are open ecosystems because they exchange energy and matter with their surroundings through migration, nutrient cycles, and atmospheric interactions.