Question

Student to attempt either option (A) or (B).
(A) 
(i) Explain giving three reasons why tropics show greatest levels of species diversity. 
(ii) Draw a graph showing species-area relationship. Name the naturalist who studied such relationship. Write the observation made by him. 
OR
(B) 
(i) The world is facing the accelerated rate of species extinctions due to human activities. Explain any three major causes of biodiversity losses. 
(ii) Describe ‘Ex situ’ approach for conserving biodiversity. Give any two examples.

Hint:

Tropical diversity is due to stable climate and productivity. Ex situ methods protect species off-site, while habitat destruction is a leading cause of extinction.

Answer 1

(A):
Step 1: For (i), tropics show the greatest species diversity because: 
1. They have a stable climate with less seasonal variation, allowing uninterrupted evolutionary processes. 
2. High solar energy and moisture contribute to high productivity, supporting a wide variety of species. 
3. Tropical regions have existed for a longer period without glaciation, giving more time for species diversification. 
Step 2: For (ii), the species-area relationship graph shows a rectangular hyperbola when plotted on a standard scale, and a straight line on a log scale. Alexander von Humboldt studied this relationship and observed that species richness increases with area but only up to a limit. His equation is \( S = CA^Z \), where \( S \) is species richness, \( A \) is area, \( C \) is a constant, and \( Z \) ranges between 0.1 to 0.2 for small areas. 
OR 
(B): 
Step 3: For (i), three major causes of biodiversity losses are: 
1. Habitat loss and fragmentation: Deforestation and urbanization destroy habitats. 
2. Over-exploitation: Excessive hunting, fishing, and harvesting reduce populations. 
3. Introduction of alien species: Non-native species may outcompete or prey on native species, disrupting ecosystems. 
Step 4: For (ii), ‘Ex situ’ conservation involves conserving biodiversity outside its natural habitat. Examples include: 
1. Gene banks (e.g., seed banks) 
2. Zoological parks and botanical gardens 
These methods help preserve genetic material and endangered species.