Consider the following statements concerning food chains
(i) Removal of 80% tigers from an area resulted in greatly increased growth of vegetation
(ii) Removal of most of the carnivores resulted in an increased population of deers
(iii) The length of food chains is generally limited to 3 - 4 trophic levels due to energy loss
(iv) The length of food chains may vary from 2 to 8 trophic levels
Which two of the above statements are correct?

Options

A. (i), (ii)
B. (ii), (iii)
C. (iii), (iv)
D. (i), (iv)

Answer

To determine which two statements concerning food chains are correct, let's analyze each statement step by step.

### Step 1: Analyze Statement (i)
**Statement (i): Removal of 80% tigers from an area resulted in greatly increased growth of vegetation.**

- **Analysis**: Tigers are apex predators and play a crucial role in controlling the population of herbivores (like deer). If 80% of the tiger population is removed, the herbivore population (deer) would likely increase due to reduced predation. As the herbivore population increases, they would consume more vegetation, leading to a decrease in plant growth, not an increase.
- **Conclusion**: This statement is **incorrect**.

### Step 2: Analyze Statement (ii)
**Statement (ii): Removal of most of the carnivores resulted in an increased population of deers.**

- **Analysis**: Carnivores, including tigers, prey on herbivores such as deer. If most carnivores are removed, there would be fewer predators to control the deer population. Consequently, the deer population would increase due to the lack of predation.
- **Conclusion**: This statement is **correct**.

### Step 3: Analyze Statement (iii)
**Statement (iii): The length of food chains is generally limited to 3 - 4 trophic levels due to energy loss.**

- **Analysis**: According to the 10% rule of energy transfer in ecosystems, only about 10% of the energy is transferred from one trophic level to the next. This significant energy loss limits the number of trophic levels that can be sustained in a food chain. Typically, food chains consist of 3 to 4 levels because beyond this, the energy available becomes insufficient to support higher trophic levels.
- **Conclusion**: This statement is **correct**.

### Step 4: Analyze Statement (iv)
**Statement (iv): The length of food chains may vary from 2 to 8 trophic levels.**

- **Analysis**: While food chains can theoretically have varying lengths, in practice, they rarely exceed 4 trophic levels due to the energy loss mentioned earlier. Having 8 trophic levels would imply a very high energy transfer efficiency, which is not realistic in natural ecosystems. Therefore, this statement is misleading.
- **Conclusion**: This statement is **incorrect**.

### Final Conclusion
The two correct statements are:
- Statement (ii): Removal of most of the carnivores resulted in an increased population of deers.
- Statement (iii): The length of food chains is generally limited to 3 - 4 trophic levels due to energy loss.

### Answer
The correct statements are (ii) and (iii).

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