68. Among the following ecological factor which is not a density dependent factor
    (1) Food (2) Predation
    (3) Disease (4) Extreme temperatures

Introduction

Population sizes in nature are regulated by a mix of ecological factors. These are broadly classified as density-dependent and density-independent factors. Recognizing which factors belong to each category is essential for understanding population dynamics, wildlife management, and conservation biology.

What Are Density-Dependent Factors?

Density-dependent factors are those whose effects on a population intensify as the population density increases. In other words, the impact of these factors depends on how crowded a population is.

Common density-dependent factors include:

• Food: As population density rises, competition for limited food resources becomes more intense, leading to increased mortality or reduced reproduction.

• Predation: Higher population densities often attract more predators, increasing predation rates.

• Disease: Diseases spread more easily in dense populations due to closer contact among individuals.

These factors are typically biotic (living) and act as natural checks on population growth, helping maintain ecological balance.

What Are Density-Independent Factors?

Density-independent factors affect populations regardless of their density. Their impact is not related to how many individuals are present.

Examples include:

• Extreme temperatures

• Natural disasters (e.g., floods, hurricanes, wildfires)

• Habitat destruction

These are usually abiotic (non-living) factors and can cause sudden, unpredictable changes in population size.

Which Factor Is Not Density Dependent?

Let’s evaluate the options:

1. Food: Density dependent—competition increases as population grows.

2. Predation: Density dependent—predators are more effective at higher prey densities.

3. Disease: Density dependent—spreads faster in crowded populations.

4. Extreme temperatures: Not density dependent—affects populations regardless of their size or density; a sudden freeze or heatwave impacts all individuals equally, whether the population is large or small.

Conclusion

Extreme temperatures are not a density-dependent factor. Unlike food, predation, and disease—which become more influential as population density increases—extreme temperatures impact populations no matter how many individuals are present.

Correct answer: (4) Extreme temperatures