Vertical distribution of different species occupying different levels is called stratification.

Answer

### Step-by-Step Text Solution:

1. **Understanding the Concept of Stratification**:
- Stratification refers to the vertical distribution of different species within an ecosystem, where various species occupy different levels or strata.

2. **Components of an Ecosystem**:
- An ecosystem consists of two main components: abiotic (non-living) and biotic (living).
- Abiotic components include factors like temperature, wind, and pressure, while biotic components include various species of plants and animals.

3. **Species Composition**:
- In an ecosystem, the distribution and concentration of species are important for understanding the overall species composition. This composition indicates how many species are present and at what levels they exist.

4. **Example of Stratification in a Forest Ecosystem**:
- In a forest ecosystem, there are distinct vertical layers:
- **Top Stratum**: Large trees occupy the highest level.
- **Middle Stratum**: Below the trees, smaller shrubs and herbs are found.
- **Bottom Stratum**: At the lowest level, grasses grow.
- Each of these groups represents different species occupying different levels of the forest ecosystem.

5. **Conclusion**:
- Therefore, the statement that the vertical distribution of different species occupying different levels is known as stratification is true.