List the important structural characteristics of an ecosystem.

Explanation

To answer the question regarding the important structural characteristics of an ecosystem, we can break it down into four main components:

### Step-by-Step Solution:

1. **Species Diversity**:
- Species diversity refers to the variety of different species present in an ecosystem. A healthy ecosystem should have a wide range of species, including various plants (flora) and animals (fauna). This diversity is crucial for maintaining ecological balance and resilience against environmental changes.

2. **Stratification**:
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