...........are unstable due to absence of diversity and self - regulating mechanisms.

Explanation

**Step-by-Step Solution:**

1. **Identify the Key Terms:** The question mentions "unstable," "absence of diversity," and "self-regulating mechanisms." We need to find an ecosystem type that fits these characteristics.

2. **Understand Ecosystem Stability:** Ecosystems that are stable typically have a variety of species (high diversity) and self-regulating mechanisms that allow them to recover from disturbances. Conversely, unstable ecosystems lack these features.

3. **Consider Different Ecosystem Types:** Reflect on various ecosystems, such as natural ecosystems (forests, grasslands, wetlands) and human-made ecosystems (agroecosystems, urban areas).

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