David Tilman's long-term ecosystem experiments using outdoor plots showed that

Options

A. Increased diversity contributed to higher productivity
B. Plots with more species showed less year to year variation in the total biomass
C. Biodiversity has no relation with productivity, resistance and stability
D. Both (1) and (2)

Answer

To solve the question regarding David Tilman's long-term ecosystem experiments, we will analyze the information provided and draw conclusions based on the findings of these experiments.

### Step-by-Step Solution:

1. **Understanding the Context**: David Tilman conducted long-term ecosystem experiments using outdoor plots to study the relationship between biodiversity and ecosystem productivity.

**Hint**: Think about what biodiversity means in an ecosystem and why it might be important.

2. **Key Findings**: One of Tilman's main findings was that increased biodiversity (more species present in a plot) contributed to higher productivity. This means that plots with a greater variety of species were able to produce more biomass over time.

**Hint**: Consider how different species might interact and contribute to the overall productivity of an ecosystem.

3. **Year-to-Year Variation**: Tilman also observed that plots with more species showed less year-to-year variation in total biomass. This indicates that diverse ecosystems are more stable and resilient to changes, whether they are natural disturbances or human-induced.

**Hint**: Reflect on how having a variety of species might buffer an ecosystem against fluctuations in conditions.

4. **Evaluating the Options**: Based on the findings:
- Option 1 states that increased diversity contributed to higher productivity, which is true.
- Option 2 states that plots with more species showed less year-to-year variation in total biomass, which is also true.
- Option 3 claims that biodiversity has no relation with productivity, which contradicts Tilman's findings.
- Option 4 suggests resistance and stability, which are linked to the first two points.

5. **Conclusion**: The correct answer is both 1 and 2, as they accurately reflect Tilman's findings regarding the benefits of increased biodiversity in ecosystems.

**Final Answer**: Both 1 and 2.