Who observed that 'within a region, species richess increased with increasing explored area but only upto a limit'

Options

A. Paul Ehrlich
B. David Tilman
C. Alexander von Humboldt
D. Edward Wilson

Answer

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks about a scientist who observed that species richness increases with the explored area but only up to a certain limit.

2. **Identifying the Scientist**: The key to answering this question is to recall significant contributions to biodiversity and species richness studies.

3. **Researching the Observation**: The observation pertains to the relationship between species richness and area explored. This is a well-known concept in ecology.

4. **Recognizing the Naturalist**: The scientist who made this observation is Alexander von Humboldt. He was a naturalist and geographer who conducted extensive explorations, particularly in South America.

5. **Summarizing the Findings**: Humboldt noted that as the area explored increases, the number of species found also increases, but only up to a certain limit, beyond which this trend does not continue.

6. **Conclusion**: Therefore, the correct answer to the question is Alexander von Humboldt.

### Final Answer:
The scientist who observed that 'within a region, species richness increased with increasing explored area but only up to a limit' is Alexander von Humboldt.

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