Beta `(beta)`diversity refers to diversity :

Options

A. in a community
B. between communities
C. in a mountain gradient
D. on a plain

Explanation

To solve the question regarding beta diversity, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Diversity Terms**:
- Familiarize yourself with the terms used in ecology: alpha diversity, beta diversity, and gamma diversity.
- Alpha diversity refers to the diversity within a single community or habitat.
- Gamma diversity refers to the total diversity in a larger region that encompasses multiple communities.

**Hint**: Remember that alpha is local, gamma is regional, and beta is the comparison between them.

2. **Defining Beta Diversity**:
- Beta diversity is defined as the measure of diversity between different communities. It quantifies how species composition changes from one community to another.
- It reflects the rate of change of species diversity as you move across different habitats or environments.

**Hint**: Think of beta diversity as a bridge connecting different communities and showing how they differ from each other.

3. **Identifying the Correct Option**:
- The question asks specifically about what beta diversity refers to. Among the provided options, we need to identify which one accurately describes this concept.
- The correct option is "between communities," as beta diversity is all about comparing the species diversity of different communities.

**Hint**: Look for keywords in the options that indicate comparison or relationships between different groups.

4. **Conclusion**:
- Based on the definitions and understanding of the terms, we conclude that beta diversity refers to the diversity between communities.

### Final Answer:
Beta diversity refers to diversity **between communities**.