The exponent z of the species-area curve measured at continental scales is

Options

A. smaller than the value of z at regional scales
B. equal to the value of z at regional scales
C. greater than the value of z at regional scales
D. unrelated to the value of z at regional scales

Answer

To solve the question regarding the exponent \( z \) of the species-area curve measured at continental scales, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Species-Area Curve**:
The species-area curve is a graphical representation that shows the relationship between the area of a habitat and the number of species found within that area. It is commonly expressed in logarithmic form.

2. **Mathematical Representation**:
The relationship can be represented by the equation:
\[ \log S = \log C + z \log A \]
where:
- \( S \) = number of species
- \( A \) = area
- \( C \) = a constant
- \( z \) = the exponent that indicates the rate at which species richness increases with area.

3. **Graphical Interpretation**:
When plotted, the graph shows that as the area \( A \) increases, the number of species \( S \) also increases. The slope of this logarithmic graph is represented by the exponent \( z \).

4. **Comparing Scales**:
- At continental scales, the area is much larger compared to regional scales.
- Therefore, it is expected that the value of \( z \) at continental scales will be greater than that at regional scales. This is because larger areas can support more species due to greater habitat diversity and availability of resources.

5. **Evaluating Options**:
- The options provided suggest comparisons of \( z \) at continental and regional scales.
- We conclude that \( z \) at continental scales is greater than \( z \) at regional scales due to the larger area and the associated increase in species diversity.

6. **Final Answer**:
Thus, the correct option is that the exponent \( z \) at continental scales is **greater than** the value of \( z \) at regional scales.