A student investigated the biodiversity of organisms on a rocky shore using a belt transect. A 100 m transect line was laid perpendicular to the shoreline, from the low tide mark (0 m) to the high tide mark (100 m). At three positions along the transect (10 m, 50 m, and 90 m), a 1 m × 1 m quadrat was placed, and the number of individuals of each species of macroalga and invertebrate was recorded. The table shows the abundance (number of individuals) of the four most common species at each position.
| Species | 10 m (low shore) | 50 m (mid shore) | 90 m (high shore) |
|---|---|---|---|
| A | 85 | 12 | 2 |
| B | 3 | 40 | 1 |
| C | 0 | 18 | 55 |
| D | 2 | 30 | 42 |
Simpson's index of diversity (D) was calculated for each position:
- At 10 m: D = 0.18
- At 50 m: D = 0.72
- At 90 m: D = 0.53
Describe how the biodiversity changes along the transect and explain the reasons for these changes. In your answer, refer to the methods used to collect the data and the significance of the D values.