A temperate coniferous forest was cleared and left to naturally regenerate. Species numbers were surveyed across three successional stages, and the findings are summarized in Table 1.
Table 1: The number of organisms found in each successional stage for selected species
| Species | Early | Intermediate | Late |
|---|---|---|---|
| Red huckleberry (Vaccinium parvifolium) | 100 | 80 | 70 |
| Western hemlock (Tsuga heterophylla) | 0 | 20 | 60 |
| Douglas fir (Pseudotsuga menziesii) | 50 | 132 | 90 |
| Keen’s mouse (Peromyscus keeni) | 80 | 96 | 90 |
| Douglas squirrel (Tamiasciurus douglasii) | 5 | 30 | 40 |
| American pine marten (Martes americana) | 0 | 2 | 10 |
| Total number of organisms | 235 | 360 | 360 |
| Simpson’s diversity index (D) | 2.94 | 3.80 | --- |
Figure 2: Keen’s mouse was found in all three successional stages
Define species diversity.
species diversity is the function of the number of species/richness and their relative proportions/abundance/evenness (in an area)
Explain why the diversity changes in the different successional stages.
Award
Species diversity increases toward the later stage...
- because there is an increase in habitats;
- as new species move or are transported into the area;
- because primary productivity tends to increase as you move through the stages;
- because nutrient cycling becomes more developed;
- because evenness/richness increases;
State one method to determine the population size of the Keen’s mouse.
Award
e.g. capture–mark–release–recapture / Lincoln index;
Note: Do not credit “full count/total census” or methods that would only give data of relative abundance e.g. mouse droppings.
