Outline two reasons why the species within pioneer communities in Figure 1 are more likely to be r-strategists than K-strategists.

Outline two reasons why the climax community in Figure 1 is more stable than the intermediate community.

Distinguish between zonation and succession.

Outline two ways in which the food web is likely to change as a result of succession.

Outline two ways in which the soil quality in the pioneer stages of the succession model shown in Figure 1 will differ from that in the climax ecosystem.

r-strategists produce greater numbers/many offspring/fast population growth;
r-strategists distribute themselves more widely/colonize more quickly;
r-strategists mature quickly/reproduce earlier/establish themselves faster;
r-strategists better adapted to harsh/low-nutrient conditions/less specialised niches;

Do not accept just ANY valid characteristic of r-strategists (eg short life-span) ...only those directly relevant to a pioneer community as above.

[2 max]

greater number of species/habitat/ecological niches/genetic diversity in climax community;
gross productivity/stored biomass is higher in climax community;
more complex/diverse energy pathways/food webs;
more established nutrient cycling;
more favourable abiotic conditions/soil properties;
more established negative feedback mechanisms;

[2 max]

succession is the process of changes in community/ecosystem over time, whereas zonation is the process of changes over an environmental gradient/space;

[1]

increasing numbers of trophic levels / longer food chains;
will be composed of new/different species;
more branching / greater complexity / more species at each trophic level;
greater gross productivity/energy transferred at each trophic level;
more biomass stored at each trophic level;
increased prominence of decomposer community;

[2]

In pioneer communities...
there will be lower organic content/leaf litter (due to combustion from the fire);
there may be a higher concentration of available minerals (released from ashes);
there may be fewer soil organisms (following deaths from fire);
it will be more prone to erosion/evaporation losses (through lack of vegetation cover/roots by fire);
less established nutrient recycling / reduced decomposer community;

Accept converse of these statements for climax community.
Note: The model shows SECONDARY succession (after fire), so not all generic features of a pioneer community in PRIMARY succession would be valid. eg in primary succession soil nutrients may be higher in climax community, but in secondary succession reverse is more likely (although processes of nutrient cycling/decomposition may still be more advanced established in climax community as in primary succession).

[2 max]

Most were able to give one relevant feature of r strategists.

Most were able to give one feature of a climax community contributing to its stability.

Probably around half the candidates were sufficiently familiar with both concepts to clearly distinguish zonation from succession.

Most were able to give one way in which food webs change.

Many candidates failed to appreciate this was an example of secondary succession and hence, although organic matter may be low in pioneer soils, mineral content would be high.