Identify four ways in which solar energy reaching vegetation may be lost from an ecosystem before it contributes to the biomass of herbivores.

Suggest a series of procedures that could be used to estimate the net productivity of an insect population in kg m^–2 yr^–1.

To what extent are the concepts of net productivity and natural income useful in managing the sustainable harvesting of named resources from natural ecosystems?

reflected from the leaf surface;
absorbed by non-photosynthetic surface;
heat/some wavelengths are absorbed by leaf but not used in photosynthesis/not converted into chemical energy;
(chemical energy/GPP) respired by vegetation;
(chemical energy/GPP) not eaten/harvested by consumer / dead material consumed by decomposers;
eaten but not absorbed by herbivore / lost in faeces;
absorbed by herbivore, but lost through respiration.

Award [1] for each correct way identified, up to [4 max].

measure change in population size over year;
using Lincoln Index/mark-release-recapture;
set traps/capture a sample, mark and release them;
re-set traps for a second capture and calculate the proportion marked and unmarked;

use the equation: _{$N=\frac{n_1\times n_2}{n_3}$}

weigh a sample of insects to find (wet) weight;
use a conversion factor to calculate dry weight from (wet) weight;
calculate mean dry weight/biomass per individual;
from mean dry weights and population sizes calculate total weight change over year;
estimate area occupied by population using measuring tapes/scale maps;
divide total change in dry mass by area in m₂;

Award [1] for each correct suggestion, up to [7 max].
Credit any alternative sequence of procedures that is equally appropriate to finding net secondary productivity eg using lab population and weighing dry weight of food, faeces, respiration rates, etc, awarding marks similarly to scheme above.

The following guide for using the markbands suggests certain features that may be offered in responses. The five headings coincide with the criteria given in each of the markbands (although “ESS terminology” has been conflated with “Understanding concepts”). This guide simply provides some possible inclusions and should not be seen as requisite or comprehensive. It outlines the kind of elements to look for when deciding on the appropriate markband and the specific mark within that band.

Answers may include:

• understanding concepts and terminology of natural income, net productivity, natural capital, stock sustainability, replenishment, maximum sustainable yield, rates of harvest, renewable/non-renewable, goods/services, etc
• breadth in addressing and linking net productivity and natural income with sustainable harvesting, maximum sustainable yield, impacts of extraction/transport/processing, management of resources, remaining stock/capital, their applicability to abiotic/biotic resources, renewable/nonrenewable resources, goods/services, etc
• examples of net productivity/natural income of named resources eg timber, freshwater, fish populations, river processing organic waste, fossil fuels, impacts of unsustainable extraction eg bycatch, access roads/infrastructure in forests, etc
• balanced analysis of the extent to which net productivity and natural income are applicable and sufficient concepts for ensuring sustainable use of a range of resources
• a conclusion that is consistent with, and supported by, analysis and examples given eg “Both concepts can be very useful in assessing the sustainability of harvesting but net productivity is more limited in its applications
  since it can only be applied to biotic resources and neither of the concepts take into account any unsustainable damage that may occur through the actual extraction of a resource.”

Refer to paper 2 markbands, available under the "your tests" tab > supplemental materials.

Question 4 was the least popular question and generated very few good responses. Most candidates focused on energy losses in the atmosphere before reaching the vegetation …which was not addressed by the question.

A good proportion of candidates gained some credit for describing a protocol to estimate population size, but few could go on to find productivity.

Most could link net productivity and natural income with sustainable harvesting …although some confused natural income with financial gain. Very few were able to evaluate this in different contexts however, particularly so in regard to the weakness in these quantities/models.