Outline one method for measuring the impact of a build-up of dead organic matter in an aquatic ecosystem.

Explain how models of ecosystems might be used in species conservation.

Discuss how the introduction and re-introduction of a species can affect an ecosystem.

1. use of a biotic index/indicator species;
2. take samples from water source using kick samples/drag nets;
3. sort/identify species and count number of individuals;
4. calculate diversity index for samples;
5. presence of indicator species that are particularly sensitive to pollution will indicate water is clean/unpolluted;
6. a biotic index is based on species tolerance, diversity and relative abundance;
7. impact judged by changes in diversity over a range of time or space;
   
   OR
   
   
8. measuring Biological Oxygen Demand (BOD) / the amount of dissolved oxygen required to break down the organic material in a given volume of water through aerobic biological activity;
9. collect samples from the water source upstream, at source, downstream following a standard procedure;
10. measure dissolved oxygen in collected samples;
11. place sealed samples in dark for five days and re-measure dissolved oxygen in samples / BOD calculated by the change in the dissolved O₂ measurements over 5 days (mg L^–1);
12. repeat dissolved oxygen measurements after a suitable time frame (e.g. 1 month);
13. impact judged by changes in BOD over a range of time or space;

Notes: Credit can be similarly awarded for impacts on other valid components of ecosystem e.g. turbidity / dissolved O₂.
If candidate addresses more than one method then only give credit for most high scoring.

Notes: Award [2 max] for valid named examples of ecosystem models e.g. food chains / webs / pyramids / systems diagrams / flow charts / aquaria / zoos / microcosms / biodiversity indices / computer programmes / mathematical models.
Credit can be given for any of the following ways in which models may assist conservation:

1. models of ecosystems can give holistic perspective on conservation;
2. flows of energy and matter / box-and-arrow models can be used to identify key storages/processes for conservation;
3. modelling may consider biodiversity measures to help in evaluating conservation;
4. measures of genetic diversity help to determine breeding plans for species conservation;
5. physical models can help in studying abiotic needs of a species;
6. modelling feeding interactions / predator-prey interactions allows conservationists to determine the needs of species;
7. modelling feeding interactions can demonstrate possible trophic cascades and provide information about benefits of conservation;
8. modelling biotic interactions can help identify potential threats/essential interactions to the conservation of a species;
9. modelling energy/matter flows helps determine habitat needs/area for a species;
10. modelling is likely to be used in combination with field observations/community needs;
11. modelling may miss emergent properties of a system and therefore not help in species conservation;
12. modelling may not take account of human activities / unpredictable events;
13. modelling may not take account of rare events, such as natural disasters;
14. mathematical modelling may quantify population dynamics;
15. ....thus allow predictions on probability of extinction/recovery;
16. microcosm may study effects of disturbance on species;
17. single species models may be too simplistic and fail to predict actual behaviour of ecosystem
18. zoos can be designed to reflect the specific features of an endangered species niche;

Refer to paper 2 markbands, available under “your tests”  tab > supplemental materials.

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 introduction of species as alien species; introduction of species that become invasive species; re-introduction of species that were previously removed from an ecosystem; restoration; competition; biodiversity; food chain interactions; resource partitioning and evolution of niche (fundamental vs realised); limiting factors/carrying capacity; extinction; trophic cascades and keystone species;
• breadth in addressing and linking explains difference between introduction and re-introduction of a species; considers both positive and negative effects; impact on biodiversity; addresses cultural / societal perspectives; considers role of community / government / NGOs in success;
• examples include both alien species and re-introduced species in a variety of habitats;
• balanced analysis needs to consider value of both introduction and re-introduction and the benefits and challenges in the local communities and ecosystems; accidental or deliberate;
• a conclusion that is consistent with, and supported by, analysis andexamples given e.g. the introduction of a species can result in a range of impacts, including only minor changes in competition for indigenous species and realignments of realised niches through resource partitioning, to very large impacts through competition, loss of biodiversity and ultimately extinction of native species, e.g. after the introduction of brown snakes into Guam or the American crayfish into UK freshwater systems. The re-introduction of a species, e.g. wolves to Yellowstone National Park, also leads to increased competition and changes in distribution and population size of native species but can also lead to positive trophic cascades and an increase in biodiversity;

Not many responses went beyond measuring oxygen as an indication of organic water pollution. Most responses had no practical details of procedure.

Great majority of candidates were unable to identify examples of ecosystem models (food chains/pyramids/flow charts/aquaria/indices/computer models, etc.) so answers were very vague.

Candidates appeared very familiar with issues of introduced species but had little to add when it came to issue of reintroduction.