Identify four ways to ensure reliability of the mark–release–recapture method in estimating population size.

Explain how the interactions between a species and its environment give rise to the S-shape of its population growth curve.

The future growth of human populations is unlikely to be limited by the availability of energy resources. However, they could easily be limited by the impacts of energy production.

Discuss the validity of this statement.

ensure process of capture does not reduce/increase potential for recapture / generate trap-shy/trap-happy individuals;
ensure marking process does not impact individual’s survival;
ensure method of marking is durable for period of investigation;
ensure sufficient proportion of population is caught/marked in first capture;
repeat procedure/recapture to increase reliability;
ensure traps are well distributed throughout area of population;
ensure sufficient time between captures to allow mixing of population;
only apply procedure to motile species that do not travel outside study area;

the slow initial growth rate is due to low numbers reproducing;
…and/or unfamiliarity with resources / threats of the newly colonized habitat;
growth rates/numbers increase more rapidly due to abundance/accessibility of resources/greater numbers reproducing;
…leading to positive feedback/exponential growth;
growth rate subsequently decrease/numbers increase more slowly due to limiting/density dependent environmental factors/environmental resistance;
…e.g. limited food/greater predation/competition/nesting sites, etc.;
growth rate eventually becomes zero / population stabilizes / fluctuates around carrying capacity;
due to reaching the carrying capacity of the environment;
…kept stable by density dependent factors / negative feedback / predator–prey cycles;

Note: These marking points may be achieved through an appropriately annotated diagram.

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 of human population growth, limiting factors, “limits to growth”, renewable/non-renewable energy, sustainable development; natural capital/income, carrying capacity, ecological footprints, energy choice, energy security, impacts of climate change, air, water pollution, soil degradation on food production/water availability/disease, etc., predictive models on growth and resource availability;
• breadth in addressing and linking longevity/sustainability of a range of energy sources with human population growth and a range of impacts of energy production from extraction to transportation to infrastructure with a range of limits to human population growth, etc.;
• examples of non-renewable energy sources e.g. oil, coal, fracking, natural gas, nuclear, etc. and renewable sources e.g. hydropower, geothermal, wind, wave, tidal, etc and impacts of energy production eg climate change/shifting biomes/agricultural conditions/food production/water availability/scarcity/disease and possible limits to growth e.g. pollution, disease, potable water, arable land, food, etc.;
• balanced analysis of likelihood of energy itself becoming a limiting factor to human population growth compared to a variety of limiting factors resulting from energy production, including counter arguments (possible sustainability of energy choices), etc.;
• a conclusion that is consistent with, and supported by, analysis and examples given e.g. “despite the development of sustainable energy that would prevent energy itself becoming a limiting factor, countries still persisting in their dependence on fossil fuels may well impair the availability of food and water and spread of disease, each of which could soon become a limiting factor to the growth of human populations”;

Many candidates gained a mark or two for identifying aspects of reliable mark-release-recapture techniques, but a significant minority seemed unfamiliar with the process.

Most candidates had some idea about population growth and interactions with the environment, but a good number mistakenly focused solely upon the population oscillations in the plateau phase rather than the full scope of the S-curve.

There were some excellent responses to this question with candidates well-prepared to take the claim of the question stem to task, with apt and well-explained examples. Weaker essays simply lacked a broad enough scope of such examples.