Topic F: Applied Ecology (Elective)

This elective develops the ecology met in Part C into a more quantitative and applied study. You learn how populations change and how communities are sampled and measured, examine the causes and effects of major pollutants, and consider how conservation and sustainable management protect biodiversity. DSE questions in this area are strongly data-based, so confident handling of sampling methods, population graphs and pollution data, with clear reasoning, will earn the most marks.

Populations and population growth

A population is a group of organisms of the same species living in the same area at the same time. Population size changes through births, deaths, immigration and emigration. When conditions are favourable a population may grow rapidly, but growth slows as resources such as food, space and light run short and as predators, disease and competition increase; these factors limit further growth around the carrying capacity, the maximum population the environment can support. You should be able to interpret population-growth curves, describe the phases of slow start, rapid rise and levelling off, and explain the factors that limit growth, distinguishing density-dependent factors such as competition and disease from density-independent ones such as weather.

Communities and ecological niches

A community is all the populations of different species living and interacting in the same habitat. Within a community each species occupies an ecological niche, its particular role including what it eats, where it lives and how it interacts with others. Species interact through feeding relationships, competition for shared resources, and partnerships such as predator and prey. Competition is most intense between organisms with very similar niches, which helps explain how species are distributed. You should be able to describe relationships within a community, predict the effect of a change such as removing a predator, and use the niche idea to explain why two species with identical requirements cannot usually coexist indefinitely in the same place.

Sampling and measuring ecosystems

Because it is impossible to count every organism, ecologists take samples. A quadrat, a square frame of known area, is used to estimate the abundance of plants and slow-moving animals: you record the number or percentage cover in many randomly placed quadrats and scale up to the whole area. A line or belt transect records how species change across a gradient, such as from the shore inland. Mobile animals can be estimated by the mark-release-recapture method. Abiotic factors such as light, temperature, pH and soil moisture are measured to explain distributions. You should be able to choose an appropriate method, explain why sampling must be random and repeated, and use sample data to estimate population size or abundance.

Pollution and its effects

Pollution is the addition of harmful substances to the environment by human activity. Air pollution from burning fossil fuels releases sulfur dioxide and nitrogen oxides that cause acid rain, damaging trees and acidifying lakes, and carbon dioxide that contributes to global warming. Water pollution by sewage and fertiliser causes eutrophication, while toxic substances such as heavy metals and some pesticides accumulate in organisms and become more concentrated along a food chain in bioaccumulation, harming top predators most. Solid and plastic waste damages habitats and wildlife. You should be able to identify the source and effects of a named pollutant, explain the biological mechanism by which it causes harm, and interpret pollution data presented in graphs or tables.

Pollution control and indicators

Pollution can be reduced at source or treated before release. Cleaner technology, catalytic converters and switching to renewable energy cut air pollution, while treating sewage and limiting fertiliser use reduce eutrophication. Recycling and proper waste disposal reduce solid pollution. Living things can be used to monitor pollution: indicator species, such as certain lichens that are sensitive to sulfur dioxide or freshwater invertebrates sensitive to low oxygen, reveal the level of pollution by their presence or absence. You should be able to suggest realistic, specific control measures for a given pollution problem and explain how an indicator species shows the degree of pollution, linking its tolerance to the conditions it can survive.

Conservation of biodiversity

Biodiversity is the variety of species in an ecosystem, and it is valuable for stability, for resources such as medicines and food, and for its own sake. Human activities including habitat destruction, pollution, overexploitation and the introduction of foreign species reduce biodiversity and drive species towards extinction. Conservation aims to protect species and habitats through measures such as establishing nature reserves and country parks, protecting endangered species, controlling hunting and trade, restoring damaged habitats and educating the public. You should be able to explain why a particular human activity threatens biodiversity, propose suitable conservation measures, and discuss the difficulty of balancing conservation against the demand for development and resources.

Sustainable use of resources

Sustainable use means using natural resources in a way that meets present needs without preventing future generations from meeting theirs, so that the resource is not exhausted. In fisheries, setting catch limits, controlling net mesh size and creating protected breeding areas allow fish stocks to recover. In forestry, replanting and selective felling maintain woodland and habitats. Reducing, reusing and recycling materials, and using renewable energy, lower the demand on resources and the output of pollution. You should be able to explain why a resource is being depleted, describe how a named management practice makes its use sustainable, and weigh the social and economic costs against the environmental benefits when discussing a management decision.