6.3.1. Ecosystems & 6.3.2. Populations and Sustainability

Ecosystem

All the living organisms found in one area, and the non-living aspects of their environment. Can range in size e.g. rock pool, tree, field. Known as 'dynamic' as they depend on interactions between biotic and abiotic factors.

Biotic factors

Living features of an ecosystem e.g. predators, disease.

Abiotic factors

Non-living features of an ecosystem e.g. light, temperature.

Biomass

The total weight of living matter in a certain area, transferred up trophic levels through consumption. Can be measured in terms of mass of carbon, or dry mass of tissue.

Efficiency of biomass transfer

Efficiency = (biomass transferred / biomass intake) x 100

Human activities affecting biomass transfer

Light, water, temperature maximised. Increased nutrients in soil. Pests and weeds removed. Growth rates boosted through steroids, selective breeding, etc.

Roles of microorganisms in the nitrogen cycle

Nitrogen-fixing bacteria e.g. Rhizobium in roots and Azotobacter in soil, convert gaseous nitrogen into ammonia. Nitrifying bacteria e.g. Nitrosomonas convert ammonium compounds into nitrites. Nitrobacter then convert nitrites to nitrates.

Role of organisms in the carbon cycle

Respiration of plants and animals add carbon dioxide into the atmosphere. Photosynthesis of plants removes carbon dioxide from the atmosphere. Decomposers (microorganisms) decay plant and animal material into carbon dioxide.

Primary succession

Where an area previously devoid of life is colonised by a community of organisms.

Process of primary succession

Pioneer species, able to survive harsh conditions, colonise the area. They die, decompose, and add nutrients to the ground. Over time, this allows more complex organisms to survive.

Climax community

The final stage of succession, where the ecosystem is balanced and stable. It is reached when the soil is rich enough to support large trees or shrubs, and the environment is no longer changing.

Deflected succession

Where succession is interrupted, usually by human interference.

Sampling

Selecting a group of individuals that will represent the whole target population.

Methods of sampling

Techniques used to measure the distribution and abundance of organisms.

Quadrats

Used in small areas, randomly or regularly placed across habitat. Frequency or % cover calculated.

Transects

Used in larger areas, a sample taken along a line that crosses the habitat. Can be combined with quadrats in the form of a belt transect.

Carrying capacity

The maximum population size that a habitat can support, defined by the presence of limiting factors.

Limiting factors

Factors that limit the maximum size of a population, including food, water, light, oxygen, nesting sites, shelter, parasites, and predators.

Predator-prey relationship

A pattern where prey is eaten by predators, leading to an increase in predator population and a decrease in prey population, followed by increased competition for food, causing predator population to decrease, allowing prey population to recover.

Intraspecific competition

Competition between organisms of the same species.

Interspecific competition

Competition between organisms of different species.

Conservation

Maintains biodiversity of a habitat by allowing sustainable use of the resources there.

Preservation

Maintains biodiversity of a habitat by minimizing human impact.

Reasons for conservation and preservation

Economic reasons include food source, natural pest control, and boosting tourism; social reasons include medicinal uses and aesthetics; ethical reasons include the responsibility to maintain habitats for future generations.

Sustainability

Using resources in a way that also maintains them for future generations.

Sustainable use methods

Methods such as timber production through coppicing, replacing felled trees, selective cutting, and fishing practices that ensure stocks are not depleted and avoid overfishing.

Balancing conservation and human needs

In the Terai region (Nepal), locals have a responsibility to look after the forest, with 'corridors' placed to enable migration.

Controlling human effects in ecosystems

In the Galapagos islands, efforts are made to control human impacts due to hunting and tourism, while trying to find a balance to protect native species.