In a food chain:

• Autotrophs produce biomass. The rate they do this is the GPP. About half of this is used by plants for respiration. The rest is stored or utilised for new biomass production. This remaining biomass is available for consumption by heterotrophs.

• Energy is further moved between trophic levels as food is assimilated into new biomass (secondary productivity). Only 10% of the energy is passed on to the next trophic level because of respiration, movement, heat and indigestible waste.

• This loss of energy limits most food chains to four or five links, although ectotherms may have longer chains as they pass on more energy (15% vs 7%). 

In a population, growth depends on the birth and death rate. Different models of population growth include:

• Exponential - not sustainable, resources will limit

• Logistic - reaches carrying capacity and remains stable

Density dependent factors which can influence population size include:

• Competition (inter- and intra-specific)

• Predator-prey cycles

• Grazing

• Parasitism

• Disease

Density-independent factors include natural disasters and human induced controls.

Population size can be estimated using capture-mark-recapture and a biotic index (e.g. Lincoln index).

Considerations when using capture-mark-recapture include:

• Marks may alter behaviour pattern

• Animals becoming trap-happy or trap-shy

• Assumes that all animals are equally catchable

• Assumes a closed population

Biodiversity is made up of:

• Genetic diversity

• Species diversity

• Ecosystems diversity

The population of individual species can be measured in terms of the:

• Density

• Relative abundance

• Percentage cover

• Frequency

• Distribution

A sampling strategy (simple random, stratified random, systematic random) can be used alongside belt and line transects.

The species richness and relative abundance can be used to understand how biodiverse a habitat is. The biotic index used to assess biodiversity in a terrestrial environment is Simpson's biodiversity index.

Habitats can develop in different ways:

• Primary succession from an inorganic beginning (e.g. bare rock) to a climax community. Pioneer species can tolerate harsh conditions and allow succession to proceed.

• Secondary succession from existing soil (e.g. after fire) to a climax community. This happens quicker as one seral stage has already been completed.

Features of a climax community include:

• Stable community

• High biodiversity

• Complex food webs

• High biomass

Abiotic (climate and edaphic) and biotic factors can influence the rates and limits of succession.

Humans may influence the final seral stage reached and cause plagioclimax.

Habitats can be degraded, fragmented or destroyed. Some examples include:

• Deforestation of rainforests

• Drainage of wetlands

• Dredging of seabed

These reduce biodiversity and the loss of keystone species can have a big impact on an ecosystem.

Rewilding and conservation practices look to start or speed up the recovery of habitats. They include:

• Erosion control

• Reforestation

• Removal of non-native species

• Removal of invasive plants

• Creation of wildlife or habitat corridors

• Reintroduction of native and keystone species

The reintroduction of some nationally extinct species (e.g. beaver) and the potential for reintroduction (e.g. lynx) can cause conflict with different land users.

Sustainable harvesting practices can limit over-exploitation of resources.

Conservation practices can include:

• protecting sites (e.g. SSSI, MPA), 

• targeting action on priority species or habitats (e.g. IUCN red list)

• embedding biodiversity in policy and decision making (e.g. SDGs)

• engaging people and encouraging behavioural change (e.g. No Mow May).

In a terrestrial (land) ecosystem, you can measure:

• temperature

• light intensity

• soil moisture

• soil pH and nitrate/nutrient levels

• wind velocity and direction

• precipitation

• slope

In an aquatic (water) ecosystem, you can measure:

• temperature

• water flow rate

• dissolved oxygen content

• biological oxygen demand (BOD)

• pH

• salinity

• tidal effects

Incidents of point pollution are discharged from a single location. These are usually minor but can combine to have a significant impact.

Diffuse pollution comes from land use activities spread across a wide area, or from a number of incidents of point pollution. This includes:

• runoff from farmland

• forestry activities

• urban areas

• roads and sealed surfaces

• industrial premises

Pollution can be monitored using kick sampling, indicator species and a biotic index (e.g. Trent Biotic Index).

SEPA is a key environmental agency in Scotland who has a role in monitoring incidences of pollution.

Environmental Impact Assessment (EIA) aims to protect the environment by ensuring that a local planning authority has full knowledge of environmental effects of a proposed development and mitigation for these.

Strategic Environmental Assessment (SEA) aims to provide high level protection from development. 

Both of these are informed by environmental monitoring to characterise and assess environmental quality.

A policy is a plan of action that focuses on a specific target - the way to do this is set out in a strategy. Legislation (laws) and initiatives (actions) are then implemented to achieve the aims of the strategy and policy.