Monitoring and maintaining the environment

What you'll learn

• How scientists investigate the distribution and abundance of organisms in a habitat.
• How to use quadrats, transects and capture-recapture to estimate population size.
• How human activities can damage or protect biodiversity.
• How to judge evidence linking environmental changes to where organisms live.

The big picture: why monitor ecosystems?

An ecosystem is a community of organisms interacting with each other and with the non-living environment. Ecosystems are not fixed: they change when temperature, water, food supply, pollution, land use or hunting pressure changes.

Monitoring means collecting data over time so we can spot patterns, such as a species becoming rarer, moving into a new area, or recovering after conservation work.

A community is affected by biotic factors, which are living factors such as predators, disease, competition and food, and abiotic factors, which are non-living conditions such as light intensity, temperature, water availability, pH and gases in the air or water.

Sampling: estimating without counting everything

In a large habitat, it is usually impossible to count every organism. Instead, ecologists take a sample, which is a smaller part of the habitat used to estimate what is happening in the whole area.

A good sample should be representative, meaning it reflects the habitat fairly. Scientists use repeat samples, calculate a mean, and avoid biased choices such as only sampling the easiest places to reach.

Random quadrat sampling

A quadrat is a square frame placed on the ground to sample organisms in a known area. Quadrats are useful for plants and slow-moving animals, such as limpets or snails.

For random sampling, you might:

1. Mark out the study area using tape measures.
2. Use a grid and random coordinates to choose quadrat positions.
3. Place the quadrat at each coordinate.
4. Count the number of organisms, or estimate percentage cover.
5. Calculate a mean and scale up to the total area.

This diagram compares random quadrat sampling with transect sampling, which you’ll meet next.

The scaling-up idea is:

$$estimated\; population=mean\; per\; quadrat\times \frac{total\; habitat\; area}{area\; of\; one\; quadrat}$$

Transects: sampling along a gradient

A transect is a line across a habitat. Transects are useful when you expect conditions to change gradually, such as from a shaded woodland edge into open grassland.

In a line transect, you record organisms touching the tape. In a belt transect, you place quadrats at regular intervals along the tape and count organisms within each quadrat.

Transects are especially good for showing changes in distribution, not just total abundance. For example, moss may be common in shaded damp areas but less common in bright dry areas.

A sensible graph might show distance along the transect on the x-axis and number of organisms on the y-axis. If the x-axis is continuous data, such as distance in metres, a line graph or scatter graph is often suitable.

Equipment for field investigations

Ecologists also use:

• Keys: step-by-step identification guides based on features of organisms.
• Pooters: small devices used to collect tiny invertebrates safely.
• Nets: sweep nets for insects in long grass, or pond nets for aquatic animals.

The method you choose depends on the organism. Plants do not run away, so quadrats work well. Flying insects or pond animals usually need nets or traps.

Capture-recapture for mobile animals

Capture-recapture, also called mark-release-recapture, estimates the population size of mobile animals.

The basic method is:

1. Capture a first sample.
2. Mark them safely.
3. Release them and allow time for them to mix back into the population.
4. Capture a second sample.
5. Count how many in the second sample are already marked.

The formula is:

$$N=\frac{n_1\times n_2}{R}$$

where $N$ is the estimated population size, $n_1$ is the number caught first, $n_2$ is the number caught second, and $R$ is the number of marked animals recaptured in the second sample.

Human interactions and biodiversity

Humans can affect ecosystems negatively or positively. It is important not to assume every human interaction is harmful.

Negative interactions include:

• Land use changes, such as deforestation, farming, road building and housing, which destroy or fragment habitats.
• Hunting, poaching and overfishing, which can remove organisms faster than they reproduce.
• Pollution, including air pollution, water pollution and acid rain.
• Introduction of invasive species, which may outcompete native species.

Positive interactions include:

• Protecting individual species using laws, breeding programmes and anti-poaching work.
• Conserving selected habitats, such as woodlands, wetlands, coral reefs or wildflower meadows.
• Restoring damaged habitats by planting native species or creating wildlife corridors.
• Reducing pollution and managing resources sustainably.

Maintaining biodiversity: benefits and challenges

Maintaining biodiversity has many benefits. Diverse ecosystems are often more stable because if one species declines, others may still carry out similar roles. Biodiversity also supports pollination, soil formation, clean water, medicines, food security and genetic resources for future crops.

Ecotourism means tourism based on wildlife or natural habitats. If managed carefully, it can provide jobs and money for conservation while encouraging local people to protect ecosystems.

But conservation is not simple. Challenges include:

• Cost of monitoring and protecting habitats.
• Conflict between conservation and farming, housing, mining or transport.
• Difficulty getting agreements between countries for global issues.
• Illegal hunting and wildlife trade.
• Climate change affecting habitats across national borders.
• Tourism disturbing wildlife if visitor numbers are not controlled.

Evaluating evidence for environmental change

This next skill is Higher Tier only, and for OCR Gateway it is in separate Biology J247 rather than Combined Science.

Environmental changes can affect where organisms are found. For example, water conditions such as pH, temperature, dissolved oxygen or pollutants can affect aquatic life. Atmospheric gases can also matter: increased carbon dioxide is linked with climate change, while sulfur dioxide pollution can affect lichens and contribute to acid rain.

When you evaluate evidence, ask whether the data really supports the conclusion. Look for sample size, repeats, controls, a sensible sampling method, and whether other variables could explain the pattern.

A percentile tells you where a value sits within a data set. For example, the 90th percentile is higher than about 90% of the readings. Percentiles can help compare pollution levels or biodiversity data between sites.