Biodiversity and the Effect of Human Interaction on Ecosystems¶

Part of 4.7 Ecology.

Human activity can reduce biodiversity and destabilise ecosystems, but it can also be managed in ways that protect them. This topic links ecological science directly to environmental decisions.

Learning Objectives¶

Biodiversity¶

Biodiversity is the variety of different species in an ecosystem or on Earth as a whole. A high biodiversity means: - More complex food webs with many overlapping links — fewer species rely entirely on just one other species. - Greater resilience: if one species declines, others can fill the gap. - Better ecosystem "health" and stability.

A low biodiversity means fewer overlapping relationships. If one key species is lost, it can collapse much of the food web — a cascade effect.

Biodiversity is measured using species richness (number of different species) and species evenness (how evenly distributed the individuals are between species).

Human Impacts on Biodiversity¶

1. Deforestation¶

Deforestation is the large-scale removal of trees. It occurs mainly for: - Agricultural land (crops and livestock, including cattle ranching and palm oil plantations). - Timber production. - Urban and industrial development. - Biofuel crop production (e.g. maize for ethanol).

Consequences of deforestation: - Habitat destruction — organisms lose shelter, food sources and nesting sites. - Extinction — species with no alternative habitat die out, reducing biodiversity. - Soil erosion — tree roots anchor soil; their removal exposes soil to rain and wind erosion. - Nutrient leaching — without trees absorbing nutrients, rainfall washes them away, leaving infertile soil. - Flooding — trees slow rainfall reaching the ground; without them, surface runoff increases. - Increased atmospheric CO₂ — trees are carbon stores. Felling removes active photosynthesis; burning them releases stored CO₂. - Disruption of the water cycle — less transpiration means less water returned to the atmosphere, making local climates drier.

2. Land Use Changes¶

The human population has grown rapidly, requiring more land for housing, farming, quarrying, landfill, and industry. This directly reduces the habitats available for other species.

Peat bogs are particularly important: - Peat bogs are acidic, waterlogged wetlands with very low oxygen levels. - Because decomposition is slowed in these anaerobic conditions, organic material accumulates as peat — storing large amounts of carbon. - Peat bogs support unique communities of mosses, insects and birds. - When peat is extracted for garden compost or burned as fuel, stored CO₂ is released, and the specialist habitat is destroyed, reducing biodiversity.

3. Pollution¶

Water pollution: - Agricultural fertilisers (nitrates and phosphates) wash into water bodies during rain — this is called eutrophication: 1. Excess nutrients cause algae to multiply rapidly (algal bloom). 2. Algal bloom blocks light reaching aquatic plants below. 3. Plants die; decomposers multiply to break them down. 4. Decomposers use up dissolved oxygen through aerobic respiration. 5. Aquatic animals suffocate due to lack of oxygen — death of many species. - Untreated sewage in rivers carries disease and removes oxygen. - Hormones from contraceptives in water courses can cause feminisation in fish. - Pesticides and herbicides can enter waterways and accumulate in food chains (bioaccumulation).

Air pollution: - Burning fossil fuels releases CO₂ (greenhouse gas causing global warming) and SO₂ (causing acid rain). - Acid rain damages vegetation and acidifies lakes, killing organisms not adapted to low pH. - Air pollution kills sensitive species such as lichens, which are used as indicator species for air quality.

Land pollution: - Landfill takes up habitat and can leach toxic chemicals (e.g. battery acid) into soil. - Non-biodegradable plastic persists in the environment, harming wildlife.

4. Global Warming and Climate Change¶

Greenhouse gases (CO₂, methane, water vapour, nitrous oxide, CFCs) trap heat in the atmosphere, causing global temperatures to rise.

Effects on ecosystems: - Species that cannot tolerate warmer conditions decline or become extinct. - Species ranges shift — animals and plants move towards higher latitudes or altitudes. - Warmer conditions favour some disease organisms (e.g. mosquitoes spreading to new regions). - Polar ice caps melt → sea levels rise → coastal habitats (salt marshes, mangroves) are lost. - Changes in rainfall patterns affect migration routes and breeding seasons. - Coral bleaching occurs when ocean temperatures rise, killing coral reef ecosystems.

Indicator Species¶

Some species are sensitive to particular pollutants and their presence or absence reveals pollution levels:

Maintaining Biodiversity¶

Despite human pressures, several strategies can protect and restore biodiversity:

Benefits of maintaining biodiversity:¶

• Protects food chains and pollination services that underpin human food production.
• Preserves potential medicines — many drugs come from wild plants; undiscovered compounds may be lost with extinction.
• Protects resources (timber, fibres, fuels) for future generations.
• Enables ecotourism — income generated by wildlife tourism can fund conservation.
• Maintains stable ecosystems that regulate climate, clean water, and cycle nutrients.

Challenges:¶

• International cooperation is difficult — countries may prioritise economic development over conservation.
• Enforcing fishing quotas or anti-poaching laws is challenging, especially in less-resourced countries.
• Captive breeding is expensive and individuals may struggle to survive when reintroduced to the wild.

Common Confusions¶

• Biodiversity and abundance: Biodiversity is about the variety of species present, not just the total number of organisms. A habitat with millions of one type of weed has low biodiversity even though it has a large population.
• Eutrophication mechanism: Students often say "fertilisers kill fish directly." In fact, the chain goes: fertilisers → algal bloom → blocked light → plant death → decomposers multiply → oxygen depletion → fish suffocate. The fertilisers themselves do not poison the fish.
• Deforestation and CO₂: Two effects operate: (1) loss of trees reduces photosynthesis, so less CO₂ is absorbed; (2) burning felled trees releases their stored carbon as CO₂. Both increase atmospheric CO₂.
• Peat bogs and carbon: Peat bogs are carbon sinks (they store carbon). When peat is burned or exposed, they become carbon sources. This is why their destruction worsens climate change.
• Indicator species: Lichens indicate air quality (SO₂ levels). Freshwater shrimps indicate water quality (oxygen levels). Do not swap these.

Key Terms¶

• Biodiversity: the variety of different species in an ecosystem or across the planet.
• Deforestation: the large-scale removal of trees, reducing habitat and increasing atmospheric CO₂.
• Eutrophication: the process by which excess nutrients in water cause algal growth, oxygen depletion and death of aquatic organisms.
• Global warming: the long-term rise in Earth's average temperature due to increased greenhouse gas concentrations.
• Greenhouse gas: a gas (e.g. CO₂, methane, water vapour) that traps heat in the atmosphere.
• Acid rain: rain made acidic by dissolved SO₂ and NOₓ from burning fossil fuels; damages plants and acidifies water bodies.
• Conservation: protecting and managing species and habitats to prevent loss of biodiversity.
• Seed bank: a store of seeds at low temperature and humidity, used to preserve plant genetic material.
• Peat bog: a waterlogged, anaerobic wetland ecosystem that accumulates peat and stores large amounts of carbon.
• Indicator species: a species whose presence, absence or abundance reveals information about environmental quality (e.g. pollution levels).
• Bioaccumulation: the increase in concentration of a toxic substance in organisms at higher levels of the food chain.
• Ecotourism: tourism that promotes appreciation of natural environments while funding their conservation.

Connected Pages¶

• 4.7.2 Organisation of an Ecosystem
• 4.7.4 Trophic Levels in an Ecosystem
• GCSE Biology Key Terms Glossary
• Required Practical Reference