How do human activities reduce biodiversity, and how can it be protected?
Human impacts on biodiversity: habitat loss, pollution, overexploitation, invasive species and climate change; the effects of population growth and resource demand; and conservation methods including biological control.
An SQA National 5 Environmental Science answer on human impacts on biodiversity, covering habitat loss, pollution, overexploitation, invasive species and climate change, the role of human population growth and resource demand, and conservation methods including protected areas and biological control.
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What this dot point is asking
The SQA wants you to describe the main human activities that reduce biodiversity, explain how a growing human population and its demand for resources drive these pressures, and describe conservation methods used to protect biodiversity, including biological control as an alternative to chemical pesticides.
Why human population growth matters
The human population has grown rapidly and keeps growing. More people means greater demand for food, land, water, energy and raw materials. Meeting that demand drives the activities that damage biodiversity: forests are cleared for farms and cities, more waste and pollution are produced, and more species are harvested. Population growth and rising resource demand are the underlying pressures behind the specific threats below.
The main threats to biodiversity
- Habitat loss. Clearing or fragmenting habitats, especially deforestation for farming, timber and building, destroys the homes and food sources of species. This is the greatest threat to biodiversity.
- Pollution. Chemicals (pesticides and fertilisers), plastics, oil and untreated sewage poison organisms and damage habitats. Fertiliser run-off can cause eutrophication, which lowers oxygen in water and kills aquatic life.
- Overexploitation. Taking species faster than they can reproduce, through overfishing and overhunting, drives populations down and can cause extinctions.
- Invasive (non-native) species. Species introduced to a new area can outcompete, prey on or bring disease to native species, which have no defences against them, reducing native biodiversity.
- Climate change. Rising temperatures and changing rainfall shift where species can live, disrupt food supplies and breeding times, and can drive species that cannot move or adapt to extinction.
Conservation: protecting biodiversity
Action to protect biodiversity is called conservation, and it works at the species level and the habitat level:
- Legal protection of endangered species and important habitats, making it illegal to harm or destroy them.
- Protected areas such as nature reserves and national parks, which keep habitats intact.
- Regulation of hunting and fishing (for example quotas and closed seasons) so populations are not overexploited.
- Habitat restoration, repairing damaged ecosystems such as replanting native woodland or restoring wetlands.
- Education and raising awareness, so people understand why biodiversity matters and support its protection.
Biological control
A classic example is releasing ladybirds to eat aphids on a crop. The main advantage over chemical pesticides is that it does not add toxic chemicals to the environment, so it avoids poisoning non-target species and avoids polluting soil and water. It can also give longer-lasting control and pests are less likely to become resistant. The risk to manage is that the introduced control organism could itself become a problem if it spreads beyond the target pest, so it must be chosen carefully.
Examples in context
Example 1. An invasive plant crowding out natives. A fast-growing introduced plant with no local pests or grazers can spread rapidly, shading and crowding out native plants and the insects that depend on them. Because the natives have no defences against the newcomer, local biodiversity falls, illustrating why invasive species are a serious threat.
Example 2. Marine protected areas and fish stocks. Setting up a no-take marine reserve lets overfished populations recover by stopping fishing in a defined area. Fish numbers and sizes increase inside the reserve, and young fish can spill over into surrounding waters, showing how protected areas and regulation work together to conserve biodiversity.
Try this
Q1. State the human activity that is the single greatest threat to biodiversity. [1 mark]
- Cue. Habitat loss (especially deforestation for farming and development).
Q2. Give one advantage and one risk of using biological control instead of a chemical pesticide. [2 marks]
- Cue. Advantage: no toxic chemicals, so no harm to non-target species or chemical pollution. Risk: the introduced control organism could spread and become a problem itself.
Exam-style practice questions
Practice questions written in the style of SQA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
SQA N5 style4 marksDescribe two human activities that reduce biodiversity and, for each, explain how it does so.Show worked answer →
A 4-mark describe-and-explain answer needs two activities, each with a mechanism, so plan two activity marks and two explanation marks.
Activity 1. Habitat loss through deforestation: clearing forest for farming or building destroys the homes and food sources of many species, so their populations fall and some are lost. Habitat loss is the greatest single threat to biodiversity.
Activity 2. Pollution: chemicals such as pesticides, plastics or untreated sewage poison organisms or damage their habitats, killing sensitive species and reducing the variety that can survive.
Other valid pairs include overexploitation (overfishing or overhunting removes species faster than they can replace themselves) and introducing invasive species (which outcompete or prey on natives).
Markers reward each named activity and a clear explanation of how it lowers biodiversity. Naming an activity without a mechanism may lose the mark.
SQA N5 style3 marksDescribe what is meant by biological control and give one advantage of using it instead of chemical pesticides.Show worked answer →
This asks for a definition plus an advantage, so plan a clear description (up to 2 marks) and one advantage (1 mark).
Biological control is the use of a living organism, usually a natural predator, parasite or disease, to reduce the numbers of a pest species, instead of using a chemical pesticide. For example, ladybirds can be used to control aphids.
Advantage: it does not add toxic chemicals to the environment, so it avoids poisoning other (non-target) species and avoids chemical pollution of soil and water. It can also provide longer-lasting control, and pests are less likely to become resistant.
Markers reward a correct description of biological control and a valid advantage over chemical pesticides.
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