Human impacts on biodiversity (Edexcel GCSE Biology Combined Science): Revision Notes

Human impacts on biodiversity

Biodiversity - Variety of living organisms in an ecosystem affected by human interactions within ecosystems either positive or negative.

Fish Farming:

• Pollution: Waste from fish farms, such as uneaten food, chemicals, and antibiotics, can leak into the surrounding water, polluting the environment and harming other aquatic species.
• Disease and Parasites: High densities of fish in farming enclosures promote the spread of diseases and parasites, which can spread to wild fish populations and reduce their numbers.
• Feeding: Carnivorous farmed fish, such as salmon, require large amounts of protein in their diet. This often comes from wild fish populations, which are harvested to produce fishmeal, depleting the stocks of wild fish and impacting biodiversity.
• Escaped Fish: If farmed fish escape into the wild, they may compete with indigenous species for resources such as food and breeding grounds, reducing the population of native species.
• Predator Trapping: Predators, such as sea lions and birds, may be attracted to the fish farms but can become trapped in nets, leading to injury or death.

1. Food is added to nets to feed fish, which produces huge amounts of waste. (Food & waste leak into water, causing eutrophication & death of species.)

2. Fish farms in water often act as a breeding ground for parasites, which can get out of the farm & infect wild animals (can kill).

3. Predators are attracted to the nets & can become trapped & die.

4. Sometimes farmed fish can escape into the wild, causing problems for wild populations of indigenous species.

Introduction of Non-Indigenous Species:

• Out-competing Native Species: Non-indigenous species may have no natural predators and can out-compete indigenous species (species that naturally occur in the area) for resources such as food, shelter, or mates. This can lead to a decline or extinction of native species.
• Predation: Some non-indigenous species may become predators of local wildlife, killing native species and further reducing biodiversity. Example:

The introduction of cane toads to Australia in the 1930s is a well-known example. The cane toads were introduced to control pests that were damaging sugar cane crops. However, the toads have had several negative impacts:

• Poisonous: Cane toads are toxic to many animals that attempt to eat them, which has led to declines in native predator populations.
• Competition: Cane toads eat insects, competing with local species for food, and their population has exploded to over 200 million.

The introduction of non-indigenous species can reduce biodiversity

Non-indigenous species:

Species that don't naturally occur in an area

• Can occur:

  • Intentionally
  • Unintentionally

• Causes problems for indigenous species

• Compete with indigenous species for resources (food/shelter). If they out-compete indigenous species, then they die out. Example: Signal crayfish were introduced to the UK for food, but they prey on and out-compete many indigenous river species.

• Non-indigenous species also bring new diseases to the habitat, which infect/kill indigenous species, reducing habitat biodiversity.

Eutrophication:

• Algal Blooms: The excess nutrients cause the rapid growth of algae in the water, which forms a dense layer on the surface.
• Blocked Light: The algae block sunlight from reaching underwater plants, preventing them from performing photosynthesis, which leads to their death.
• Decomposition: When the plants die, bacteria break them down, and in the process, they use up oxygen in the water.
• Oxygen Depletion: The decrease in oxygen levels, known as hypoxia, makes the water uninhabitable for many aquatic animals, such as fish, causing them to die.

Fertilisers can leach into water & cause eutrophication

1. Nitrates are put on fields (fertilisers).
2. If too much is used & it rains too much after, the nitrates find their way into rivers/lakes.
3. Results in eutrophication (excess of nutrients in water than plants can take in).
4. This can lead to death of many species & reduces biodiversity of the habitat as:

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What happens…

• Algae grow fast, which blocks light.
• Plants can't then photosynthesise, so they die and decompose.
• As more food becomes available, microorganisms that feed on decomposing plants increase in number and use up O₂ in the water.

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Positive Human Interactions	Negative Human Interactions
Maintaining rainforests: Protecting these critical habitats to prevent their destruction.	Greenhouse gas emissions: Contributing to global warming, which leads to habitat loss.
Reducing water pollution: Monitoring and minimising pollutants to protect aquatic ecosystems.	Acid rain: Caused by sulfur-dioxide emissions from factories, damaging habitats.
Preserving areas of scientific interest: Restricting human access to protect sensitive ecosystems.	Chemical pollution from farming: Pesticides and fertilisers leach into the environment, harming wildlife.
Replanting hedgerows and woodlands: Restoring habitats that were previously destroyed.	Land clearance for development: Reducing the number of available habitats by building on natural land.