5.3 - Human Impact on Biodiversity

Biodiversity and reducing it

• Biodiversity is the variety of all the different species of organisms living on Earth, or within a particular ecosystem, together with the number of individuals within each species.
• A woodland or rainforest - full of animals, plants, fungi, and bacteria - has a far higher biodiversity than a single ploughed field.

Why a high biodiversity matters

• More stable ecosystems - When many species live together, losing any one of them (to disease, for example) is less damaging. The other species have many other feeding and supporting relationships to fall back on, rather than depending heavily on the one that's gone.
• Crops need pollinators - A great many of our crops depend on animal pollinators.
• Source of medicines - More than half of new medicines are derived in some way from living organisms.
• Every species lost is a possible food source or medicine lost with it, so the future of the human species relies on maintaining a good level of biodiversity across the planet.

The problem

• Many human activities are reducing biodiversity:
  • Using up resources
  • Destroying habitats
  • Producing pollution and waste
• As biodiversity falls, so does the stability and the benefits it provides.

Bioaccumulation in food chains

• Some toxic substances released by human activity don't break down and aren't excreted by the organisms that take them in.
• Instead, they stay in the body and build up. When this happens along a food chain, it's called bioaccumulation.

Common sources

• Heavy metals - Released from industrial waste
• Pesticides - Sprayed onto crops

How the toxin builds up along the chain

1. A small amount enters the organisms at the bottom of the food chain.
2. Each predator eats many of the organisms below it, taking in all of their stored toxin.
3. The concentration therefore rises at each step up the chain.
4. Organisms at the top end up with the highest concentrations - sometimes high enough to harm or kill them, even though the amount in any single organism lower down was small.