1. Biodiversity
Biodiversity refers to the number of different species present in a community.

2. Biodiversity
Biodiversity refers to the number of different species present in a community.
Communities with high biodiversity survive environmental change well.
If something destroys one of the organisms in the food chain then the other organisms simply switch to different food sources.

3. Biodiversity
Communities with low biodiversity have little or no ability to switch to other food sources and may die off as a result of change in the environment.
If the herbivore animals in a community eat only one particular plant species, then they will die out if that plant species is destroyed by a disease or some other disaster.
The carnivores that eat the herbivores would die out too. If the herbivores had a variety of plants to choose from they would probably survive the loss of one particular species.

4. Biodiversity Humans have reduced the biodiversity of many ecosystems.
Natural vegetation has been removed and replaced by crops or forests of only one plant species.
As a result, many species are now endangered or extinct.
Pine plantations and fields of wheat and sugarcane, for example, have very low biodiversity.

5. Relationships between organisms
Organisms do not live by themselves but interact with the other organisms in the ecosystem.
Some interactions benefit both organisms while other interactions benefit one organism while harming the other.

6. Benefiting both organisms
Mutualism (symbiosis) is when both organisms benefit from their relationship with each other.
For example, some sharks have their mouths nibbled by small fish. The fish get an easy meal and the sharks get their teeth scrubbed clean.
Bees collect pollen for their hive, but they also spread it to other plants allowing their reproduction.

7. Symbiosis (mutualism)
Clownfish have a mucous coating that allows them to live among these poisonous tentacles without being stung.
Clownfish receive protection from predators and feed on the anemone’s leftovers.
In return the anemone gets cleaned. This is an example of symbiosis or mutualism.
Sea anemones are animals. Their tentacles contain stinging cells with which they stun passing fish and then drag their prey towards their mouth.

8. Hitching a ride
Sea anemones sometimes hitch a ride on the back of hermit crabs.
The hermit crab is camouflaged and protected by the anemone, and the anemone gains mobility.
Both benefit from the relationship.

9. Benefiting one organism
Commensalism is when one species benefits while the other species is unaffected.
Remora are tropical fish that attach themselves to faster-swimming fish such as sharks.
The sharks are not harmed by their presence but do not benefit from it either.
The remora benefit in two ways: they get a free ride and they consume any of the shark’s ‘leftovers’.

10. Harming one organism
Amensalism is when one species is harmed while the other species is unaffected.
Trails caused by cows and sheep throughout feeding areas may not affect the animals, but the plants they walk on are destroyed.

11. No benefit at all
Competition is when animals compete for food, water or nesting materials.
Plants compete for nutrients, water, and light. Weeds in the garden often crowd out other plants.
They grow so quickly that other plants suffer and die.

12. Benefiting one organism, harming another
Exploitation is when one species benefits from the interaction while the other is harmed.
• Predation: where one animal kills another for food. A seal catching a fish or a perentie lizard snatching a wallaby are examples of predation.
• Herbivory: where a herbivore eats a plant, reducing it in size but not killing it. This happens when kangaroos graze on grass, possums eat bottlebrushes or when dugongs feed on sea grasses.
• Parasitism: where one organism (the parasite) lives on or in another (the host). The host is usually not killed but is robbed of its nutrients, making it ill. Tapeworms are parasites that live in the gut of animals. Dogs and cats often have tapeworms if not treated. Humans sometimes have parasites such as head lice and threadworms.

13. Eating from the inside out
Parasitoids are parasites that kill their hosts. An example of a parasitoid is the braconid wasp, which lays its eggs inside the cabbage caterpillar.
When the eggs hatch, the wasp grubs eat the caterpillar from the inside out!