1. Species Interdependence

What you need to know...
  • What are ecosystems and biomes?
  • How do animals and plants depend on each other?

Ecosystems and Biomes
Ecosystems are balanced biological units. They are made up of living things (animals, plants, micro-organisms) and their habitat (the area in which they live). Ecosystems can be very small such as a pond, or very large such as a whole rainforest. 
The world can be divided into very large ecosystems called biomes. Biomes are regions of our planet characterised by their climate, animals and plants
Map of the world's major biomes from Wikimedia Commons

Examples of world biomes include:

Coniferous forest 

All pictures above from Wikimedia Commons - Click on picture for link
Different biomes will have different types of animals and plants living there which are adapted to survive in that environment.

Animals and plants depend on each other

In ecosystems, animals and plants depend on each other in many different ways.

Plants carry out photosynthesis and help regulate the levels of oxygen and carbon dioxide in the atmosphere. The more plants there are the more carbon dioxide is "locked up" in the tissues in those plants

Plants also provide food for animals. Animals which eat plant matter are called herbivores. Omnivores are animals that eat both plant and animal matter. Animals that mainly eat other animals are known as carnivores. 

Animals can also provide important services for plants. Animals such as bees can act as pollinators for flowering plants. Pollination is the process where pollen (the male sex cell in plants) is transferred from one flower to another flower where it joins with an ovule (the female sex cell in plants). Without pollinators, pollination would not take place, seeds would not be produced and flowering plants would fail to reproduce.
Some animals depend on plants to provide them with a home or provide shelter from the environment. This pictures shows a sociable weaver bird nest in a quiver tree in Namibia.

Of course, humans are no exception and we are equally dependent on plants and animals for our survival. Animals and plants provide us with food, raw materials that we use to build homes, make clothes, make medicines and other important resources. Preserving and protecting ecosystems are as important to humans as it is to other animals and plants.
All pictures above from Wikimedia Commons - Click on picture for link.
Food Webs
Food webs are diagrams that show the feeding relationships between living things. The arrows show the flow of energy and so point from the plant or prey animal being consumed to the animal which is consuming it. Food webs are also useful for demonstrating how species which may appear to be unconnected actually do depend on each other.
The diagram below shows a food web from the North Sea. The diagram shows that cod feed on mackerel and sand eels; that plant plankton are eaten by shrimp and animal plankton; and so on. The food web also helps us understand some more complicated relationships. For example, North Sea cod populations have decreased significantly due to over fishing. You can see that without cod as a predator, populations of mackerel and sand eels could increase. This in turn could decrease the number of animals plankton which means that herring numbers may also suffer. The effects of disrupting food webs can be far reaching and unpredictable.