Biotic factors affecting the abundance & distribution

• Availability of food

  All animals require food to live. The availability of food is a major factor in how many animals live in an ecosystem. Areas like rainforests with rich food supplies have more species of life than other areas like deserts and the Polar Regions where there is less food.
• In balanced ecosystems, predators and prey have evolved together, where predators can catch enough prey to survive, but not so many that they kill all of their food
• The arrival of a new predator in an ecosystem can upset this balance
• Example: the introduction of the red fox to Australia has caused concern over their effect on native birds and small mammals
• Introducing new predators can cause a rapid decline in the numbers of prey, which then reduces the food supply for existing predators
• New pathogens

  When organisms inhabit new ecosystems they often bring new pathogens. As an example, Europeans first colonised North America, and introduced new pathogens, like the influenza virus.