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The natural environment

An organism's environment can be divided into different components:

  • Habitat: the part of the environment where an organism lives.
  • A rabbit's habitat is an open grassy area.

  • Population: All the living members of a species in a habitat.
  • All the red squirrels in a forest are part of the same population.

  • Community: All of the organisms living in the same habitat.
  • In a pond, the algae, plants and fish that all live together make up the pond community.

  • Ecosystem: describes the interaction between all living and non-living things in an environment.
  • An ecosystem does not have a defined size.

Let's use an example: Below is a picture of the African plains - this is a habitat. The grass, zebra and wildebeest that live here are three separate populations that are part of the same community. Zebra use the grasses as a food source.

The zebra and blue wildebeest are two examples of populations in this community.
The zebra and blue wildebeest are two examples of populations in this community.

In any environment, an organism will be affected by two sets of factors:

Biotic factors: include all living things in an environment that influence an organism.

For a lion, antelope are an important biotic factor that provide a source of food.

Other members of the same species are also biotic factors. Competition for resources such as food and sexual partners is strongest within a population!

Abiotic factors: include all non-living things in the environment.

In a field, abiotic factors include wind speed, air temperature, soil temperature, light intensity and soil pH.

Important! Changing a single biotic or abiotic factor in an ecosystem can have major consequences. Every factor usually influences multiple species.

Any ecosystem includes both biotic AND abiotic factors.
Any ecosystem includes both biotic AND abiotic factors.

Organisms are adapted to the environment in which they live. These adaptations have arisen over a long period of time (thousands of years!) through evolution.

Organisms need to adapt in order to survive and reproduce successfully. However, their individual adaptations depend on what they need:

  • Animals need water, oxygen and other organisms to feed on.
  • Plants need light, carbon dioxide, water, oxygen and nutrients.
  • Microorganisms vary in their needs. Some bacteria can survive without light or oxygen!

Extremophiles are adapted to survive in extreme conditions, such as high temperatures, pressures and salt concentrations.

Thermophiles are a group of organisms that can live in hot springs and deep sea vents. They can survive in temperatures over 100$$^{\circ}$$C!

Fish that live in the deep sea are adapted to survive in complete darkness at very high pressures and low temperatures.
Fish that live in the deep sea are adapted to survive in complete darkness at very high pressures and low temperatures.

Environmental temperature is an important abiotic factor that animals have to adapt to. Below is a comparison of two animals that are adapted to different temperatures.

Polar bears are adapted to the extremely cold environment of the Arctic:

  • Large body : decreases the polar bear’s surface area to volume ratio. This minimises heat loss.
  • Thick blubber layer : helps to insulate the body, trapping heat.
  • Thick coat of fur : also helps to insulate the body.

Camels live in very hot climates with very little water:

  • Large surface area to volume ratio : increases heat loss.
  • Thin hair : reduces insulation of the animal, increasing heat loss.
  • Behaviour : most active in the early morning and late evening to avoid the midday heat.

Important! As well as being adapted to abiotic factors, organisms also have adaptations based on other organisms.

Camouflage allows organisms to blend into their surroundings, protecting them from predators or allowing them to hunt more efficiently.

Organisms living in the same areas compete for resources that are required for survival and reproduction.

For animals, there are three important things that organisms compete for:

  • Food: all animals need to consume other organisms to survive.
  • Territory: having a well-defended territory can be important for mating and for protecting a food source.
  • Mates: many animals have displays used to attract mates.

Organisms compete with members of different species (interspecific competition) and members of the same species (intraspecific competition).

Intraspecific competition is often very strong because all the organisms need the same resources!

The peacock’s spectacular tail may help it to attract a mate.
The peacock’s spectacular tail may help it to attract a mate.

Interdependence states that the survival of different species in the same ecosystem can be dependent on each other.

Interdependence is best illustrated by the predator-prey scenario:

This graph shows the variation in numbers of predator and prey over many years.
This graph shows the variation in numbers of predator and prey over many years.

The number of predators is initially higher than the number of prey:

  • A large population of predators will eat a lot of prey, decreasing the number of prey.
  • Low prey numbers means there is a food shortage for predators. Intense competition between predators will lead to a decrease in the predator population (e.g. due to starvation).
  • Decrease in predator numbers allows the prey population to start growing again.

Important! This cycle will continue as long as the predator population is dependent on the number of a particular prey.

In some ecosystems, predators can eat many different types of prey, so the fluctuation in numbers of one prey species is less important.