Organisms and Their Environment

Competition

Competition for resources

Living organisms that live with other organisms are continuously competing for resources to survive.

They compete for:

1. Space
2. Food
3. Water
4. Mates.

For example, Lions and hyenas compete with each other for food, since they are both carnivores which share a habitat.

In the exam, you will need to analyse graphs of population growth over time and identify whats going on, in terms of competition.

Interdependance of species

In a community (lots of different species sharing a habitat), one major change to one of the species can have a huge knock on effect of all the other species. This is because the species all depend on each other for food, shelter, pollination, disguise from predators etc.

Picture of birds looking out for predators before searching for parasites from the deer’s fur. The two species are interdependent on each other

For example

If something happens to massively reduce the population of greenflies in a habitat; ladybirds would have little to eat. The ladybirds would have to compete with each other more for food and the majority of them will starve. Since the population of Swallows (birds) now have less ladybirds to eat, they will start competing with each other more for food. A large proportion of the Swallow population will starve and die. Swallows also eat ants, since there are less Swallows to eat the Ants, the Ant population will increase in number! This knock on effect doesn’t stop here, it can spread throughout the whole community, fluctuating population size of different species!

Abiotic and Biotic Factors

Abiotic factors are nonliving factors that affect an ecosystem, such as wind, rainfall, temperature, soil pH.

Changes in abiotic factors affect the population size of species living in that habitat.

For example, a decrease in light intensity will decrease the amount of photosynthesis that happens in plants. Plant population sizes will begin to decrease.

Biotic factors are living factors that affect an ecosystem. Fo example, competition among species, new pathogens, new predators, availability of food.

Changes in biotic factors affect the population size of other species living in that habitat.

For example, a decrease in plant population will decrease the amount of food that is available for caterpillars. Caterpillar population sizes will begin to decrease.

Adaptations

An adaptation is a feature of a living thing that makes it suited to its environment. All living things (including bacteria) are adapted to their environment, some more than others. The organisms that are better adapted to their environment have a better chance of survival.

There are three different kinds of adaptations:

Structural adaptations

These are adaptations in the physical body of the organism.

For example, polar bears have white fur, this acts as camouflage so they can more easily sneak up on prey!

Behavioural adaptations

These are adaptations in the behaviour of the organism.

For example, meerkats take it in turn to keep watch for predators. This means that (more often than not), the whole group of meerkats are safe from predators.

Functional adaptations

These are adaptations in how the chemical reactions happen inside the body of the organism.

For example, squirrels hibernate in winter (go into a long long sleep). When they do this, their metabolism slows which conserves energy. They do not need to hunt when in hibernation mode, food is scarce in winter.

In the exam you will need to be able to identify how an animal is adapted to its environment. You will need to state which kind of adaptations it has.

Food Chains

A food chain shows what is eaten by what in an ecosystem. It shows the flow of energy through part of an ecosystem.

Plants are ‘producers’. They convert sun energy into glucose, which is used to make more plant molecules. These plant molecules are biomass.

When something eats a plant, the plants biomass is transferred to the animal as the animals biomass. When another animal eats the first animal, the biomass is tranferred to this new animal, and so on…

For example, here is a food chain:

It shows that caterpillars eat leaves, chameleons eat caterpillars, snakes eat chameleons and the mongoose eats snakes! The arrow always points in the direction of mass transfer (which way the food moving).

Producers: These are usually plants, they get their energy from the sun. They convert sun energy into biomass.

Primary consumers: These are the organisms that eat the producers. The producers biomass is transferred to the primary consumer.

Secondary consumers: These are the organisms that eat the primary consumers and gain biomass.

Tertiary consumers: These are the organisms that eat the secondary consumers and gain biomass.

Quaternary consumers: These are the organisms that eat the tertiary consumers and gain biomass.

Predator-prey cycles

A predator is something that eats another organism. A prey is something that is eaten by another organism. Organisms can be both predator and prey. For example, the chameleon is the snake’s prey but it is also the caterpillar’s predator.

An increase or decrease in population size of an organism will affect the population size of its prey. For example, if there are more predators, the prey population will decrease since more predators are eating them!

An increase or decrease in population size of an organism will affect the population size of its predator..

Here is a graph of how the population sizes of wolves and rabbits vary in a habitat over time.

1. Something may happen to decrease the population size of rabbit (for example, less grass).
2. Less rabbits means less food for the wolves. The wolf population starts to decrease.
3. Less wolves means less rabbits being killed, so the population of rabbits increases.
4. More rabbits means more food for the wolves, so the wolf population starts to increase.
5. More wolves to hunt the rabbits means less rabbits, so the rabbit population starts to decrease.
6. Less rabbits means less food for the wolves. The wolf population starts to decrease.

Are you starting to see a pattern?! The cycle goes on and on. The cycles are always out of phase with one another. This is because it takes time for the population size of one to affect the size of another.