What Is an Ecosystem?
An ecosystem is all the living things (plants, animals, insects, fungi) and non-living things (soil, water, air, sunlight) in one area, all interacting with each other. A pond, a forest, a desert, or even your school garden can be an ecosystem.
Everything in an ecosystem is connected. If one part changes, it can affect everything else.
Biotic and Abiotic Factors
Every ecosystem is made up of two types of factors that affect how living things survive and interact:
Biotic factors are the living parts of an ecosystem — any organism that affects another organism.
Examples: Plants (producers), Animals (predators, prey, herbivores, etc.), Bacteria and fungi (decomposers, which break down dead material).
Abiotic factors are the non-living parts of an ecosystem — physical or chemical conditions that affect where and how organisms live.
Examples: Temperature, Light (sunlight availability), Water/rainfall, Soil pH and quality, Oxygen and carbon dioxide level and Wind e.t.c.
Why does this matter?
Both types of factors affect population size and distribution. For example:
- A drop in temperature (abiotic) could mean fewer insects survive, which means birds that eat those insects (biotic) have less food, so their numbers might fall too.
- If a new predator (biotic) is introduced to an area, it could reduce the numbers of its prey species.
A simple way to remember it: biotic = biological (living), abiotic = "a" (without) + "biotic" (life) = without life.
Producers and Consumers
Every food chain starts with a producer. Producers are organisms that can make their own food using sunlight — this is mainly plants, algae, and some bacteria, through a process called photosynthesis.
Everything else in the food chain is a consumer, because they get their energy by eating other organisms. Consumers are grouped by what they eat:
- Herbivores – eat only plants (e.g. a rabbit eating grass)
- Carnivores – eat only other animals (e.g. a fox eating a rabbit)
- Omnivores – eat both plants and animals (e.g. a bear eating berries and fish)
- Decomposers – break down dead plants and animals, returning nutrients to the soil (e.g. fungi and bacteria)
A food chain is a linear feeding relationship between living organisms in their natural habitat in which organisms feeding are also fed on.
A simple food chain might look like this:
Grass → Rabbit → Fox
The arrows show the direction energy flows — from the grass, to the rabbit that eats it, to the fox that eats the rabbit.
Here is another food chain in the diagram below. The sun is the source of light for the green plant and then the food cycles moves from 1 all the way to 5.
Food chain summary
- The initial source of energy for all food chains is the sun
- A food chain always starts with a producer – usually a green plant
- A producer is a plant that makes its own food from sunlight
- Next comes a consumer that eats the producer
- A consumer is a living thing that eats other plants and animals.
- The arrows in a food chain show the way in which energy is moving.
- A predator is an animal that eats other animals.
- Prey are the animals that predators eat.
Predators and Prey
A predator is an animal that hunts and eats other animals. The animal being hunted is called the prey.
Predator and prey populations are closely linked. If there are lots of prey animals (like rabbits), predators (like foxes) have plenty of food, so the fox population can grow. But as fox numbers increase, they eat more rabbits, so the rabbit population falls. With fewer rabbits, some foxes won't find enough food, so the fox population falls too — and the cycle continues.
This constant rise and fall keeps populations balanced over time. It's nature's way of making sure no single species takes over completely.
Pyramids of Numbers
A pyramid of numbers is a diagram that shows how many organisms exist at each level of a food chain. It's shaped like a pyramid because:
- There are usually lots of producers (like grass) at the bottom
- Fewer herbivores that eat the producers
- Even fewer carnivores at the top
This happens because energy is lost at each stage — some energy is used for movement, breathing, and staying warm, and some is lost as heat. So there's less energy available to support organisms at the next level up. This is why top predators (like lions or eagles) are always much rarer than the plants or small animals below them in the chain.
Food Webs
Real ecosystems are far more complicated than a single food chain. Most animals eat more than one type of food, and are eaten by more than one predator. A food web shows all these different food chains linked together, giving a much more realistic picture of how energy moves through an ecosystem.
A food web is a complex representation of the feeding relationships among organisms within an ecosystem, illustrating how energy and nutrients flow through various species.
The image below give a typical example of a food web.
Changes to Food Webs
Because everything in a food web is connected, a change to one species can affect many others. For example, if a disease wipes out most of the rabbits in an area:
- Foxes that rely on rabbits may struggle to find food and their numbers could drop
- Plants that rabbits used to eat might grow more, since fewer rabbits are eating them
Even removing or adding just one species can cause a ripple effect through the whole web.
Food Security
Food security means having reliable access to enough safe, nutritious food. Ecosystems play a huge role in food security — healthy ecosystems support the crops, livestock, and fish that people rely on for food. Things like climate change, pollution, and the loss of habitats can disrupt food webs and make it harder to produce enough food for everyone.
Toxic Materials in the Food Chain
Sometimes harmful chemicals — like pesticides used on crops — can enter a food chain. A process called bioaccumulation happens when these toxins build up in an organism's body over time, often because the organism cannot easily get rid of them.
The real danger comes with biomagnification: as one animal eats many smaller organisms, the toxins they've all absorbed add up. This means animals at the top of the food chain (top predators) often end up with the highest concentration of toxins in their bodies — even if the original chemical was only used in small amounts at the bottom of the chain.
This is one reason why scientists carefully monitor the use of pesticides and pollution levels in our environment — protecting the smallest organisms in a food chain ultimately protects the largest ones too.
Quick Recap
- An ecosystem includes all living and non-living things in an area, all connected
- Producers make their own food; consumers eat other organisms
- Predator and prey populations rise and fall in a natural balance
- Pyramids of numbers show fewer organisms at each level as you go up
- Food webs show how multiple food chains connect and depend on each other
- Toxins can build up through a food chain, with top predators most affected
