Ecology and Ecosystem Dynamics

Biotic and Abiotic Factors

Everything in a habitat works together. A habitat is a place where plants and animals live. In a habitat, some things are living and some things are nonliving.

Scientists use two special words to talk about these things. Biotic means living or once living. Abiotic means nonliving and never alive.

When we learn about biotic and abiotic factors, we are learning about what makes up an ecosystem. An ecosystem is a place where living things and nonliving things interact, or work together.

What are biotic factors?

Biotic factors are the living parts of an ecosystem, or things that were once alive.

• plants
• animals
• trees
• grass
• flowers
• birds
• bugs
• mushrooms
• fallen leaves
• dead wood

A tree is biotic because it is alive. A bird is biotic because it is alive. A fallen leaf is also biotic because it was once part of a living plant.

What are abiotic factors?

Abiotic factors are the nonliving parts of an ecosystem. They were never alive.

• sunlight
• water
• air
• rocks
• soil
• temperature
• sand

Sunlight is abiotic because it is not alive. Water is abiotic because it is not alive. Rocks are abiotic because they were never alive.

Why are biotic and abiotic factors important?

Living things need nonliving things to survive. A plant needs sunlight, water, air, and soil. These are abiotic factors.

Animals need water and air too. Many animals also need plants or other animals for food. That means animals depend on both biotic and abiotic factors.

Biotic and abiotic factors work together every day. If one part changes, the ecosystem can change too.

For example, if there is not enough rain, plants may not grow well. Then animals may have less food or less shelter. One abiotic change can affect many biotic factors.

How can we tell the difference?

You can ask two simple questions:

1. Is it living now?
2. Was it once living?

If the answer is yes to either question, it is biotic.

If the answer is no to both questions, it is abiotic.

Examples in different habitats

Pond habitat

• Biotic: fish, frogs, ducks, water plants
• Abiotic: water, sunlight, mud, rocks

Forest habitat

• Biotic: trees, deer, birds, insects, mushrooms
• Abiotic: soil, rain, air, sunlight, temperature

Desert habitat

• Biotic: cactus, lizards, snakes, desert flowers
• Abiotic: sand, hot sunlight, little water, rocks

Worked Example 1: Easy sorting

Look at these things: rabbit, rock, grass, water.

Step 1: Find the living things or things that were once alive.

• rabbit = biotic
• grass = biotic

Step 2: Find the nonliving things that were never alive.

• rock = abiotic
• water = abiotic

Answer: Rabbit and grass are biotic. Rock and water are abiotic.

Worked Example 2: Was it once living?

Look at these things: fallen leaf, sun, stick, air.

Step 1: Ask, “Was it once living?”

• fallen leaf = yes, it came from a plant, so it is biotic
• stick = yes, it came from a tree, so it is biotic

Step 2: Ask, “Was it never alive?”

• sun = abiotic
• air = abiotic

Answer: Fallen leaf and stick are biotic. Sun and air are abiotic.

Worked Example 3: What does a plant need?

A flower is growing in a garden. What abiotic factors help it grow?

• sunlight
• water
• air
• soil

These are all nonliving things, so they are abiotic factors.

What biotic factors might be nearby?

• other flowers
• bees
• worms
• grass

Answer: The flower needs abiotic factors like sunlight and water. It also lives near biotic factors like bees and grass.

Worked Example 4: What happens when one factor changes?

In a pond, the water level gets very low.

Water is an abiotic factor. If there is less water, fish and frogs may have trouble living there.

• less water = abiotic change
• fish may have less space
• frogs may have trouble finding a good place to live
• plants in the pond may not grow well

Answer: A change in one abiotic factor, like water, can affect many biotic factors, like fish, frogs, and plants.

Let’s remember

• Biotic = living or once living
• Abiotic = nonliving and never alive
• Plants and animals need abiotic factors like water, air, and sunlight
• Ecosystems stay healthy when biotic and abiotic factors work together

Quick check

Try sorting these on your own:

• tree
• sand
• bird
• rain
• dead log
• sunlight

Answers:

• Biotic: tree, bird, dead log
• Abiotic: sand, rain, sunlight

Summary

Biotic factors are the living parts of an ecosystem, or things that were once alive. Abiotic factors are the nonliving parts, like water, sunlight, air, and rocks.

Living things depend on abiotic factors to live and grow. When biotic and abiotic factors work together, they make a healthy ecosystem.