Ecosystems and Interactions

Introduction

Every ecosystem is made up of both living and non-living components. These components constantly interact, creating the conditions necessary for life. Plants, animals, fungi, and microorganisms all depend on sunlight, water, air, soil, and suitable temperatures to survive. At the same time, living organisms also depend on one another for food, shelter, reproduction, and nutrient cycling.

Scientists divide the components of an ecosystem into two categories: biotic factors and abiotic factors. Understanding the relationship between these factors helps us explain why different organisms live in different environments and how changes in environmental conditions can affect entire ecosystems.

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What Are Biotic and Abiotic Factors?

Every ecosystem contains two main types of factors.

Biotic Factors

Biotic factors are the living or once-living parts of an ecosystem.

Examples include:

• Plants
• Animals
• Fungi
• Bacteria
• Algae
• Dead leaves
• Fallen trees
• Animal waste

Even organisms that have recently died are considered biotic because they were once alive.

Abiotic Factors

Abiotic factors are the non-living physical and chemical parts of an ecosystem.

Examples include:

• Sunlight
• Water
• Air
• Soil
• Rocks
• Minerals
• Temperature
• Rainfall
• Wind
• Humidity
• pH
• Salinity

Abiotic factors create the environmental conditions that living organisms must adapt to.

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Figure 1. Ecosystems contain both living (biotic) and non-living (abiotic) factors that interact continuously.

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Comparing Biotic and Abiotic Factors

Although they are different, both are equally important for maintaining healthy ecosystems.

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How Abiotic Factors Influence Living Organisms

Abiotic factors determine where organisms can live, how well they survive, and how they reproduce.

Sunlight

Plants need sunlight for photosynthesis, the process of making food.

Without enough sunlight:

• Plant growth slows.
• Less food is available for herbivores.
• Entire food chains may be affected.

Water

Water is essential for all living organisms.

It is needed for:

• Photosynthesis
• Transporting nutrients
• Chemical reactions
• Temperature regulation

Animals living in deserts have evolved ways to conserve water, while aquatic organisms depend on lakes, rivers, and oceans.

Temperature

Temperature affects:

• Growth
• Reproduction
• Enzyme activity
• Metabolism

For example:

• Polar bears are adapted to cold Arctic climates.
• Cacti thrive in hot deserts.
• Tropical fish require warm water to survive.

Soil

Soil provides:

• Nutrients
• Water
• Support for plant roots

Different soil types support different plant communities.

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Figure 2. Abiotic factors such as sunlight, water, temperature, and soil determine which organisms can survive in different habitats.

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How Organisms Depend on Biotic Factors

Living organisms also depend on each other.

Examples include:

Food

• Rabbits eat grass.
• Foxes eat rabbits.
• Hawks eat small mammals.

Shelter

• Birds nest in trees.
• Fish hide among aquatic plants.
• Insects shelter beneath logs.

Pollination

Bees transfer pollen between flowers, allowing many plants to reproduce.

Decomposition

Fungi and bacteria break down dead organisms and recycle nutrients back into the soil.

Without decomposers, nutrients would become locked inside dead plants and animals.

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Biotic and Abiotic Factors Work Together

Biotic and abiotic factors are closely connected.

Consider a forest ecosystem:

• Trees require sunlight, water, and nutrients.
• Birds nest in trees.
• Insects feed on leaves.
• Fungi decompose fallen logs.
• Nutrients return to the soil.
• Trees absorb those nutrients and continue growing.

A change in one factor often affects many others.

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Environmental Changes Can Affect Ecosystems

Changes in abiotic conditions can have major consequences for living organisms.

Drought

Less rainfall means:

• Plants produce less food.
• Herbivores struggle to survive.
• Predator populations may decline.

Flooding

Floods can:

• Destroy habitats
• Wash away soil
• Reduce oxygen levels in water

Wildfires

Although destructive, some ecosystems rely on periodic fires to:

• Clear old vegetation
• Release nutrients into the soil
• Trigger seed germination

Climate Change

Rising temperatures and changing rainfall patterns are altering ecosystems worldwide by changing habitats and species distributions.

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Figure 3. Changes in abiotic factors such as rainfall can affect entire ecosystems and the organisms living within them.

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Worked Example

Question

Classify each item as either biotic or abiotic.

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Real-World Connection

Farmers carefully monitor abiotic factors such as soil quality, rainfall, temperature, and sunlight to grow healthy crops. They may irrigate fields during dry weather, improve soil with fertilizers or compost, or use greenhouses to control temperature. Understanding biotic and abiotic factors helps increase food production while protecting the environment.

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Did You Know?

The Atacama Desert in South America is one of the driest places on Earth. Some areas may go years without measurable rainfall, yet specially adapted plants, insects, and microorganisms are still able to survive under these extreme abiotic conditions.

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Key Terms

Abiotic factor – A non-living physical or chemical component of an ecosystem.

Biotic factor – A living or once-living component of an ecosystem.

Environment – The surroundings in which an organism lives.

Habitat – The natural place where an organism lives.

Photosynthesis – The process by which plants use sunlight to produce food.

Decomposer – An organism that breaks down dead organic matter and recycles nutrients.

Adaptation – A characteristic that helps an organism survive in its environment.

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Key Takeaways

• Ecosystems contain both biotic (living) and abiotic (non-living) factors.
• Abiotic factors determine the environmental conditions that organisms experience.
• Organisms depend on both living and non-living components for survival.
• Changes in abiotic factors can affect food webs, populations, and entire ecosystems.
• Healthy ecosystems depend on the continuous interaction between biotic and abiotic factors.