Organisms and Environment » Ecosystem Concepts

What you'll learn this session

Study time: 30 minutes

The concept of ecosystems and their components
Food chains, food webs and trophic levels
Energy transfer and efficiency in ecosystems
Ecological pyramids and their significance
Nutrient cycles (carbon and nitrogen)
Human impacts on ecosystems

Introduction to Ecosystems

Ecosystems are all around us - from the vast Amazon rainforest to a small pond in your local park. They're fascinating systems where living organisms interact with each other and their physical environment. Let's explore how these natural communities function!

Key Definitions:

Ecosystem: A community of living organisms interacting with each other and their physical environment.
Habitat: The specific place where an organism lives.
Population: A group of organisms of the same species living in the same area.
Community: All the populations of different species living and interacting in an area.
Biotic factors: Living components of an ecosystem (plants, animals, microorganisms).
Abiotic factors: Non-living components (temperature, light, water, soil, pH).

🏠 Ecosystem Components

Every ecosystem has two main components:

Biotic components: All living organisms - producers (plants), consumers (animals) and decomposers (fungi, bacteria).
Abiotic components: Physical and chemical factors like sunlight, temperature, rainfall, soil type and minerals.

🌍 Types of Ecosystems

Ecosystems come in various sizes and types:

Terrestrial: Forests, grasslands, deserts
Aquatic: Freshwater (ponds, rivers) and marine (oceans, coral reefs)
Microecosystems: Small-scale systems like a rotting log or a puddle

Feeding Relationships in Ecosystems

Energy flows through ecosystems via feeding relationships. Understanding these relationships helps us see how all living things are connected.

Food Chains and Food Webs

Food chains show the linear transfer of energy from one organism to another. They always start with a producer (usually a plant) that captures energy from the sun through photosynthesis.

A simple food chain might look like this:
Grass → Rabbit → Fox

But in reality, feeding relationships are more complex. Food webs show the interconnected food chains in an ecosystem, providing a more realistic picture of energy flow.

Important Feeding Terms

Producers: Organisms that make their own food (plants, algae)
Consumers: Organisms that eat other organisms
Herbivores: Animals that eat only plants (primary consumers)
Carnivores: Animals that eat other animals (secondary/tertiary consumers)
Omnivores: Animals that eat both plants and animals
Decomposers: Organisms that break down dead material (fungi, bacteria)

Trophic Levels and Energy Transfer

Each step in a food chain is called a trophic level. Energy is transferred from one trophic level to the next, but this transfer is not 100% efficient.

🌾 Producers

First trophic level. Plants and algae capture about 1% of sunlight energy through photosynthesis.

🐰 Primary Consumers

Second trophic level. Herbivores that eat plants, receiving about 10% of the energy from the level below.

🐺 Secondary Consumers

Third trophic level. Carnivores that eat herbivores, again receiving only about 10% of energy from the level below.

Energy Loss in Food Chains

Only about 10% of the energy from one trophic level is transferred to the next. The rest is lost as:

Heat energy during respiration
Movement and other life processes
Undigested material in faeces
Parts of organisms that aren't eaten

This explains why food chains rarely have more than 4 or 5 trophic levels - there simply isn't enough energy left to support another level!

Ecological Pyramids

Ecological pyramids are visual representations of the structure of food chains. There are three main types:

📊 Pyramid of Numbers

Shows the number of organisms at each trophic level. Usually pyramid-shaped, but can be inverted (e.g., one tree supporting many insects).

📸 Pyramid of Biomass

Shows the total dry mass of organisms at each trophic level. More reliable than numbers, always pyramid-shaped in terrestrial ecosystems.

🔥 Pyramid of Energy

Shows the energy content at each trophic level. Always pyramid-shaped and the most accurate representation.

Nutrient Cycles

Unlike energy, which flows through ecosystems, nutrients are recycled. Two important nutrient cycles are the carbon cycle and the nitrogen cycle.

The Carbon Cycle

Carbon is a key element in all living organisms. It cycles through the ecosystem in these ways:

Photosynthesis: Plants take in carbon dioxide from the atmosphere
Respiration: All organisms release carbon dioxide back to the atmosphere
Feeding: Carbon compounds pass along food chains
Decomposition: Dead organisms are broken down, releasing carbon
Combustion: Burning fossil fuels releases carbon dioxide

The Nitrogen Cycle

Nitrogen is essential for making proteins. It cycles through ecosystems via:

Nitrogen fixation: Converting atmospheric nitrogen into compounds plants can use (by bacteria or lightning)
Nitrification: Ammonia is converted to nitrates by bacteria
Assimilation: Plants absorb nitrates to make proteins
Feeding: Animals get nitrogen by eating plants or other animals
Decomposition: Dead organisms are broken down, releasing ammonia
Denitrification: Some bacteria convert nitrates back to nitrogen gas

Case Study: Human Impacts on Ecosystems

Humans affect nutrient cycles and ecosystems in many ways:

Deforestation: Reduces carbon dioxide uptake by plants, contributing to climate change
Burning fossil fuels: Releases stored carbon into the atmosphere
Fertiliser use: Adds excess nitrogen to ecosystems, causing eutrophication in water bodies
Overfishing: Disrupts marine food webs and ecosystems

Example: The Great Barrier Reef in Australia is experiencing coral bleaching due to rising sea temperatures from climate change. This affects the entire reef ecosystem, as corals provide habitat for numerous marine species.

Biodiversity and Ecosystem Stability

Biodiversity refers to the variety of living organisms in an ecosystem. High biodiversity generally leads to more stable ecosystems because:

More complex food webs can withstand the loss of some species
Greater genetic diversity helps species adapt to environmental changes
More diverse ecosystems often have higher productivity

When we protect biodiversity, we're helping to maintain the delicate balance of ecosystems that ultimately support all life on Earth, including humans.

🧠 Test Your Knowledge!