Ecosystems and Interactions
| Site: | Young Education |
| Course: | Ecology and Environmental Systems |
| Book: | Ecosystems and Interactions |
| Printed by: | 访客用户 |
| Date: | Monday, 5 October 2026, 4:59 AM |
1. What Is an Ecosystem?
Learning outcomes
- I can define an ecosystem and describe its components.
- I can identify living and non-living parts of an ecosystem.
- I can explain how organisms interact with their environment.
- I can compare different types of ecosystems.
- I can describe how ecosystems function as interconnected systems.
Introduction
Every living thing on Earth depends on its surroundings to survive. Plants need sunlight, water, and nutrients, while animals require food, water, shelter, and suitable environmental conditions. Together, organisms and their physical surroundings form ecosystems.
An ecosystem can be as small as a puddle or as large as an ocean. Regardless of size, every ecosystem is made up of living organisms interacting with each other and with the non-living world around them.
What Is an Ecosystem?
An ecosystem is a community of living organisms interacting with each other and with their non-living environment.
It includes everything found within a particular area:
- Plants
- Animals
- Fungi
- Microorganisms
- Water
- Air
- Soil
- Rocks
- Sunlight
- Climate
Figure 1. An ecosystem contains both living (biotic) and non-living (abiotic) components that constantly interact.
Biotic and Abiotic Components
Every ecosystem has two main types of components.
Biotic Factors (Living)
Biotic factors are the living or once-living parts of an ecosystem.
Examples include:
- Trees
- Birds
- Fish
- Insects
- Fungi
- Bacteria
Abiotic Factors (Non-Living)
Abiotic factors are the physical and chemical parts of the environment.
Examples include:
- Sunlight
- Water
- Air
- Rocks
- Soil
- Temperature
- Rainfall
These conditions determine which organisms can survive.
Figure 2. Living organisms depend on abiotic factors such as sunlight, water, air, and soil for survival.
Organisms Interact with Their Environment
Living things constantly interact with one another and with the environment.
Examples include:
- Plants absorb sunlight to make food.
- Bees pollinate flowers.
- Birds build nests in trees.
- Fish obtain oxygen from water.
- Earthworms improve soil quality.
- Predators hunt prey.
These interactions help ecosystems remain balanced.
Ecosystems Are Interconnected Systems
Nothing in nature exists completely on its own.
For example:
Plants → Herbivores → Carnivores → Decomposers → Nutrients → Plants
This continuous cycling of energy and nutrients keeps ecosystems functioning.
Types of Ecosystems
Major ecosystem types include:
- Forests
- Grasslands
- Deserts
- Freshwater
- Marine
Each has different climates, organisms, and environmental conditions.
Figure 3. Earth contains many different ecosystems, each supporting unique communities of organisms.
Example: A Pond Ecosystem
Biotic:
- Fish
- Frogs
- Insects
- Algae
- Ducks
- Bacteria
Abiotic:
- Water
- Rocks
- Mud
- Sunlight
- Oxygen
- Temperature
If pollution enters the pond, nearly every organism may be affected because all parts of the ecosystem are connected.
Worked Example
Question
Identify whether each of the following is biotic or abiotic.
| Item | Biotic or Abiotic? |
|---|---|
| Oak tree | Biotic |
| Soil | Abiotic |
| Rabbit | Biotic |
| Sunlight | Abiotic |
| Mushroom. | Biotic |
| Rainfall | Abiotic |
| Bacteria | Biotic |
| Air | Abiotic |
Real-World Connection
Healthy ecosystems provide many ecosystem services that humans rely on every day, including:
- Producing oxygen
- Purifying water
- Pollinating crops
- Recycling nutrients
- Controlling pests
- Regulating climate
- Providing food, medicines, and raw materials
Protecting ecosystems helps protect our own quality of life.
Did You Know?
Many coral reefs occupy less than 1% of the ocean floor, yet they support about 25% of all known marine species. Because of this incredible biodiversity, coral reefs are often called the "rainforests of the sea."
Key Terms
Abiotic factor – A non-living part of an ecosystem.
Biotic factor – A living or once-living part of an ecosystem.
Community – All the populations of different species living in an area.
Ecosystem – A community of organisms interacting with one another and with their physical environment.
Environment – The surroundings in which an organism lives.
Habitat – The natural place where an organism lives.
Interaction – The way organisms affect one another or their environment.
Key Takeaways
- An ecosystem is made up of living organisms and their non-living environment.
- Living (biotic) and non-living (abiotic) components interact continuously.
- Organisms depend on one another and on their physical surroundings for survival.
- Ecosystems exist in many forms, including forests, deserts, grasslands, freshwater, and marine environments.
- Changes to one part of an ecosystem can affect the entire interconnected system.
2. Biotic and Abiotic Factors
Learning outcomes
- I can distinguish between biotic and abiotic factors.
- I can identify examples of biotic and abiotic factors in ecosystems.
- I can explain how abiotic factors influence living organisms.
- I can describe how organisms depend on both biotic and abiotic factors.
- I can analyze ecosystem changes caused by environmental conditions.
3. Habitats and Niches
Learning outcomes
- I can define habitat and niche.
- I can explain the difference between a habitat and a niche.
- I can describe how organisms are adapted to their habitats.
- I can explain how niches reduce competition between species.
- I can identify habitats and niches in real ecosystems.
Introduction
Every organism needs a suitable place to live and a role to play within its ecosystem. A fish lives in water, a cactus grows in dry deserts, and a squirrel lives in forests. These places provide the food, shelter, and environmental conditions organisms need to survive. Scientists call this place an organism's habitat.
However, simply knowing where an organism lives does not tell the whole story. Every species also has a specific niche—its role or "job" within the ecosystem. An organism's niche includes what it eats, how it obtains food, where it reproduces, when it is active, and how it interacts with other organisms. Together, habitats and niches help explain how many different species can survive together in the same ecosystem.
What Is a Habitat?
A habitat is the natural environment where an organism lives.
A habitat provides everything an organism needs, including:
- Food
- Water
- Shelter
- Space
- Suitable temperature
- Places to reproduce
Different organisms require different habitats because they have different survival needs.
Examples of Habitats
| Organism | Habitat |
|---|---|
| Polar bear | Arctic sea ice |
| Camel | Desert |
| Frog | Pond or wetland |
| Eagle | Mountains and forests |
| Clownfish | Coral reef |
| Earthworm. | Moist soil |
Figure 1. Different organisms are adapted to different habitats, each providing the resources needed for survival.
What Is a Niche?
A niche is the role or function of an organism within its ecosystem.
A niche includes:
- What it eats
- What eats it
- Where it lives
- When it is active
- How it reproduces
- How it obtains food
- How it interacts with other organisms
- How it responds to environmental conditions
Every species occupies its own ecological niche.
Example
A honeybee's niche includes:
- Collecting nectar and pollen
- Pollinating flowering plants
- Serving as food for birds and spiders
- Being active during the daytime
Its habitat may simply be a meadow or forest, but its niche describes everything it does there.
Habitat vs Niche
These two terms are often confused.
A simple way to remember the difference is:
- Habitat = Where an organism lives
- Niche = What an organism does
| Habitat | Niche |
|---|---|
| Place or environment. | Role or job |
| "Home" | "Occupation" |
| Forest | Seed disperser |
| Pond | Predator of insects |
| Desert | Pollinator of cacti |
Think About It
Imagine a school.
- The school building is like a habitat.
- The teacher, principal, students, librarian, and caretaker each have different niches because they perform different roles.
Figure 2. A habitat describes where an organism lives, while a niche describes its role within the ecosystem.
Adaptations Help Organisms Survive
Organisms possess adaptations that allow them to survive in their habitats.
Adaptations may be:
Structural Adaptations
Physical features.
Examples:
- Thick fur on polar bears
- Long roots on desert plants
- Webbed feet on ducks
- Sharp claws on eagles
Behavioural Adaptations
Ways an organism behaves.
Examples:
- Birds migrating during winter
- Owls hunting at night
- Penguins huddling together for warmth
Physiological Adaptations
Internal body processes.
Examples:
- Camels storing fat in humps
- Fish regulating salt levels
- Snakes producing venom
Adaptations help organisms survive and reproduce successfully in their habitats.
Why Are Niches Important?
If many species competed for exactly the same food and space, some would struggle to survive.
Different niches help reduce competition by allowing species to use resources in different ways.
For example, in the same forest:
- Woodpeckers search for insects inside tree bark.
- Hawks hunt small mammals from the air.
- Deer eat leaves and grasses.
- Squirrels collect seeds and nuts.
- Earthworms feed on decaying organic matter.
Because each species uses different resources, they can all live in the same habitat.
Figure 3. Different species occupy different niches, reducing competition for resources within the same habitat.
The Competitive Exclusion Principle
Scientists have discovered that two species cannot occupy exactly the same niche in the same habitat for long periods.
This idea is called the Competitive Exclusion Principle.
If two species compete for exactly the same resources:
- One species may outcompete the other.
- One species may move to another habitat.
- One species may adapt to use different resources.
Over time, this helps create greater biodiversity.
Real Ecosystem Example: A Pond
Many organisms share the same pond habitat.
| Organism | Habitat. | Niche |
|---|---|---|
| Frog | Pond | Eats insects and serves as prey for birds |
| Duck | Pond | Eats aquatic plants and insects; disperses seeds |
| Dragonfly | Pond | Predator of mosquitoes and other insects |
| Water lily | Pond | Produces food through photosynthesis and provides shelter |
| Bacteria | Pond | Decompose dead organisms and recycle nutrients |
Although they all live in the same habitat, each species has a unique niche.
Worked Example
Question
Identify whether each statement describes a habitat or a niche.
| Statement | Answer |
|---|---|
| A coral reef where clownfish live. | Habitat |
| Pollinating flowers | Niche |
| Arctic sea ice | Habitat |
| Hunting mice at night | Niche |
| A freshwater lake | Habitat |
| Breaking down dead leaves | Niche |
Real-World Connection
Wildlife conservation involves protecting both habitats and niches. Saving a forest is not enough if important food sources, nesting sites, or pollinators disappear. Conservationists work to preserve entire ecosystems so that every species can continue performing its ecological role. For example, protecting wetlands helps conserve frogs, fish, birds, insects, and the plants they depend on, while also maintaining clean water and reducing flooding.
Did You Know?
Several species of Galápagos finches live on the same islands, but each species has a different-sized beak adapted to eating different foods, such as seeds, insects, or cactus flowers. By occupying different niches, they reduce competition and can live together successfully.
Key Terms
Adaptation – A characteristic that helps an organism survive and reproduce in its environment.
Competitive Exclusion Principle – The idea that two species cannot occupy exactly the same niche in the same habitat indefinitely.
Habitat – The natural environment where an organism lives.
Niche – The role or function of an organism within its ecosystem.
Resource – Anything an organism needs to survive, such as food, water, or shelter.
Species – A group of organisms that can reproduce and produce fertile offspring.
Key Takeaways
- A habitat is the place where an organism lives.
- A niche is the organism's role within its ecosystem.
- Adaptations help organisms survive in their habitats.
- Different niches allow many species to live together by reducing competition.
- Protecting ecosystems means preserving both habitats and the ecological roles that organisms perform.
4. Interactions Between Organisms
Learning outcomes
- I can describe different types of interactions between organisms.
- I can distinguish between competition, predation, and symbiosis.
- I can explain mutualism, commensalism, and parasitism.
- I can analyze how interactions affect survival and reproduction.
- I can identify examples of species interactions in ecosystems.
5. Population Dynamics
Learning outcomes
- I can define population and population size.
- I can explain factors that influence population growth.
- I can describe carrying capacity and limiting factors.
- I can interpret population data and trends.
- I can predict how environmental changes affect populations.
Introduction
Populations of living organisms are constantly changing. Some populations grow rapidly when food is plentiful and conditions are favourable, while others decline because of disease, predators, or habitat loss. Ecologists study these changes to understand how ecosystems function and to help protect wildlife.
The study of how and why populations change over time is called population dynamics. By understanding the factors that influence population size, scientists can predict future changes, manage endangered species, and monitor the health of ecosystems.
What Is a Population?
A population is a group of individuals of the same species living in the same area at the same time.
Examples include:
- All the deer living in a forest.
- All the clownfish living on a coral reef.
- All the oak trees growing in a woodland.
- All the frogs living in a pond.
Populations are one part of a larger ecosystem and interact with other populations.
Population Size
Population size is simply the number of individuals in a population.
For example:
- 250 rabbits in a grassland.
- 12,000 penguins in a breeding colony.
- 75 oak trees in a park.
Population size is always changing as individuals are born, die, enter, or leave a population.
Figure 1. A population is a group of individuals of the same species living in the same area.
Factors That Influence Population Growth
Population size changes because of four main processes.
Births (Natality)
When organisms reproduce, new individuals are added to the population.
More births generally increase population size.
Deaths (Mortality)
Deaths remove individuals from the population.
Disease, starvation, old age, predation, and accidents all contribute to mortality.
Immigration
Immigration occurs when individuals move into a population.
This increases population size.
Example:
A group of birds moves into a nearby forest.
Emigration
Emigration occurs when individuals leave a population.
This decreases population size.
Example:
Young wolves leave their pack to establish new territories.
Population Growth
A population grows when:
- Births are greater than deaths.
- Immigration is greater than emigration.
A population declines when:
- Deaths exceed births.
- Emigration exceeds immigration.
Limiting Factors
Although populations can grow, they cannot increase forever.
Limiting factors are environmental conditions that restrict population growth.
Some limiting factors include:
Food Availability
Less food means:
- Increased competition
- Slower growth
- Lower survival
Water Availability
Water shortages can reduce plant growth and affect every level of the food chain.
Space
Animals require territory, nesting sites, or shelter.
Limited space increases competition.
Predation
Predators remove individuals from prey populations.
Disease
Diseases spread more easily in crowded populations.
Climate
Extreme temperatures, droughts, floods, and storms may reduce population sizes.
Figure 2. Population growth is limited by environmental factors such as food, water, disease, and available space.
Carrying Capacity
Every ecosystem has a maximum population size that it can support.
This is called the carrying capacity.
Carrying capacity is the largest population that an environment can support over a long period without damaging its resources.
If a population exceeds the carrying capacity:
- Food becomes scarce.
- Competition increases.
- Disease spreads more easily.
- Death rates rise.
- Population growth slows or declines.
Eventually, the population usually stabilises near the carrying capacity.
Population Growth Curves
Scientists often represent population growth using graphs.
Exponential Growth
When resources are abundant, populations may grow rapidly.
Characteristics:
- Unlimited resources
- Rapid increase
- J-shaped curve
Examples:
- Bacteria in a laboratory
- Invasive species entering a new habitat
Logistic Growth
As resources become limited, growth slows and levels off near the carrying capacity.
Characteristics:
- Growth slows over time
- Population stabilises
- S-shaped curve
Most natural populations follow this pattern.
The logistic growth curve shows how a population grows quickly at first but slows as it approaches the environment's carrying capacity. This pattern is common in natural ecosystems where food, space, and other resources are limited.
Figure 3. Exponential growth occurs when resources are abundant, while logistic growth levels off as populations reach carrying capacity.
Interpreting Population Trends
Ecologists collect data over many years to understand how populations change.
A graph may show:
- Rapid population growth
- Stable populations
- Seasonal fluctuations
- Population decline
- Population recovery
Scientists use this information to:
- Protect endangered species.
- Manage fisheries.
- Monitor forests.
- Predict environmental changes.
How Environmental Changes Affect Populations
Changes to the environment often affect population size.
Habitat Loss
Building cities or clearing forests reduces available habitat.
Result:
- Population decreases.
Drought
Reduced rainfall means less water and less food.
Result:
- Smaller populations.
Introduction of a New Predator
A new predator may reduce prey populations.
Result:
- Population decline.
Conservation Efforts
Protecting habitats and reducing hunting can help endangered species recover.
Result:
- Population increases.
Figure 4. Environmental changes such as habitat destruction can cause populations to decline dramatically.
Worked Example
Question
A rabbit population changes over one year:
- Initial population: 120 rabbits
- Births: 35
- Deaths: 18
- Immigration: 12
- Emigration: 9
What is the population at the end of the year?
Solution
Population = Initial population + Births − Deaths + Immigration − Emigration
= 120 + 35 − 18 + 12 − 9
= 140 rabbits
The population increased because births and immigration were greater than deaths and emigration.
Real-World Connection
Wildlife biologists regularly monitor populations of endangered species such as sea turtles, pandas, and orangutans. By tracking population size and identifying limiting factors like habitat loss or illegal hunting, conservationists can develop strategies to help these species recover. Population studies are also used to manage fisheries, control invasive species, and protect biodiversity.
Did You Know?
The reintroduction of wolves to Yellowstone National Park in the United States changed much more than just the wolf population. By reducing elk numbers, wolves allowed young trees and shrubs to recover. This created new habitats for birds, beavers, insects, and many other species, demonstrating how changes in one population can affect an entire ecosystem.
Key Terms
Carrying capacity – The maximum population size an environment can support over a long period.
Emigration – The movement of individuals out of a population.
Immigration – The movement of individuals into a population.
Limiting factor – A factor that restricts population growth.
Mortality – The death rate within a population.
Natality – The birth rate within a population.
Population – A group of individuals of the same species living in the same area.
Population dynamics – The study of how and why populations change over time.
Population size – The number of individuals in a population.
Key Takeaways
- A population consists of members of the same species living in one area.
- Population size changes through births, deaths, immigration, and emigration.
- Limiting factors such as food, water, disease, and predators prevent unlimited population growth.
- Carrying capacity is the maximum population an environment can sustainably support.
- Environmental changes can cause populations to grow, decline, or stabilise over time.