Ecosystems and biodiversity

Introduction: The Giant Web of Life

Welcome! In this chapter, we are exploring Ecosystems and Biodiversity. Think of an ecosystem as a huge, busy city where every living thing—from the smallest blade of grass to the biggest bird—has a specific job to do. If one person stops working, it affects everyone else. We’ll learn how living things interact, why variety is the "spice of life" for our planet, and how humans are trying to fix the mistakes of the past. Understanding this helps us explain change in our world.

4.4.2.1 Levels of Organisation

Scientists don’t just look at nature as one big blur. They break it down into layers, like a set of Russian nesting dolls.
Don't worry if this seems like a lot of definitions! Just remember we are moving from "one single thing" to "the whole world."

• Individual Organism: Just one single living thing (e.g., one rabbit).
• Population: All the individuals of the same species living in the same area (e.g., all the rabbits in a field).
• Community: All the different populations of different species living together (e.g., the rabbits, the grass, the foxes, and the insects in that field).
• Habitat: The specific place where an organism lives (its "address").
• Ecosystem: The community of living organisms interacting with the non-living parts of their environment (like soil, water, and air).

Feeding Relationships

Energy flows through a community via food chains.
1. Producers: Almost always green plants or algae. They use light from the Sun to make their own food (glucose).
2. Primary Consumers: Animals that eat the producers (herbivores).
3. Secondary Consumers: Animals that eat the primary consumers (carnivores).
4. Tertiary Consumers: Animals that eat the secondary consumers.

Analogy: Think of the Producer as a chef making a meal from scratch, and the consumers as the customers at the restaurant eating that meal!

Predators and Prey

In a healthy community, the numbers of predators (the hunters) and prey (the hunted) rise and fall in cycles. If the number of prey goes up, the predators have more food, so their numbers go up too. But then, more predators eat more prey, so the prey numbers fall... and the cycle starts again.

Quick Review:
- Predator: An animal that kills and eats other animals.
- Prey: The animal that gets eaten.

Key Takeaway: Nature is organised into layers, and energy moves through those layers by eating!

4.4.2.2 Interdependence and Competition

In an ecosystem, no organism is an island. They all need each other to survive. This is called interdependence.

• Plants depend on animals for pollination and seed dispersal.
• Animals depend on plants for food and shelter.
• If one species is removed, it can ruin the balance of the whole community.

The Fight for Resources (Competition)

Resources are limited, so organisms have to compete to get what they need.
- Plants compete for: Light, space, water, and mineral ions from the soil.
- Animals compete for: Food, mates, and territory.

Did you know? A "stable community" is one where all the species and environmental factors are in balance, so population sizes stay roughly the same.

Key Takeaway: Organisms rely on each other (interdependence) but also fight for what they need (competition).

4.4.2.3 Factors that Affect Communities

Why do some animals live in one place but not another? It depends on two types of factors: Abiotic and Biotic.

Memory Trick:
A-biotic = A is for Away from life (Non-living).
Biotic = B is for Biological (Living).

Abiotic Factors (Non-living)

• Light intensity: Plants need light for photosynthesis.
• Temperature: Affects how quickly organisms can grow.
• Moisture levels: Most things need water to survive!
• Soil pH and mineral content: Different plants like different soil types.
• Wind intensity and direction: Can affect plant growth and seed dispersal.
• Carbon dioxide (\(CO_2\)) levels: Important for plants.
• Oxygen (\(O_2\)) levels: Crucial for animals living in water.

Biotic Factors (Living)

• Availability of food: More food means more survival.
• New predators arriving: Can wipe out a population.
• New diseases (pathogens): Can spread quickly through a community.
• One species outcompeting another: If one species is better at getting food, the other might die out.

Common Mistake: Students often forget that "food" is a biotic factor (because food comes from other living things), while "water" is an abiotic factor.

Key Takeaway: Living things are shaped by both their physical environment and the other living things around them.

4.4.2.4 Field Investigations

How do scientists know how many organisms are in an ecosystem? They can't count every single blade of grass! Instead, they use sampling.

1. Quadrats: These are square frames (usually \(0.5m \times 0.5m\)). You place them randomly on the ground and count the organisms inside.
2. Transects: This is a line (like a tape measure) stretched across a habitat. You count organisms along the line to see how they change from one area to another (e.g., moving from a sunny field into a dark woods).

Calculating the Mean

To get a good estimate, you must take many samples and calculate the arithmetic mean:
\( \text{Mean} = \frac{\text{Total number of organisms counted}}{\text{Number of samples (quadrats)}} \)

Key Takeaway: Sampling with quadrats and transects lets us estimate population sizes without counting everything.

4.4.2.5 Biodiversity

Biodiversity is the variety of all the different species of organisms on Earth or within an ecosystem.

Why is high biodiversity good?
High biodiversity makes an ecosystem more stable. It reduces the dependence of one species on another for food or shelter. If one food source disappears, there are others to choose from.

Key Takeaway: More variety = A healthier, tougher planet.

4.4.2.6 & 4.4.2.7 Human Impact: The Bad and The Good

Human activities can change ecosystems in massive ways. Some are negative, but we are learning how to make positive changes too.

Negative Impacts (How we hurt biodiversity)

• Land Use: Building, quarrying, and farming destroy habitats.
• Peat Bogs: Destroying bogs to make garden compost releases \(CO_2\) and kills unique species.
• Pollution: Sewage and toxic chemicals in water; smoke and gases in the air.
• Global Warming: Caused by human activities like burning fossil fuels.

Positive Impacts (How we help biodiversity)

We are trying to reduce our negative effects through conservation:

• Breeding programmes: For endangered species (like pandas or tigers).
• Protection/Regeneration: Protecting rare habitats like coral reefs or wetlands.
• Field margins and hedgerows: Reintroducing these around farms gives many species a place to live.
• Recycling: Reducing the amount of waste that goes to landfills.
• Reducing deforestation: To keep habitats intact and lower \(CO_2\).

Key Takeaway: Humans have a huge impact on the planet, but through science and effort, we can protect and restore biodiversity.

Quick Summary Review

1. Community: All living things in a habitat.
2. Abiotic: Non-living (e.g., Temp).
3. Biotic: Living (e.g., Predators).
4. Quadrat: A tool for random sampling.
5. Biodiversity: The variety of life.