Biology (9201) | The effect of human interaction on ecosystems and biodiversity

Welcome to the Ecology Section: Human Impact on Ecosystems

Hello Biologists! In this important chapter, we step away from how nature works by itself and look at how we – humans – fit into the picture. We are the most powerful species on Earth, and our actions have huge effects on every ecosystem. Understanding these effects is crucial not just for your exams, but for being a responsible global citizen!

Don’t worry if some of these topics sound serious; we will break down the causes, effects, and – most importantly – the solutions in simple, clear steps. Let’s get started!

1. Understanding Biodiversity and Why It Matters

What is Biodiversity?

Biodiversity simply means the variety of life in an area. It includes the variety of different species, the variety within a species (genetic variation), and the variety of different habitats.

Quick Review: The Importance of High Biodiversity

A diverse ecosystem is a stable ecosystem. Think of it like a football team: if one player gets injured, a strong team with many different skilled players can cope. If an ecosystem has low biodiversity, and one key species dies out, the whole system might collapse.

We rely on high biodiversity for many things:

• Resources: We get food (crops, fish), building materials (wood), and clothing fibres directly from species.
• Medicine: Many modern medicines were first discovered in wild plants and organisms (e.g., penicillin came from a fungus).
• Ecosystem Services: Nature provides essential services like purifying water, forming soil, and pollinating crops.
• Aesthetics: The beauty of nature adds value to our lives.

Key Takeaway: High biodiversity equals a healthy, stable, and useful environment for humans and all other life.

2. Human Interaction 1: Habitat Destruction (Deforestation)

The single greatest threat to biodiversity is habitat destruction, where the place an organism lives is destroyed or drastically changed. The main way this happens globally is through deforestation.

What is Deforestation?

Deforestation is the large-scale cutting down and clearing of forests. We do this primarily for three reasons:

1. To clear land for agriculture (farming, especially cattle ranching or growing single crops like palm oil).
2. To harvest timber (wood) for construction, paper, and fuel.
3. To clear space for urban development (building cities, roads, and factories).

The Domino Effects of Deforestation

Cutting down huge areas of forest causes serious problems:

A. Loss of Biodiversity

When you cut down a rainforest, you destroy the home of thousands of species immediately. These species often have nowhere else to go and quickly become endangered or extinct.

B. Soil Erosion

Forest soil is held together by the massive network of roots from trees and plants.

Step-by-Step Erosion:

1. Trees are cut down.
2. Rain falls directly onto the exposed soil.
3. Without roots to hold it, the topsoil (the fertile layer) is washed away into rivers.
4. This leaves behind infertile ground, making it impossible for new plants to grow naturally (desertification).

Analogy: Imagine sweeping a dirt floor. If you had water spilled (roots), the dirt stays put. If it’s dry (no roots), the dirt flies away!

C. Contribution to Climate Change

Trees are vital because they absorb carbon dioxide (\(CO_2\)) from the atmosphere during photosynthesis. They act as "carbon sinks."

• When forests are cut down and burned, all the carbon stored in the wood is released back into the atmosphere as \(CO_2\).
• Fewer trees mean less \(CO_2\) is absorbed from the atmosphere in the future.

Both of these factors increase the concentration of \(CO_2\), which is a greenhouse gas, leading to global warming (a rise in average global temperatures).

3. Human Interaction 2: Pollution

Pollution is the introduction of harmful substances into the environment. We can divide pollution into three main types: air, water, and land pollution.

A. Air Pollution

Most air pollution comes from burning fossil fuels (coal, oil, gas) in cars, power stations, and factories.

The Greenhouse Effect and Global Warming

Certain gases in the atmosphere (like \(CO_2\), methane, and water vapour) trap heat radiating from the Earth. This is the natural greenhouse effect, and it keeps the planet warm enough for life.

However, human activities (like burning fossil fuels and deforestation) increase the concentration of these gases, especially \(CO_2\). This causes an enhanced greenhouse effect, leading to global warming (climate change).

Did You Know? Methane is a much more potent greenhouse gas than \(CO_2\), but there is far less of it in the atmosphere. It comes from natural gas leaks, rice fields, and cattle farming.

Acid Rain

When fossil fuels are burned, they release gases like sulfur dioxide and nitrogen oxides.

Step-by-Step Acid Rain Formation:

1. Sulfur dioxide and nitrogen oxides rise into the atmosphere.
2. They dissolve in the clouds and react with water vapour.
3. This forms weak acids (like sulfuric acid and nitric acid).
4. The polluted clouds release this acid in the form of rain or snow.

Acid rain damages ecosystems by lowering the pH of lakes (killing fish) and damaging the leaves and roots of trees.

B. Water Pollution

Water pollution severely harms aquatic ecosystems and human health.

Eutrophication (The Fertilizer Problem)

Farmers often use artificial fertilizers to help crops grow. If it rains heavily, these fertilizers can wash (run off) into nearby rivers and lakes. This causes a devastating process called eutrophication.

Eutrophication Step-by-Step (The Death of a Lake):

1. Run-off: Excess nitrates and phosphates (nutrients) from fertilizers enter the water.
2. Algal Bloom: The sudden large supply of nutrients causes a massive, rapid growth of algae on the surface (an "algal bloom").
3. Light Blocked: The thick layer of algae blocks sunlight from reaching the plants living deeper underwater. These plants die.
4. Decomposition: When the surface algae eventually die, they sink to the bottom.
5. Oxygen Depletion: Bacteria break down (decompose) the dead plants and algae. This decomposition process uses up huge amounts of the dissolved oxygen in the water.
6. Mass Mortality: Fish and other aquatic organisms suffocate and die due to lack of oxygen.

Common Mistake Alert: Students often think the algae itself kills the fish. It doesn't! It’s the bacteria decomposing the dead algae that uses up the oxygen, leading to the death of the fish.

C. Land Pollution

The main sources of land pollution are:

• Landfill Waste: Dumping non-biodegradable waste (like plastics, glass, and metals) in large pits. These materials take hundreds of years to break down, contaminating soil and water.
• Chemical Dumping: Improper disposal of industrial waste, which can poison soil and enter the food chain.

Key Takeaway: Pollution introduces harmful chemicals and gases, leading to climate change, habitat destruction (acid rain), and oxygen depletion in water (eutrophication).

4. Conservation: Protecting Our Future

Humans must find ways to reduce their negative impact and protect the remaining ecosystems. This active protection is called conservation.

What is Conservation?

Conservation involves managing and protecting natural resources, habitats, and species to maintain biodiversity and ensure sustainability.

The Goal: Sustainability

The core concept is sustainability. This means using natural resources (like wood, water, or fish) at a rate that allows them to be naturally replaced. We meet the needs of the present population without harming the ability of future generations to meet their own needs.

Methods of Conservation

Conservation strategies are usually split into protecting the species itself and protecting its environment.

A. Protecting the Environment (In Situ Conservation)

This means protecting the species in its natural habitat.

• Protected Areas: Establishing National Parks and Nature Reserves where human activity is restricted (e.g., no hunting, no deforestation).
• Sustainable Forestry/Fishing: Implementing strict rules on how many trees can be cut or how many fish can be caught to allow populations time to recover.

B. Protecting the Species (Ex Situ Conservation)

This means protecting the species outside its natural habitat.

• Zoos and Captive Breeding: Breeding endangered animals in zoos and controlled environments, with the eventual aim of releasing them back into the wild.
• Seed Banks: Storing seeds from thousands of different plant species to protect the genetic diversity of plants in case of catastrophe.
• Botanical Gardens: Maintaining collections of diverse plants for research and conservation.

Why is Conservation Difficult?

Conservation efforts often face challenges:

• Economic Conflict: Protecting a forest means local people cannot use the land for farming or profit, leading to clashes between economic needs and environmental needs.
• Climate Change: Protecting an area doesn't stop the effects of global warming, which can still destroy a species' habitat.
• Poaching: Illegal hunting for profit remains a major threat to specific endangered animals.

Final Key Takeaway: Conservation, through sustainable practices and protection programs (both in situ and ex situ), is essential to reversing the damage done by human interactions and ensuring a healthy planet for the future.