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24 June 2026
Module 5: Ecology – NQF4 Online Field Guide Course
Module 5 of 18

Ecology

Discover how Earth’s systems work together — from the six spheres to the great nutrient cycles that sustain all life. Understand the water, oxygen, carbon, and nitrogen cycles, ecological niches, and the limits that shape where organisms can survive.

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Lecture & Materials

Live lecture recording, presentation slides & key learning outcomes
What You’ll Learn By the end of this module, you should be able to identify and describe the six spheres of Earth, explain the water, oxygen, carbon, and nitrogen cycles in detail, distinguish between fundamental and realized niches, identify key limiting factors, and apply ecological principles to explain species distribution and community composition in the field.
✓ Identify and describe the six spheres of Earth (geosphere, atmosphere, hydrosphere, cryosphere, biosphere, anthroposphere) and how humans affect each
✓ Explain the water cycle processes: evaporation, condensation, precipitation, transpiration, sublimation, infiltration, and groundwater flow
✓ Describe the oxygen cycle including photosynthesis, cellular respiration, and combustion
✓ Explain the carbon cycle and how human activity (burning fossil fuels) has disrupted the natural balance
✓ Describe the nitrogen cycle: nitrogen fixation, nitrification, denitrification, and why nitrogen is often the most limiting nutrient
✓ Distinguish between fundamental niche and realized niche with real-world examples
✓ Identify key limiting factors (light, climate, soil, fire, toxins) and explain how they restrict species distribution
✓ Apply Shelford’s Law of Tolerance and the Law of Minimum to predict species survival and growth

🧠 Earth’s Systems — The Spheres, Cycles & Limits

This infographic summarises the six spheres of Earth, the four major biogeochemical cycles, ecological niches, and limiting factors covered in this module. Generated from our course source documents using NotebookLM.

Earth's Systems: The Spheres, Cycles and Limits - Infographic

🎥 Video Lesson Recording

Watch the full Module 5: Ecology lecture recording with Richard Davis. Use full-screen for the best viewing experience.

📋 Presentation Slides

Review the full slide deck from the live lecture below.

If the PDF doesn’t load, please contact elearning@ecotraining.co.za for assistance.

Lecture Content Overview

This module covers six major themes: the six spheres of Earth, the water cycle, the oxygen cycle, the carbon cycle, the nitrogen cycle, and ecological niches & limiting factors. Duration: approximately 120 minutes.

Part 1: The Six Spheres of Earth
Geosphere — The solid Earth comprised of rocks, minerals, and continental plates. Foundation of all terrestrial ecosystems.
Atmosphere — The gaseous envelope surrounding Earth. Contains nitrogen (78%), oxygen (21%), argon (0.93%), and carbon dioxide (0.04%), plus water vapour. Regulates temperature through the greenhouse effect.
Hydrosphere — All water on Earth: 96.5% saltwater in oceans, 3.5% freshwater (mostly frozen in glaciers and ice caps). Only 0.01% is surface freshwater in lakes, rivers, and marshes — the tiny fraction humans interact with daily.
Cryosphere — The frozen portion of Earth: glaciers, ice caps, sea ice, and permafrost. Critical for reflecting sunlight and regulating global temperature.
Biosphere — All living organisms on Earth: an estimated 5-30 million species. Exists in a thin shell from the soil to the upper atmosphere.
Anthroposphere — The human-altered sphere. Humans have modified approximately 75% of Earth’s land surface, fundamentally changing ecosystems and biogeochemical cycles.
Part 2: The Water Cycle
The Processes — Evaporation (water from oceans, lakes, soil to atmosphere), transpiration (water from plants), condensation (water vapour to clouds), precipitation (rain, snow, sleet), infiltration (water into soil), groundwater flow (slow movement through rock layers), and runoff (water flowing back to oceans).
Water Budget on Earth — 96.5% oceans, 3.5% freshwater. Of freshwater: 68.7% frozen in glaciers and ice caps, 30.1% groundwater, 1.2% surface freshwater. River water is renewed every 16 days, atmospheric water every 8 days, but groundwater takes thousands of years.
The Hydrological Cycle in Ecosystems — Plants pull water from soil through roots (transpiration), returning it to the atmosphere. Soil moisture and groundwater support vegetation growth. Wetlands act as water filters and storage. The cycle connects geology, climate, vegetation, and animals.
Part 3: The Oxygen Cycle
Photosynthesis — Plants (and some bacteria) combine carbon dioxide, water, and sunlight to produce glucose and oxygen. Formula: CO2 + H2O + light energy → glucose + O2. This is the primary source of energy for almost all life on Earth (a few specialised ecosystems, such as deep-sea vents, run on chemosynthesis instead).
Cellular Respiration — All organisms use oxygen to break down glucose for energy. Formula: glucose + O2 → energy + CO2 + water. This is the reverse of photosynthesis.
Combustion — Burning of fossil fuels (coal, oil, gas) in oxygen consumes O2 and releases CO2. A major contributor to carbon cycle disruption.
Ocean Oxygen Production — Marine photosynthesis (phytoplankton, seagrass, and algae) is estimated to produce around half of the oxygen in Earth’s atmosphere — as important as terrestrial plants. The oceans are a vast oxygen factory, not just a store.
Part 4: The Carbon Cycle
Natural Carbon Cycle — Atmosphere (CO2) → plants (photosynthesis) → animals (eating plants) → respiration (returns CO2) → death → decomposition (returns CO2 to soil and atmosphere). Carbon stored in organic matter, soil, sedimentary rock, and dissolved in oceans.
Fossil Fuels & Human Disruption — Coal, oil, and natural gas are carbon stored for millions of years by ancient organisms. Humans burn these in decades, releasing vast amounts of CO2 into the atmosphere far faster than natural cycles can absorb. Atmospheric CO2 has increased 50% since the Industrial Revolution.
Solutions — Reforestation (plants absorb CO2), renewable energy (reduces fossil fuel burning), carbon capture technology, and protecting soil carbon through regenerative agriculture.
Part 5: The Nitrogen Cycle
Nitrogen in the Atmosphere — N2 makes up 78% of the atmosphere but is not directly usable by plants. Only nitrogen-fixing bacteria can convert atmospheric N2 into ammonia (NH3), which plants can use.
Nitrogen Fixation — Bacteria (free-living and symbiotic in root nodules of legumes) convert N2 to ammonia. Legumes (acacia, beans, clover) are nitrogen factories — animals eating legumes gain protein-building nitrogen.
Nitrification & Plant Uptake — Bacteria convert ammonia to nitrite, then nitrate (NO3-), which plants absorb through roots. This is the plant-available form of nitrogen.
Denitrification & Return to Atmosphere — When organic matter decays and nitrogen is not immediately used, bacteria convert nitrate back to N2 gas, returning it to the atmosphere. The cycle completes.
Nitrogen as Limiting Nutrient — Nitrogen is often the most limiting nutrient for plant growth because the fixation step is slow and requires specific bacteria. Adding nitrogen fertiliser boosts crop yields dramatically, but excess nitrogen causes water pollution (eutrophication) and dead zones in coastal waters.
Cation Exchange & Soil Chemistry — Clay soils hold and exchange nutrients (including nitrogen compounds) better than sandy soils. Understanding soil type is key to predicting plant nutrition and vegetation patterns.
Part 6: Ecology & Limiting Factors
Ecological Niche — An organism’s niche is its unique role and place in nature: what it eats, where it lives, what eats it, when it is active, and how it interacts with its environment. The barnacle is a classic example: its fundamental niche is much broader than its realized niche (only where dominant competitors are absent).
Fundamental vs Realized Niche — Fundamental niche = the full range of conditions an organism could theoretically survive in. Realized niche = where it actually lives in nature, often limited by competition, predation, and other factors.
Limiting Factors — Light, climate (temperature, rainfall), soil type and nutrients, fire, toxins, and competition. Any single limiting factor can restrict where a species can survive, regardless of how favourable other conditions are.
Shelford’s Law of Tolerance — Organisms have an optimal range for each environmental factor, with zones of stress and intolerance on either side. An organism thrives in the optimal zone, tolerates stress zones, and dies in intolerance zones.
Law of Minimum — Plant growth is limited by the scarcest essential resource (Liebig’s Law). If nitrogen is scarce but water is abundant, nitrogen becomes the limiting factor. Add nitrogen, and a different nutrient may become limiting.
Did You Know?

Only 0.01% of all water on Earth is surface freshwater in lakes, rivers, and marshes — that tiny fraction is what we interact with every day. The rest is saltwater (96.5%), frozen in glaciers, or locked in groundwater thousands of metres underground. Every raindrop is recycled: it has rained on dinosaurs, flowed through ancient civilisations, and will rain on your grandchildren. You are literally made of recycled water from billions of years of Earth history.

Guide Pro Tip

Everything connects: Geology creates soil → Soil determines water and nutrient availability → This drives which plants grow → Plants determine which animals thrive. Master the cycles in this module and you can explain any ecosystem to any guest. When you see a patch of acacia trees in otherwise grass-dominated savanna, you can tell guests: “Acacias are nitrogen-fixing legumes — they add nitrogen to the soil, which is why the soil here is richer and can support woody growth. Over time, they create islands of fertility.” That’s not just ecology; that’s storytelling that transforms a curiosity into understanding.

📖 Key Terminology

Examiners expect precise use of the correct terms. Make sure you can define each of these in your own words.

Biogeochemical cycle — The movement of an element (water, carbon, nitrogen, oxygen) between living organisms and the non-living environment.
Nitrogen fixation — The conversion of atmospheric N₂ into ammonia by specialised bacteria; the only natural way nitrogen becomes available to plants.
Nitrification — Bacteria converting ammonia → nitrite → nitrate (the plant-usable form). Not the same as fixation.
Denitrification — Bacteria converting nitrate back to N₂ gas, returning nitrogen to the atmosphere and completing the cycle.
Eutrophication — Nutrient over-enrichment (often excess nitrogen) of water, causing algal blooms and oxygen-starved dead zones.
Transpiration — Water loss from plants to the atmosphere; a key part of the water cycle, not a separate process.
Fundamental niche — The full range of conditions in which a species could theoretically survive.
Realized niche — The narrower range a species actually occupies, limited by competition, predation, and other factors.
Limiting factor — Any single resource or condition (light, water, nutrients, fire, toxins) that restricts where a species can live.
Shelford’s Law of Tolerance — Every species has an optimal range for each environmental factor, with stress and intolerance zones either side.
Liebig’s Law of the Minimum — Growth is limited by the single scarcest essential resource, not by the total resources available.
⚠ Examiner’s Note — where students lose marks Common slips at NQF4: confusing nitrogen fixation (N₂ → ammonia) with nitrification (ammonia → nitrate); claiming plants absorb atmospheric nitrogen directly (they cannot — only bacteria fix it); reversing fundamental and realized niche (the realized niche is the smaller, real-world one); and forgetting transpiration as part of the water cycle. Know the direction of each cycle, not just its name.

📚 Recommended Reading

The core references every serious field guide should know — these go deeper than any single lecture.

Beat About the Bush: Mammals & Birds — Trevor Carnaby. The guide’s companion for understanding how species fit their environment.
The Safari Companion — Richard D. Estes. A field reference on animal behaviour and ecological roles.
FGASA Field Guide (NQF4) study material — Your prescribed manual; cross-reference the cycles and niche concepts here for exam preparation.
SANBI resources — sanbi.org for South African biomes, soils, and vegetation patterns that bring limiting factors to life.
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Enrichment & Resources

Videos, documentaries, research, organisations & apps to deepen your ecology knowledge

Go beyond the lecture — these resources will help you understand Earth’s life-support systems and explain to guests why ecosystems are as interconnected and finely balanced as they are.

🌿 EcoTraining in the Field

Breaking Down Barriers — Making the Kruger Park Bigger

Everything in this module connects — and nowhere is that clearer than on the ground. Watch how dropping the fences between reserves restores the natural flow of animals, water, and nutrients across the landscape, letting ecosystems function as one connected whole. A real EcoTraining example of the spheres, cycles, niches, and limiting factors you’ve just studied, working together in the wild.

🎬 Recommended Videos

The Water Cycle

NASA’s comprehensive look at water movement

The Carbon Cycle

How carbon moves through Earth’s systems

Nitrogen Cycle Explained

Essential nutrient cycling for life

Ecological Niches

How organisms fit into ecosystems

📺 Must-Watch Documentaries

Documentary • Netflix/YouTube • Free Trailers

Our Planet

David Attenborough explores Earth’s ecosystems and the cascading impact of human activity on habitats and wildlife. Every episode connects directly to the ecological concepts in this module — water cycles, limiting factors, species niches, and ecosystem collapse.

Watch Trailer
Documentary • Netflix • Streaming

A Life on Our Planet

David Attenborough’s witness statement on the natural world, charting biodiversity loss and ecosystem collapse over his lifetime. A profound exploration of how human activity disrupts Earth’s cycles and niches.

Watch on Netflix
Documentary • Free • Streaming

Kiss the Ground

Explores the critical connection between soil health, carbon sequestration, and climate change. Directly relevant to the carbon and nitrogen cycles and how human land management affects biogeochemical processes.

Watch Free
Documentary • YouTube • Free

Home

Yann Arthus-Bertrand’s stunning aerial documentary showing Earth’s ecosystems and human impact from above. Visually powerful exploration of how ecosystems are distributed and how humans have disrupted them.

Watch on YouTube

📚 Research & Further Reading

Research • IPCC Climate Reports

IPCC Climate Reports

The latest scientific assessments on climate change, carbon cycles, and human impact on Earth systems. Essential reading for understanding the science behind conservation and how carbon and other cycles are disrupted by human activity.

View Reports
Research • NASA Earth Observatory

NASA Earth Observatory

Satellite imagery and research on Earth’s atmosphere, water, carbon, and nitrogen cycles. Visual data and measurements that bring ecological cycles to life — see cloud formation, ocean currents, carbon dioxide concentrations in real time.

Explore Data

📱 Useful Field Apps

Monitor Earth’s vital signs, document species, and understand ecological processes in real time.

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Earth Now (NASA)

Real-time visualisation of Earth’s vital signs: CO2 levels, sea level rise, temperature anomalies. See the cycles in action.

Get App
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iNaturalist

Document and identify species in the field. Build your understanding of biodiversity and ecological niches through citizen science and community identification.

Get App
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Water Footprint Calculator

Calculate your personal water footprint and understand how the water cycle connects to your daily life and consumption patterns.

Use Tool

🏢 Organisations & Communities

SANBI (South African National Biodiversity Institute)

South Africa’s authority on biodiversity. Research, conservation status assessments, and educational resources on local ecosystems and how ecological principles apply to South African conservation.

Visit SANBI

WWF South Africa

Conservation organisation working to protect South Africa’s ecosystems. Resources on climate, water cycles, biodiversity, and how ecological limits shape conservation strategy.

Visit WWF South Africa

Earthwatch Institute

Citizen science expeditions and research programmes. Get involved in real ecological research and contribute to understanding Earth’s systems and human impact on cycles and niches.

Join Expeditions
Guide Pro Tip

When guests ask why the landscape looks the way it does, you now have a complete explanation framework: “Here we see more grass because the water cycle brings 700mm of rain annually. But there — on that rocky ridge with poor soil — we see shrubs. Why? That dry slope limits water availability (limiting factor). The plants that survive here are shade-tolerant and drought-resistant. They occupy a realised niche determined by water, light, and competition. Elsewhere, where water is more available, grasslands can thrive instead.” That’s ecology applied to the landscape your guests can see.

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Discussion & Community

Reflect on what you’ve learned and connect with fellow guides

Great guides explain how Earth’s systems work. Use these prompts to practise applying ecological cycles and limiting factors to real landscapes — and share your insights with your classmates.

1 Cycle Spotter

Choose one of the four major cycles (water, oxygen, carbon, nitrogen) and find three real-world examples of it happening around you today. Share your observations. For example: “Water cycle: I saw dew on grass this morning (condensation), the sun evaporated it into the sky, and rain fell last night (precipitation).”

2 The Human Footprint

Which of the six Earth spheres do you think humans have impacted most severely? Make your case with specific examples from the lecture. How has human activity disrupted the natural cycles in that sphere?

3 Niche Detective

Pick any animal you’ve observed in the wild. Describe its ecological niche (what does it eat, where does it live, when is it active, what competes with it?). What do you think its fundamental niche might be versus its realised niche? What factors limit it?

4 The Carbon Conversation

A guest asks: “What’s the big deal about carbon dioxide?” Explain the carbon cycle and human disruption in 3-4 sentences using what you learned. Then explain why the nitrogen cycle is different (and why nitrogen is often limiting instead).

Join the Conversation Share your cycle observations, niche discoveries, limiting factor insights, and questions with your fellow students and the EcoTraining eLearning team in our WhatsApp group.
EcoTraining eLearning — Bringing Nature Home

Questions? Contact us at elearning@ecotraining.co.za
www.ecotrainingonline.co.za  •  WhatsApp Group

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