Ecology and Evolution

MYP Unit Framework

Key Concept: CHANGE Related Concepts: Balance. Environment. Evolution. Global Context: Globalization and Sustainability (How are human activities fundamentally altering ecosystems and evolutionary processes?) Statement of Inquiry: Ecosystems and species evolve through dynamic interactions that human activity is now fundamentally altering.

Inquiry Questions

1. Evolution by Natural Selection

Darwin's Revolutionary Idea

'In 1859, Charles Darwin published "On the Origin of Species." His central idea — evolution by NATURAL SELECTION — is the UNIFYING THEORY of all biology. It explains the DIVERSITY of life on Earth, the SIMILARITIES between species, and how organisms are ADAPTED to their environments.'

The Four Principles of Natural Selection

'Over GENERATIONS, the frequency of advantageous traits INCREASES in the population. The population EVOLVES. This is NOT a purposeful process — it is the RESULT of variation and differential survival. There is no "goal" or "direction" in evolution.'

Evidence for Evolution

Speciation — The Formation of New Species

'Speciation occurs when populations become REPRODUCTIVELY ISOLATED — they can no longer interbreed. Over time, MUTATIONS and NATURAL SELECTION cause the isolated populations to become so DIFFERENT that they are distinct species.'

'Darwin's finches in the Galapagos Islands are a CLASSIC example. Finches from different islands had DIFFERENT BEAK SHAPES — adapted to the specific food sources available on their island. A single ancestral species had DIVERSIFIED into multiple species, each occupying a different NICHE.'

2. Ecology — The Web of Life

Ecosystems

'An ECOSYSTEM includes ALL the organisms in a given area AND the non-living (abiotic) factors they interact with — soil, water, air, sunlight, temperature. Ecosystems can be as SMALL as a pond or as LARGE as a rainforest.'

Energy Flow — Trophic Levels

'Energy flows through an ecosystem in ONE DIRECTION — from the Sun, to producers, to consumers, to decomposers.'

The 10% Rule

'Only about 10% of the energy at one trophic level is TRANSFERRED to the next. The rest is used for METABOLISM or lost as HEAT. This is why food chains are LIMITED in length — and why TOP PREDATORS are RARE. It takes a LOT of producers to support one lion.'

Nutrient Cycles — Carbon and Nitrogen

Carbon cycle: 'Carbon moves between the atmosphere (CO₂), living organisms (organic compounds), oceans (dissolved CO₂), and the Earth's crust (fossil fuels, limestone). PHOTOSYNTHESIS removes CO₂ from the atmosphere. RESPIRATION, DECOMPOSITION, and COMBUSTION (including burning fossil fuels) RELEASE CO₂ back. Human activity — especially burning fossil fuels and deforestation — is UPSETTING this balance, causing atmospheric CO₂ to RISE.'

Nitrogen cycle: 'Nitrogen is ESSENTIAL for proteins and DNA — but most organisms cannot use atmospheric N₂ DIRECTLY. NITROGEN-FIXING bacteria convert N₂ into ammonia (NH₃). Nitrifying bacteria convert ammonia into nitrates (NO₃⁻) that plants can ABSORB. Denitrifying bacteria return nitrogen to the atmosphere.'

3. Biodiversity — The Variety of Life

Why Biodiversity Matters

'Biodiversity — the variety of life at ALL levels (genes, species, ecosystems) — is ESSENTIAL for ecosystem health. High biodiversity means MORE RESILIENCE — an ecosystem with many species can BETTER withstand disturbance than a monoculture. Biodiversity provides ECOSYSTEM SERVICES: pollination, water purification, climate regulation, nutrient cycling, and CULTURAL value.'

Threats to Biodiversity

Habitat destruction: 'The SINGLE BIGGEST threat. Forests are cleared. Wetlands are drained. Coral reefs are bleached. An area of rainforest the size of a FOOTBALL FIELD is destroyed every SECOND.'

Overexploitation: 'Overfishing, poaching, and hunting have driven many species to the brink. The NORTHERN WHITE RHINO is functionally EXTINCT — only TWO females remain, both infertile.'

Invasive species: 'When species are INTRODUCED to new habitats (deliberately or accidentally), they can OUTCOMPETE, PREDATE UPON, or INTRODUCE DISEASES to native species. Cane toads in Australia. Brown tree snakes in Guam.'

Pollution: 'Plastics, pesticides, heavy metals, and nutrient pollution (fertiliser runoff causing ALGAL BLOOMS and dead zones) harm wildlife and disrupt ecosystems.'

Climate change: 'Climate change is AMPLIFYING all other threats. Species that CANNOT adapt or MIGRATE fast enough face EXTINCTION. The IPCC estimates that 20–30% of species face an INCREASED risk of extinction if global warming exceeds 1.5°C.'

4. Climate Change Science

The Greenhouse Effect — A Natural Process

'The greenhouse effect is NATURAL — and ESSENTIAL for life. Greenhouse gases (CO₂, CH₄, H₂O) in the atmosphere TRAP some of the heat radiated from Earth's surface. Without them, Earth would be about –18°C (below freezing). The problem is that human activity is INCREASING the concentration of greenhouse gases — amplifying the greenhouse effect and causing GLOBAL WARMING.'

Human Contribution

'Since the Industrial Revolution, CO₂ concentrations have risen from ~280 ppm to over 420 ppm — a 50% increase. This is PRIMARILY from: Burning fossil fuels (coal, oil, gas) for energy and transport. DEFORESTATION (forests are carbon SINKS — cutting them releases stored carbon and reduces future absorption). AGRICULTURE (livestock produce methane; fertilisers produce nitrous oxide).'

The Consequences

'Global average temperature has risen by ~1.2°C since pre-industrial times. Consequences include: MELTING ice sheets and glaciers. SEA LEVEL RISE (about 3.3 mm per year, accelerating). MORE FREQUENT and INTENSE extreme weather: heatwaves, droughts, floods, hurricanes. ECOSYSTEM COLLAPSE — coral bleaching, forest dieback, species extinction. FOOD and WATER insecurity. CLIMATE MIGRATION — people forced to leave their homes due to climate impacts.'

5. Conservation Strategies

What Can Be Done?

Protected areas: National parks, wildlife reserves, and marine protected areas provide SAFE HAVENS for biodiversity. 'But protected areas cover only about 15% of land and 7% of oceans — and many are poorly ENFORCED.'

Restoration ecology: Actively restoring degraded ecosystems — replanting forests, removing invasive species, reintroducing native species. 'The "BIG GREEN WALL" project in China aims to plant 100 billion trees across 4,500 km to combat desertification.'

Sustainable resource use: Fishing quotas, sustainable forestry, wildlife-friendly farming. 'The Marine Stewardship Council (MSC) certifies sustainable fisheries — look for the blue label on fish products.'

Climate action: Reducing greenhouse gas emissions. Transitioning to renewable energy. Protecting and restoring carbon sinks (forests, wetlands, oceans). 'The Paris Agreement (2015) commits nations to limit global warming to well below 2°C — but current policies are NOT ON TRACK to meet this goal.'

Captive breeding and rewilding: Breeding endangered species in captivity and reintroducing them to the wild. 'The CALIFORNIA CONDOR was brought back from the brink — from only 27 individuals (1987) to over 500 today.'

Your Summative Assessment — The Ecology Research Report

Task: Investigate a LOCAL ECOSYSTEM (a park, pond, forest, coastal area, or even a school garden). Conduct a FIELD STUDY: identify at least FIVE species present, draw a FOOD WEB showing their relationships, and describe the ecosystem's features. Then write a 1200–1500 word report analysing: What HUMAN IMPACTS are affecting this ecosystem? What is the THREAT or CONSERVATION STATUS of any notable species? What CONSERVATION STRATEGIES could protect or restore this ecosystem? Connect your local findings to GLOBAL ecological patterns (climate change, biodiversity loss, conservation).

'This assessment connects LOCAL observation with GLOBAL understanding — a key skill for IB DP Environmental Systems and Societies (ESS) and Biology.'

ATL Skills

Formative Assessments

Interdisciplinary Connections

• Chemistry: Carbon cycle, greenhouse gases, ocean acidification.
• Geography: Biomes, climate zones, human-environment interaction, climate change impacts.
• Mathematics: Population growth models, biodiversity indices, statistical analysis of ecological data.
• TOK: What counts as 'evidence' in evolutionary biology? Can we observe evolution directly?

Service as Action

• Tree planting: Participate in or organise a tree-planting event in your local community.
• Clean-up drive: Organise a litter clean-up at a local park, beach, or river.
• School garden: Create or maintain a native plant garden to support local biodiversity.
• Climate awareness campaign: Create materials to educate the school community about climate change and actions they can take.

IB Learner Profile Attributes

Self-Test Questions

1. Explain the FOUR principles of natural selection using an ORIGINAL example.

2. List FOUR types of evidence for evolution and give an example of each.

3. Draw a food web for a forest ecosystem with at least 8 organisms and label the trophic levels.

4. Explain the 10% RULE of energy transfer. Why are top predators rare?

5. Describe the CARBON CYCLE. How has human activity disrupted it?

6. List and explain FIVE threats to biodiversity.

7. What is the greenhouse effect? Why is human activity enhancing it?

8. Describe THREE conservation strategies and give a specific example of each.