IB DP Biology Stability and change Study Notes

IB DP Biology Stability and change Study Notes at IITian Academy focus on specific topic and type of questions asked in actual exam. Study Notes focus on IB Biology syllabus with guiding questions of

What features of ecosystems allow stability over unlimited time periods?
What changes caused by humans threaten the stability of ecosystems?

Standard level and higher level: 4 hours
Additional higher level: 2 hours

IBDP Biology 2025 -Study Notes -All Topics

D4.2.1 – Stability as a Property of Natural Ecosystems

🧠 What is Ecosystem Stability?

Ecosystem stability means maintaining structure and function over time despite environmental changes.
Stable ecosystems can recover from disturbances and continue supporting diverse species.

🌿 Evidence of Ecosystem Stability

Ecosystem	Evidence of Stability
Tropical rainforests	Fossil records show rainforests in similar form for over 100 million years; rich biodiversity and complex food webs maintained.
Deserts	Exist in some form for millions of years, with specialized plants and animals adapted to arid conditions.
Coral reefs	Persisted for millions of years, showing resilience and recovery after storms or bleaching events.

🔍 Why Stability Matters

Supports biodiversity and ecosystem services like oxygen production and nutrient cycling.
Helps ecosystems resist collapse or drastic changes.
Indicates healthy, balanced interactions among organisms and environment.

📍 Key Features Supporting Stability

Diverse species with overlapping roles (redundancy).
Feedback mechanisms that regulate populations and resource use.
Ability to recover after disturbances (resilience).

🧠 Summary Box:
Ecosystem stability means maintaining structure and function over time.
Some ecosystems like tropical forests and deserts have existed for millions of years.
Stability is crucial for sustaining biodiversity and ecosystem services.
Diverse, resilient ecosystems show strong stability.

D4.2.2 – Requirements for Stability in Ecosystems

🧠 What Does Ecosystem Stability Need?

For an ecosystem to stay stable over time, several key factors must be maintained:

🌞 1. Continuous Supply of Energy

Energy mainly comes from the sun (solar energy).
Plants capture this energy via photosynthesis.
Energy flows through the ecosystem via food chains/webs.
Without steady energy input, ecosystems collapse.

🔄 2. Recycling of Nutrients

Nutrients like carbon, nitrogen, and phosphorus must be recycled continuously.
Decomposers (bacteria, fungi) break down dead matter, returning nutrients to soil and water.
Nutrient recycling supports plant growth and sustains all life.

🌱 3. Genetic Diversity

High genetic diversity within species allows populations to adapt to environmental changes.
Genetic variation supports disease resistance and resilience.
Low diversity can lead to population collapse.

🌡️ 4. Climatic Variables Within Tolerance Limits

Temperature, rainfall, humidity, and other climate factors must stay within levels that organisms can tolerate.
Extreme changes can stress or kill species, disrupting ecosystem balance.

📍 Summary Table: Requirements for Ecosystem Stability

Requirement	Role in Stability
Continuous energy supply	Powers all biological processes
Nutrient recycling	Maintains soil fertility and supports growth
Genetic diversity	Enables adaptation and resilience
Stable climatic conditions	Prevents stress and supports species survival

🧠 Why These Matter

All factors interact to keep ecosystems functioning smoothly.
Disruption to any can cause loss of stability, leading to ecosystem degradation or collapse.

🧠 Summary Box:
Ecosystem stability relies on energy flow, nutrient cycling, genetic diversity, and stable climate.
Maintaining these factors ensures ecosystems can resist and recover from disturbances.
Healthy ecosystems provide vital services and support biodiversity.

D4.2.3 – Deforestation of Amazon Rainforest as a Possible Tipping Point in Ecosystem Stability

🧠 What is a Tipping Point?

A tipping point is when an ecosystem changes suddenly and irreversibly to a new state.
Small changes can cause large effects, leading to loss of stability.

🌿 Importance of Large Rainforest Area

The Amazon rainforest generates huge amounts of atmospheric water vapor via transpiration (water released by plants).
This water vapor helps:
- Cool the air
- Drive airflows
- Cause rainfall that sustains the rainforest itself and surrounding regions.

🔍 Effect of Deforestation

Cutting down large areas reduces transpiration.
This can decrease rainfall and raise temperatures.
Reduced rainfall may cause the forest to dry out, leading to further loss.
There is uncertainty about the minimum forest area needed to maintain this water cycle.
Crossing this threshold could push the ecosystem past the tipping point.

📊 Calculating Percentage Change in Deforestation

To assess deforestation impact, calculate the percentage change in forest area:

Percentage change = ((Original area − Current area) / Original area) × 100

Example: If original forest was 5 million km² and 1 million km² is lost,

Percentage change = ((5 − 4) / 5) × 100 = 20%

📍 Why This Matters

Deforestation threatens the Amazon’s ecosystem stability and climate regulation.
Passing the tipping point could lead to irreversible forest loss and global climate effects.

🧠 Summary Box:
The Amazon rainforest relies on a large area for transpiration-driven water cycles.
Deforestation reduces rainfall and cooling, risking a tipping point.
Percentage change calculations help monitor deforestation extent.
Protecting large forest areas is critical to maintaining ecosystem stability.

D4.2.4 – Use of a Model to Investigate the Effect of Variables on Ecosystem Stability

🧠 What is a Mesocosm?

A mesocosm is a controlled experimental ecosystem used to study ecological processes.
It mimics natural ecosystems but allows control over variables.

🌿 Types of Mesocosms

Can be set up in:
- Open tanks (matter can enter/exit)
- Sealed glass vessels (matter is contained, but energy can still enter/exit)

🔍 Why Use Sealed Glass Vessels?

Prevents entry or exit of matter (like nutrients or organisms), allowing study of closed-system dynamics.
Still allows energy transfer (light and heat from the environment).
Provides more precise control over variables affecting stability.

🌊 Best Ecosystem Types for Mesocosms

Aquatic or microbial ecosystems tend to be more successful because:
- Easier to maintain balance.
- Faster life cycles allow quicker observations.
- Terrestrial ecosystems are harder to replicate in small, controlled environments.

📌 Care and Maintenance

Must follow IB experimental guidelines:
- Regular monitoring of temperature, light, and nutrient levels.
- Prevent contamination.
- Maintain stable conditions to ensure valid results.

🧠 Why Use Mesocosms?

Helps investigate how variables like nutrient levels, temperature, or species diversity affect ecosystem stability.
Allows testing hypotheses in a controlled environment before applying to natural systems.

🧠 Summary Box:
Mesocosms are controlled mini-ecosystems for experiments.
Sealed glass vessels are ideal for controlling matter exchange while allowing energy flow.
Aquatic/microbial ecosystems work best in mesocosms.
Proper care and IB guidelines ensure reliable data on ecosystem stability.

D4.2.5 – Role of Keystone Species in Ecosystem Stability

🧠 What Are Keystone Species?

Keystone species have a disproportionate impact on their ecosystem relative to their abundance.
They play a critical role in maintaining community structure and ecosystem stability.

🌿 Why Are Keystone Species Important?

They help regulate populations of other species.
Maintain balance by controlling species that might otherwise dominate.
Support biodiversity by creating niches for multiple organisms.

🔍 Examples of Keystone Species

Species	Role	Ecosystem Impact
Sea otters	Prey on sea urchins that damage kelp forests	Protects kelp forests and supports marine life
Wolves in Yellowstone	Control deer populations, allowing vegetation to recover	Maintains forest and river ecosystem health
Fig trees in tropical forests	Provide year-round food for many animals	Supports diverse wildlife during scarce periods

📍 Consequences of Removing Keystone Species

Can cause ecosystem collapse or drastic changes in community structure.
Leads to overpopulation of some species, extinction of others.
Reduces ecosystem resilience and function.

🧠 Summary Box:
Keystone species are crucial for ecosystem balance.
Their removal disrupts food webs and community dynamics.
Protecting keystone species helps maintain biodiversity and ecosystem health.

D4.2.6 – Assessing Sustainability of Resource Harvesting from Natural Ecosystems

🧠 What is Sustainability in Resource Harvesting?

Sustainability means harvesting resources at a rate lower than their natural replacement.
Ensures resources are available for future generations.
Prevents ecosystem degradation and species decline.

🌿 Key Principle

The rate of harvesting < rate of replacement (growth or reproduction).
Overharvesting leads to resource depletion and loss of ecosystem services.

🔍 Examples

Species	Type	Sustainability Assessment
Quercus robur (English oak)	Terrestrial plant	Monitor growth rates and seedling regeneration; use selective logging to allow regrowth
Atlantic cod (Gadus morhua)	Marine fish	Track population sizes with fishery data; set quotas and fishing seasons to prevent overfishing

📍 How to Assess Sustainability

Population monitoring: Regular surveys to estimate population size and growth.
Reproductive rates: Understand how quickly species reproduce or regrow.
Harvest limits: Set quotas or permits based on scientific data.
Impact studies: Assess effects of harvesting on ecosystems.

🧠 Why This Matters

Helps balance human needs with ecosystem health.
Protects biodiversity and supports long-term economic benefits.

🧠 Summary Box:
Sustainable harvesting requires rates lower than natural replacement.
Monitoring and management are essential.
English oak and Atlantic cod illustrate terrestrial and marine renewable resources.
Effective assessment prevents resource depletion and supports ecosystem stability.

D4.2.7 – Factors Affecting the Sustainability of Agriculture

🧠 What is Agricultural Sustainability?

Agricultural sustainability means producing food without damaging the environment or depleting resources, so farming can continue long-term.

🌿 Key Factors Affecting Sustainability

Soil Erosion
Loss of topsoil reduces soil fertility.
Caused by wind, water runoff, and poor farming practices.
Leads to lower crop yields and land degradation.
Leaching of Nutrients
Nutrients like nitrogen and phosphorus wash away from soil into water bodies.
Causes soil nutrient loss and water pollution (eutrophication).
Supply of Fertilizers and Other Inputs
Fertilizers replace nutrients lost from soil.
Overuse leads to pollution and can harm beneficial soil organisms.
Sustainable farming balances input use to maintain soil health.
Pollution Due to Agrochemicals
Pesticides and herbicides can contaminate soil, water, and harm non-target species.
Can affect human health and biodiversity.
Integrated pest management can reduce chemical use.
Carbon Footprint
Agriculture contributes to greenhouse gas emissions (methane, nitrous oxide).
Includes fuel use for machinery, fertilizer production, and livestock digestion.
Sustainable practices aim to reduce emissions (e.g., crop rotation, reduced tillage).

📍 Why These Factors Matter

Addressing them helps maintain soil fertility, protect ecosystems, and reduce environmental harm.
Supports food production for future generations.

🧠 Summary Box:
Sustainable agriculture requires managing soil erosion, nutrient leaching, input use, pollution, and carbon emissions.
Balancing productivity with environmental care ensures long-term farm viability.
Reducing chemical inputs and emissions benefits both ecosystem and human health.

D4.2.8 – Eutrophication of Aquatic and Marine Ecosystems Due to Leaching

🧠 What is Eutrophication?

Eutrophication is the excessive growth of algae and aquatic plants caused by high nutrient levels.
Mainly due to leaching of nitrogen and phosphate fertilizers into water bodies.

🌿 How Does Leaching Cause Eutrophication?

Fertilizers applied to farmland can wash away (leach) into rivers, lakes, and oceans.
Increased nutrients, especially nitrates (NO₃⁻) and phosphates (PO₄³⁻), stimulate rapid algae growth.

🔍 Effects of Eutrophication

Algal blooms block sunlight, killing underwater plants.
When algae die, decomposers use oxygen to break them down, increasing Biochemical Oxygen Demand (BOD).
High BOD means less oxygen is available for fish and other aquatic animals.
Results in hypoxia (low oxygen), causing fish kills and loss of biodiversity.

📍 Summary of Process

Step	Effect
Nutrients leach into water	Algae grow rapidly (algal bloom)
Algae block sunlight	Underwater plants die
Dead algae decomposed	Oxygen is consumed, BOD increases
Oxygen depletion	Aquatic animals die, ecosystem damage

🧠 Why Eutrophication is a Problem

Disrupts aquatic ecosystems and food chains.
Affects water quality for human use.
Can lead to long-term damage to lakes, rivers, and coastal waters.

🧠 Summary Box:
Eutrophication is caused by nutrient runoff from fertilizers.
Leads to algal blooms and oxygen depletion in water.
Increases BOD, harming aquatic life and biodiversity.
Preventing excess fertilizer leaching is key to protecting water ecosystems.

D4.2.9 – Biomagnification of Pollutants in Natural Ecosystems

🧠 What is Biomagnification?

Biomagnification is the increase in concentration of toxic substances in the tissues of organisms at higher trophic levels.

Toxins become more concentrated as they move up the food chain.

🌿 How Biomagnification Works

Pollutants like DDT and mercury enter the ecosystem at low levels (e.g., in water or soil).
Producers (plants, algae) absorb or accumulate toxins.
Primary consumers eat producers and accumulate more toxins.
At each higher trophic level (secondary, tertiary consumers), toxin concentration increases because organisms consume many contaminated prey.
Predators at the top have the highest toxin levels, risking health effects.

🔍 Examples of Biomagnifying Pollutants

Pollutant	Source	Effects
DDT	Insecticide once widely used	Causes thinning of bird eggshells, reproductive failure
Mercury	Industrial pollution, coal burning	Neurotoxic effects in fish and humans, impairs nervous system

📍 Why Biomagnification is Dangerous

High toxin levels harm animal health: reproductive issues, developmental problems, death.
Humans consuming contaminated fish or animals can suffer serious health risks.
Pollutants persist in the environment for long periods (bioaccumulative).

🧠 Summary Box:
Biomagnification causes toxin levels to increase up the food chain.
DDT and mercury are common pollutants that biomagnify.
Top predators, including humans, face the greatest risk.
Monitoring and controlling pollutant release protects ecosystems and health.

D4.2.10 – Effects of Microplastic and Macroplastic Pollution of the Oceans

🧠 What Are Microplastics and Macroplastics?

Microplastics: Tiny plastic particles (<5mm) from breakdown of larger plastics or microbeads in products.
Macroplastics: Large plastic debris like bags, bottles, fishing nets.

🌿 Why Plastics Persist

Plastics are non-biodegradable – they don’t break down naturally.
They accumulate in oceans, persisting for decades or centuries.

🔍 Effects on Marine Life

Type of Plastic	Effect on Marine Life	Examples
Macroplastics	Entanglement leading to injury or death; Ingestion causing internal injury or starvation	Turtles trapped in plastic bags; Seabirds eating plastic mistaken for food
Microplastics	Ingested by small marine animals, entering food chains; Can carry toxic chemicals absorbed from the environment	Fish and plankton consuming microplastics; Toxins bioaccumulate up the food chain

📌 Impact Beyond Wildlife

Plastic pollution damages ecosystem health and biodiversity.
Affects fisheries and humans relying on seafood.

🌍 Role of Scientists and Media

Scientists provide clear research findings on plastic pollution.
Media coverage raises public awareness worldwide.
This has driven policies to reduce plastic use and improve waste management.

🧠 Summary Box:
Plastics persist in oceans due to non-biodegradability.
Both microplastics and macroplastics harm marine animals through ingestion and entanglement.
Public awareness influenced by science and media is key to addressing the problem.
Reducing plastic pollution is critical for ocean and human health.

D4.2.11 – Restoration of Natural Processes in Ecosystems by Rewilding

🧠 What is Rewilding?

Rewilding is the process of restoring natural ecosystems by allowing or encouraging natural processes to return.
Focuses on bringing back species and restoring habitat connections.

🌿 Key Methods of Rewilding

Reintroduction of Apex Predators and Keystone Species
Apex predators control prey populations, maintaining ecosystem balance.
Keystone species have critical roles in supporting biodiversity.
Re-establishment of Habitat Connectivity
Connecting isolated habitats across large areas helps species migrate, breed, and survive.
Prevents genetic isolation and supports ecosystem resilience.
Minimizing Human Impact
Ecological management reduces human disturbances like farming, logging, or pollution.
Encourages natural regeneration and species recovery.

🔍 Example: Hinewai Reserve, New Zealand

A 1,000-hectare nature reserve where farming was stopped to allow natural regeneration.
Native forests and wildlife have recovered without active planting or predator control.
Demonstrates success of letting ecosystems restore through natural processes.

📍 Why Rewilding Matters

Helps reverse biodiversity loss.
Restores ecosystem functions and services.
Builds resilience to climate change and human pressures.

🧠 Summary Box:
Rewilding restores ecosystems by reintroducing key species, reconnecting habitats, and limiting human impact.
Apex predators and keystone species are essential for balanced ecosystems.
Hinewai Reserve shows natural recovery when human pressure is removed.
Rewilding supports long-term ecosystem health and biodiversity.

D4.2.12 – Ecological Succession and Its Causes

🧠 What is Ecological Succession?

Succession is the gradual, natural change in the species composition of an ecosystem over time.
It leads to the development of a stable climax community.

🌿 Types of Succession

Primary succession: Starts on bare, lifeless surfaces (e.g., after a volcanic eruption).
Secondary succession: Occurs where an ecosystem has been disturbed but soil remains (e.g., after a forest fire).

🔍 Causes of Succession

Succession can be triggered by:

Abiotic Changes
Changes in non-living factors like:
Soil formation or erosion
Changes in light availability
Water availability
Temperature shifts
These changes create new conditions favoring different species.
Biotic Changes
Changes caused by living organisms such as:
Arrival or removal of species (e.g., invasive species)
Competition between species
Activities like grazing or predation altering the community structure.

📍 Succession Process

Early species (pioneer species) colonize the area.
These species alter the environment (e.g., soil quality improves).
New species replace pioneers as conditions change.
Over time, a complex and stable ecosystem develops.

🧠 Summary Box:
Ecological succession is the natural, gradual change in ecosystems over time.
Triggered by abiotic factors (climate, soil) and biotic factors (species interactions).
Leads from simple pioneer communities to stable climax communities.

D4.2.13 – Changes Occurring During Primary Succession

🧠 What Happens During Primary Succession?

Primary succession begins on bare, lifeless land (e.g., after a volcanic eruption or glacier retreat).
Over time, the ecosystem develops from simple to complex.

🌿 Key Changes During Primary Succession

Aspect	Change Over Time
Plant size	Small pioneer species (mosses, lichens) grow first, gradually replaced by larger plants like shrubs and trees.
Primary production	Amount of energy captured by plants increases as biomass builds up.
Species diversity	Starts low, increases as more species colonize and survive.
Food web complexity	Simple food chains develop into complex food webs with multiple trophic levels.
Nutrient cycling	Initially limited, improves as plants and decomposers add organic matter to soil.

🔍 Example: Volcanic Island Formation

Bare rock is colonized by lichens and mosses which break down rock into soil.
Soil builds up, allowing grasses and herbs to grow.
Over decades, shrubs and trees establish, supporting animals.
Nutrient cycling improves as dead organic matter decomposes.

📍 Why These Changes Matter

Increased plant size and diversity support more animal species.
More complex food webs improve ecosystem stability.
Improved nutrient cycling sustains long-term productivity.

🧠 Summary Box:
Primary succession transforms bare land into a rich ecosystem.
Plant size, diversity, and productivity all increase over time.
Food webs become more complex, and nutrient cycling strengthens.
Example: Volcanic island succession shows these gradual changes clearly.

D4.2.14 – Cyclical Succession in Ecosystems

🧠 What is Cyclical Succession?

Cyclical succession refers to ecosystems where communities cycle repeatedly through different stages.
Unlike a single stable climax, the ecosystem does not settle into one permanent community.
Instead, it experiences regular, predictable changes over time.

🌿 Why Does Cyclical Succession Occur?

Caused by periodic disturbances or natural cycles.
Disturbances reset or shift the community, but the ecosystem returns to earlier stages in a cycle.

🔍 Example: Heathland Ecosystem

Heathlands cycle between:
- Grass-dominated stage
- Shrub-dominated stage
- Tree-dominated stage
Natural fires or grazing can reset succession to earlier stages.
This cycling maintains biodiversity and ecosystem functions.

📍 Key Features of Cyclical Succession

Feature	Description
Repeated stages	Ecosystem moves through a sequence of communities repeatedly.
Maintains diversity	Cycling prevents dominance by one community, supporting various species.
Driven by disturbances	Fire, grazing, flooding, or seasonal changes cause the cycle.

🧠 Summary Box:
Cyclical succession means ecosystems cycle through different communities over time.
It is common where regular disturbances occur.
Example: Heathlands show repeated transitions between grass, shrubs, and trees.
This process maintains ecosystem diversity and resilience.

D4.2.15 – Climax Communities and Arrested Succession

🧠 What is a Climax Community?

A climax community is the stable, final stage of ecological succession.
It remains relatively unchanged unless disturbed.
The type of climax community depends on local environmental conditions (climate, soil, etc.).

🌿 What is Arrested Succession?

Arrested succession happens when human activities prevent an ecosystem from reaching its climax stage.
The ecosystem is stuck in an earlier successional stage.

🔍 Examples of Arrested Succession

Human Influence	Effect on Succession
Grazing by farm livestock	Continuous grazing prevents growth of shrubs and trees, maintaining grassland or early succession stages instead of climax forest.
Drainage of wetlands	Draining wet areas stops wetland plants from establishing, preventing natural succession to wetland climax communities.

📍 Why Arrested Succession Matters

Can reduce biodiversity by preventing complex communities from developing.
Maintains ecosystems that are less stable and provide fewer services.
Sometimes used intentionally for farming or land use but may have environmental costs.

🧠 Summary Box:
Climax communities are stable endpoints of succession shaped by environmental conditions.
Human activities like livestock grazing and wetland drainage can arrest succession.
Arrested succession keeps ecosystems in earlier stages, limiting biodiversity and stability.

IB DP Biology Stability and change Study Notes

IB DP Biology Stability and change Study Notes