IB DP Biology Ecological niches Study Notes - New Syllabus
IB DP Biology Ecological niches Study Notes
IB DP Biology Ecological niches 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 are the advantages of specialized modes of nutrition to living organisms?
- How are the adaptations of a species related to its niche in an ecosystem?
Standard level and higher level: 3 hours
B4.2.1 – Ecological Niche: The Role of a Species in an Ecosystem
🧠 What is an Ecological Niche?
An ecological niche is the role a species plays in its ecosystem – not just where it lives, but how it lives.
Think of it as a species’ “job” or “lifestyle” in its habitat.
It includes:
- Where it lives (habitat)
- What it eats and how it gets food
- How it interacts with other species
- When it is active (day/night, seasonal patterns)
- How it reproduces
- Its tolerance to abiotic conditions
🔗 Biotic and Abiotic Interactions
🌱 Abiotic Factors (non-living):
- Temperature: e.g. Arctic fox survives in cold; tropical frog cannot.
- Water availability: e.g. Cacti thrive in deserts; ferns need humidity.
- Light: Needed for photosynthesis; some plants adapted to shade.
- Soil pH or nutrients: Some plants only grow in acidic soils.
- Oxygen levels: Aquatic species may need high dissolved oxygen.
🐾 Biotic Factors (living):
- Food sources: What the organism eats and how it obtains it.
- A tiger hunts prey like deer.
- A bee collects nectar and also helps in pollination.
- Predators: Who eats the organism.
- Competitors: Species competing for the same resources (food, space, mates).
- Symbiosis: Mutually beneficial relationships (e.g., clownfish & anemone).
🍽️ How Species Obtain Food
Every species fits into a feeding role in the ecosystem:
- Producers: Make their own food via photosynthesis (e.g., trees, algae).
- Herbivores: Eat plants (e.g., deer, caterpillars).
- Carnivores: Eat other animals (e.g., lions, hawks).
- Omnivores: Eat both plants and animals (e.g., bears, humans).
- Decomposers: Break down dead material (e.g., fungi, bacteria).
🧩 Example: The Niche of a Woodpecker
- Habitat: Forests with trees.
- Food: Insects inside tree bark.
- Feeding strategy: Uses strong beak to drill holes.
- Time active: Diurnal (active during the day).
- Competition: May compete with other insect-eating birds.
- Abiotic tolerance: Prefers temperate climates.
A species’ ecological niche includes all the biotic and abiotic factors it interacts with — from how it gets food, to its predators, competitors, and environmental tolerances. No two species can occupy exactly the same niche in the same place for long — this leads to competition and niche separation.
B4.2.2 – Types of Organisms Based on Oxygen Requirement
🌬️ Oxygen and Microorganisms: Who Needs It?
Different organisms have different tolerances to oxygen depending on how they generate energy. This gives rise to three main categories:
1. Obligate Aerobes (Strict Oxygen Users)
🌱 “I need oxygen to survive!”
- Require oxygen to live.
- Use aerobic respiration to generate ATP (energy).
- Cannot survive without oxygen – oxygen is essential.
Example: Humans, most animals, Mycobacterium tuberculosis
2. Obligate Anaerobes (Strictly No Oxygen)
☠️ “Oxygen is toxic to me!”
- Cannot survive in the presence of oxygen.
- Use anaerobic respiration or fermentation.
- Oxygen can damage their enzymes and DNA.
Example: Clostridium botulinum (causes botulism), some gut bacteria
3. Facultative Anaerobes (Flexible Users)
🔄 “I prefer oxygen, but I can manage without it.”
- Can survive with or without oxygen.
- Use aerobic respiration when oxygen is available (more efficient).
- Switch to anaerobic respiration or fermentation in low/no oxygen.
🧪 Example: Escherichia coli (E. coli), some yeasts
🔬 Comparison Table
| Feature | Obligate Aerobes | Obligate Anaerobes | Facultative Anaerobes |
|---|---|---|---|
| Oxygen Requirement | Must have oxygen | Cannot tolerate oxygen | Can live with or without O₂ |
| Type of Respiration | Aerobic only | Anaerobic/Fermentation | Aerobic preferred; can switch |
| Survival without Oxygen | No | Yes | Yes |
| Survival with Oxygen | Yes | No | Yes |
– Obligate aerobes die without oxygen.
– Obligate anaerobes die with oxygen.
– Facultative anaerobes are adaptable – they thrive with oxygen but can switch to fermentation if needed.
Understanding these differences is key in medical microbiology and biotechnology, especially when culturing bacteria or treating infections.
B4.2.3 – Photosynthesis as the Mode of Nutrition in Plants, Algae, and Photosynthetic Prokaryotes
☀️ What Is Photosynthesis?
Photosynthesis is the process by which organisms convert light energy into chemical energy (glucose), using carbon dioxide and water.
🧪 Basic Equation:
6CO2 + 6H2O → C6H12O6 + 6O2 (in the presence of light + chlorophyll)
- Carbon dioxide from the air
- Water from the soil
- Light energy from the Sun
- Chlorophyll (green pigment) captures the light
🌱 Who Performs Photosynthesis?
1. Plants
- Main photosynthetic organs = Leaves
- Chloroplasts contain chlorophyll
- Use sunlight to make food and release oxygen
- Example: Sunflower
2. Algae
- Found in freshwater, marine, or damp environments
- Unicellular or multicellular
- Also use chlorophyll (and other pigments) in chloroplasts
- Example: Green algae (Chlorella), brown algae (Kelp)
3. Photosynthetic Prokaryotes (like Cyanobacteria)
- Do not have chloroplasts, but contain photosynthetic pigments in internal membranes
- Use light to make food similarly to plants
- Found in aquatic environments, even extreme habitats
- Example: Nostoc, Anabaena
🛑 Note: No need to study the different types of prokaryotic photosynthesis for this course.
🌍 Why It Matters
- Primary producers in ecosystems – form the base of food chains
- Produce oxygen vital for life
- Help regulate carbon dioxide in the atmosphere
– Photosynthesis is the main way plants, algae, and some prokaryotes make food.
– It uses light energy, CO₂, and H₂O to make glucose and O₂.
– Photosynthetic organisms are essential for life on Earth — they supply food and oxygen.
B4.2.4 – Holozoic Nutrition in Animals
🐾 What is Holozoic Nutrition?
All animals are heterotrophs – they cannot make their own food and must obtain energy by consuming other organisms.
Most animals use a type of heterotrophic nutrition called holozoic nutrition.
🔄 Stages of Holozoic Nutrition
- Ingestion: Food is taken in through the mouth.
- Digestion: Food is broken down mechanically (chewing) and chemically (enzymes) into smaller, soluble molecules (e.g. sugars, amino acids).
- Absorption: Nutrients are absorbed into the bloodstream from the intestines.
- Assimilation: Absorbed nutrients are used by cells for growth, repair, and energy.
- Egestion: Undigested waste is eliminated from the body as faeces.
🐍 Example Organisms
- Humans: All 5 stages occur in the digestive tract.
- Earthworms: Use a simpler but complete holozoic process.
- Insects: Have specialized mouthparts for ingestion and unique digestive systems.
🕷️ Exception: Extracellular Digestion
Some animals like spiders digest food outside their bodies:
- They inject enzymes into prey to liquefy tissues and then ingest the digested material.
- Still considered holozoic, but with a twist.
– All animals are heterotrophs and use holozoic nutrition.
– Involves ingestion, digestion, absorption, assimilation, and egestion.
– Essential for growth, repair, and energy.
B4.2.5 – Mixotrophic Nutrition in Some Protists
🧬 What is Mixotrophic Nutrition?
Mixotrophs are organisms that combine autotrophic (self-feeding) and heterotrophic (feeding on others) modes of nutrition.
They can photosynthesise like plants and ingest food like animals – depending on their needs and environment.
🧪 Types of Mixotrophs
| Type | Description | Example |
|---|---|---|
| Facultative Mixotrophs | Switch between autotrophy and heterotrophy based on conditions (e.g. light availability) | Euglena |
| Obligate Mixotrophs | Require both modes of nutrition to survive | Some oceanic plankton species |
🐛 Euglena: A Classic Example
- Habitat: Freshwater ponds, ditches.
- Photosynthesis: Uses chloroplasts when exposed to sunlight.
- Heterotrophy: Absorbs or engulfs food particles in the dark.
- Adaptability: Helps it survive in changing environments.
🌊 Other Mixotrophs in Plankton
- Many marine protists in oceanic plankton are mixotrophs.
- They play a major role in marine food webs and nutrient cycles.
- Examples include some dinoflagellates and radiolarians.
– Mixotrophic protists can photosynthesise and ingest food.
– Euglena is a freshwater example that switches modes based on light.
– Some are facultative, while others are obligate mixotrophs.
– Important for ecosystem flexibility and food web dynamics.
B4.2.6 – Saprotrophic Nutrition in Some Fungi and Bacteria
💡 What is Saprotrophic Nutrition?
- A type of heterotrophic nutrition where organisms feed on dead or decaying organic matter.
- They digest food externally by secreting enzymes onto the material, then absorb the nutrients.
- Organisms that do this are often called decomposers.
🍂 Who Are the Saprotrophs?
| Organism Type | Example | Role |
|---|---|---|
| Fungi | Mucor, Rhizopus, mushrooms | Break down leaf litter, wood, dead organisms |
| Bacteria | Bacillus subtilis, Pseudomonas | Decompose organic matter in soil and water |
🧪 How It Works
- Detection – The organism detects nearby dead material.
- Secretion of Enzymes – Powerful enzymes (e.g. proteases, cellulases) are released.
- External Digestion – The enzymes break down complex molecules like proteins and starch into simpler forms.
- Absorption – The organism absorbs the soluble nutrients through its cell wall/membrane.
🌍 Why Decomposers Matter
- Nutrient Cycling: Return essential nutrients (like nitrogen and carbon) to the ecosystem.
- Soil Fertility: Improve soil quality by breaking down organic matter.
- Ecosystem Clean-up: Help prevent the build-up of dead organisms and waste.
– Saprotrophs digest dead material outside their bodies.
– Common examples: fungi (like moulds) and bacteria.
– They’re vital decomposers in ecosystems, enabling recycling of nutrients.
– This mode is essential for maintaining ecosystem balance.
B4.2.7 – Diversity of Nutrition in Archaea
🌍 Who Are Archaea?
- Archaea are one of the three domains of life, alongside Bacteria and Eukarya.
- Like bacteria, they are prokaryotic (no nucleus), but their genetics and biochemistry are quite different.
- Many are extremophiles, thriving in places like acidic hot springs, salt lakes, and deep-sea hydrothermal vents.
⚡ Metabolic Diversity: How Archaea Get Energy
Archaea are metabolically versatile, meaning they have multiple ways to produce energy (ATP):
| Mode of Nutrition | Energy Source | Notes |
|---|---|---|
| Phototrophic | Light | Some use non-chlorophyll pigments to capture light (not photosynthesis like plants). |
| Chemotrophic (inorganic) | Oxidation of inorganic compounds (e.g. sulfur, hydrogen, iron) | Called chemoautotrophs – crucial in extreme, mineral-rich environments. |
| Heterotrophic | Oxidation of carbon-based compounds | Break down organic molecules from other organisms. |
🔁 Why It Matters
- Global Cycles: Archaea contribute to carbon, nitrogen, and sulfur cycling in ecosystems.
- Adaptability: Their ability to survive in extreme environments makes them models for astrobiology (life on other planets).
- Biotechnology Use: Some archaeal enzymes work at high temperatures and are used in industrial and lab processes.
– Archaea are a unique domain of life with diverse metabolic pathways.
– They use light, inorganic chemicals, or organic matter to generate energy.
– Many live in extreme environments and contribute to ecosystem nutrient cycles.
– Their versatility makes them vital for ecology, evolution, and biotech research.
B4.2.8 – Relationship Between Dentition and Diet in the Hominidae Family
🧠 What’s This About?
This topic explores how teeth structure (dentition) reveals information about an animal’s diet, especially in omnivorous vs. herbivorous members of the Hominidae family – including humans and extinct human relatives.
🔎 Key Concept: Dentition Reflects Diet
Dentition = the number, type, and shape of teeth in the jaw.
It tells us whether a species mainly eats plants, meat, or both.
| Tooth Type | Function | Prominent In |
|---|---|---|
| Incisors | Cutting food | Both herbivores & omnivores |
| Canines | Tearing food | Omnivores & some herbivores (for defense or display) |
| Premolars & Molars | Grinding food | Large & flat in herbivores, mixed in omnivores |
🌿 Herbivorous Hominids
- Example: Paranthropus robustus
- Small canines, large molars with thick enamel
- Wide, strong jaws for chewing fibrous plant material
- Adapted to a plant-based diet (roots, fruits, leaves)
- Sagittal crest (ridge on top of the skull) for anchoring large jaw muscles
🍗 Omnivorous Hominids
- Example: Homo sapiens (modern humans)
- Moderate-sized canines
- Mix of sharp and grinding teeth — suitable for meat and plants
- Flexible diet helped survival in varied environments
- Smaller jaws than Paranthropus, indicating less chewing of tough plant material
🧬 Application: Skulls and Diet Inference
| Species | Dentition Clues | Diet Inferred |
|---|---|---|
| Homo sapiens | Mixed dentition | Omnivorous |
| Paranthropus robustus | Huge molars, small canines | Herbivorous |
| Homo floresiensis | Small teeth, reduced jaw | Likely omnivorous |
🧪 Nature of Science (NOS)
- “Deductions can be made from theories.”
- Studying living mammals helped form theories connecting teeth with diet.
- These theories are now used to deduce the diet of extinct species.
- This is a great example of inference from observable evidence in evolutionary biology.
– Dentition is closely linked to diet in primates.
– Herbivorous hominids have flat grinding teeth and powerful jaws.
– Omnivorous hominids have a balanced set of teeth for varied diets.
– By comparing skulls, scientists infer the diets of extinct species.
– This supports how scientific theories evolve from observations.
B4.2.9 – Adaptations of Herbivores for Feeding on Plants and of Plants for Resisting Herbivory
🌱 Plant-Herbivore Arms Race
- Plants don’t want to be eaten. Herbivores want to eat them.
- This ongoing struggle leads to co-evolution: as plants develop defenses, herbivores evolve new adaptations to overcome them.
🐛 Adaptations of Herbivores
To eat plants efficiently, herbivores have specialized features:
Mouthpart Adaptations (especially in insects):
| Mouthpart Type | Function | Example |
|---|---|---|
| Chewing | Bite and grind leaves | Caterpillars, beetles |
| Piercing-sucking | Puncture plant tissue and suck out sap | Aphids, leafhoppers |
Metabolic Adaptations:
- Some herbivores detoxify plant toxins using specialized enzymes.
- Example: Koalas can break down toxins in eucalyptus leaves.
- Others have gut microbes to help digest tough plant materials or break down chemicals.
🌾 Adaptations of Plants to Resist Herbivory
Plants use both physical and chemical defenses to deter herbivores:
Physical Defenses:
| Structure | Purpose |
|---|---|
| Thorns & spines | Protect stems and leaves from grazing |
| Tough leaves / thick cuticles | Harder to chew or digest |
| Hairy surfaces (trichomes) | Can trap or irritate insects |
Chemical Defenses:
| Compound Type | Function |
|---|---|
| Alkaloids (e.g. caffeine, morphine) | Toxic or distasteful to herbivores |
| Tannins | Bind to proteins, reduce digestibility |
| Cyanogenic glycosides | Release cyanide when plant is chewed |
Seeds and young leaves often have higher toxin levels to protect future generations.
🧬 Co-evolution: Detoxifying the Defenses
Some herbivores specialize in eating toxic plants and have evolved enzymes or gut symbionts to break down these chemicals.
Example: Monarch butterfly caterpillars feed on milkweed, which is toxic to many animals. They store the toxins to make themselves poisonous to predators!
– Herbivores use specialized mouthparts and metabolic tricks to feed on plants.
– Plants fight back with thorns, tough tissues, and toxins in leaves and seeds.
– Some animals evolve detox strategies to eat even the most well-defended plants.
– This dynamic shows a classic example of co-evolution in action.
B4.2.10 – Adaptations of Predators and Prey
⚔️ Evolutionary Arms Race: Predator vs Prey
- Just like plants and herbivores, predators and prey are constantly evolving new strategies:
- Predators aim to be more efficient at finding, catching, and killing.
- Prey evolve ways to avoid being eaten.
🐾 Predator Adaptations
1. Finding Prey
- Keen senses:
- Sharp vision (e.g. hawks, cats)
- Acute hearing (e.g. owls)
- Strong sense of smell (e.g. wolves, sharks)
- Camouflage: To stalk prey undetected (e.g. tigers in tall grass)
2. Catching Prey
- Speed & agility: Cheetahs can outrun prey in short bursts.
- Ambush tactics: Crocodiles hide underwater and strike suddenly.
- Traps or webs: Spiders spin webs to trap insects.
3. Killing Prey
- Claws & teeth: For piercing and gripping (e.g. lions, wolves)
- Venom: To immobilize prey (e.g. snakes, spiders)
- Strength: To overpower large prey (e.g. bears)
🐇 Prey Adaptations
1. Chemical Defenses
- Toxins or bad taste: Poison dart frogs, monarch butterflies
- Sprays: Skunks release foul-smelling chemicals
2. Physical Defenses
- Armor: Turtles have hard shells, armadillos curl up
- Spines/thorns: Porcupines and hedgehogs deter attackers
- Camouflage: Stick insects, leaf frogs blend in
3. Behavioural Adaptations
- Fleeing: Deer and antelope run at high speeds
- Freezing or playing dead: Opossums
- Herding: Safety in numbers (e.g. zebras)
- Warning signals: Bright colors (aposematism) to warn predators of toxicity
Mimicry: A Clever Trick
- Batesian mimicry: Harmless species imitate harmful ones
→ e.g. hoverflies mimic bees. - Müllerian mimicry: Several toxic species evolve similar warning signals
→ e.g. different species of poisonous butterflies.
– Predators have sensory, physical, and behavioral traits to find and kill prey.
– Prey use chemical, physical, and behavioral strategies to avoid being eaten.
– These dynamic drives co-evolution, with each side adapting in response to the other.
– Examples like mimicry and camouflage highlight the complexity of these relationships.
B4.2.11 – Adaptations of Plant Form for Harvesting Light
🔆 Why Compete for Light?
In forest ecosystems, light is limited especially under the dense canopy. Plants must adapt in form and strategy to maximize their access to sunlight, which is essential for photosynthesis.
🌲 Strategies for Reaching the Light in Forests
1. Tall Trees (Canopy Reachers)
- Strategy: Grow tall, straight trunks to access direct sunlight above the canopy.
- Example: Emergent Dipterocarp trees in tropical rainforests.
- Features:
- Rapid vertical growth
- Broad crowns for light capture
2. Lianas (Climbing Vines)
- Strategy: Use other trees as support to reach the light without investing energy in thick trunks.
- Example: Bauhinia or rattan palms
- Features:
- Woody vines with strong tendrils
- Flexible stems that twine or hook
3. Epiphytes (Tree-Dwellers)
- Strategy: Grow on branches of tall trees to access filtered sunlight without needing soil contact.
- Example: Orchids, ferns, bromeliads
- Features:
- Modified roots for anchoring
- Specialized leaves to absorb moisture from air
4. Strangler Epiphytes
- Strategy: Start life as epiphytes and grow roots downward to the ground, eventually surrounding and killing the host tree.
- Example: Strangler fig (Ficus spp.)
- Features:
- Rapid root and shoot growth
- Form a dense, light-capturing canopy
5. Shade-Tolerant Shrubs and Herbs
- Strategy: Survive with low light on the forest floor.
- Examples: Fatsia, ferns, wild ginger
- Features:
- Large, thin leaves to absorb more light
- Slower growth rates
- Efficient light-harvesting pigments
🌱 Structural Adaptations for Light Harvesting
| Adaptation | Purpose | Example |
|---|---|---|
| Broad leaves | Maximize surface area for light | Rainforest shrubs |
| Phototropism | Grow towards light | Most plants |
| Climbing mechanisms | Reach light via other plants | Lianas |
| Epiphytic growth | Avoid ground competition | Orchids |
| Thick, straight trunks | Fast canopy access | Tropical emergents |
– Light is a major limiting factor in forest ecosystems.
– Plants adopt different structural and growth strategies to access sunlight.
– These include: growing tall, climbing, living on trees, and tolerating shade.
– Forest biodiversity is shaped by how species adapt to the vertical light gradient.
B4.2.12 – Fundamental and Realized Niches
🌱 What is a Niche?
A niche is the role a species plays in its ecosystem – including:
- What it eats
- Where it lives
- How it interacts with other organisms and the environment
🔍 Two Types of Niches
1. Fundamental Niche
- The entire range of environmental conditions a species could occupy and use.
- Determined by:
- Adaptations
- Physiological tolerance limits (e.g., temperature, salinity)
- Resource availability
- It represents the potential lifestyle of a species without competition or threats.
- 🧪 Think of it as the “ideal world” for a species.
2. Realized Niche
- The actual role and space a species occupies in the presence of:
- Competition
- Predators
- Diseases
- Limited resources
- It’s often smaller than the fundamental niche.
- 🧪 This is the “real world” -where interactions with other species shape where it survives.
🔁 Comparison Table
| Feature | Fundamental Niche | Realized Niche |
|---|---|---|
| Definition | Potential range a species can occupy | Actual range a species does occupy |
| Influenced by | Abiotic factors only | Both abiotic and biotic factors |
| Includes | Full range of resources and habitats | Subset of resources and habitats used |
| Competition | Not considered | Strongly limits niche size |
🐚 Example: Barnacles on a Rocky Shore
On rocky coasts:
- Balanus and Chthamalus barnacles occupy different zones.
- Chthamalus has a wider fundamental niche, but its realized niche is restricted to the upper shore due to competition with Balanus.
– A fundamental niche is what a species could potentially do.
– A realized niche is what it actually does, due to biotic interactions.
– Competition is a major factor limiting the realized niche.
– These concepts help ecologists understand species distribution and coexistence.
B4.2.13 – Competitive Exclusion and the Uniqueness of Ecological Niches
⚔️ What is Competitive Exclusion?
Competitive Exclusion Principle (Gause’s Principle):
“No two species can occupy the exact same niche in the same ecosystem for a long time.”
- If two species compete for the same resources (food, space, shelter), one will:
- Outcompete the other
- Drive it to local extinction
- Or force it to adapt by changing its niche
🎯 Why Are Niches Unique?
- Each species has a unique ecological niche – a specific role in the ecosystem.
- This uniqueness reduces competition and promotes biodiversity.
🧪 Possible Outcomes of Competition
| Scenario | Outcome | Example |
|---|---|---|
| One species wins | The other is excluded (dies out or moves away) | Paramecium aurelia outcompetes P. caudatum in lab experiments |
| Both adjust | Each species uses only part of its fundamental niche (niche partitioning) | Different warbler species feed on different parts of the same tree |
| Temporal or spatial separation | Species avoid direct competition by using resources at different times or places | Desert rodents active at different times of day |
🐚 Real-World Example: Barnacles Again!
- Balanus vs. Chthamalus:
- In absence of Balanus, Chthamalus can grow lower down the shore.
- But in real life, Balanus outcompetes it in lower zones.
- So Chthamalus is restricted to the upper shore — a reduced realized niche.
📌 Key Concepts Recap
- Competitive exclusion: No two species can occupy the exact same niche forever.
- Leads to:
- Local extinction of one species
- Or niche differentiation
- This process explains the diversity and specialization seen in ecosystems.
– Each species has a unique niche shaped by evolution and competition.
– If niches overlap, competition occurs.
– The competitive exclusion principle explains how one species may outcompete another or force niche shifts.
– This drives biodiversity and ecosystem structure.