IB MYP 4-5 Biology-Speciation and extinction- Study Notes - New Syllabus
IB MYP 4-5 Biology-Speciation and extinction- Study Notes – New syllabus
IB MYP 4-5 Biology-Speciation and extinction- Study Notes – IB MYP 4-5 Biology – per latest IB MYP Biology Syllabus.
Key Concepts:
- Allopatric and sympatric speciation
- Isolating mechanisms (geographic, behavioral, temporal)
- Mass extinctions vs background extinction rates
- Human impact on extinction rates
Allopatric and Sympatric Speciation
What Is Speciation?
- Speciation is the process by which new species are formed from an existing population.
- A species is a group of organisms that can interbreed and produce fertile offspring.
- Speciation occurs when populations become reproductively isolated, meaning they can no longer mate and produce fertile young – even if they look similar.
1. Allopatric Speciation (“allo” = other, “patric” = place)
Speciation that occurs when a population is physically separated by a geographical barrier.
How It Works:
- A population is split by a mountain, river, desert, etc.
- No gene flow between the two groups
- Each adapts to different environmental pressures
- Over time, they become so different they can’t interbreed
Example:
A lizard species is separated by a river. One group lives in dry habitats, the other in forests. Over generations, they evolve different traits and become separate species.
2. Sympatric Speciation (“sym” = same, “patric” = place)
Speciation that occurs without physical separation – both populations live in the same area but evolve separately.
How It Happens:
- Genetic changes (e.g., mutation, polyploidy)
- Behavioral isolation (e.g., different mating calls)
- Feeding or activity time differences
Example:
Insects in the same habitat feed and mate on different fruits. Over time, the groups no longer interbreed and become separate species.
Comparison Table: Allopatric vs Sympatric
| Feature | Allopatric Speciation | Sympatric Speciation |
|---|---|---|
| Physical separation? | Yes – by a geographic barrier | No – same location |
| Gene flow blocked by | Geography | Reproductive isolation |
| Speed of speciation | Often slower | Can be quicker (especially in plants) |
| Common in… | Animals, island populations | Plants, some insects |
| Example | Darwin’s finches on islands | Apple maggot flies |
Allopatric speciation = populations are separated by barriers
Sympatric speciation = populations are not physically separated but evolve apart
Both lead to new species through isolation, time, and genetic change
Isolating Mechanisms (Geographic, Behavioral, Temporal)
What Are Isolating Mechanisms?
Isolating mechanisms are barriers that prevent organisms from mating or producing fertile offspring. They are key in speciation – the process by which new species form.
Types of Isolating Mechanisms
1. Geographic Isolation (Allopatric Isolation)
Definition: When populations are separated by physical barriers (like rivers, mountains, deserts, oceans).
- Populations can’t meet to mate
- Each group adapts to its own environment
- Genetic differences build up
- Eventually, they become separate species
Example: Squirrels on opposite sides of the Grand Canyon; Darwin’s finches on different Galápagos islands
2. Behavioral Isolation
Definition: When populations are capable of mating but have different behaviors – especially in courtship.
- One group doesn’t recognize the other’s signals
- No mating happens, even if they live nearby
Example: Birds of paradise with different dances, frogs that croak differently to attract mates
3. Temporal Isolation
Definition: When populations reproduce at different times – seasons, months, or time of day.
- Even if they live in the same place, their breeding periods don’t overlap
Example: Two flower species blooming in different seasons; frogs mating in early vs late spring
Why Isolation Leads to Speciation
- Populations are isolated → no gene flow
- Each group faces different environments or pressures
- Genetic changes accumulate over generations
- Eventually, they can’t interbreed – speciation has occurred
Summary Table
| Type of Isolation | Barrier Type | Example |
|---|---|---|
| Geographic | Physical barrier | River separating two lizard populations |
| Behavioral | Different courtship behavior | Birds of paradise with unique dances |
| Temporal | Different mating times | Frogs mating in different seasons |
Isolating mechanisms stop populations from breeding together.
Whether it’s location, behavior, or timing, these barriers help drive evolution and the formation of new species.
Mass Extinctions vs Background Extinction Rates
What Is Extinction?
Extinction happens when a species completely dies out – there are no living individuals left anywhere on Earth. It can occur gradually or in sudden, catastrophic waves.
1. Background Extinction Rate
Definition: The normal, ongoing rate at which species naturally go extinct over time.
Causes:
- Natural climate shifts
- Predation or competition
- Natural habitat loss
- Low genetic variation
Key Facts:
- Occurs continuously over Earth’s history
- Estimated 1–5 species per year
- Maintains gradual ecosystem evolution
2. Mass Extinction Events
Definition: A rapid loss of at least 75% of species globally in a short geological time frame.
Causes:
- Asteroid impacts
- Volcanic eruptions
- Sudden climate change
- Ocean acidification
- Rapid disease spread
Key Facts:
- Five major mass extinctions recorded
- Caused collapse of ecosystems
- Often followed by rapid evolution and diversification
Examples of Mass Extinction Events
| Event | When? (Millions of Years Ago) | What Happened? |
|---|---|---|
| Ordovician-Silurian | ~444 Mya | Sea level fall – marine life loss |
| Devonian | ~375 Mya | Widespread marine extinction |
| Permian-Triassic | ~252 Mya | 96% marine species extinct – “The Great Dying” |
| Triassic-Jurassic | ~201 Mya | Allowed dinosaurs to rise |
| Cretaceous-Paleogene (K-Pg) | ~66 Mya | Asteroid impact – dinosaurs extinct |
Mass vs Background Extinction: Key Differences
| Feature | Background Extinction | Mass Extinction |
|---|---|---|
| Speed | Slow and ongoing | Rapid (geological time) |
| Species loss | 1–5 species/year | Up to 75% of all species |
| Cause | Natural evolution & pressure | Catastrophic global events |
| Impact | Local or limited | Worldwide |
| Frequency | Continuous | Very rare (5 known) |
Are We in a Sixth Mass Extinction?
Many scientists believe we are currently entering a sixth mass extinction caused by human activities:
- Deforestation and habitat destruction
- Pollution and climate change
- Overfishing, hunting, and poaching
- Invasive species disrupting ecosystems
Background extinction is slow, natural, and ongoing.
Mass extinction is rare, sudden, and global.
Scientists warn that a sixth extinction may be underway – caused by human impact on the planet.
Human Impact on Extinction Rates
What’s Happening?
Throughout Earth’s history, species have gone extinct due to natural causes. But today, extinction rates are much higher than normal and humans are the main reason.
Major Human Activities Driving Extinction
1. Habitat Destruction
- What it is: Clearing forests, draining wetlands, and building cities, farms, and roads.
- Impact: Loss of homes, food sources, and breeding areas for species.
- Example: Deforestation in the Amazon is endangering jaguars, tree frogs, and many others.
2. Pollution
- What it is: Air, water, and soil pollution from industries, vehicles, and waste.
- Impact: Harms animal health and disrupts delicate ecosystems.
- Example: Ocean plastic kills sea turtles; oil spills destroy marine habitats.
3. Climate Change
- What it is: Human activities like burning fossil fuels raise global temperatures.
- Impact: Alters habitats, melts ice, shifts food sources, and causes extreme weather.
- Example: Coral bleaching; polar bears losing ice to hunt seals.
4. Introduction of Invasive Species
- What it is: Humans move non-native species to new environments.
- Impact: These species compete, prey on, or spread disease to native wildlife.
- Example: Cane toads in Australia harming predators; rats eating bird eggs on islands.
5. Overexploitation
- What it is: Over-hunting, overfishing, or harvesting faster than species can recover.
- Impact: Populations collapse, driving species to extinction.
- Example: Tigers hunted for body parts; sharks and tuna overfished.
Why This Matters
- Biodiversity loss weakens ecosystems
- Fewer species = less stability and resilience to changes like drought or disease
- Humans rely on biodiversity for food, medicine, clean air, and water
Real Data Snapshot
| Human Activity | Example Species Threatened |
|---|---|
| Deforestation | Orangutans, Bengal tigers |
| Ocean pollution | Sea turtles, whales |
| Climate change | Coral reefs, Arctic foxes |
| Invasive species | Island birds |
| Illegal wildlife trade | Pangolins, rhinos, elephants |
Is This a Mass Extinction?
Many scientists believe we are living through the Sixth Mass Extinction – this time caused by human activity, not natural disasters.
What Can Be Done?
- Protect habitats through national parks and conservation areas
- Reduce pollution and plastic use
- Switch to clean, renewable energy
- Stop illegal hunting and wildlife trade
- Educate people about biodiversity and sustainability
Human activities are the main driver of today’s high extinction rates.
From cutting forests to changing the climate, our choices directly impact Earth’s biodiversity.
But with action and awareness, we can reverse the trend and protect life on our planet.