AP Biology 8.7 Disruptions to Ecosystems Study Notes - New Syllabus Effective 2025
AP Biology 8.7 Disruptions to Ecosystems Study Notes – New syllabus
AP Biology 8.7 Disruptions to Ecosystems Study Notes – AP Biology – per latest AP Biology Syllabus.
LEARNING OBJECTIVE
Explain the interaction between the environment and random or preexisting variations in populations.
Key Concepts:
- Disruptions to Ecosystems
8.7.A – Disruptions in Ecosystems
🧠 Big Idea:
Ecosystems face constant environmental change from natural disasters to human actions.
💡 Populations survive or struggle based on the genetic variation they already have or gain through random mutations.
🔁 Variation + Environment = Evolutionary Response
| Environmental Change | Response Depends On |
|---|---|
| Heatwaves, floods, droughts | Genes related to heat tolerance, water use |
| Disease outbreaks | Immune system variation in the population |
| Pollution or chemicals | Ability to detox or resist toxins |
| Habitat destruction | Traits that help escape, adapt, or relocate |
🔬 Types of Variation That Help:
- Preexisting variation: Traits already in the gene pool (e.g., some insects naturally resist pesticides 🐜)
- Random mutation: New traits that arise by chance (e.g., bacteria evolving antibiotic resistance 🦠)
➡️ Those with helpful traits survive + reproduce → population evolves.
🌱 Real Example: Peppered Moths
- Pre-Industrial Era: Light moths blended in with lichen-covered trees.
- Post-Industrial Pollution: Dark moths became more camouflaged on soot-covered trees.
- Result: Dark variety increased due to better survival.
📌 Key Takeaway:
When the environment changes, some traits suddenly become more or less beneficial.
Populations with more genetic variation have a better chance of adapting and surviving>
8.7.A.1 – What Is an Adaptation?
An adaptation is a genetic variation that is favored by natural selection and shows up as a trait that gives an advantage to the organism in a specific environment.
🧠 Let’s Break It Down:
Adaptation = Helpful Trait:
- It’s not just any trait – it’s one that:
- Comes from a genetic variation (mutation or inheritance),
- Improves survival or reproduction in a certain environment.
Favored by Selection:
- If it helps the organism live longer or reproduce more, it becomes more common in the population over generations.
🌱 Examples of Adaptations:
| Environment 🌍 | Adaptation (Trait) 🐾 | Advantage ✅ |
|---|---|---|
| Desert | Thick waxy skin in plants (like cacti) | Reduces water loss |
| Arctic | Thick fur in polar bears | Retains heat |
| Predation | Camouflage in insects | Avoid being eaten |
| Disease | Antibiotic resistance in bacteria | Survive medicine |
💡 Important Reminder:
- Not every trait is an adaptation.
- Only traits that give a survival or reproductive benefit in a particular setting and are passed on are considered adaptations.
8.7.A.2 – What Is Heterozygote Advantage?
Heterozygote advantage happens when individuals with a heterozygous genotype (Aa) have higher fitness than those with either homozygous genotype (AA or aa).
🧠 What Does That Mean?
- A heterozygote is someone who has two different alleles for a trait – one dominant and one recessive.
- In some cases, this combination gives them a survival or reproductive benefit that neither of the homozygotes has!
🔬 Example: Sickle Cell & Malaria
| Genotype | Trait | Fitness in Malaria Regions |
|---|---|---|
| AA | Normal red blood cells | Susceptible to malaria |
| aa | Sickle cell disease | Severe illness |
| Aa | Carrier (some sickled cells) | Resistant to malaria and no severe disease |
🌍 In regions where malaria is common (like parts of Africa), the heterozygotes (Aa) have the highest survival rate.
💡 Why It Matters:
- This keeps both alleles (A and a) in the gene pool – even though aa causes a disease.
- It’s a real-world example of natural selection maintaining genetic variation.
📌 Summary:
Heterozygote advantage = better survival with one dominant + one recessive allele.
It explains how harmful alleles can still exist in a population — because they give a benefit when combined in heterozygotes.
8.7.A.3 – Are Mutations Controlled by the Environment?
Mutations are not directed by environmental pressures — they happen randomly and not because an organism “needs” them.
🧠 Let’s Break That Down:
- Mutations are random changes in the DNA sequence.
- They do not occur on purpose – an organism can’t choose to mutate just because the environment changes.
🧪 For example:
- If the climate becomes colder, animals don’t suddenly develop fur because they need it.
- But if a random mutation already gave one animal thicker fur, that animal might survive better and pass it on — that’s natural selection.
📌 Key Point:
✅ Environment selects but doesn’t create mutations.
🔁 Mutations happen first → then the environment decides which ones help or hurt.
🔍 Real Example:
- Bacteria don’t mutate to resist antibiotics just because you took a pill.
- But if one bacterium randomly has a resistance mutation, it may survive the antibiotic and reproduce leading to resistant bacteria over time.
💡 Summary:
- Mutations = random, not purposeful.
- Natural selection = picks the best-fit mutations from what’s already there.
- Evolution is a trial-and-error process, not a plan.
8.7.B – How Invasive Species Affect Ecosystem Dynamics
🧠 Key Idea:
Invasive species are non-native organisms introduced into a new ecosystem and they can seriously disrupt how that ecosystem works.
🚨 What Are Invasive Species?
- Species that don’t naturally belong in an area
- Often introduced by humans (intentionally or accidentally)
- Can reproduce quickly, outcompete natives, and cause damage
🌍 How Do They Affect Ecosystems?
Competition for Resources.
Invasive species often outcompete native species for:
- Food
- Water
- Shelter
This can lead to declines or extinction of native species.
No Natural Predators 😈
- Many invasive species don’t have predators in the new ecosystem.
- They can spread unchecked and throw the food web out of balance.
Disruption of Food Chains 🍃
If an invasive species kills off or replaces a native, it may affect:
- Predator-prey relationships
- Pollination systems
- Nutrient cycling
Habitat Changes 🏞️
Some invasives alter the environment itself:
- Plants that change soil chemistry
- Animals that destroy forests or wetlands
🐟 Example: Zebra Mussels in North America
Native to Russia; introduced via ships
Spread rapidly in freshwater systems
Clog water pipes, damage boats, and outcompete native mussels
📌 Summary:
- Invasive species = non-native troublemakers
- They disrupt balance by competing, spreading, and changing ecosystems
- Can lead to loss of biodiversity and ecosystem collapse
8.7.B.1 – How Invasive Species Gain an Advantage
🧠 Key Concept:
Invasive species often succeed in new ecosystems because they face less competition or no predators.
💥 How They Thrive:
Exploit New Niches
- Invasive species can find unused resources in the environment
- They fill roles (niches) that no native species were using
No Natural Predators
- In their new environment, predators or parasites that kept them in check don’t exist
- Result: Population explodes
Outcompete Native Species
- They may reproduce faster, grow faster, or need fewer resources
- Native species may decline or be pushed out
🌾 Example: Kudzu plant in the southern U.S.
- Introduced from Asia for erosion control
- Grows rapidly, smothers trees, and blocks sunlight
- Native plants can’t compete = loss of biodiversity
📝 Summary:
- Invasive species often take over ecosystems
- Lack of competition + no predators = easy advantage
- This leads to major ecological disruptions
8.7.C – Human Activities & Ecosystem Changes
🧠 Big Idea:
Humans can dramatically alter ecosystems – sometimes without realizing the long-term effects.
🔧 How Human Actions Change Ecosystems:
Habitat Destruction 🏗️
- Deforestation, urbanization, agriculture
- Reduces habitat for species → leads to loss of biodiversity
Pollution ☠️
- Chemicals, plastics, oil spills, fertilizer runoff
- Can poison food chains, cause dead zones (like in oceans), disrupt hormones in wildlife
Climate Change 🌡️
- Burning fossil fuels = more greenhouse gases → global warming
- Alters weather, shifts habitats, melts ice caps, affects migration/breeding
Overharvesting 🐟
- Overfishing, hunting, or logging at unsustainable rates
- Can cause species extinction or ecosystem collapse
Introduction of Invasive Species 🐍
- Human travel or trade brings species to new places
- These organisms outcompete native species, disrupting the food web
Fragmentation 🚧
- Roads or buildings divide habitats into smaller, isolated patches
- Harder for species to migrate, mate, or find food = population declines
🧬 Result of Human Impact:
- Loss of biodiversity 🐾
- Disrupted food webs
- Reduced ecosystem services (like clean water, air, pollination)
✨ Summary:
Human actions like pollution, deforestation, and introducing non-native species can destabilize ecosystems, threaten species, and cause long-term ecological consequences.
8.7.C.1 – How Human Impact Accelerates Ecosystem Changes
🧠 Big Idea:
Human activities are changing ecosystems at both local and global levels — and in some cases, causing extinctions.
🌎 Examples of Human-Caused Ecosystem Disruptions:
1️⃣ Biomagnification ☠️
🔍 Definition:
A process where toxic substances (like mercury or pesticides) become more concentrated as they move up the food chain.
🔗 How It Works:
- Small fish absorb toxins from water
- Bigger fish eat many small fish = more toxin buildup
- Top predators (and sometimes humans) get the highest dose
⚠️ Result:
- Affects predators like eagles, whales, or humans
- Causes reproductive failure, illness, or death
- Can lead to species decline or extinction
2️⃣ Eutrophication 🧪
🔍 Definition:
A process where excess nutrients (usually from fertilizers or sewage) enter water bodies, causing overgrowth of algae.
🔗 How It Works:
- Nitrogen & phosphorus enter lakes/rivers
- Algae blooms block sunlight ☀️
- Algae die → decomposers use up oxygen
- Water becomes anoxic (no oxygen)
⚠️ Result:
- Fish and aquatic life suffocate
- Ecosystem collapses into a dead zone
- Reduces biodiversity and water quality
📌 Summary:
- Human activities (pollution, agriculture, waste) cause rapid changes in ecosystems.
- Processes like biomagnification and eutrophication lead to species decline and extinction.
- These effects are often irreversible if not addressed.
8.7.D – How Geological & Meteorological Activity Affects Ecosystems
🧠 Big Idea:
Natural events like earthquakes, volcanoes, storms, and climate shifts can drastically change the structure, biodiversity, and functioning of ecosystems.
🌍 Geological Activity
These are earth-based physical processes:
Volcanic Eruptions
- Release lava, ash, and gases
- Destroys local ecosystems, but…
- Over time, creates new land and opportunities for ecological succession
Earthquakes & Landslides
- Sudden shifts in the Earth’s crust
- Can fragment habitats, alter rivers, or cause landform changes
- May isolate populations = allopatric speciation
🌦️ Meteorological Activity
These involve weather and climate:
Hurricanes & Cyclones
- Cause mass flooding, uproot forests, displace animals
- Coastal ecosystems like mangroves or coral reefs take decades to recover
- Introduce new selection pressures for survival
Droughts & Heatwaves
- Reduce water availability
- Stress populations, affect plant growth
- Can lead to die-offs and loss of biodiversity
Climate Shifts
- Long-term changes (like global warming) alter rainfall, temperature
- Affects migration patterns, breeding, plant blooming
- Some species adapt or migrate, others may go extinct
📌 Summary:
| Type of Activity | Ecosystem Effects |
|---|---|
| Volcanic Eruption | Destruction followed by new habitat creation |
| Earthquake/Landslide | Habitat fragmentation, possible isolation |
| Hurricanes | Mass destruction, disrupt food chains |
| Drought/Heatwave | Stress on water-dependent species |
| Climate Change | Alters long-term species survival & distribution |
8.7.D.1 – Geological & Meteorological Events + Biogeography
🧠 Key Idea:
Events like earthquakes, volcanoes, or storms can change habitats and shift ecosystems — and scientists use biogeographical studies to track and understand these changes over time.
🌋 Geological Events Affect Ecosystems
Plate tectonics, volcanoes, and earthquakes can:
- Shift continents or ocean basins
- Create or destroy land
- Isolate species, leading to speciation
🔁 Example: Movement of continents explains why similar fossils are found in South America and Africa — they were once connected!
🌪️ Meteorological Events Impact Habitats
Includes things like:
- Hurricanes
- Tsunamis
- Droughts
- Ice ages
These can:
- Alter ecosystems suddenly (e.g., forest to grassland)
- Displace species or wipe out populations
- Lead to new selection pressures and evolutionary responses
🌍 Biogeography = Evidence of Evolution
Biogeography is the study of species distribution across Earth.
Scientists use it to:
- Track how land movement & climate changes affect species
- Understand where species originated and how they spread
- Provide evidence for common ancestry and adaptive radiation
🦎 Example: Darwin’s finches evolved differently on various Galapagos Islands based on environmental conditions – classic biogeographic pattern.
✅ Summary Table:
| Event Type | Example | Impact on Ecosystems |
|---|---|---|
| Geological (e.g., volcano) | Mt. St. Helens eruption | Destroyed then restructured the habitat |
| Meteorological (e.g., drought) | African Sahel | Species decline and migration |
| Biogeography | Galapagos Islands | Shows how isolation drives speciation |