AP Biology 8.6 Biodiversity Study Notes - New Syllabus Effective 2025
AP Biology 8.6 Biodiversity Study Notes- New syllabus
AP Biology 8.6 Biodiversity Study Notes – AP Biology – per latest AP Biology Syllabus.
LEARNING OBJECTIVE
Describe the relationship between ecosystem diversity and its resilience to changes in the environment.
Key Concepts:
- Biodiversity
8.6.A – Ecosystem Diversity & Resilience
🧠 What Is Ecosystem Diversity?
It refers to the variety of ecosystems in a region – including deserts, forests, coral reefs, grasslands, etc.
Each ecosystem has different:
- 🌿 Species
- 🌍 Abiotic conditions
- 🔄 Energy & nutrient cycles
🔁 What Is Resilience?
Resilience = the ability of an ecosystem to:
- Resist environmental changes
- Recover from disturbances like storms, wildfires, pollution, or climate shifts
🔗 What’s the Connection?
More ecosystem diversity = more resilience
| 🌍 High Diversity Ecosystems | 🌾 Low Diversity Ecosystems |
|---|---|
| Many species with varied roles | Few species, less variety |
| More likely to have backup functions | If one species goes extinct, big impact |
| Better at adapting to change | More fragile in the face of stress |
| Examples: tropical rainforests, coral reefs | Examples: monoculture farms, arctic tundra |
🔬 How It Works:
- When multiple species do similar jobs (e.g., pollinators, decomposers), the system can keep functioning if one species is lost.
- Genetic variation within populations can help some individuals survive extreme conditions (like drought or disease).
- Interactions between many organisms lead to stronger food webs and more stable ecosystems.
💡 Key Takeaway:
🌎 Ecosystems with greater biodiversity are stronger and more likely to bounce back from disturbances or adapt to new conditions.
8.6.A.1 – Ecosystem Resilience Depends on Diversity
🧠 Big Idea:
Ecosystems that lack diversity in species or structure are often less resilient to environmental changes.
🔬 What Does That Mean?
- Fewer component parts = fewer species, fewer ecological roles
- Low diversity = less genetic variation, fewer food sources, and fewer functional backups
- Less flexibility when conditions shift (like temperature, disease, or drought)
🏞️ Examples:
1. Artificial Ecosystem – Crop Field (Monoculture)
- Grows just one crop (e.g., corn or wheat)
- Low species and genetic diversity
- One pest or drought can collapse the system → low resilience
2. Natural Ecosystem – Old-Growth Forest
- Many tree species, insects, fungi, animals, and microbes
- Complex food web with layered energy transfer
- If one species is lost, others can step in → high resilience
💥 Why Low Diversity = Less Resilience:
| ⚠️ Problem | 🌾 Low Diversity Ecosystem Reaction | 🌳 High Diversity Ecosystem Reaction |
|---|---|---|
| Disease or pest | Spreads fast, wipes out species | Some species resist, buffer the impact |
| Environmental change | Whole system collapses | Other species adapt and maintain balance |
| Resource disturbance | No backup species for key roles | Functional redundancy supports recovery |
💡 Key Takeaway:
🌱 The more diverse an ecosystem is, the more resilient it becomes to environmental stress or change.
8.6.A.2 – Key Factors That Maintain Ecosystem Diversity
🧠 Big Idea:
The stability and diversity of an ecosystem depend on certain key species and critical abiotic and biotic components.
🌟 1. Keystone Species: The Ecosystem MVPs
- A keystone species has a disproportionate impact on its ecosystem, even if it’s not the most abundant.
- Removing it can drastically affect the entire ecosystem’s structure and diversity.
- 🔍 Example:
- Sea otters: control sea urchin populations → protect kelp forests
- Without otters, urchins overgraze and destroy kelp → collapse of kelp-based ecosystems
🌱 2. Producers: Base of the Food Web
Also called autotrophs (like plants or algae)
- Convert sunlight or chemicals into energy (photosynthesis or chemosynthesis)
- Support all trophic levels (herbivores → carnivores → decomposers)
- Without producers → no energy input → food web collapse
⚖️ 3. Abiotic & Biotic Factors: Balance Matters
🔹 Abiotic Factors (Non-living)
- Sunlight
- Water availability
- Temperature
- Soil type
- pH and nutrients
These determine which organisms can survive and thrive in an area.
🔸 Biotic Factors (Living)
- Predators, prey
- Plant life
- Competitors
- Decomposers, parasites
They influence interactions, food webs, and species survival.
🧬 Why It Matters:
- Maintain biodiversity
- Keep energy flowing and nutrients cycling
- Preserve resilience of ecosystems
If one major part is removed, it can lead to loss of species and ecosystem instability.
✅ Summary:
- To keep ecosystems diverse and stable, we need:
- Keystone species
- Strong producer base
- Balanced abiotic and biotic conditions
- They’re like the pillars of a bridge if one weakens, the whole system can fall apart.
8.6.B – How Changes to an Ecosystem Affect Its Structure (Short-Term & Long-Term)
🧠 Key Concept:
Ecosystems are interconnected systems when one component is added or removed, it can cause chain reactions that impact the entire system, both right away and over time.
🔄 Short-Term Effects (Immediate)
These are changes that happen quickly (days to months):
🔺 Example: Removal of a Predator
- Removing a predator = population explosion of prey (e.g., deer)
- This leads to overgrazing → decrease in plant life → other herbivores suffer
🔺 Example: Invasive Species Added
- Invasive species may outcompete native species for resources
- Can quickly reduce biodiversity and change food web dynamics
⏳ Long-Term Effects (Over Years/Generations)
These changes happen slowly but may be more permanent:
⚠️ Ecosystem Collapse
- Removing keystone species can cause entire food webs to unravel
- Species may go extinct, habitats may be lost
🔁 Shift in Species Composition
- If a new species dominates (invasive or adapted), native species may decline or migrate
- The ecosystem “restructures” itself over time
🌡️ Climate Feedback Loops
- Removal of plants = less CO₂ absorption → contributes to climate change
- Over time, this alters weather patterns, habitats, and species survival
🔍 Real-World Examples:
| Ecosystem Change | Short-Term Impact | Long-Term Impact |
|---|---|---|
| Wolf removal in Yellowstone | More elk, less vegetation | Riverbanks erode, biodiversity drops |
| Coral bleaching | Loss of marine biodiversity | Collapse of reef ecosystems |
| Invasive plant species | Native plants outcompeted | Soil chemistry & pollinator networks disrupted |
🧬 Summary:
- Adding or removing even one species or resource can:
- Quickly shift food webs and population sizes
- Lead to long-term structural changes and loss of biodiversity
- Affect both biotic and abiotic parts of the system
- Everything is connected – one change can ripple through the whole ecosystem.
8.6.B.1 – Keystone Species: Small in Number, Big in Impact!
🧠 What’s the Big Idea?
A keystone species has a huge impact on its ecosystem even if it’s not abundant. Think of them like the keystone in an arch – remove it, and the whole structure can fall apart.
💥 What Happens If They’re Removed?
- The ecosystem can collapse or change drastically.
- Food webs get disrupted
- Other species may overpopulate or die off.
- The entire balance of the ecosystem shifts
🧬 Why Are They So Important?
- Maintain biodiversity
- Regulate populations
- Support critical interactions (e.g., predator-prey, pollination)
- Even if they’re rare or low in numbers, their role holds the system together.
🔍 Real Examples:
| Keystone Species | Role | What Happens If Removed |
|---|---|---|
| Sea Otters | Control sea urchins | Urchins overgraze kelp → kelp forests die |
| Wolves (Yellowstone) | Control elk population | Elk overgraze → less vegetation → riverbanks erode |
| Elephants | Shape the landscape by knocking down trees | Savannah becomes overgrown with woodland → change in species balance |
| Pollinators | Pollinate many plant species | Plants can’t reproduce → food chains collapse |
🔁 Trick:
Keystone species = ecosystem superheroes
➡️ Remove them, and things can go very wrong for many other species.