Understanding ecosystems, biodiversity, and how living things interact with their environment.
Why Ecology Matters
Understanding ecology helps you:
- Make informed environmental decisions
- Appreciate interconnections in nature
- Understand conservation issues
- Recognize human impacts on ecosystems
- Evaluate environmental claims
- Teach children about nature
Core Concepts
Ecology Defined
Ecology is the study of how organisms interact with each other and their environment.
| Level | What It Studies | Example |
|---|
| Organismal | Individual adaptations | How a polar bear survives cold |
| Population | Groups of same species | Wolf pack dynamics |
| Community | Multiple species interactions | Forest food web |
| Ecosystem | Community plus environment | Lake ecosystem |
| Biosphere | All life on Earth | Global carbon cycle |
Key Terms
| Term | Definition |
|---|
| Habitat | Where an organism lives |
| Niche | Role an organism plays in ecosystem |
| Population | Group of same species in an area |
| Community | All species in an area |
| Ecosystem | Community plus physical environment |
| Biome | Large region with similar climate and life |
Ecosystems
Components
| Component | Description | Examples |
|---|
| Abiotic | Non-living factors | Sunlight, water, temperature, soil |
| Biotic | Living factors | Plants, animals, bacteria, fungi |
| Producers | Make own food | Plants, algae |
| Consumers | Eat other organisms | Animals |
| Decomposers | Break down dead matter | Bacteria, fungi |
Energy Flow
Energy moves through ecosystems in one direction:
| Level | Role | Example |
|---|
| Producers (1st trophic) | Convert sunlight to food | Grass |
| Primary consumers (2nd) | Eat producers | Grasshopper |
| Secondary consumers (3rd) | Eat primary consumers | Frog |
| Tertiary consumers (4th) | Eat secondary consumers | Snake |
| Apex predators (5th) | Top of food chain | Eagle |
The 10% Rule
Only about 10% of energy transfers to the next trophic level.
| Level | Energy Available |
|---|
| Producers | 100% |
| Primary consumers | 10% |
| Secondary consumers | 1% |
| Tertiary consumers | 0.1% |
Why this matters: Explains why there are fewer top predators than prey.
Food Webs
Real ecosystems have complex food webs, not simple chains.
| Feature | Description |
|---|
| Multiple pathways | Energy flows through many routes |
| Omnivores | Animals eating at multiple levels |
| Keystone species | Disproportionate impact on ecosystem |
| Trophic cascades | Changes at one level affect many others |
Biogeochemical Cycles
Carbon Cycle
| Process | Direction | Mechanism |
|---|
| Photosynthesis | CO2 → Organic carbon | Plants absorb CO2 |
| Respiration | Organic carbon → CO2 | Organisms release CO2 |
| Decomposition | Organic carbon → CO2 | Dead matter breaks down |
| Combustion | Fossil carbon → CO2 | Burning fuels |
| Ocean absorption | CO2 → Dissolved carbon | Oceans absorb CO2 |
Nitrogen Cycle
| Process | What Happens |
|---|
| Nitrogen fixation | N2 → Ammonia (by bacteria) |
| Nitrification | Ammonia → Nitrates |
| Assimilation | Plants absorb nitrates |
| Ammonification | Decomposers release ammonia |
| Denitrification | Nitrates → N2 (returns to atmosphere) |
Water Cycle
| Process | Description |
|---|
| Evaporation | Water → Vapor (from surfaces) |
| Transpiration | Water → Vapor (from plants) |
| Condensation | Vapor → Water droplets (clouds) |
| Precipitation | Water falls as rain, snow, etc. |
| Runoff | Water flows to bodies of water |
| Infiltration | Water enters groundwater |
Biomes
Major Terrestrial Biomes
| Biome | Climate | Key Features |
|---|
| Tropical rainforest | Hot, wet year-round | Highest biodiversity |
| Savanna | Warm, seasonal rain | Grassland with scattered trees |
| Desert | Hot or cold, very dry | Sparse vegetation |
| Temperate grassland | Moderate, seasonal | Prairies, steppes |
| Temperate forest | Moderate, seasonal | Deciduous trees |
| Boreal forest (taiga) | Cold, long winters | Coniferous trees |
| Tundra | Very cold, permafrost | Low vegetation |
Aquatic Ecosystems
| Type | Characteristics |
|---|
| Freshwater lakes | Standing water, varying depths |
| Rivers and streams | Flowing water |
| Wetlands | Transition zones, very productive |
| Estuaries | Where rivers meet ocean, brackish |
| Coral reefs | Tropical, high biodiversity |
| Open ocean | Vast, mostly low nutrients |
| Deep sea | Dark, high pressure, unique life |
Species Interactions
Types of Interactions
| Interaction | Species A | Species B | Example |
|---|
| Competition | Harmed | Harmed | Lions and hyenas |
| Predation | Benefits | Harmed | Wolf and deer |
| Parasitism | Benefits | Harmed | Tick and dog |
| Mutualism | Benefits | Benefits | Bee and flower |
| Commensalism | Benefits | Unaffected | Remora and shark |
Symbiosis Examples
| Relationship | Description |
|---|
| Coral and algae | Algae provide food; coral provides shelter |
| Mycorrhizae | Fungi help plant roots absorb nutrients |
| Cleaner fish | Clean parasites off larger fish |
| Gut bacteria | Help digestion; receive food and shelter |
| Lichens | Fungus and algae living together |
Keystone Species
| Concept | Explanation |
|---|
| Definition | Species with outsized ecosystem impact |
| Removal effect | Dramatic ecosystem changes |
| Examples | Sea otters, wolves, elephants |
| Why they matter | Maintain ecosystem structure |
Case study: When wolves were removed from Yellowstone, elk overgrazed, riverbanks eroded, and the entire ecosystem changed. Reintroducing wolves reversed these effects.
Biodiversity
What Is Biodiversity?
| Level | Description |
|---|
| Genetic | Variety of genes within species |
| Species | Variety of species in an area |
| Ecosystem | Variety of ecosystems in a region |
Why Biodiversity Matters
| Benefit | Explanation |
|---|
| Ecosystem stability | More species = more resilience |
| Food security | Diverse crops resist disease |
| Medicine | Many drugs derived from nature |
| Ecosystem services | Pollination, water purification, etc. |
| Unknown future value | Species may become important |
Biodiversity Hotspots
| Region | Why Important |
|---|
| Tropical rainforests | 50% of species on 6% of land |
| Coral reefs | "Rainforests of the sea" |
| Mediterranean regions | High endemism |
| Islands | Unique, isolated species |
Threats to Biodiversity
| Threat | Impact |
|---|
| Habitat loss | Main cause of species decline |
| Climate change | Shifting ranges, timing mismatches |
| Overexploitation | Overfishing, hunting, harvesting |
| Pollution | Pesticides, plastics, runoff |
| Invasive species | Outcompete native species |
Human Impacts
Ecosystem Services
| Service Type | Examples |
|---|
| Provisioning | Food, water, timber, medicines |
| Regulating | Climate regulation, flood control, pollination |
| Supporting | Nutrient cycling, soil formation |
| Cultural | Recreation, spiritual value |
Human Disruptions
| Activity | Ecological Impact |
|---|
| Deforestation | Habitat loss, carbon release, erosion |
| Urbanization | Habitat fragmentation, heat islands |
| Agriculture | Monocultures, pesticides, runoff |
| Overfishing | Depleted fish stocks, ecosystem changes |
| Pollution | Toxic effects, eutrophication |
Eutrophication
| Step | What Happens |
|---|
| 1 | Excess nutrients (fertilizers) enter water |
| 2 | Algae grow rapidly (bloom) |
| 3 | Algae die and decompose |
| 4 | Decomposition uses up oxygen |
| 5 | Fish and other life suffocate |
Invasive Species
| Characteristic | Why Problematic |
|---|
| No natural predators | Population explodes |
| Outcompete natives | Take resources |
| Change ecosystems | Alter food webs |
| Difficult to remove | Costly, often impossible |
Examples: Kudzu, zebra mussels, Burmese pythons, Asian carp.
Conservation
Approaches
| Strategy | Description |
|---|
| Protected areas | Parks, reserves, marine sanctuaries |
| Habitat restoration | Returning areas to natural state |
| Species protection | Endangered species laws |
| Sustainable use | Harvesting without depleting |
| Captive breeding | Breeding endangered species |
| Corridors | Connecting habitat fragments |
What Individuals Can Do
| Action | Impact |
|---|
| Reduce consumption | Less resource extraction |
| Choose sustainable products | Support better practices |
| Native gardening | Support local species |
| Reduce pesticides | Protect pollinators |
| Prevent invasive spread | Don't release pets or plants |
| Support conservation | Donate, volunteer, advocate |
Success Stories
| Species/Area | Recovery |
|---|
| Bald eagle | DDT ban, population recovered |
| Wolves in Yellowstone | Reintroduction restored ecosystem |
| Ozone layer | Montreal Protocol reduced damage |
| Humpback whales | Hunting ban, population increasing |
Practical Ecology
In Your Yard
| Practice | Ecological Benefit |
|---|
| Native plants | Support local insects, birds |
| Reduce lawn | Less water, pesticides |
| Leave leaves | Habitat for insects |
| Avoid pesticides | Protect pollinators |
| Bird feeders/baths | Support wildlife |
| Compost | Return nutrients to soil |
Understanding Nature
| Observation | What It Tells You |
|---|
| Bird variety | Ecosystem health indicator |
| Insect decline | Possible pesticide or habitat issues |
| Algae blooms | Nutrient pollution |
| Plant community | Climate, soil conditions |
Key Takeaways
Everything is connected - Organisms depend on each other and their environment
Energy flows, nutrients cycle - Energy moves one direction; matter is recycled
The 10% rule limits food chains - Energy loss explains ecosystem structure
Keystone species have outsized effects - Removing one species can cascade through the system
Biodiversity provides stability - More species means more resilient ecosystems
Human activities impact ecosystems - Habitat loss is the greatest threat
Ecosystem services are valuable - Nature provides essential functions for free
Invasive species cause major damage - Prevention is far easier than control
Conservation works when applied - Many success stories show recovery is possible
Individual actions matter - Your yard, purchases, and advocacy make a difference