Responses to the Environment
Organisms respond to environmental stimuli through behaviors that enhance survival and reproduction.
| Behavior | Description | Example |
|---|---|---|
| Taxis | Directed movement toward/away from stimulus | Phototaxis (toward light) |
| Kinesis | Random movement, speed changes with stimulus | Pill bugs in dry areas |
| Innate | Genetically programmed, no learning | Suckling reflex |
| Learned | Modified by experience | Bird songs |
Peacock displays
Bird songs
Pheromones
Bee dance
Energy Flow Through Ecosystems
Energy flows ONE direction: sun → producers → consumers. Only ~10% transfers between trophic levels.
Net Primary Productivity = energy available for consumers
Population Ecology
Population ecology studies how populations grow and what limits them.
Unlimited resources → unlimited growth
Limited resources → levels off at K
Effect of Density on Populations
Intensity increases with density:
- Competition
- Predation
- Disease
- Parasitism
Affects all regardless of density:
- Weather/disasters
- Human activities
- Seasonal changes
| Feature | r-Selected | K-Selected |
|---|---|---|
| Offspring | Many, small | Few, large |
| Parental care | Little | Extensive |
| Lifespan | Short | Long |
| Examples | Bacteria, insects | Elephants, humans |
Community Ecology
| Interaction | Effect | Example |
|---|---|---|
| Competition (−/−) | Both harmed | Lions vs hyenas |
| Predation (+/−) | Predator benefits | Wolf eats deer |
| Parasitism (+/−) | Parasite benefits | Tick on dog |
| Mutualism (+/+) | Both benefit | Bee and flower |
| Commensalism (+/0) | One benefits | Barnacles on whale |
Niche: Species' role (food, habitat, behavior)
Competitive exclusion: Two species can't occupy same niche
Resource partitioning: Species divide resources to coexist
Keystone species: Disproportionate effect on community (sea otters, wolves)
Starts on bare rock (no soil)
Pioneer: lichens, mosses
Takes centuries
Soil already present
Pioneer: grasses, weeds
Faster — decades
Biodiversity
Allele variety within species
Richness + evenness
Habitat variety
• Stability: More species = resilience
• Ecosystem services: Clean air/water, pollination
• Medicine: Many drugs from nature
• Food security: Crop diversity
Disruptions in Ecosystems
| Disruption | Cause | Effect |
|---|---|---|
| Climate Change | Greenhouse gases (CO₂) | Warming, sea rise, extreme weather |
| Invasive Species | Introduction to new area | Outcompete natives, alter food webs |
| Eutrophication | Excess N, P (fertilizers) | Algal blooms → dead zones |
| Ocean Acidification | CO₂ dissolves in water | Harms shell-builders (coral) |
Changes at one level ripple through food web:
Example: Yellowstone wolves → fewer elk → vegetation recovery!
Natural: Photosynthesis removes CO₂; respiration/decomposition releases it
Human impact: Burning fossil fuels + deforestation → more CO₂ → warming
Flows one-way, 10% rule
Cycles (C, N, H₂O, P)
Exponential vs logistic; K
Interactions, succession