1. Chapters 3-5 Biology – Miller • Levine
Ecology
Chapters 3-5
Biology – Miller • Levine

2. What is Ecology? The scientific study of:
Interactions among organisms
Interactions between organisms and their environment
Biosphere – portions of the Earth where life exists (land, water, and air)

3. Levels of Organization
Species – group of organisms that can breed and produce fertile offspring
Population – a group of individuals of the same species that live in the same area
Community – different populations that live in the same area
Ecosystem – all the organisms plus the nonliving environment
Biome – group of ecosystems with the same climate and similar communities

4. Levels of Organization

5. Energy Flow Sunlight is the main energy source for life on Earth.
Autotrophs (producers) – organisms that make their own food
Photosynthesis – use light energy to make food
Chemosynthesis – use chemical energy to make food

6. Energy Flow
Heterotrophs (consumers) – organisms that must feed on other organisms for energy
Herbivores – eat only plants
Carnivores – eat other animals
Omnivores – eat both plants and animals
Detrivores – feed on dead matter
Decomposers – break down organic matter

7. Feeding Relationships
Energy flows through an ecosystem in one direction (sun → producers → consumers)
Food chain – a series of steps in which organisms transfer energy by eating and being eaten

8. Feeding Relationships
Food web – a network of complex feeding interactions
Trophic levels – each step in a food chain or food web
1st – producers
2nd – primary consumers
3rd – secondary consumers
4th – tertiary consumers

9. Ecological Pyramids
Energy Pyramid – shows the amount of energy available at each trophic level
Only about 10% of the energy is transferred to the next level
Biomass Pyramid – shows the amount of living tissue within each trophic level
Pyramid of numbers – shows the number of organisms at each trophic level

10. Ecological Pyramids

11. Biotic and Abiotic Factors
Biotic factors – the living things that influence organisms
Abiotic factors – the nonliving things that influence organisms
Light
Soil
Wind
Water
Temperature

12. Habitat and Niche Habitat – the area where an organism lives
Niche – the role an organism plays in its habitat
No two species can share the same niche in the same habitat

13. Community Interactions
Symbiosis – any relationship in which two species live closely together
Mutualism – both species benefit (flowers & insects)
Commensalism – one species benefits while the other is neither helped nor harmed (orchids in a rainforest)
Parasitism – one organism benefits while the other is harmed (fleas on a dog)

14. Symbiosis

15. Populations
Population density – the number of individuals per unit area
Population growth – increase in size of a population
Population size can be affected by:
Number of births
Number of deaths
Immigration – organisms moving into an area
Emigration – organisms moving out of an area

16. Exponential Growth
Under ideal conditions with unlimited resources, a population will grow exponentially
J-shaped curve

17. Logistic Growth
As resources become less available, the growth of a population slows or stops
S-shaped curve

18. Limiting Factors A factor that causes population growth to decrease
The population size will usually remain constant
Creates the s-shaped curve
Two kinds of limiting factors:
Density-dependent
Density-independent

19. Density-Dependent Factors
A limiting factor that depends on population size
Competition – organisms compete for resources
Between members of the same species
Between members of different species
Parasitism and disease

20. Density-Dependent Factors
Predation – when one species feeds on another
Predator – the organism that feeds on the prey
Prey – the organism being eaten

21. Density-Independent Factors
Affects all populations, regardless of the population size
Unusual weather – heavy storms
Natural disasters – tornado, volcanic eruption
Seasonal cycles – insects die during winter
Human activities – clear-cutting forests

22. Evolution of Populations
Directional selection - form of natural selection in which the entire curve moves; occurs when individuals at one end of a distribution curve have higher fitness than individuals in the middle or at the other end of the curve

23. Evolution of Populations
Stabilizing selection - form of natural selection by which the center of the curve remains in its current position; occurs when individuals near the center of a distribution curve have higher fitness than individuals at either end

24. Evolution of Populations
Disruptive selection - form of natural selection in which a single curve splits into two; occurs when individuals at the upper and lower ends of a distribution curve have higher fitness than individuals near the middle

25. Human Population Growth
At first the human population grew slowly
About 500 years ago it started increasing rapidly
Resembles the J-shaped curve
US & World
Populations

26. Survivorship Curves

27. Ecological Succession
The series of changes that occurs in a community over time
Primary succession – occurs on surfaces where no soil exists (no previous life)
Pioneer species – the first species to populate the area
Lichens → mosses → grasses → shrubs → trees

28. Primary Succession

29. Ecological Succession
Secondary Succession – when a disturbance changes the existing community without removing the soil
Tornadoes, fire, clear cutting
Occurs much quicker than primary succession
Climax community – the relatively stable final community
Ex. Mt. St. Helens