1. Community Ecology
Chapter 41

2. Community Interactions
Community: populations of different species living in the same area.
1. Interspecific competition: members of different species compete for resources (food, space, water, sun, etc).
Gause’s competitive exclusion principle: the niches of two species can’t overlap significantly for very long.

3. Gause’s Experiment

4. Fundamental vs. Realized Niches

5. Species Interactions cont.
3. Predation/Herbivory – members of one species feed directly on another species, without living in or on the prey.
Symbiosis:
4. Parasitism -- one species lives in or on another species, causing harm to the host.
5. Mutualism – two closely associated species benefit each other.
6. Commensalism – one species benefits; other species not harmed nor helped.

6. “Extra important” species
Dominant species – often the most abundant, highest biomass in the community; shapes the habitat for other species (often vegetation).
It’s not uncommon for invasive species to take over, pushing out native species, and changing the entire community.
Keystone species – may not be abundant, but control community structure (otters).

7. Ecosystems
Chapter 42

8. Solar Energy
Most solar energy that reaches Earth is reflected or absorbed by atmosphere.
What reaches us:
Visible light
Infrared radiation (heat)
Ultraviolet radiation (UV)
What it does for us:
Warms troposphere and land (w/ help of greenhouse effect).
Drives the water cycle.
Fuels photosynthesis

9. Greenhouse Effect

10. Living Components of Ecosystems
Producers (autotrophs) – photosynthetic organisms that convert light, water, and carbon dioxide into glucose and oxygen. (Chemosynthesizers use heat and H2S.) Ex: plants, algae, phytoplankton, some bacteria.

11. Classification of Consumers
Consumers (heterotrophs) – get energy by feeding on other organisms or their wastes.
Primary consumers (herbivores) – feed on producers.
Secondary/Tertiary consumers (carnivores) – feed on consumers.
Omnivores – eat plants and animals.
Scavengers – feed on dead organisms.
Detritivores – feed on dead organisms and wastes. (detritus feeders, decomposers)

12. Energy/Matter Flow in Ecosystems
About 1% of solar energy reaching earth is harnessed by producers and converted to chemical energy (Gross Primary Productivity).
About 90% of that energy is used by the producer and lost as heat, leaving 10% available for the next trophic level (Net Primary Productivity).
Limits to productivity include amounts of light, water, and nutrients.

13. Ecological Pyramids
Ecological efficiency is % usable energy transferred from one level to the next in the form of matter (usually about 10%).
For most land ecosystems, amount of biomass decreases with each higher trophic level.
Also, number of organisms at each higher level decreases.

15. Pyramid of Biomass

16. Primary Productivity
Gross primary productivity – rate at which producers convert light energy into biomass. (greatest in shallow ocean and coral reefs; lowest in deserts and open ocean)
Net primary productivity – rate at which producers store biomass for use by consumers.

17. Nutrients cycle through ecosystems
Biogeochemical processes recycle chemical elements essential to life.
Water cycle
Carbon cycle
Nitrogen cycle
Phosphorus cycle

18. Keystone species and trophic cascades