1. Ecology – Community Interactions
As populations interact with one another and influence each other’s survival and reproduction, they serve as agents of natural selection – leads to Coevolution
Biotic Interactions:
Predator-prey – very close relationship
Results in coevolution because each exerts intensive environmental pressure on the other
Generally fewer predators than prey
Most predators are larger than prey or hunt collectively (wolf pack)

2. Includes herbivores eating plants (coevolve also)
Produce a “saw-tooth” curve

3. Symbiosis – means “living together”, close interaction between organisms of different species for extended period of time
Mutualism – both benefit – ex. Plants and pollinators, cows and intestinal bacteria
Commensalism – one benefits, the other is unaffected – ex. Barnacles riding on a whale
Parasitism – parasite benefits, host is harmed
Parasite harms and weakens host but does not kill it immediately
In parasitism and mutualism, both species coevolve since they exert very intense natural selection pressures on each other

4. Keystone species – some communities have certain key species that play a major role in determining community structure
Role is out of proportion to its abundance in community
Removal drastically alters community
Ex. Starfish (Pisaster) in rocky intertidal (overgrowth of mussels eliminates other species)
otters along Calif. coast (prevent overgrowth of urchins and destruction of kelp forests)
elephants in the savanna prevent encroachment of forest in grasslands

6. Succession
Structural change in a community and it’s nonliving environment over time
Occurs because successional communities tend to alter the area in which they occur in such a way as to make it less favorable for themselves and more favorable for other communities
Two types: Primary and Secondary Succession

7. Primary Succession
Community gradually colonizes bare rock, sand, or clear glacial pool where there is no trace of a previous community (“from scratch”)
Typically requires thousands or tens of thousands of years
First species to arrive are the pioneers – very hardy, lichens, mosses – change the environment (breakdown bare rock) so new life can enter
Pioneer community replaced by seral communities – intermediate communities such as woody shrubs, trees (that need sunlight)
Shade-tolerant, faster growing tree seedlings replace seral communities leading to climax community
Climax community – most diverse and stable community, permanent

8. Primary Succession

9. Secondary Succession
New community develops after an existing ecosystem is disturbed (forest fire, volcano eruption, abandoned farm field)
Occurs much more rapidly (only a few hundred years)
Pioneer species are typically grasses, weeds, wildflowers

11. Succession occurs in lakes and ponds
Start as clear, clean pools of water – oligotrophic
Sediments and nutrients begin to accumulate and fill water – eutrophication
Eventually water fills and becomes a marsh, then a meadow, then a forest

13. Common trends in succession:
Species composition changes continuously but more rapid in earlier stages
Total number of species represented increases initially, declines slightly, and finally stabilizes in older stages
Net primary productivity increases and is highest in climax community
Store of inorganic nutrients in organisms and plants increase with older stages
Total biomass and amount of nonliving organic matter increases with older stages
Height and massiveness of plants increases
Food webs become more complex

14. Climax communities found in similar climates are somewhat alike
Factors such as annual temperature and precipitation along with wind, humidity, latitude, altitude, and topography result in biotic regions called biomes
Biomes are characterized by different climates, plants and animals
Read about different biomes in textbook