1. Community Ecology Community Community Ecology
all the organisms that live together in a given place
Community Ecology
study of interactions among all populations in a common environment
To answer:
In what way do the populations interact?

2. Why is the beetle rolling the fecal ball?
Niche
An organism’s niche is its ecological role
habitat = address vs. niche = job
Ex: what it eats, what it lives in, time of day when active, behavior, etc…
“How it fits into that ecosystem.”
Why is the beetle rolling the fecal ball?
Is that frog noctural?

3. Competitive Exclusion Principle
No two similar species can occupy the same niche at the same time. Or else…..
High tide
Competitive Exclusion
If Species 2 is removed, then Species 1 will occupy whole tidal zone. But at lower depths Species 2 out-competes Species 1, excluding it from its potential (fundamental) niche.
Species 1
Low tide
Chthamalus sp.
Species 2
Fundamental
niches
Realized
niches
Semibalanus sp.

4. Symbiotic Relationships
competition (-/-)
predation / parasitism (-/+)
herbivory (-/+)
commensalism (+/0)
mutualism (+/+)
lichens (algae & fungus)
“Freddy fungus and Annie algae took
a Lichen to each other!”

5. Predation drives evolution
Predators adaptations
locate & subdue prey
Prey adaptations
elude & defend
Predation provides a strong selection pressure on both prey & predator
horns, speed, coloration
spines, thorns, toxins
Predation provides a strong selective pressure on prey populations. Any feature that would decrease the probability of capture should be strongly favored.

6. Defensive Adapations Mechanical Defense Chemical Defense
Aposematic coloration
Cryptic coloration
Batesian Mimicry
Mullarian Mimicry
**All heavily rely on operant conditioning, trial and error learning, in order to be successful. They rely on predators learning what not to eat, and the predator remembering what not to eat.

7. Batesian Mimicry Convergent evolution green parrot snake
palatable or harmless species mimics a harmful model
green parrot snake
Hawkmoth larva puffs up to look like poisonous snake
hawkmoth larvae

8. Mullerian mimicry cuckoo bee yellow jacket
two or more poisonous species look like each other
cuckoo bee
yellow jacket
- group defense?
- predators may evolve innate avoidance

9. Coevolution in Community
Predator-prey relationships
Parasite-host relationships
Flowers & pollinators
Long term evolutionary adjustments between species

10. Predator/Prey Coevolution…
Biowarfare arms race with garter snakes and newts.

11. Community Structure Species diversity Ecological Succession
How many different species?
Who’s dominant?
most abundant or highest biomass (total weight)
Keystone species
Ecological Succession

12. Species diversity greater diversity = greater stability
Greater biodiversity offers:
more food resources
more habitats
more resilience in face of environmental change

13. The impact of reduced biodiversity
compare these communities
suburban lawn
agricultural “monoculture”
“old field”
In the early 1970's, a new corn genotype was released in the US; the "Texas male sterile" (TMS). Hybrids that contained this new characteristic had many desirable properties, and growers were excited about them, planting them over miles and miles of corn acreage in US. They were, of course, bred to be resistant to the most common corn diseases. However, they were not resistant to a previously unimportant strain of a fungal disease; the southern corn leaf blight (caused by the fungus Helminthosporium maydis). Ninety percent of the corn sowed in the US in 1970 contained the TMS trait and also shared genetic susceptibility to this pathogen. The fungus encountered all this acreage of susceptible host and wiped out one fourth of the US corn crop in 1970, a loss of over one billion dollars in production! If the corn acreage hadn't been such a monoculture, the fungus wouldn't have been able to spread as rapidly, as it would have encountered barriers of genetically resistant plants.
Irish potato famine
1970 US corn crop failure

14. Keystone species Influential ecological role
A species that has a large effect on its environment relative to its abundance
A consumer organism (herbivore or carnivore)
Low biomass in numbers

15. Keystone Species
diversity increases
diversity decreases
mussels out-compete other species
Following the removal of Pisaster, richness fell from 15 to 8 species
Pisaster promotes species diversity by preventing competitive exclusion by Mytilus

16. Ecological succession
Sequence of community changes
transition in species composition over time
years or decades
usually after a disturbance
Mt. St. Helens

17. Progress of Succession
Tolerance
early species are weedy (r-selective)
tolerant of harsh conditions
Facilitation & Inhibition
early species facilitate habitat changes
change soil pH
change soil fertility
change light levels
allows other species to out-compete

18. Primary succession
Begins with virtually lifeless area without soil, then…
bacteria
lichens & mosses
grasses
shrubs
trees
make soil {

19. Secondary succession
Existing community cleared, but base soil is still intact
burning releases nutrients formerly locked up in the tissues of tree
the disturbance starts the process of succession over again

20. Climax forest Stable plant community dominated by trees
Representing final stage of natural succession for a specific location
remains unchanged in species composition as long as site remains undisturbed
birch, beech, maple, hemlock
oak, hickory, pine

21. Climax forest Hmm…Biomes?
taiga
The species mix of a climax forest is dependent on the abiotic factors of the region
solar energy levels
temperature
rainfall
fertility & depth of soil
temperate deciduous forest birch, beech, maple, hemlock