1. Community Properties

2. Definitions What is the definition – quick review…
An area where plants, animals and microbes interact with each other

3. Examples
Within a grassland biome, you have grassland ecosystems, river ecosystems, etc.
Within a grassland ecosystem, you can have a short grass community, a tall grass community, a riparian (area next to stream) forest community

4. Community Structure
If we look at a grassland community, we can look at what organisms fill the producer role
Big Bluestem, Little Bluestem, Switchgrass, Indiangrass, Dropseed, Lovegrass
What organisms fill the herbivore or primary consumer role
Bison, grasshoppers, mice, voles, prairie dogs
What organisms are carnivores
Coyotes, snakes, hawks, skunks, racoons, etc.

5. Communities and Food Webs
Food webs show the interconnection between the organisms in a community
See that in “real world” there is no such thing as a food chain

7. More Community Structure
Food webs deal only with one type of interaction between organisms – predation
Other interactions are also important
Competition
Symbiosis
Commensalism
Parasitic

8. Definition of Interactions
Interaction Type
Organism 1
Organism 2
Competition
negative
Symbiosis
positive
Commensalism
neutral
Parasitic
Predation

9. Community change over time -- succession
If you have a community that is disturbed by some agent (e.g. fire, plowing, landslide, flooding), the community structure in that community is altered. Gradually the community will rebuild itself, tending towards a more stable structure that can be supported by the environment in that particular climate – The Climatic Climax

10. Forest Succession
Pioneer
Comm.
Climax
Comm.

11. Secondary Succession
Succession that occurs following a disturbance is called Secondary Succession

13. Community change over time -- succession
Organisms also invade spaces that did not previously support life, e.g. bare rocks, sand dunes, volcanic flows.
This is known as
Primary
Succession

14. Comparison of Primary and Secondary Succession
Primary Secondary
Pioneer organisms are lichens and mosses
Takes very long to reach climatic climax community stage because soil must be created through physical and biotic interactions
Pioneer organisms are typically small, weedy plants
Time it takes to reach climatic climax stage variable, dependant on climate (short in tropics, long in arctic)

15. Details on Succession
Intervening communities found in succession after pioneer and before climax community are known as “seres”.
Types of communities that area grows through during succession are important, will work on during group exercise
Succession is driven by competition between organisms in each sere.

16. Community Structure Details
Each sere has a different structure than the one preceeding it.
Pioneer sere tends to be made of small plants with little control over their own “microenvironment”.
How do ecologists quantify community structure?

17. Dominance
Dominance – how prevalent a species is, how many individuals there are.
The most dominant species are usually the ones whose name is given to the community, e.g. redwood forest
The redwood forest has lots of species in it besides redwoods, but redwoods are the dominant tree.

18. Diversity Diversity = how many different kinds of species are present.
Usually find highest diversity in tropical, moist areas and lowest diversity in arctic or dry areas.

19. Diversity & Stability
There is a huge controversy in ecology right now about whether or not diversity increases ecosystem stability.

20. Diversity & Stability Stability in an ecosystem is defined as
Resistance: The ability to resist change
Resilience: The ability to recover from change

21. Diversity & Stability
If you look at two extremes, a corn field and a tallgrass prairie, which is most diverse?
Which would be the most stable if a virus attacked the dominant plant species?

22. Diversity & Stability
We see that stability does not increase with the addition of more and more species, but rather there is a point above which – more species make a system less stable.
Stability
Species number

23. Species distribution
Random Uniform Clumped

24. Odum’s laws about succession
Ecosystem/Community property
Pioneer
Climax
Control over abiotic environ.
Low
High
Species diversity
Productivity
Production
Leakiness of Nutrient Cycles

25. Group Exercise Assignment 1
Succession can take over 100 years to re-establish a climax community. You are a young assistant professor wanting to get tenure at a major University. You have 6 years to publish several interesting and important papers to accomplish this. How could you possibly figure out what the successional seres are for a grassland in Central Oklahoma in time to get tenure?

26. Group Exercise Assignment 2
You are interested in determining what types of interactions are going on among several coral reef fish species. It’s too expensive for you to go to the Bahamas all the time, so how would you determine what interactions they have in aquariums here in Central Oklahoma? (remember you need to keep enough alive to do multiple experiments).

27. The steps in a good experiment
Observe the system
Make a hypothesis on how it works
Design a method that will determine whether or not that hypothesis is false
Implement your methods & collect data
Analyze data
Conclusions
Share your information with others