1. Community Ecology I. Intro II. Community interactions
A. What is a community?
B. Questions
II. Community interactions
A. Types of interactions
B. Which interactions structure communities? Ecobeaker demo
III. Community Structure
A. Measures of diversity
B. Trophic structure
IV. Control of community structure
A. Dominant and keystone species
B. Top-down vs. bottom-up
C. Disturbance and succession
D. Biogeography
Community Ecology
Reading: Chap. 53
As humans have altered ecosystems and caused species extinctions world-wide, a critical question is the extent to which such biotic modifications influence ecosystem-level processes.

2. I.A.What is a community?
Definition: Any assemblage of populations in an area or habitat, i.e., all the different species interacting in a given location
Encompasses many populations of different species.

3. What is a community?
Individualistic or Interactive?
Fig. 53.1

4. Questions
How do biotic interactions affect the distribution of particular species?
What biotic interactions structure communities?
What factors cause changes in species richness across community types?

5. California Serpentine Grassland

6. Questions Important applications: Effects of invasive species?
Fig. 55.7
Caulerpa
Argentine ants
Brown tree snake
Nile perch

7. Questions Important applications:
Effects of biodiversity loss on ecosystem functioning?

8. Responses of Productivity to Changing Plant Diversity
Tilman et al. 1996
Hector et al. 2001
A number of experiments
debate about both pattern and mechanism
particularly, degree of comp vs. sampling effect
define
yr)
Hooper and Vitousek 1997
Figure from Inchausti 2001

9. II. Interactions in communities
A. Types of interactions
Competition: -/-
Predation: +/-
Mutualism: +/+
Commensalism: +/0

10. 1. Competition (-/-)
Multiple organisms or species trying to maximize their own use of a limited pool of resources.

11. Competition Intraspecific Interspecific
- among individuals of one species
- implicit in the logistic population growth curve (density dependence)
Interspecific
- among individuals of different species
- may restrict the range of one or the other species

12. Competitive exclusion and the niche
Gause: Competitive exclusion principle.
Ricklefs Fig. 19.6

13. Competitive exclusion and the niche
Ecological niche: total of species abiotic and biotic resource use.
- Two components:
1) what it needs to live (abiotic conditions, resources)
2) what it does
- Niches can’t overlap exactly or species can’t coexist (i.e., need resource partitioning).
- Tough to prove!

14. Intraspecific competition and niches
And NUH is the letter I use to spell Nutches Who live in small caves, known as Niches, for hutches. These Nutches have troubles, the biggest of which is The fact that there are many more Nutches than Niches. Each Nutch in a Nich knows that some other Nutch Would like to move into his Nich very much. So each Nutch in a Nich has to watch that small Nich or Nutches who haven't got Niches will snitch.
“On beyond zebra”, Dr. Suess (Geisel, 1955)

15. Niches: fundamental and realized
fundamental niche
The fundamental niche is defined by an organism’s adaptations to persist in a given abiotic environment
realized niche
The realized niche of an organism is often smaller than the fundamental niche due to competition, predation, parasitism, and recruitment limitations

16. 2. Predation (+/-) broadly defined
Predation - one organism kills and eats another
Parasitism
Herbivory
Parasitoids
Pathogens

17. Predation - broadly defined
Parasitism - one organism feeds from or benefits from another, at the other’s expense
Herbivory
Parasitoids
Pathogens
Fig
Ak picture
Mosquito - ectoparasite
Tapeworm - endoparasite

18. Predation - broadly defined
Parasitism
Herbivory - animal eats a plant.
-Some like predation (whole plant consumed)
- Some like parasitism (only parts consumed, individual not killed).
Parasitoids
Pathogens

19. Predation - broadly defined
Parasitism
Herbivory
Parasitoids - eggs laid inside host, larvae kills…eventually
Pathogens
Ricklefs Fig. 17.2

20. Predation - broadly defined
Parasitism
Herbivory
Parasitoids
Pathogens - cause disease, usually microscopic (virus, bacteria, protists, some fungi)

21. Predation - adaptations of predators and prey
Cryptic coloration
Aposematic coloration
Mimicry
(Batesian and Müllerian)

22. 3. Mutualism (+/+) Mutualism vs. symbiosis Currency - who gets what?
Corals: anthozoan + dinoflagellate
(fig. 33.6)
Ants/Acacia’s
Mycorrhizae: plant + fungus
(Raven et al. 1999)

23. Mutualism (+/+)
Specific
vs. generalist

24. Mutualism (+/+) Obligate vs. facultative Lichens Coral bleaching
Ants and aphids

25. Coevolution
Reciprocal evolutionary adaptations between two interacting species.
Each species is a strong selective force on the other.
One species adapts to the second, and these changes engender new adaptations in the second, which cause further change in the first…and so on.
NOT just with mutualisms!
Tough to demonstrate.

26. B. Which interactions structure communities?
Ecobeaker Demo: intertidal barnacle distributions

27. III. Community structure
A. Measures of diversity
B. Trophic structure

28. III.A. Measures of diversity
Species richness - the number of different species present in a system
Species evenness (relative abundance) - proportion of community biomass or number of individuals contributed by each species

29. Richness and Evenness
Fig

30. Relative abundance
Typically only a few species are common, many more are in moderate abundance, some are quite rare.

31. III.B. Trophic structure
Food chains Food webs
- Strength of
interactions
length of food-
chains
harder to denote
exact trophic
level.
Richness and evenness typically look at species within a trophic level, e.g., plants. When looking across levels, start assessing trophic structure.
Trophic just means “eating” – e.g., autotroph, heterotroph.
Food webs – relative strength of interactions matter (“interaction coefficients”)
Fig
Fig

32. III.B. Trophic structure
What limits the length of a food chain?
Energy? (Fig )

33. III.B. Trophic structure
What limits the length of a food chain?
Stability? (Fig )

34. III.B. Trophic structure
What limits the length of a food chain?
Energy - Queensland tree holes (Fig )

35. IV. Control of community structure
A. Dominant and keystone species
B. Top-down vs. bottom-up control
C. Disturbance and succession
D. Biogeography