1. Chapter 53 (pgs. 1174 – 1196) Community Ecology
AP minknow
The difference between a fundamental niche and a realized niche
The role of competitive exclusion in interspecific competition.
The symbiotic relationships of parasitism, mutualism, and commensalism.
The impact of keystone species on community structure.
The difference between primary and secondary succession.

2. What Is a Community?
 1.Explain the relationship between species richness and relative abundance. 
2.Define and compare the individualistic hypothesis of H.A. Gleason and the interactive hypothesis of F.E. Clements with respect to communities.
Interspecific Interactions and Community Structure
3.List four possible specific interactions and explain how the relationships affect the population densities of the two species. 
4.Explain how interspecific competition may affect community structure. 
5.Describe the competitive exclusion principle and explain how competitive exclusion may affect community structure. 
6.Define an ecological niche and restate the competitive exclusion principle using the niche concept. 
7.Explain how resource partitioning can affect species diversity. 
8.Define and compare predation, herbivory, and parasitism. 
9.Relate some specific predatory adaptations to the properties of the prey. 
10.Describe the defense mechanisms that evolved in plants to reduce predation by herbivores. 

3. 11.Explain how cryptic coloration and warning coloration aid an animal in avoiding predators. 
12.Distinguish between Batesian mimicry and Müllerian mimicry. 
13.Describe how predators use mimicry to obtain prey. 
14.Distinguish among endoparasites, ectoparasites, and pathogens. 
15.Distinguish among parasitism, mutualism, and commensalism. 
16.Distinguish between a food chain and a food web. Describe the factors that transform food chains into food webs. 
17.Describe two ways to simplify food webs. 
18.Summarize two hypotheses that explain why food chains are relatively short. 
19.Explain how dominant and keystone species exert strong control on community structure. Give several examples of each. 
20.Describe and distinguish between the bottom-up and top-down models of community organization. Also describe some models that are intermediate between those two extremes.

4. Disturbance and Community Structure
21.Describe how disturbances affect community structure and composition. Illustrate this point with several well-studied examples. 
22.Give examples of humans as widespread agents of disturbance. 
23.Describe and distinguish between primary and secondary succession. 
24.Describe and distinguish among facilitation, inhibition, and toleration. 
25.Describe the process and pattern of succession on moraines in Glacier Bay.
Biogeographic Factors Affecting the Biodiversity of Communities
26.Describe and distinguish between species richness and relative abundance. 
27.Describe the data necessary to measure biodiversity. 
28.Describe and explain how species richness varies along the equatorial-polar gradient. 
29.Define the species-area curve. 
30.Explain how species richness on islands varies according to island size and distance from the mainland.

5. What Is a Community? A biological community
Is an assemblage of populations of various species living close enough for potential interaction
The various animals and plants surrounding this watering hole
Are all members of a savanna community in southern Africa

6. Populations are linked by interspecific interactions
53.1: A community’s interactions include competition, predation, herbivory, symbiosis, and disease
Populations are linked by interspecific interactions
That affect the survival and reproduction of the species engaged in the interaction
These interaction can have differing effects on the populations involved

7. Competition Interspecific competition
Click on picture to watch movie
Interspecific competition
Occurs when species compete for a particular resource that is in short supply
Strong competition can lead to competitive exclusion
The local elimination of one of the two competing species
The Competitive Exclusion Principle
The competitive exclusion principle
States that two species competing for the same limiting resources cannot coexist in the same place

8. Ecological Niches
Habitat - the area where an organism lives, including the biotic and abiotic factors that affect the organism.
Resources - any necessity of life, such as water, nutrients, light, food, or space.
Habitat + Resources = ?????
The ecological niche
Is the total of an organism’s use of the biotic and abiotic resources in its environment

9. Warbler Niches
Can you have two separate organisms occupying the same exact niche???

10. NO
The niche concept allows restatement of the competitive exclusion principle
Two species cannot coexist in a community if their niches are identical

11. However, ecologically similar species can coexist in a community
If there are one or more significant difference in their niches
As a result of competition
A species’ fundamental niche may be different from its realized niche

12. When Connell removed Balanus from the lower strata, the Chthamalus population spread into that area.
The spread of Chthamalus when Balanus was removed indicates that competitive exclusion makes the realized niche of Chthamalus much smaller than its fundamental niche.
RESULTS
CONCLUSION
Ocean
Ecologist Joseph Connell studied two barnacle speciesBalanus balanoides and Chthamalus stellatus that have a stratified distribution on rocks along the coast of Scotland.
EXPERIMENT
In nature, Balanus fails to survive high on the rocks because it is unable to resist desiccation (drying out) during low tides. Its realized niche is therefore similar to its fundamental niche. In contrast, Chthamalus is usually concentrated on the upper strata of rocks. To determine the fundamental of niche of Chthamalus, Connell removed Balanus from the lower strata.
Low tide
High tide
Chthamalus fundamental niche
Chthamalus realized niche
Chthamalus
Balanus realized niche
Balanus

13. Resource Partitioning
Resource partitioning is the differentiation of niches
That enables similar species to coexist in a community
A. insolitus usually perches on shady branches.
A. distichus perches on fence posts and other sunny surfaces.
A. distichus
A. ricordii
A. insolitus
A. christophei
A. cybotes
A. etheridgei
A. alinigar

14. Character Displacement
G. fortis
Beak depth (mm)
G. fuliginosa
Beak depth
Los Hermanos
Daphne
Santa María, San Cristóbal
Sympatric populations
G. fuliginosa, allopatric
G. fortis, allopatric
Percentages of individuals in each size class 40 20 8 10 12 14 16
Figure 53.4
In character displacement
There is a tendency for characteristics to be more divergent in sympatric populations of two species than in allopatric populations of the same two species
Sympatric population – geographically overlapping
Allopatric population – geographically isolated

15. Predation Predation refers to an interaction
Where one species, the predator, kills and eats the other, the prey
Feeding adaptations of predators include
Claws, teeth, fangs, stingers, and poison
Animals also display
A great variety of defensive adaptations

16. Defensive Adaptations
Cryptic coloration
Aposematic coloration
Batesian mimicry
Mullerian mimicry

17. Cryptic coloration, or camouflage
Makes prey difficult to spot
Figure 53.5

18. Aposematic coloration
Warns predators to stay away from prey
Poison arrow frog
Figure 53.6

19. In Batesian mimicry
A palatable or harmless species mimics an unpalatable or harmful model
(a) Hawkmoth larva
(b) Green parrot snake
Figure 53.7a, b

20. In Müllerian mimicry
Two or more unpalatable species resemble each other
(a) Cuckoo bee
(b) Yellow jacket
Figure 53.8a, b

21. Herbivory
Herbivory, the process in which an herbivore eats parts of a plant
Has led to the evolution of plant mechanical and chemical defenses and consequent adaptations by herbivores

22. Community Interactions
Symbiosis – any relationship in which two species live closely together.
There are three types of Symbiosis
Parasitism
Disease
Mutualism
Commensalism

23. Parasitism In parasitism, one organism, the parasite
Derives its nourishment from another organism, its host, which is harmed in the process

24. Parasitism Parasitism exerts substantial influence on populations
And the structure of communities
Parasite
Host
Endoparasites
Ectoparasites
Parasitoidism

25. Disease The effects of disease on populations and communities
Is similar to that of parasites
Pathogens, disease-causing agents
Are typically bacteria, viruses, or protists

26. Mutualism Mutualistic symbiosis, or mutualism
Is an interspecific interaction that benefits both species
Figure 53.9

27. Commensalism In commensalism
One species benefits and the other is not affected
Commensal interactions have been difficult to document in nature
Because any close association between species likely affects both species
Figure 53.10

28. Interspecific Interactions and Adaptation
Evidence for coevolution
Which involves reciprocal genetic change by interacting populations, is scarce
However, generalized adaptation of organisms to other organisms in their environment
Is a fundamental feature of life

29. In general, a small number of species in a community
53.2: Dominant and keystone species exert strong controls on community structure
In general, a small number of species in a community
Exert strong control on that community’s structure
Dominant Species – Those species in a community that have the highest abundance or highest biomass. These species exert a powerful control over the occurrence and distribution of other species.
Keystone Species – A species that is not necessarily abundant in a community yet exerts strong control on community structure by the nature of its ecological role or niche

30. Species Diversity The species diversity of a community
Is the variety of different kinds of organisms that make up the community
Has two components
Species richness
Is the total number of different species in the community
Relative abundance
Is the proportion each species represents of the total individuals in the community

31. Species Diversity Two different communities
Can have the same species richness, but a different relative abundance
Community 1
A: 25% B: 25% C: 25% D: 25%
Community 2
A: 80% B: 5% C: 5% D: 10% D C B A
Figure 53.11
A community with an even species abundance
Is more diverse than one in which one or two species are abundant and the remainder rare

32. Trophic Structure Trophic structure
Is the feeding relationships between organisms in a community
Is a key factor in community dynamics
We can look at trophic structure through
Food Chains
Food Webs

33. A terrestrial food chain
Food chains
Quaternary consumers
Tertiary consumers
Secondary consumers
Primary consumers
Primary producers
Carnivore
Herbivore
Plant
Zooplankton
Phytoplankton
A terrestrial food chain
A marine food chain
Figure 53.12
Link the trophic levels from producers to top carnivores
Help to show the flow of energy through an ecosystem

34. Smaller toothed whales
Food Webs
Humans
Baleen whales
Crab-eater seals
Birds
Fishes
Squids
Leopard
seals
Elephant
Smaller toothed whales
Sperm whales
Carnivorous
plankton
Euphausids
(krill)
Copepods
Phyto- plankton
Figure 53.13
Is a branching food chain with complex trophic interactions

35. Food Webs Food webs can be simplified
By isolating a portion of a community that interacts very little with the rest of the community
Sea nettle
Fish larvae
Zooplankton
Fish eggs
Juvenile striped bass
Figure 53.14

36. Limits on Food Chain Length
Each food chain in a food web
Is usually only a few links long
There are two hypotheses
That attempt to explain food chain length
The energetic hypothesis
suggests that the length of a food chain Is limited by the inefficiency of energy transfer along the chain
The dynamic stability hypothesis
Proposes that long food chains are less stable than short ones

37. Limits on Food Chain Lengths
Most of the available data
Support the energetic hypothesis
High (control)
Medium
Low
Productivity
No. of species
No. of trophic links
Number of species
Number of trophic links 1 2 3 4 5 6
Figure 53.15
Reduction of energy input in a tree-hole community (Queensland, Australia) had a direct affect on the length of the food chain

38. Species with a Large Impact
Certain species have an especially large impact on the structure of entire communities
Either because they are highly abundant r because they play a pivotal role in community dynamics
Dominant Species
Keystone Species

39. Dominant Species One hypothesis suggests that dominant species
Are most competitive in exploiting limited resources
Another hypothesis for dominant species success
Is that they are most successful at avoiding predators

40. Number of species present
Keystone Species
Field studies of sea stars
Exhibit their role as a keystone species in intertidal communities
(a) The sea star Pisaster ochraceous feeds preferentially on mussels but will consume other invertebrates.
With Pisaster (control)
Without Pisaster (experimental)
Number of species present 5 10 15 20
1963
´64
´65
´66
´67
´68
´69
´70
´71
´72
´73
(b) When Pisaster was removed from an intertidal zone, mussels eventually took over the rock face and eliminated most other invertebrates and algae. In a control area from which Pisaster was not removed, there was little change in species diversity.

41. Otter number (% max. count)
Keystone Species
Observation of sea otter populations and their predation
Figure 53.17
Food chain before killer whale involve- ment in chain
(a) Sea otter abundance
(b) Sea urchin biomass
(c) Total kelp density
Number per 0.25 m2
1972
1985
1989
1993
1997 2 4 6 8 10
100
200
300
400
Grams per 0.25 m2
Otter number (% max. count) 40 20 60 80
Year
Food chain after killer whales started preying on otters
Shows the effect the otters have on ocean communities

42. Ecosystem “Engineers” (Foundation Species)
Some organisms exert their influence
By causing physical changes in the environment that affect community structure

43. Foundation Species Some foundation species act as facilitators
Salt marsh with Juncus (foreground)
With Juncus
Without Juncus
Number of plant species 2 4 6 8
Conditions
Some foundation species act as facilitators
That have positive effects on the survival and reproduction of some of the other species in the community

44. Bottom-Up and Top-Down Controls
The bottom-up model of community organization
Proposes a unidirectional influence from lower to higher trophic levels
In this case, the presence or absence of abiotic nutrients
Determines community structure, including the abundance of primary producers

45. Bottom-Up and Top-Down Controls
The top-down model of community organization
Proposes that control comes from the trophic level above
In this case, predators control herbivores
Which in turn control primary producers

46. Long-term experiment studies have shown
That communities can shift periodically from bottom-up to top-down
100
200
300
400
Rainfall (mm) 25 50 75
Percentage of herbaceous plant cover
Bottom-Up
Rainfall determines community controls in this Chilean desert comm.
(Non-El Nino) Dry
(El Nino) Wet
Top-Down

47. Pollution But through biomanipulation Can affect community dynamics
Polluted communities can be restored
Fish
Zooplankton
Algae
Abundant
Rare
Polluted State
Restored State

48. 53.3: Disturbance influences species diversity and composition
Decades ago, most ecologists favored the traditional view
That communities are in a state of equilibrium
However, a recent emphasis on change has led to a nonequilibrium model
Which describes communities as constantly changing after being buffeted by disturbances

49. What Is Disturbance? A disturbance
Is an event that changes a community
Removes organisms from a community
Alters resource availability

50. Fire - Is a significant disturbance in most terrestrial ecosystems
Is often a necessity in some communities
(a) Before a controlled burn. A prairie that has not burned for several years has a high propor- tion of detritus (dead grass).
(b) During the burn. The detritus serves as fuel for fires.
(c) After the burn. Approximately one month after the controlled burn, virtually all of the biomass in this prairie is living.
The intermediate disturbance hypothesis
Suggests that moderate levels of disturbance can foster higher species diversity than low levels of disturbance

51. The large-scale fire in Yellowstone National Park in 1988
Demonstrated that communities can often respond very rapidly to a massive disturbance
(a) Soon after fire. As this photo taken soon after the fire shows, the burn left a patchy landscape. Note the unburned trees in the distance.
(b) One year after fire. This photo of the same general area taken the following year indicates how rapidly the community began to recover. A variety of herbaceous plants, different from those in the former forest, cover the ground.
Figure 53.22a, b

52. Human Disturbance Humans Human disturbance to communities
Are the most widespread agents of disturbance
Human disturbance to communities
Usually reduces species diversity
Humans also prevent some naturally occurring disturbances
Which can be important to community structure

53. Ecological Succession
Ecosystems are constantly in flux.
Ecological Succession – is the series of predictable changes that occurs in an ecosystem over time.
Primary succession
Secondary succession

54. Primary Succession
Occurs on surfaces where no soil exists, usually after a volcanic eruption. (receding glaciers)
1. Bare rock community is populated by an pioneer species (first species to populate an area). Usually lichens (fungus and alga).
2. Pioneer species help to form soil and puts nutrients into soil.
3. Plants begin to grow  then off to the races

55. Secondary Succession
Occurs in an community where everything has been removed but the soil.
What could cause the process of primary succession to begin?

56. Succession on the moraines in Glacier Bay, Alaska
Follows a predictable pattern of change in vegetation and soil characteristics
(b) Dryas stage
(c) Spruce stage
(d) Nitrogen fixation by Dryas and alder increases the soil nitrogen content.
Soil nitrogen (g/m2)
Successional stage
Pioneer
Dryas
Alder
Spruce 10 20 30 40 50 60
(a) Pioneer stage, with fireweed dominant

57. Further Your Information
Read 53.4 and 53.5 Page 1175  Page 1180