1. Chapter 54
Community Ecology

2. Overview: A Sense of Community
A biological community is an assemblage of populations of various species living close enough for potential interaction

3. 1. Give an example of a community.
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1. Give an example of a community.

4. Concept 54.1: Community interactions are classified by whether they help, harm, or have no effect on the species involved
Ecologists call relationships between species in a community interspecific interactions
Examples are competition, predation, herbivory, and symbiosis (parasitism, mutualism, and commensalism)
Interspecific interactions can affect the survival and reproduction of each species, and the effects can be summarized as positive (+), negative (–), or no effect (0)

5. 2. List the three types of symbiosis.
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2. List the three types of symbiosis.
Parasitism, mutualism, and commensalism

6. Competition
Interspecific competition (–/– interaction) occurs when species compete for a resource in short supply
Examples:
Owls and Foxes, they both eat rodents. Humans and wolves or elephants (for land area) Sharks and Orcas (both eat seals) Any two different species that eat the same type of stuff (may even display convergent evolution)

7. Competitive Exclusion
Strong competition can lead to competitive exclusion, local elimination of a competing species
The competitive exclusion principle states that two species competing for the same limiting resources cannot coexist in the same place

8. Ecological Niches
The total of a species’ use of biotic and abiotic resources is called the species’ ecological niche
An ecological niche can also be thought of as an organism’s ecological role
Ecologically similar species can coexist in a community if there are one or more significant differences in their niches

9. 3. Take notes on the following video by Paul Anderson
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3. Take notes on the following video by Paul Anderson

10. Resource partitioning is differentiation of ecological niches, enabling similar species to coexist in a community
Example
One of the best known cases of resource partitioning occurs among Caribbean anoles. As many as five different species of anoles may exist in the same forest, but each stays restricted to a particular space: some occupy tree canopies, some occupy trunks, some forage close to the ground.

11. A. distichus perches on fence posts and other sunny surfaces.
Fig. 54-2
A. distichus perches on fence
posts and other sunny surfaces.
A. insolitus usually perches
on shady branches.
A. ricordii
Figure 54.2 Resource partitioning among Dominican Republic lizards
A. insolitus
A. aliniger
A. christophei
A. distichus
A. cybotes
A. etheridgei

12. Character Displacement
Character displacement is a tendency for characteristics to be more divergent in sympatric populations of two species than in allopatric populations of the same two species
An example is variation in beak size between populations of two species of Galápagos finches

13. Pop Up Notes
Allopatric Speciation: speciation that occurs when biological populations of the same species become isolated from each other to an extent that prevents or interferes with genetic interchange
Sympatric Speciation: the process through which new species evolve from a single ancestral species while inhabiting the same geographic region.

14. Predation
Predation (+/– interaction) refers to interaction where one species, the predator, kills and eats the other, the prey
Some feeding adaptations of predators are claws, teeth, fangs, stingers, and poison

15. Video: Seahorse Camouflage
Prey display various defensive adaptations
Behavioral defenses include hiding, fleeing, forming herds or schools, self-defense, and alarm calls
Animals also have morphological and physiological defense adaptations
Cryptic coloration, or camouflage, makes prey difficult to spot
Video: Seahorse Camouflage

16. (c) Batesian mimicry: A harmless species mimics a harmful one.
Fig. 54-5
(a)
Cryptic
coloration
Canyon tree frog
(b)
Aposematic
coloration
Poison dart frog
(c) Batesian mimicry: A harmless species mimics a harmful one.
Hawkmoth
larva
Figure 54.5 Examples of defensive coloration in animals
(d)
Müllerian mimicry: Two unpalatable species
mimic each other.
Cuckoo bee
Green parrot snake
Yellow jacket

17. (a) Cryptic coloration Canyon tree frog Fig. 54-5a
Figure 54.5a Examples of defensive coloration in animals

18. Pop Up Question
4. Give two examples of organisms that display cryptic coloration. Explain why cryptic coloration is important.

19. Animals with effective chemical defense often exhibit bright warning coloration, called aposematic coloration
Predators are particularly cautious in dealing with prey that display such coloration

20. (b) Aposematic coloration Poison dart frog Fig. 54-5b
Figure 54.5b Examples of defensive coloration in animals

21. In some cases, a prey species may gain significant protection by mimicking the appearance of another species
In Batesian mimicry, a palatable or harmless species mimics an unpalatable or harmful model
Unpalatable: unpleasant in taste

22. (c) Batesian mimicry: A harmless species mimics a harmful one.
Fig. 54-5c
(c) Batesian mimicry: A harmless species mimics a harmful one.
Hawkmoth
larva
Green parrot snake
Figure 54.5c Examples of defensive coloration in animals

23. In Müllerian mimicry, two or more unpalatable species resemble each other

24. Müllerian mimicry: Two unpalatable species mimic each other.
Fig. 54-5d
(d)
Müllerian mimicry: Two unpalatable species
mimic each other.
Cuckoo bee
Yellow jacket
Figure 54.5d Examples of defensive coloration in animals

25. Herbivory
Herbivory (+/– interaction) refers to an interaction in which an herbivore eats parts of a plant or alga
It has led to evolution of plant mechanical and chemical defenses and adaptations by herbivores

26. 5. Give an example of herbivory.
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5. Give an example of herbivory.

27. Symbiosis
Symbiosis is a relationship where two or more species live in direct and intimate contact with one another
There are three types/forms of symbiosis.

28. Parasitism
In parasitism (+/– interaction), one organism, the parasite, derives nourishment from another organism, its host, which is harmed in the process
Parasites that live within the body of their host are called endoparasites; parasites that live on the external surface of a host are ectoparasites

29. 6.What’s the difference between endo and ecto parasites?
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6.What’s the difference between endo and ecto parasites?

30. Many parasites have a complex life cycle involving a number of hosts
Some parasites change the behavior of the host to increase their own fitness

31. Video: Clownfish and Anemone
Mutualism
Mutualistic symbiosis, or mutualism (+/+ interaction), is an interspecific interaction that benefits both species
A mutualism can be
Obligate, where one species cannot survive without the other
Facultative, where both species can survive alone
Video: Clownfish and Anemone

32. Commensalism
In commensalism (+/0 interaction), one species benefits and the other is apparently unaffected
Commensal interactions are hard to document in nature because any close association likely affects both species

33. Fig. 54-8
Figure 54.8 A possible example of commensalism between cattle egrets and water buffalo
Cattle egrets eat little bugs that bite and tend to bother the cattle

34. In your lab groups, complete the symbiosis worksheet notes page.
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In your lab groups, complete the symbiosis worksheet notes page.

35. Concept 54.2: Dominant and keystone species exert strong controls on community structure
In general, a few species in a community exert strong control on that community’s structure
Two fundamental features of community structure are species diversity and feeding relationships

36. Species Diversity
Species diversity of a community is the variety of organisms that make up the community
It has two components: species richness and relative abundance
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

37. Which forest is more diverse?
Fig. 54-9
Which forest is more diverse? A B C D
Community 1
Community 2
Figure 54.9 Which forest is more diverse?
A: 25% B: 25% C: 25% D: 25%
A: 80% B: 5% C: 5% D: 10%

38. H = –[(pA ln pA) + (pB ln pB) + (pC ln pC) + …]
Two communities can have the same species richness but a different relative abundance
Diversity can be compared using a diversity index
Shannon diversity index (H):
H = –[(pA ln pA) + (pB ln pB) + (pC ln pC) + …]

39. Determining the number and abundance of species in a community is difficult, especially for small organisms
Molecular tools can be used to help determine microbial diversity

40. With your table complete the Shannon Index Lab. Grab a calculator.
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With your table complete the Shannon Index Lab. Grab a calculator.

41. Limits on Food Chain Length
Each food chain in a food web is usually only a few links long
Two hypotheses attempt to explain food chain length: the energetic hypothesis and the dynamic stability hypothesis

42. The energetic hypothesis suggests that length is limited by inefficient energy transfer
The dynamic stability hypothesis proposes that long food chains are less stable than short ones
Most data support the energetic hypothesis

43. Pop Up Question
7. In your own words, explain why the energetic hypothesis makes sense.

44. Species with a Large Impact
Certain species have a very large impact on community structure
Such species are highly abundant or play a pivotal role in community dynamics

45. Dominant Species
Dominant species are those that are most abundant or have the highest biomass
Biomass is the total mass of all individuals in a population
Dominant species exert powerful control over the occurrence and distribution of other species

46. One hypothesis suggests that dominant species are most competitive in exploiting resources
Another hypothesis is that they are most successful at avoiding predators
Invasive species, typically introduced to a new environment by humans, often lack predators or disease

47. Pop Up Question
8. Are humans a dominant species? Do we exploit our resources? Give an Example

48. Keystone Species
Keystone species exert strong control on a community by their ecological roles, or niches
In contrast to dominant species, they are not necessarily abundant in a community

49. Observation of sea otter populations and their predation shows how otters affect ocean communities

50. Keystone Species Reading
Pop Up Activity
Keystone Species Reading

51. Otter number (% max. count) Grams per 0.25 m2 Number per 0.25 m2
Fig
100 80
Otter number
(% max. count) 60 40 20
(a) Sea otter abundance
400
300
Grams per
0.25 m2
200
100
(b) Sea urchin biomass
Figure Sea otters as keystone predators in the North Pacific 10 8
Number per
0.25 m2 6 4 2
1972
1985
1989
1993
1997
Year
(c) Total kelp density
Food chain

52. Foundation Species (Ecosystem “Engineers”)
Foundation species (ecosystem “engineers”) cause physical changes in the environment that affect community structure
For example, beaver dams can transform landscapes on a very large scale

53. Fig
Figure Beavers as ecosystem “engineers”

54. Some foundation species act as facilitators that have positive effects on survival and reproduction of some other species in the community

55. Number of plant species
Fig 8 6
Number of plant species 4 2
Figure Facilitation by black rush (Juncus gerardi) in New England salt marshes. Juncus is a genus of monocotyledonous flowering plants, commonly known as rushes. It is the largest genus in the family Juncaceae, containing around 300 species
(a)
Salt marsh with Juncus
(foreground)
With Juncus
Without Juncus
(b)

56. (a) Salt marsh with Juncus (foreground) Fig. 54-18a
Figure Facilitation by black rush (Juncus gerardi) in New England salt marshes
(a)
Salt marsh with Juncus
(foreground)

57. Number of plant species
Fig b 8 6
Number of plant species 4 2
Figure Facilitation by black rush (Juncus gerardi) in New England salt marshes
With Juncus
Without Juncus
(b)

58. 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, presence or absence of mineral nutrients determines community structure, including abundance of primary producers

59. The top-down model, also called the trophic cascade model, proposes that control comes from the trophic level above
In this case, predators control herbivores, which in turn control primary producers

60. Long-term experimental studies have shown that communities vary in their relative degree of bottom-up to top-down control

61. Top Down, Bottom Up Article Analysis
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Top Down, Bottom Up Article Analysis

62. (number of individuals
Fig
RESULTS
Control plots
300
Warmed plots
(number of individuals
Nematode density
per kg soil)
200
100
Figure Are soil nematode communities in Antarctica controlled by bottom-up or top-down factors?
E. antarcticus
S. lindsayae

63. Pollution can affect community dynamics
Biomanipulation can help restore polluted communities

64. Polluted State Restored State Fish Abundant Rare Zooplankton Rare
Fig. 54-UN1
Polluted State
Restored State
Fish
Abundant
Rare
Zooplankton
Rare
Abundant
Algae
Abundant
Rare

65. Concept 54.3: Disturbance influences species diversity and composition
Decades ago, most ecologists favored the view that communities are in a state of equilibrium
This view was supported by F. E. Clements who suggested that species in a climax community function as a superorganism

66. Other ecologists, including A. G. Tansley and H. A
Other ecologists, including A. G. Tansley and H. A. Gleason, challenged whether communities were at equilibrium
Recent evidence of change has led to a nonequilibrium model, which describes communities as constantly changing after being buffeted by disturbances

67. Characterizing Disturbance
A disturbance is an event that changes a community, removes organisms from it, and alters resource availability
Fire is a significant disturbance in most terrestrial ecosystems
It is often a necessity in some communities

68. The large-scale fire in Yellowstone National Park in 1988 demonstrated that communities can often respond very rapidly to a massive disturbance

69. (a) Soon after fire (b) One year after fire Fig. 54-21
Figure Recovery following a large-scale disturbance
(a) Soon after fire
(b) One year after fire

70. (a) Soon after fire Fig. 54-21a
Figure Recovery following a large-scale disturbance
(a) Soon after fire

71. (b) One year after fire Fig. 54-21b
Figure Recovery following a large-scale disturbance
(b) One year after fire

72. Ecological Succession
Ecological succession is the sequence of community and ecosystem changes after a disturbance
Primary succession occurs where no soil exists when succession begins
Secondary succession begins in an area where soil remains after a disturbance

73. Early-arriving species and later-arriving species may be linked in one of three processes:
Early arrivals may facilitate appearance of later species by making the environment favorable
They may inhibit establishment of later species
They may tolerate later species but have no impact on their establishment

74. Retreating glaciers provide a valuable field-research opportunity for observing succession
Succession on the moraines in Glacier Bay, Alaska, follows a predictable pattern of change in vegetation and soil characteristics

75. 1941 1907 Pioneer stage, with fireweed dominant 1860 Glacier Bay
Fig
1941
1907 1
Pioneer stage, with
fireweed dominant 5 10 15
1860
Kilometers
Glacier
Bay
Figure Glacial retreat and primary succession at Glacier Bay, Alaska
Alaska
1760

76. 1941 1907 Dryas stage Pioneer stage, with fireweed dominant 1860
Fig
1941
1907 2
Dryas stage 1
Pioneer stage, with
fireweed dominant 5 10 15
1860
Kilometers
Glacier
Bay
Figure Glacial retreat and primary succession at Glacier Bay, Alaska
Alaska
1760

77. 1941 1907 Dryas stage Pioneer stage, with fireweed dominant 1860
Fig
1941
1907 2
Dryas stage 1
Pioneer stage, with
fireweed dominant 5 10 15
1860
Kilometers
Glacier
Bay
Figure Glacial retreat and primary succession at Glacier Bay, Alaska
Alaska
1760 3
Alder stage

78. 1941 1907 Dryas stage Pioneer stage, with fireweed dominant 1860
Fig
1941
1907 2
Dryas stage 1
Pioneer stage, with
fireweed dominant 5 10 15
1860
Kilometers
Glacier
Bay
Figure Glacial retreat and primary succession at Glacier Bay, Alaska
Alaska
1760 4
Spruce stage 3
Alder stage

79. Pioneer stage, with fireweed dominant
Fig a
Figure Glacial retreat and primary succession at Glacier Bay, Alaska 1
Pioneer stage, with fireweed dominant

80. Fig b
Figure Glacial retreat and primary succession at Glacier Bay, Alaska 2
Dryas stage

81. Fig c
Figure Glacial retreat and primary succession at Glacier Bay, Alaska 3
Alder stage

82. Fig d
Figure Glacial retreat and primary succession at Glacier Bay, Alaska 4
Spruce stage

83. Succession is the result of changes induced by the vegetation itself
On the glacial moraines, vegetation lowers the soil pH and increases soil nitrogen content

84. 60 50 40 Soil nitrogen (g/m2) 30 20 10 Pioneer Dryas Alder Spruce
Fig 60 50 40
Soil nitrogen (g/m2) 30 20
Figure Changes in soil nitrogen content during succession at Glacier Bay 10
Pioneer
Dryas
Alder
Spruce
Successional stage

85. With your table, complete the Ecological Succession Worksheet.
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With your table, complete the Ecological Succession Worksheet.

86. Human Disturbance
Humans have the greatest impact on biological communities worldwide
Human disturbance to communities usually reduces species diversity
Humans also prevent some naturally occurring disturbances, which can be important to community structure

87. 9. Give two examples of Human Disturbances.
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9. Give two examples of Human Disturbances.

88. Concept 54.5: Community ecology is useful for understanding pathogen life cycles and controlling human disease
Ecological communities are universally affected by pathogens, which include disease-causing microorganisms, viruses, viroids, and prions
Pathogens can alter community structure quickly and extensively

89. Pathogens and Community Structure
Pathogens can have dramatic effects on communities
For example, coral reef communities are being decimated by white-band disease

90. Fig
Figure White-band disease visible on a coral
White band disease is a coral disease that affects acroporid corals and is distinguishable by the white band of dead coral tissue that it forms.[1] The disease completely destroys the coral tissue of Caribbean acroporid corals, specifically elkhorn coral (Acropora palmata) and staghorn coral (A. cervicornis).[1] The disease exhibits a pronounced division between the remaining coral tissue and the exposed coral skeleton.[2] These symptoms are similar to white plague, except that white band disease is only found on acroporid corals, and white plague has not been found on any acroporid corals.[3] It is part of a class of similar disease known as "white syndromes," many of which may be linked to species of Vibrio bacteria. While the pathogen for this disease has not been identified, Vibrio carchariae may be one of its factors. The degradation of coral tissue usually begins at the base of the coral, working its way up to the branch tips, but it can begin in the middle of a branch.[1]

91. Human activities are transporting pathogens around the world at unprecedented rates
Community ecology is needed to help study and combat them

92. Community Ecology and Zoonotic Diseases
Zoonotic pathogens have been transferred from other animals to humans
The transfer of pathogens can be direct or through an intermediate species called a vector
Many of today’s emerging human diseases are zoonotic