1. Chapter 54
Community Ecology

2. Overview: Communities in Motion
A biological community is an assemblage of populations of various species living close enough for potential interaction
Think about the community make up of LC nature preserve……the cross country course (1)
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3. Competition
Interspecific competition occurs when separate species compete for a resource in short supply
Intraspecific competition occurs when members of the same species compete for a resource in short supply
Try and give an example of each (2)
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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, symbiosis (parasitism, mutualism, and commensalism)
Intraspecific interactions occur to members within a species (mate selection, resource competition, territory)
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5. 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 (3)
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6. Ecological Niches and Natural Selection
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 (4)
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7. Resource partitioning is differentiation of ecological niches, enabling similar species to coexist in a community (5)
A good example are birds in a tree….how might a 50 ft tall and 10 ft wide tree have similar birds, but each different niches?
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8. A. distichus perches on fence posts and other sunny surfaces.
Figure 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

9. A species’ fundamental niche is the niche potentially occupied by that species
A species’ realized niche is the niche actually occupied by that species (6)
As a result of competition, a species’ fundamental niche may differ from its realized niche
For example, the presence of one barnacle species limits the realized niche of another species
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10. EXPERIMENT High tide Chthamalus Chthamalus Balanus realized niche
Figure 54.3
EXPERIMENT
High tide
Chthamalus
Balanus
Chthamalus
realized niche
Balanus
realized niche
Ocean
Low tide
RESULTS
High tide
Figure 54.3 Inquiry: Can a species’ niche be influenced by interspecific competition?
Chthamalus
fundamental niche
Ocean
Low tide

11. Both species are normally nocturnal (active during the night)
The common spiny mouse and the golden spiny mouse show temporal partitioning of their niches
Both species are normally nocturnal (active during the night)
Where they coexist, the golden spiny mouse becomes diurnal (active during the day)
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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 (7)
An example is variation in beak size between populations of two species of Galápagos finches
The idea here is that when competing species are in the same location they will morph toward opposite extremes in their roles and geographically separated populations are much more similar.
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13. Percentages of individuals in each size class
Figure 54.4
G. fuliginosa
G. fortis
Beak
depth 60
Los Hermanos 40
G. fuliginosa,
allopatric 20 60
Daphne 40
Percentages of individuals in each size class
G. fortis,
allopatric 20
Figure 54.4 Character displacement: indirect evidence of past competition. 60
Santa María, San Cristóbal
Sympatric
populations 40 20 8 10 12 14 16
Beak depth (mm)

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
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 (8 from knowledge 9-10)
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15. (11……warnings don’t have to be visual could be auditory etc.)
Figure 54.5
(11……warnings don’t have to be visual could be auditory etc.)
(a) Cryptic coloration
(b) Aposematic
coloration
Canyon tree frog
Poison dart frog
(c) Batesian mimicry: A harmless species mimics a harmful one.
(d) Müllerian mimicry: Two unpalatable species
mimic each other.
Hawkmoth
larva
Cuckoo bee
Yellow jacket
Green parrot snake
Figure 54.5 Examples of defensive coloration in animals.

16. 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
Herbivores-specialized teeth or body structures for acquisition…..think about the teeth of a cow or a the neck of a giraffe
Plant adaptations-thorns like on a rose, or chemical poision found in the berries of a pokeweed plant (12-13)
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17. Interactions
Symbiosis is a relationship where two or more species live in direct and intimate contact with one another
In parasitism (+/– interaction), one organism, the parasite, derives nourishment from another organism, its host, which is harmed in the process
Mutualistic symbiosis, or mutualism (+/+ interaction), is an interspecific interaction that benefits both species
In commensalism (+/0 interaction), one species benefits and the other is neither harmed nor helped(14 examples visualized on next few slides and 15-16)
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18. (a) Acacia tree and ants (genus Pseudomyrmex)
Figure 54.7
(a) Acacia tree and ants (genus Pseudomyrmex)
Figure 54.7 Mutualism between acacia trees and ants.
(b) Area cleared by ants at the base of an acacia tree

19. Figure 54.8
Figure 54.8 A possible example of commensalism between cattle egrets and water buffalo.

21. 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 (17)
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22. A B C D Community 1 Community 2 A: 25% B: 25% C: 25% D: 25% A: 80%
Figure 54.10 A B C D
Community 1
Community 2
Figure Which forest is more diverse?
A: 25%
B: 25%
C: 25%
D: 25%
A: 80%
B: 5%
C: 5%
D: 10%

23. Figure 54.12
Figure Study plots at the Cedar Creek Natural History Area, site of long-term experiments on manipulating plant diversity.

24. Communities with higher diversity are
More productive and more stable in their productivity
Better able to withstand and recover from environmental stresses
More resistant to invasive species, organisms that become established outside their native range
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25. Trophic Structure
Trophic structure is the feeding relationships between organisms in a community
It is a key factor in community dynamics
Food chains link trophic levels from producers to top carnivores (skip the specifics of 19, but understand the concept….can you contsruct a plausible food chain for various biomes?)
Video: Shark Eating a Seal
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26. (20) Carnivore Quaternary consumers Carnivore Carnivore Tertiary
Figure 54.13
(20)
Carnivore
Quaternary
consumers
Carnivore
Carnivore
Tertiary
consumers
Carnivore
Carnivore
Secondary
consumers
Carnivore
Figure Examples of terrestrial and marine food chains.
Herbivore
Primary
consumers
Zooplankton
Plant
Primary
producers
Phytoplankton
A terrestrial food chain
A marine food chain

27. Food Webs
A food web is a branching food chain with complex trophic interactions it summarizes the interactions (and transfer of energy) between members of the community. (18)
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28. Humans Smaller toothed whales Baleen whales Sperm whales Elephant
Figure 54.14
Humans
Smaller
toothed
whales
Baleen
whales
Sperm
whales
Elephant
seals
Crab-
eater
seals
Leopard
seals
Birds
Fishes
Squids
Figure An Antarctic marine food web.
Carniv-
orous
plankton
Euphau-
sids
(krill)
Cope-
pods
Phyto-
plankton

29. Species may play a role at more than one trophic level
Food webs can be simplified by
Grouping species with similar trophic relationships into broad functional groups
Isolating a portion of a community that interacts very little with the rest of the community
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30. Limits on Food Chain Length
Each food chain in a food web is usually only a few links long
The energetic hypothesis suggests that length is limited by inefficient energy transfer
For example, a producer level consisting of 100 kg of plant material can support about 10 kg of herbivore biomass (the total mass of all individuals in a population) * notice the steady log decrease between each step in the chain) (21)
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31. 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
Dominant species are those that are most abundant or have the highest biomass
Dominant species exert powerful control over the occurrence and distribution of other species
For example, sugar maples have a major impact on shading and soil nutrient availability in eastern North America; this affects the distribution of other plant species (22)
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32. Keystone Species and Ecosystem Engineers
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
Field studies of sea stars illustrate their role as a keystone species in intertidal communities (23)
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33. (24) EXPERIMENT RESULTS 20 15 With Pisaster (control)
Figure 54.17
EXPERIMENT
(24)
RESULTS
Figure Inquiry: Is Pisaster ochraceus a keystone predator? 20 15
With Pisaster (control)
Number of species
present 10
Without Pisaster
(experimental) 5
1963
’64
’65
’66
’67
’68
’69
’70
’71
’72
’73
Year

34. “foundation species”-cause physical changes in the environment that affect community structure
For example, beaver dams can transform landscapes on a very large scale (35)
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35. Figure 54.19
Figure Beavers as ecosystem engineers.

36. Concept 54.3: Disturbance influences species diversity and composition
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
A high level of disturbance is the result of a high intensity and high frequency of disturbance
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37. High levels of disturbance exclude many slow-growing species
The intermediate disturbance hypothesis suggests that moderate levels of disturbance can foster greater diversity than either high or low levels of disturbance
High levels of disturbance exclude many slow-growing species
Low levels of disturbance allow dominant species to exclude less competitive species (26)
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38. In a New Zealand study, richness of invertebrate taxa was highest in streams with an intermediate intensity of flooding
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39. Index of disturbance intensity (log scale)
Figure 54.20 35 30 25
Number of taxa 20 15
Figure Testing the intermediate disturbance hypothesis. 10
0.9
1.0
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9
2.0
Index of disturbance intensity (log scale)

40. 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 (27)………Also know relative time frame and pioneer species
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41. Latitudinal Gradients
Species richness is especially great in the tropics and generally declines along an equatorial-polar gradient
Two key factors in equatorial-polar gradients of species richness are probably evolutionary history and climate (28-29)
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42. Area Effects
The species-area curve quantifies the idea that, all other factors being equal, a larger geographic area has more species
A species-area curve of North American breeding birds supports this idea (30)
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43. Island Equilibrium Model
Species richness on islands depends on island size, distance from the mainland, immigration, and extinction (31)
The equilibrium model of island biogeography maintains that species richness on an ecological island levels off at a dynamic equilibrium point
Text goes crazy with island stuff skip just have an idea of the “common sense” stuff let’s discuss
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44. Concept 54.5: Pathogens alter community structure locally and globally
Ecological communities are universally affected by pathogens, which include disease-causing microorganisms, viruses, viroids, and prions
Pathogens can alter community structure quickly and extensively
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 (38-40 don’t need 3 necessarily)
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