1. Chapter 41 Community Ecology (Sections 41.1 - 41.5)

2. 41.1 Fighting Foreign Fire Ants
Red imported fire ants, Solenopsis invicta, have a venomous sting, disrupt native wildlife communities, and are not controlled by pesticides
Biological control involves phorid flies, specialized parasites (parasitoids) that kill their host by laying an egg in the ant’s tissues – the larvae eats its way through the fire ant and undergoes metamorphosis in its head
community
All species that live in a particular region

3. Phorid Fly and Fire Ant
Phorid flies insert a fertilized egg into an ant’s thorax
Parasitized ant that lost its head after a developing fly larva moved into it
Figure 41.1 Red imported fire ants and their foes. Opposite, nest mounds of fire ants in a Texas pasture. A Phorid fly. This fly uses nia and as far north as Kansas and Delaware. the hooked extension on its abdomen to insert a fertilized egg into an ant’s thorax. B Parasitized ant that lost its head after a developing the fly larva moved into it. The larva will undergo metamor phosis to an adult inside the detached head.

4. 41.2 Community Structure
The type of place where a species normally lives is its habitat, and all species living in a habitat constitute a community
Communities often are nested one inside another
habitat
Type of environment in which a species typically lives

5. Species Diversity Communities differ in their species diversity
Species diversity has two components:
Species richness (number of species)
Species evenness (relative abundance of each species)
Community structure is dynamic
Species richness and evenness change over time

6. Factors Affecting Community Structure
Community structure can change:
As the community forms and ages
As a result of natural or human-induced disturbances
With changes in physical factors such as climate and resource availability
Due to various types of species interactions

7. Species Interactions
Species interactions can be mutually beneficial, mutually harmful, or benefit one species while harming the other
Example: Commensal ferns attached to the trunk of a tree; the fern benefits from the light, and the tree is unaffected
commensalism
Species interaction that benefits one species and neither helps nor harms the other

8. Commensalism A tree with a commensal fern
The fern benefits by growing on the tree, which is unaffected by the presence of the fern
Figure 41.2 A tree with a commensal fern. The fern benefits by growing on the tree, which is unaffected by the presence of the fern.

9. Types of Two-Species Interactions
Type of Interaction Species 1 Species 2
Commensalism Helpful None
Mutualism Helpful Helpful
Interspecific competition Harmful Harmful
Predation, herbivory
parasitism, parasitoidism Helpful Harmful

10. Symbiosis
Symbiosis (“living together”) refers to a relationship in which two species have a prolonged close association
Two species that interact closely for generations can coevolve – an evolutionary process in which each species acts as a selective agent on the other
symbiosis
One species lives in or on another in a commensal, mutualistic, or parasitic relationship

11. Key Concepts Community Characteristics
A community consists of all species in a habitat
A habitat’s history, its biological and physical characteristics, and interactions among species in the habitat affect the number of species in the community and their relative abundance

12. 41.3 Mutualism
In a mutualistic interaction, two species benefit by taking advantage of one another
Example: Pollinators eat nectar and pollen, and plants receive pollen from other plants of the same species
mutualism
Species interaction that benefits both species

13. Mutualism and Coevolution
In some mutualisms, neither species can complete its life cycle without the other
Example: Yucca plants and the moths that pollinate them
The moth matures when yucca flowers bloom
Mouthparts of the female moth are specialized to collect yucca pollen
Female flies to another flower, pierces its ovary, and lays eggs inside – fertilizing the yucca as she leaves
Moth eggs develop into larvae in the ovary of the yucca

14. Yucca Plant and Yucca Moth
Figure 41.3 Mutualism on a rocky slope of the high desert in Colorado. Only one yucca moth species pollinates plants of each Yucca species; each moth cannot complete its life cycle with any other plant. The moth matures when yucca flowers blossom. The female has specialized mouthparts that collect and roll sticky pollen into a ball. She flies to another flower and pierces its ovary, where seeds will form and develop, and lays eggs inside. As the moth crawls out, she pushes a ball of pollen onto the flower’s pollenreceiving platform. After pollen grains germinate, they give rise to pollen tubes, which grow through the ovary tissues and deliver sperm to the plant’s eggs. Seeds develop after fertilization. Meanwhile, moth eggs develop into larvae that eat a few seeds, then gnaw their way out of the ovary. Seeds that larvae do not eat give rise to new yucca plants.

15. Mutualism and Defense For some mutualists, the main benefit is defense
Example: Sea anemone and anemone fish
An anemone fish has a mucus layer that shields it from stinging cells (nematocysts) of a sea anemone
Tentacles of the anemone protect the fish from predators
The anemone fish chases away the few fishes that are able to eat sea anemone tentacles

16. Sea Anemone and Anemone Fish
Figure 41.4 The sea anemone Heteractis magnifica has a mutualistic association with the pink anemone fish (Amphiprion perideraion). This tiny but aggressive fish chases away predatory butterfly fishes that would bite off tips of anemone tentacles. The fish cannot survive and reproduce without the protection of an anemone. The anemone does not need a fish to protect it, but it does better with one.

17. Mutualistic Microorganisms
Mutualistic microorganisms help plants obtain nutrients:
Nitrogen-fixing bacteria on roots of legumes (peas) provide the plant with extra nitrogen
Mycorrhizal fungi living in or on plant roots enhance a plant’s mineral uptake
Other fungi interact with photosynthetic algae or bacteria in lichens

18. 41.4 Competitive Interactions
Resources are limited and individuals of different species often compete for access to them (interspecific competition)
Competition adversely affects both species
interspecific competition
Competition between two species

19. Ecological Niche
Each species has an ecological niche defined by physical and biological factors; the more similar the niches of two species are, the more intensely they will compete
An animal’s niches include the temperature range it can tolerate, species it eats, and places it can breed
A flowering plant’s niche would include its soil, water, light, and pollinator requirements
ecological niche
All of a species’ requirements and roles in an ecosystem

20. Two Types of Interspecific Competition
Exploitative competition:
Two species reduce the amount of resources available to the other by using that resource
Example: Deer and blue jays compete for acorns
Interference competition:
One species actively prevents another from accessing some resource
Example: One species of scavenger will often chase another away from a carcass

21. Interference Competition
Figure 41.5 Interspecific competition among scavengers.

22. Interference Competition
A Golden eagle and a red fox face off over a moose carcass.
B In a dramatic demonstration of interference competition, the eagle attacks the fox with its talons. After this attack, the fox retreated, leaving the eagle to exploit the carcass.
Figure 41.5 Interspecific competition among scavengers.
Stepped Art
Fig. 41.5, p. 694

23. Effects of Competition
Species compete most intensely when a shared resource is the main limiting factor for both
Whenever two species require the same limited resource to survive or reproduce, the better competitor will drive the less competitive species to extinction in that habitat
competitive exclusion
Process whereby two species compete for a limiting resource, and one drives the other to local extinction

24. Experiment: Competitive Exclusion
Two Paramecium species compete for the same food (bacteria)
Each species thrives when grown alone
When grown together, P. aurelia drove P. caudatum to extinction
Figure 41.6 Results of competitive exclusion between two Paramecium species that compete for the same food. When the two species were grown together, P. aurelia drove P. caudatum to extinction.

25. Experiment: Competitive Exclusion

26. Experiment: Competitive Exclusion
Figure 41.6 Results of competitive exclusion between two Paramecium species that compete for the same food. When the two species were grown together, P. aurelia drove P. caudatum to extinction.
Fig , p. 695

27. Experiment: Competitive Exclusion
Figure 41.6 Results of competitive exclusion between two Paramecium species that compete for the same food. When the two species were grown together, P. aurelia drove P. caudatum to extinction.
Fig , p. 695

28. Experiment: Competitive Exclusion
Figure 41.6 Results of competitive exclusion between two Paramecium species that compete for the same food. When the two species were grown together, P. aurelia drove P. caudatum to extinction.
Fig , p. 695

29. Experiment: Competitive Exclusion
Time (days)
population density
Relative
P. caudatum alone
Time (days)
population density
Relative
Both species together
Time (days)
population density
Relative
P. aurelia alone
Figure 41.6 Results of competitive exclusion between two Paramecium species that compete for the same food. When the two species were grown together, P. aurelia drove P. caudatum to extinction.
Stepped Art
Fig. 41.6, p. 695

30. ANIMATION: Competitive Exclusion
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31. Resource Partitioning
Resource partitioning is an evolutionary process by which species become adapted to use a shared limiting resource in a way that minimizes competition
Example: Three plant species growing in the same field
resource partitioning
Species become adapted in different ways to access different portions of a limited resource
Allows species with similar needs to coexist

32. Resource Partitioning
Roots of each species take up water and mineral ions from a different soil depth
Reduces competition among the species and allows them to coexist
Figure 41.7 Resource partitioning among three annual plant species in a plowed but abandoned field. Roots of each species take up water and mineral ions from a different soil depth. This difference reduces competition among the species and allows them to coexist.

33. Character Displacement
Directional selection occurs when species with similar requirements share a habitat and compete for a limiting resource, resulting in character displacement
Example: Beak sizes in Galapagos finches
character displacement
Outcome of competition between two species
Directional selection shifts the range of variation for one or more traits in a direction that lessens competition for a limiting resource

34. ANIMATION: Hairston's Experiment
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35. ANIMATION: Resource Partitioning
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36. 41.5 Predation and Herbivory
Predation and herbivory are short-term interactions in which one species obtains nutrients and energy by feeding on another
predation
One species (the predator) captures, kills, and eats another species (the prey)

37. Predator and Prey Abundance
The abundance of prey species in a community affects how many predators it can support
With some predators, such as web-spinning spiders, the proportion of prey killed is constant
Usually, the number of prey killed depends on the time it takes predators to capture, eat, and digest prey

38. Predator and Prey Abundance (cont.)
Predator and prey populations may rise and fall in cycles
Example: Lynx and snowshoe hare populations rise and fall over a ten-year cycle
Figure 41.8 Graph of the number of Canadian lynx (dashed line) and snowshoe hares (solid line), based on counts of pelts sold by trappers to Hudson’s Bay Company during a ninety-year period.

39. Lynx and Snowshoe Hare
Figure 41.8 Graph of the number of Canadian lynx (dashed line) and snowshoe hares (solid line), based on counts of pelts sold by trappers to Hudson’s Bay Company during a ninety-year period.

40. Coevolution of Predators and Prey
Predator and prey exert selection pressure on one another
Predators exert selection pressure that favors improved prey defenses
Improved prey defenses in turn exert selection pressure on predators to improve capture skills, and so on

41. Defensive Adaptations
Defensive adaptations of prey include hard or sharp parts that make prey difficult to eat, and chemicals that taste bad or sicken predators
Other adaptations trick or startle an attacking predator
Well-defended prey often have warning coloration that predators learn to avoid, such as the black and yellow stripes of stinging wasps and bees

42. Defensive Adaptations (cont.)
In a type of mimicry, prey masquerade as a species that has a defense that they lack
Example: Some flies that can’t sting resemble stinging bees or wasps
mimicry
A species evolves traits that make it more similar in appearance to another species

43. Wasp and Mimic
Figure 41.9 Mimicry. Some edible insect species resemble toxic or unpalatable species that are not closely related.

44. Predator Adaptations
Predator adaptations include sharp teeth and claws
Predators and prey may be coevolved for speed
Example: cheetah and gazelle
Both predators and prey use camouflage (a form, patterning, color, or behavior that allows them to blend into their surroundings) to avoid detection

45. Camouflage in Prey and Predators
Figure Camouflage in prey and predators.

46. Coevolution of Herbivores and Plants
With herbivory, the number and type of plants in a community can influence the number and type of herbivores present
herbivory
An animal feeds on plant parts

47. Herbivores and Plants (cont.)
There are two types of defenses against herbivory:
Some plants have adapted to withstand and recover quickly from herbivory
Other plants have traits such as spines, tough leaves, or toxins that deter herbivory
Plant defenses favor adaptations in herbivores
Example: Koalas have special enzymes to break down toxins in eucalyptus

48. ANIMATION: Predator-Prey Interactions
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