1. APES Chapter 8 Notes
Community Ecology: Structure, Species Interactions, Succession, and Sustainability

2. General Types of Species
Native species—species that normally live and thrive in a particular ecosystem
Non-native, exotic or alien species— species that migrate into an ecosystem or are deliberately or accidentally introduced into an ecosystem humans.
Ex: Africanized Bees, Zebra Mussels, Cane Toad, Kudzo.

3. General Types of Species
Indicator species—species that serve as early warnings that a community or ecosystem is being damaged.
Birds are excellent indicators because they are found almost everywhere and respond very quickly to environmental change.
Some amphibians are also classified as indicator species.

4. General Types of Species
Keystone species—species whose roles in an ecosystem are much more important than their abundance or biomass would suggest. They play pivotal roles in the structure, function, and integrity of an ecosystem.
Ex: sea otters, wolves, elephants, great white shark, all pollinators.

5. Species Interactions: Competition and Predation
Members of species may be harmed by, benefit from , or by unaffected by the interaction.

6. Competition
Competition—Two organisms compete to obtain the same limited resource.
Intraspecific—Members of same species competing for resources.
Interspecific—Members of different species competing for resources.
The more similar the competing species, the more intense the competition.

7. Species compete in two ways:
Interference—one species limits another’s access to some resource by direct contact, such as establishing a territory and defending it.
Exploitation—occurs indirectly. Competing species have equal access to a specific resource but differ in how fast or efficiently they exploit it.

8. Competition
Competitive Exclusion Principle—No two species can occupy the same ecological niche in the same place at the same time.
Less fit species may die out or evolve into a slightly different niche.

10. Resource Partitioning
Adaptations evolved to reduce or avoid competition.
In Resource Partitioning species with similar needs use similar resources:
1. at different times (hunting: hawks-day, owls-night)
2. in different ways
3. in different places

11. Resource Partitioning
Overlapping Niche of
2 species creates
competition
Over time, species
evolve and become
specialized
Fig. 8-9 p. 175; Refer to Fig p. 152 & Fig p. 175

12. Resource Partitioning

13. Predation
One species (predator) feeds directly on another species (prey).

14. Predation Predators increase their chances by: Running fast
Keen eyesight
Hunting in packs
Camouflage
Humans have invented tools (weapons and traps)

15. Predation Prey defend themselves against predators by:
Run, swim or fly fast
Keen eyesight or sense of smell
Live in herds
Protective shells or spines
Camouflage
Thick bark
Thorns

16. Predation Chemicals-poisonous, irritating, foul smelling, bad tasting
Warning coloration-so predators know they are poisonous or bad tasting
Mimicry-taking on the appearance of another organism that may be very poisonous

17. Symbiotic Relationships
Symbiosis—Close, physical relationship between two different species. At least one species derives benefit from the interaction.
Parasitism—One organism (parasite) living in or on another organism (host), from which it derives nourishment. Parasite benefits and host is harmed.
Ectoparasites—Live on host’s surface.
Fleas
Endoparasites—Live inside host.
Tapeworms

18. Symbiotic Relationships
Commensalism—One organism benefits, while the other is unaffected.
Remoras and Sharks
Mutualism—Both species benefit. Obligatory in many cases as neither can exist without the other.
Mycorrhizae

19. Parasitism

20. Mutualism

21. Commensilism

22. Community Structure 4 Characteristics:
1. Physical appearance: size, stratification, and distribution of populations.
2. Species diversity or richness: number of different species.
3. Species abundance: number of individuals of each species.
4. Niche structure: number of ecological niches.

23. Community Structure: Appearance and Species Diversity
Stratification
Fig. 8-2 p. 166
Species diversity
Niche structure
Edge effects

24. Three Factors Affecting Biodiversity
Latitude(terrestial)- the closer to the equator, the higher the biodiversity
Highest species diversity in tropics; lowest in polar regions
Depth(aquatic)- biodiversity increases with depth to about 2000 m then begins its decrease
Pollution- as levels increase, biodiversity decreases
Species diversity 25 20 15 5 10
2,000
4,000
6,000
Depth (meters)
Coast
Deep Sea
Snails
Tube worms
Fig. 8-3 p. 167
Ants
Birds

25. Island Biodiversity
Theory of Island Biodiversity-the number of species found on an island is determined by:
Species immigration
Immigration- movement of organisms into a place
Emigration- movement of organisms out of a place
Species extinction
High
Low
Rate of immigration
or extinction
Equilibrium number
Immigration and extinction rates
Number of species on island
(a)
© 2004 Brooks/Cole – Thomson Learning

26. Communities in Transition
Ecological Succession—the gradual and fairly predictable change in species composition of a given area over a period of time.
Climax community—Stable, long- lasting community, primarily determined by climate.

27. Succession
Primary Succession—Begins with bare mineral surfaces or water and total lack of organisms.
Secondary Succession—Begins with disturbance of an existing ecosystem.
Much more commonly observed.

28. Primary Succession Terrestrial Primary Succession
Pioneer Community: Collection of organisms able to colonize bare rock
(i.e. lichens, mosses).
Lichens help break down rock, and accumulate debris helping to form a thin soil layer.
Soil layer begins to support small life forms.

29. Terrestrial Primary Succession

30. Aquatic Primary Succession
Except for oceans, most aquatic systems are considered temporary.
All aquatic systems receive inputs of soil particles and organic matter from surrounding land.
Gradual filling of shallow bodies of water.
Roots and stems below water accumulate more material.
Wet soil established.

31. Aquatic Primary Succession

32. Secondary Succession
Occurs when an existing community is disturbed or destroyed.
With most disturbances, most of the soil remains, and many nutrients necessary for plant growth may be available for reestablishment of the previous ecosystem.
Nearby undamaged communities can serve as sources of seeds and animals.
Tends to be more rapid than primary growth.

33. Terrestrial Secondary Succession

34. Secondary Succession of a Beaver Pond

35. Modern Concepts of Succession and Climax
As settlers changed “original” ecosystems to agriculture, climax communities were destroyed.
Many farms were abandoned, and land began to experience succession.
Ecologists began to recognize there was not a fixed, pre-determined community.
Only thing differentiating climax community from successional community is time scale.