1. Structure Species Interaction Succession & Sustainability
Community Ecology
CHAPTER 8
Structure
Species Interaction
Succession & Sustainability

2. Stability of ecosystems
Key Concepts
Community structure
Roles of species
Species interactions
Changes in ecosystems
Stability of ecosystems

3. CASE STUDY: FLYING FOXES
fruit-eating bats
pollinate flowers from Durian trees
 prized fruit in SE Asia
 strong odor, custard-like “delicious” fruit
mutualism (durian & flying fox)
referred to as keystone species
 pollinate plant species
 disperse plant seeds in dropping (biodiversity)

4. - stratification, relative size, distribution
COMMUNITY STRUCTURE
OBJ 8.1
CHARACTERISTICS
Physical Appearance
- stratification, relative size, distribution
Species Diversity
- richness vs. eveness
Niche Structure
- ecological Roles of Species

5. Community Structure: Appearance and Species Diversity
Stratification
Fig. 8-2 p. 144

6. SPECIES DIVERSITY Species richness: # different species
Species evenness: abundance within each of its species
Sample A could be described as being the more diverse as it contains three species to sample B's two. But there is less chance in sample B than in sample A that two randomly chosen individuals will be of the same species.

7. 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 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. 145
Ants
Birds

8. Number of diatom species
Unpolluted
stream
Polluted
Number of individuals per diatom species
Figure 8-4 Page 145

9. Island Biodiversity
Theory of Island Biogeography-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

10. Island Species Effect of island size (b)
High
Low
Rate of immigration
or extinction
Small island
Effect of island size
Number of species on island
(b)
Large island
© 2004 Brooks/Cole – Thomson Learning
High
Low
Rate of immigration
or extinction
Far island
Effect of distance from mainland
Number of species on island
(c)
Near island
© 2004 Brooks/Cole – Thomson Learning
100 50 25
12.5
6.25
2,000
4,000
6,000
8,000
10,000
Distance from New Guinea (kilometers)
Number of species (percentage of sample studied)
100 1 10
1,000
10,000
100,000
Area (square miles)
Number of amphibian and reptile species

11. General Types of Organisms
OBJ 8.2
General Types of Organisms
Native-organisms that are naturally found in an ecosystem;
Nonnative (Exotic/ Invasive/Alien)- any organism that is not found naturally in an ecosystem; usually transported in by humans
Indicator- organisms that serve as early warnings of damage to a community
Keystone- organisms whose role in more important than their numbers or biomass;
Strong interactions with other species affect the life of others
Process out materials out of proportion to their numbers or biomass

12. OBJ 8.3
Competition
Competition—Two organisms compete to obtain the same limited resource, and both are harmed to some extinct.
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.

14. OBJ 8.4
Competition
Competitive Exclusion Principle—No two species can occupy the same ecological niche in the same place at the same time.
Less fit species must evolve into a slightly different niche.

15. Resource Partitioning
OBJ 8.5
Resource Partitioning
Overlapping Niche of
2 species creates
competition
Over time, species
evolve and become
specialized
Fig. 8-7 p. 150

16. Kinds of Organism Interactions
Predation—One animal kills/eats another.
Predator benefits from food.
Prey adaptation is manifested in a higher reproduction rate.
Prey species benefits by eliminating non-adaptive genes from the gene pool.
Poorly adapted predators are less likely to obtain food and thus pass on non-adaptive genes.

17. PREY: DEFENSE MECHANISMS
adaptation the prey uses adds to the chances of survival for the species
Examples of some defense mechanisms prey use are:  Chemical combat
 Camouflage
 Speed
 Trickery: false features and mimicry

19. Symbiotic Relationships
OBJ 8.7
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.
Ectoparasites—Live on host’s surface.
Fleas
Endoparasites—Live inside host.
Tapeworms

20. 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

21. WHAT IS HAPPENING?

22. Succession
Succession—A series of regular, predictable changes in the structure of a community over time.
Activities of organisms change their surroundings and make the environment suitable for other kinds of organisms.
Climax community—Stable, long-lasting community, primarily determined by climate.

23. OBJ 8.8
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.

24. 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.

25. Terrestrial Primary Succession
Lichen community replaced by annual plants.
Annuals replaced by perennial community.
Perennial community replaced by shrubs.
Shrubs replaced by shade intolerant trees.
Shade intolerant trees replaced by shade tolerant trees.
Stable, climax community often reached.
Successional (seral) Stage—Each step in the process.

26. Terrestrial Primary Succession
OBJ 8.9
Terrestrial Primary Succession

27. Climax Community Characteristics
Maintain species diversity for extended period.
Multiple specialized ecological niches.
High level of organism interactions.
Nutrients recycled and biomass levels remain constant.

28. 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.

29. Aquatic Primary Succession

30. 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.

31. Terrestrial Secondary Succession

32. 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.