Community Ecology

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

2. 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. OBJ 8.1 COMMUNITY STRUCTURE • 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. 8-2p. 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. 25 25 Snails Tube worms Ants Birds 20 20 Species diversity 15 15 10 10 5 5 Coast Deep Sea Coast Deep Sea 0 0 0 2,000 4,000 6,000 0 2,000 4,000 6,000 Fig. 8-3 p. 145 Depth (meters) Depth (meters) 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 @ 2000 m then begins its decrease • Pollution- as levels increase, biodiversity decreases

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

9. © 2004 Brooks/Cole – Thomson Learning High Rate of immigration or extinction Low Equilibrium number Number of species on island Immigration and extinction rates (a) 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

10. © 2004 Brooks/Cole – Thomson Learning © 2004 Brooks/Cole – Thomson Learning High High 100 50 100 Rate of immigration or extinction Rate of immigration or extinction Number of species (percentage of sample studied) 25 Number of amphibian and reptile species 10 12.5 Low Low Small island Far island Large island Near island 6.25 Number of species on island Number of species on island 0 2,000 4,000 6,000 8,000 10,000 1 10 100 1,000 10,000 100,000 (c) Effect of distance from mainland Effect of island size (b) Distance from New Guinea (kilometers) Area (square miles) Island Species

11. 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. 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. 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. 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.