Chapter 8

1. Community Structure – spatial arrangement of its individuals and populations Chapter 8

2. Community Characteristics • Physical Appearance – relative size, stratification and distribution of its populations and species • Species Diversity – number of species • Species Abundance – numbers of each species • Niche Structure – number of ecological niches and how they interact

3. Biodiversity • Species Diversity – variety of different species • Genetic Diversity – variability among individuals within a species • Ecological Diversity – variability of ecosystems

4. Most Biodiversity • Tropical Rain Forests • Coral Reefs • Deep Sea • Large Tropical Lakes

5. Factors Affecting Species Diversity • Latitude • Depth (in aquatic) – species diversity increases from surface to about 2,000 m

6. © 2004 Brooks/Cole – Thomson Learning 25 25 Snails Tube worms 20 20 15 15 Species diversity 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 Depth (meters) Depth (meters)

7. Factors Affecting Species Diversity • Pollution (in aquatic) – decrease in diversity and abundance because pollution

8. Species diversity increases with…. • Increasing solar radiation • Increasing precipitation • Decreasing elevation • Pronounced seasonal variations

9. Species Equilibrium Model • The number of species found on an island depends on: • The rate at which new species immigrate to the island • The rate at which species become extinct on the island • At some point they reach an equilibrium that determines the island’s average number of different species

10. © 2004 Brooks/Cole – Thomson Learning High Rate of immigration or extinction Low Equilibrium number Number of species on island (a) Immigration and extinction rates

11. Rates are affected by: • Size • Distance

12. Smaller island has lower diversity because… • Smaller target for potential colonizers • Smaller islands have higher extinction rates because they have fewer resources and less diverse habitats for colonizing species

13. For islands of equal size – the island closest to the mainland will have the higher immigration rate and thus higher diversity

14. © 2004 Brooks/Cole – Thomson Learning High Rate of immigration or extinction Low Small island Large island Number of species on island (b) Effect of island size

15. © 2004 Brooks/Cole – Thomson Learning High Rate of immigration or extinction Low Far island Near island Number of species on island (c) Effect of distance from mainland

16. Types of Species • Native Species – species that normally live and thrive in a particular ecosystem • Nonnative Species – (invasive species or alien species) species that migrate into an ecosystem or are deliberately or accidentally introduced • Indicator Species – species that serve as early warnings of damage to a community or ecosystem

17. Types - continued • Keystone Species – species that play a pivotal role in the structure and function of an ecosystem because of their strong interactions with other species and the fact that they process material out of proportion to their numbers or biomass.

18. How Do Species Interact? • Intraspecific competition – competition between members of the same species • Interspecific competition – competition between members of two or more different species for food, space or any other limited resource.

19. Interspecific Competition • Interference competition – a species limits another’s access to some resource. • Exploitation competition – species have roughly equal access to a specific resource but differ in how fast or efficiently they exploit it

20. Competitive Exclusion Principle • Species cannot occupy the same ecological niche indefinitely.

21. High Relative population density Low 0 2 4 6 8 10 12 14 16 18 Days Each species grown alone Paramecium aurelia Paramecium caudatum

22. High Paramecium aurelia Relative population density Paramecium caudatum Low 0 2 4 6 8 10 12 14 16 18 Days Both species grown together

23. Resource Partitioning • Species that compete for the same resources evolve adaptations that reduce or avoid competition or an overlap of their fundamental niches.

25. Predator - Prey Interactions • Predation – members of one species (predator) feed directly on all or part of a living organism of another species (prey)

26. Bombardier beetle Span worm Wandering leaf insect Foul-tasting monarch butterfly When touched, the snake caterpillar changes shape to look like the head of a snake Poison dart frog Viceroy butterfly mimics monarch butterfly Hind wings of io moth resemble eyes of a much larger animal

27. Symbiosis • A relationship in which species live together in an intimate association. There are three types of symbiosis

28. Three types of symbiosis • Parasitism – one species (the parasite) feeds on part of another organism (the host) by living on or in the host. Examples include: tapeworms, fleas, ticks, mosquitoes, mistletoe plants and fungi

29. Mutualism – two species involved in a relationship interact in ways that benefit both. • Benefits include: having pollen and seeds spread; being supplied with food, or receiving protection • Examples include: mycorrhizae that live in plant roots; bacteria in the digestive tracts of animals; birds on the backs of black rhinos that remove insects

30. Mutualism

31. Commensalism – a relationship in which one species benefits but the other is neither harmed nor helped. • Examples include: redwood sorrel which grows in the shade of redwood trees; epiphytes which attach themselves to the branches of large trees.

32. Ecological Succession • The gradual change in species composition in response to changing environmental conditions. • Two types: primary and secondary • Primary is the gradual establishment of biotic communities on bare rock • Secondary is the reestablishment of biotic communities

33. Pioneer Species • Before a community of plants can become established there must be soil present • Depending on the climate, it can take several hundred to several thousand years to produce fertile soil • Soil formation begins when pioneer species attach themselves to rock (lichens and mosses)

34. Pioneer species are replaced by small perennial grasses and herbs (ferns in the tropics) • These are early successional plant species • These grow close to the ground, have short lives and can establish large populations quickly

35. Mid successional plant species – herbs, grasses and low shrubs. • These are replaced by trees that are adapted to lots of sunlight • Late successional plant species – (mostly trees) that can handle shade

36. Mature oak-hickory forest Young pine forest Shrubs Perennial weeds and grasses Annual weeds Time

37. Secondary Succession • Begins in an area where the natural community has been disturbed, removed or destroyed • Examples include abandoned farms, burned forests, polluted streams, flooded land

38. Factors Affecting Succession • Facilitation – one set of species makes an area suitable for species with different niche requirements • Inhibition – an early species hinders the establishment and growth of other species • Tolerance – late successional plants are unaffected by plants at earlier stages of succession

39. A disturbance to an ecosystem can convert a particular stage of succession to an earlier stage • Types of disturbances: habitat destruction, fire, flooding, drought, landslide, stream alteration, etc…

40. Ecosystems are continually changing • Cannot predict the course of a given succession • Cannot view it as preordained progress toward an ideally adapted climax community

41. Stability • All living systems contain feedback loops (positive and negative) that interact to provide some stability over each system’s expected life span • This stability is maintained by constant dynamic change in response to changing environmental conditions

42. Ecosystem Stability • Inertia or persistence – the ability of a living system to resist being disturbed or altered • Constancy – ability of a living system to keep its numbers within the limits imposed by the available resources • Resilience – ability of a system to bounce back after a disturbance (not drastic)