1. Ch. 52 Community Ecology: What you should already know… Community Predation Herbivory (herbivores eating plants) Symbiotic relationships= parasitism (+/-), mutualism (+/+), commensalism (+, 0) Coevolution Trophic levels, food chains, food webs Biomass Ecological succession- primary vs. secondary Humans most common source of disturbance Biodiversity

2. CHAPTER 53 COMMUNITY ECOLOGY Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Section A: What Is a Community? 1.Contrasting views of communities are rooted in the individualistic and interactive hypotheses 2. The debate continues with the rivet and redundancy models

3. What is a Community? A community is defined as an assemblage of species living close enough together for potential interaction. Communities differ in their species richness, the number of species they contain, and the relative abundance of different species. Introduction Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

4. An individualistic hypothesis depicts a community as a chance assemblage of species found in the same area because they happen to have similar abiotic requirements. 1. Contrasting views of communities are rooted in the individualistic and interactive hypotheses Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 53.1a

5. An interactive hypothesis depicts a community as an assemblage of closely linked species locked in by mandatory biotic interactions. Fig. 53.1b Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

6. These two very different hypotheses suggest different priorities in studying biological communities. In most actual cases, the composition of communities does seem to change continuously. Fig. 53.1c Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

7. The rivet model of communities is a reincarnation of the interactive model. The redundancy model states that most species in a community are not closely associated with one another. No matter which model is correct, it is important to study species relationships in communities. 2. The debate continues with the rivet and redundancy models Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

8. CHAPTER 53 COMMUNITY ECOLOGY Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Section B1: Interspecific Interactions and Community Structure 1.Populations maybe linked by competition, predation, mutualism, and commensalism

9. There are different interspecific interactions, relationships between the species of a community. Introduction Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

10. Possible interspecific interactions are introduced in Table 53.1, and are symbolized by the positive or negative affect of the interaction on the individual populations. 1. Populations may be linked by competition, predation, mutualism and commensalism Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

11. Competition. Interspecific competition for resources can occur when resources are in short supply. There is potential for competition between any two species that need the same limited resource. The competitive exclusion principle: two species with similar needs for same limiting resources cannot coexist in the same place. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

12. The ecological niche is the sum total of an organism’s use of abiotic/biotic resources in the environment. An organism’s niche is its role in the environment. The competitive exclusion principle can be restated to say that two species cannot coexist in a community if their niches are identical. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

13. Classic experiments confirm this. Fig. 53.2 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

14. Resource partitioning is the differentiation of niches that enables two similar species to coexist in a community. Fig. 53.2 Fig. 53.3 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

15. Character displacement is the tendency for characteristics to be more divergent in sympatric populations of two species than in allopatric populations of the same two species. Hereditary changes evolve that bring about resource partitioning. Fig. 53.4 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

16. Predation. A predator eats prey. Herbivory, in which animals eat plants. In parasitism, predators live on/in a host and depend on the host for nutrition. Predator adaptations: many important feeding adaptations of predators are both obvious and familiar. Claws, teeth, fangs, poison, heat-sensing organs, speed, and agility. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

17. Plant defenses against herbivores include chemical compounds that are toxic. Animal defenses against predators. Behavioral defenses include fleeing, hiding, self- defense, noises, and mobbing. Camouflage includes cryptic coloration, deceptive markings. Fig. 53.5 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

18. Mechanical defenses include spines. Chemical defenses include odors and toxins Aposematic coloration is indicated by warning colors, and is sometimes associated with other defenses (toxins). Fig. 53.6 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

19. Mimicry is when organisms resemble other species. Batesian mimicry is where a harmless species mimics a harmful one. Fig. 53.7 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

20. Müllerian mimicry is where two or more unpalatable species resemble each other. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 53.8

21. Parasites and pathogens as predators. A parasite derives nourishment from a host, which is harmed in the process. Endoparasites live inside the host and ectoparasites live on the surface of the host. Parasitoidism is a special type of parasitism where the parasite eventually kills the host. Pathogens are disease-causing organisms that can be considered predators. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

22. Mutualism is where two species benefit from their interaction. Commensalism is where one species benefits from the interaction, but other is not affected. An example would be barnacles that attach to a whale. Fig. 53.9 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

23. Coevolution and interspecific interactions. Coevolution refers to reciprocal evolutionary adaptations of two interacting species. When one species evolves, it exerts selective pressure on the other to evolve to continue the interaction. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

24. CHAPTER 53 COMMUNITY ECOLOGY Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Section B2: Interspecific Interactions and Community Structure (continued) 2. Trophic structure is a key factor in community dynamics 3.Dominant species and keystone species exert strong controls on community structure 4.The structure of a community may be controlled bottom-up by nutrients or top-down by predators

25. The trophic structure of a community is determined by the feeding relationships between organisms. The transfer of food energy from its source in photosynthetic organisms through herbivores and carnivores is called the food chain. 2. Trophic structure is a key factor in community dynamics Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

26. Charles Elton first pointed out that the length of a food chain is usually four or five links, called trophic levels. He also recognized that food chains are not isolated units but are hooked together into food webs. Fig. 53.10 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

27. Food webs. Who eats whom in a community? Trophic relationships can be diagrammed in a community. What transforms food chains into food webs? A given species may weave into the web at more than one trophic level. Fig. 53.11 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

28. What limits the length of a food chain? The energetic hypothesis suggests that the length of a food chain is limited by the inefficiency of energy transfer along the chain. The dynamic stability hypothesis states that long food chains are less stable than short chains. Fig. 53.13 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

29. Dominant species are those in a community that have the highest abundance or highest biomass (the sum weight of all individuals in a population). If we remove a dominant species from a community, it can change the entire community structure. 3. Dominant species and keystone species exert strong controls on community structure Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

30. Keystone species exert an important regulating effect on other species in a community. Fig. 53.14 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings These sea stars control a mussel species that takes over if not held in check.

31. If they are removed, community structure is greatly affected. Fig. 53.15 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Otters control sea urchins

32. Simplified models based on relationships between adjacent trophic levels are useful for discussing how communities might be organized. 4. The structure of a community may be controlled bottom-up by nutrients or top- down by predators Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

33. Consider three possible relationships between plants (V for vegetation) and herbivores (H). V  HV  HV  H Arrows indicate that a change in biomass of one trophic level causes a change in the other trophic level. The bottom-up model postulates V  H linkages, where nutrients and vegetation control community organization. The top-down model postulates that it is mainly predation that controls community organization V  H. Other models go between the bottom-up and top- down extreme models. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

34. CHAPTER 53 COMMUNITY ECOLOGY Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Section C1: Disturbance and Community Structure 1.Most communities are in a state of nonequilibrium owing to disturbances 2. Humans are the most widespread agents of disturbance

35. Disturbances affect community structure and stability. Stability is the ability of a community to persist in the face of disturbance. Introduction Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

36. Disturbances are events like fire, weather, or human activities that can alter communities. Some are routine. 1. Most communities are in a state of nonequilibrium owing to disturbances Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 53.16

37. Marine communities are subject to disturbance by tropical storms. Fig. 53.17 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

38. Fig. 53.17 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

39. We usually think that disturbances have a negative impact on communities, but in many cases they are necessary for community development and survival. Fig. 53.18 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

40. Human activities cause more disturbance than natural events and usually reduce species diversity in communities. 2. Humans are the most widespread agents of disturbance Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

41. CHAPTER 53 COMMUNITY ECOLOGY Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Section C2: Disturbance and Community Structure (continued) 3.Ecological succession is the sequence of community changes after a disturbance

42. Ecological succession is the transition in species composition over ecological time. Primary succession begins in a lifeless area where soil has not yet formed. 3. Ecological succession is the sequence of community changes after a disturbance Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

43. Fig. 53.19 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

44. Mosses and lichens colonize first and cause the development of soil. An example would be after a glacier has retreated. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

45. Secondary succession occurs where an existing community has been cleared by some event, but the soil is left intact. Grasses grow first, then trees and other organisms. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

46. Soil concentrations of nutrients show changes over time. Fig. 53.20 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

47. CHAPTER 53 COMMUNITY ECOLOGY Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Section D: Biogeographic Factors Affecting the Biodiversity of Communities 1.Community biodiversity measures the number of species and their relative abundance 2. Species richness generally declines along an equatorial-polar gradient 3.Species richness is related to a community’s geographic size 4.Species richness on an island depends on island size and distance from the mainland

48. Two key factors correlated with a community’s biodiversity (species diversity) are its size and biogeography. Introduction Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

49. The variety of different kinds of organisms that make up a community has two components. Species richness, the total number of species in the community. Relative abundance of the different species. Imagine two small forest communities with 100 individuals distributed among four different tree species. 1. Community biodiversity measures the number of species and their relative abundance Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

50. Species richness may be equal, but relative abundance may be different. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 53.21

51. Counting species in a community to determine their abundance is difficult, especially for insects and smaller organisms Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 53.22

52. Tropical habitats support much larger numbers of species of organisms than do temperate and polar regions. 2. Species richness generally declines along an equatorial-polar gradient Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

53. Fig. 53.23

54. What causes these gradients? The two key factors are probably evolutionary history and climate. Organisms have a history in an area where they are adapted to the climate. Energy and water may factor into this phenomenon. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

55. Fig. 53.24

56. The species-area curve quantifies what may seem obvious: the larger the geographic area, the greater the number of species. 3. Species richness is related to a community’s geographic size Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 23.25

57. Because of their size and isolation, islands provide great opportunities for studying some of the biogeographic factors that affect the species diversity of communities. Imagine a newly formed island some distance from the mainland. Robert MacArthur and E. O. Wilson developed a hypothesis of island biogeography to identify the determinants of species diversity on an island. 4. Species richness on islands depends on island size and distance from the mainland Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

58. Two factors will determine the number of species that eventually inhabit the island. The rate at which new species immigrate to the island. The rate at which species become extinct. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 53.26

59. Studies of plants on many island chains confirm their hypothesis. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 53.27