1. Fig. 54-1

2. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Community Ecology A biological community is an assemblage of populations of various species living close enough for potential interaction Ecologists call relationships between species in a community interspecific interactions Interspecific interactions can affect the survival and reproduction of each species, and the effects can be summarized as positive (+), negative (–), or no effect (0)

3. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Types of Community interactions Competition Predation Herbivory Symbiosis – Parasitism – Mutualism – Commensalism

4. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 54-1 WHAT INTERSPECIFIC INTERACTIONS ARE OCCURING HERE?

5. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Competition Interspecific competition (–/– interaction) occurs when species compete for a resource in short supply

6. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Competitive Exclusion Strong competition can lead to competitive exclusion, local elimination of a competing species The competitive exclusion principle states that two species competing for the same limiting resources cannot coexist in the same place

7. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Ecological Niches The total of a species’ use of biotic and abiotic resources is called the species’ ecological niche An ecological niche can also be thought of as an organism’s ecological role Ecologically similar species can coexist in a community if there are one or more significant differences in their niches

8. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Resource partitioning is differentiation of ecological niches, enabling similar species to coexist in a community

9. Fig. 54-2 A. ricordii A. insolitus usually perches on shady branches. A. distichus perches on fence posts and other sunny surfaces. A. aliniger A. distichus A. insolitus A. christophei A. cybotes A. etheridgei

10. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings As a result of competition, a species’ fundamental niche may differ from its realized niche FUNDAMENTAL vs REALIZED NICHES Lots of Chatmal us and one Balanus

11. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Barnacles Food Sex

12. Fig. 54-3b RESULTS High tide Chthamalus fundamental niche Low tide Ocean

13. Fig. 54-3a Ocean Chthamalus Balanus EXPERIMENT High tide Low tide Chthamalus realized niche Balanus realized niche

14. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Predation Predation (+/– interaction) refers to interaction where one species, the predator, kills and eats the other, the prey Some feeding adaptations of predators are claws, teeth, fangs, stingers, and poison

15. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Prey display various defensive adaptations Behavioral defenses include hiding, fleeing, forming herds or schools, self-defense, and alarm calls Animals also have morphological and physiological defense adaptations Cryptic coloration, or camouflage, makes prey difficult to spot Video: Seahorse Camouflage Video: Seahorse Camouflage Defenses against Predation

16. Fig. 54-5a Canyon tree frog (a) Cryptic coloration

17. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Animals with effective chemical defense often exhibit bright warning coloration, called aposematic coloration Predators are particularly cautious in dealing with prey that display such coloration

18. Fig. 54-5b Poison dart frog (b) Aposematic coloration

19. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings In some cases, a prey species may gain significant protection by mimicking the appearance of another species In Batesian mimicry, a palatable or harmless species mimics an unpalatable or harmful model

20. Fig. 54-5c Hawkmoth larva (c) Batesian mimicry: A harmless species mimics a harmful one. Green parrot snake

21. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings In Müllerian mimicry, two or more unpalatable species resemble each other

22. Fig. 54-5d Cuckoo bee Müllerian mimicry: Two unpalatable species mimic each other. Yellow jacket (d)

23. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Herbivory Herbivory (+/– interaction) refers to an interaction in which an herbivore eats parts of a plant or alga It has led to evolution of plant mechanical and chemical defenses and adaptations by herbivores

24. Fig. 54-6

25. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Symbiosis Symbiosis is a relationship where two or more species live in direct and intimate contact with one another

26. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Parasitism In parasitism (+/– interaction), one organism, the parasite, derives nourishment from another organism, its host, which is harmed in the process Parasites that live within the body of their host are called endoparasites; parasites that live on the external surface of a host are ectoparasites

27. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Many parasites have a complex life cycle involving a number of hosts Some parasites change the behavior of the host to increase their own fitness

28. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Mutualism Mutualistic symbiosis, or mutualism (+/+ interaction), is an interspecific interaction that benefits both species A mutualism can be – Obligate, where one species cannot survive without the other – Facultative, where both species can survive alone Video: Clownfish and Anemone Video: Clownfish and Anemone

29. Fig. 54-7a (a) Acacia tree and ants (genus Pseudomyrmex)

30. Fig. 54-7b (b) Area cleared by ants at the base of an acacia tree

31. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Commensalism In commensalism (+/0 interaction), one species benefits and the other is apparently unaffected Commensal interactions are hard to document in nature because any close association likely affects both species

32. Fig. 54-8

33. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Dominant and keystone species exert strong controls on community structure In general, a few species in a community exert strong control on that community’s structure Two fundamental features of community structure are species diversity and feeding relationships

34. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Species Diversity Species diversity of a community is the variety of organisms that make up the community It has two components: species richness and relative abundance Species richness is the total number of different species in the community Relative abundance is the proportion each species represents of the total individuals in the community

35. Fig. 54-9 Community 1 A: 25% B: 25% C: 25% D: 25% Community 2 A: 80% B: 5% C: 5% D: 10% ABCD

36. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Two communities can have the same species richness but a different relative abundance Diversity can be compared using a diversity index –Shannon diversity index (H): H = –[(p A ln p A ) + (p B ln p B ) + (p C ln p C ) + …]

37. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Determining the number and abundance of species in a community is difficult, especially for small organisms Molecular tools can be used to help determine microbial diversity

38. Fig. 54-10 Soil pH Shannon diversity (H) 3.6 RESULTS 3.4 3.2 3.0 2.8 2.6 2.4 2.2 3456789

39. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Trophic Structure Trophic structure is the feeding relationships between organisms in a community It is a key factor in community dynamics Food chains link trophic levels from producers to top carnivores Video: Shark Eating a Seal Video: Shark Eating a Seal

40. Fig. 54-11 Carnivore Herbivore Plant A terrestrial food chain Quaternary consumers Tertiary consumers Secondary consumers Primary consumers Primary producers A marine food chain Phytoplankton Zooplankton Carnivore

41. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Food Webs A food web is a branching food chain with complex trophic interactions

42. Fig. 54-12 Humans Smaller toothed whales Baleen whales Sperm whales Elephant seals Leopard seals Crab-eater seals Birds Fishes Squids Carnivorous plankton Copepods Euphausids (krill) Phyto- plankton

43. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Species may play a role at more than one trophic level Food webs can be simplified by isolating a portion of a community that interacts very little with the rest of the community

44. Fig. 54-13 Sea nettle Fish larvae Juvenile striped bass Fish eggsZooplankton

45. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Limits on Food Chain Length Each food chain in a food web is usually only a few links long Two hypotheses attempt to explain food chain length: the energetic hypothesis and the dynamic stability hypothesis

46. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The energetic hypothesis suggests that length is limited by inefficient energy transfer The dynamic stability hypothesis proposes that long food chains are less stable than short ones Most data support the energetic hypothesis

47. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Species with a Large Impact Certain species have a very large impact on community structure Such species are highly abundant or play a pivotal role in community dynamics

48. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Dominant Species Dominant species are those that are most abundant or have the highest biomass Biomass is the total mass of all individuals in a population Dominant species exert powerful control over the occurrence and distribution of other species

49. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings One hypothesis suggests that dominant species are most competitive in exploiting resources Another hypothesis is that they are most successful at avoiding predators Invasive species, typically introduced to a new environment by humans, often lack predators or disease

50. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Keystone Species Keystone species exert strong control on a community by their ecological roles, or niches In contrast to dominant species, they are not necessarily abundant in a community

51. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Field studies of sea stars exhibit their role as a keystone species in intertidal communities

52. Fig. 54-15a EXPERIMENT

53. Fig. 54-15b With Pisaster (control) Without Pisaster (experimental) Number of species present Year 20 15 10 5 0 1963’64’65’66’67’68’69’70’71’72 ’73 RESULTS

54. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Observation of sea otter populations and their predation shows how otters affect ocean communities

55. Fig. 54-16 (a) Sea otter abundance Otter number (% max. count) 100 80 60 40 20 0 400 300 200 100 0 (b) Sea urchin biomass Grams per 0.25 m 2 10 8 6 4 2 0 1972 Number per 0.25 m 2 19851997 Year (c) Total kelp density Food chain 19891993

56. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Foundation Species (Ecosystem “Engineers”) Foundation species (ecosystem “engineers”) cause physical changes in the environment that affect community structure For example, beaver dams can transform landscapes on a very large scale

57. Fig. 54-17

58. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Some foundation species act as facilitators that have positive effects on survival and reproduction of some other species in the community

59. Fig. 54-18 With JuncusWithout Juncus 0 2 4 6 8 Number of plant species Salt marsh with Juncus (foreground) (a) (b)

60. Fig. 54-18a Salt marsh with Juncus (foreground) (a)

61. Fig. 54-18b With JuncusWithout Juncus 0 2 4 6 8 Number of plant species (b)

62. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Ecological Succession Ecological succession is the sequence of community and ecosystem changes after a disturbance Primary succession occurs where no soil exists when succession begins Secondary succession begins in an area where soil remains after a disturbance

63. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Early-arriving species and later-arriving species may be linked in one of three processes: – Early arrivals may facilitate appearance of later species by making the environment favorable – They may inhibit establishment of later species – They may tolerate later species but have no impact on their establishment

64. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Retreating glaciers provide a valuable field- research opportunity for observing succession Succession on the moraines in Glacier Bay, Alaska, follows a predictable pattern of change in vegetation and soil characteristics

65. Fig. 54-22-1 Pioneer stage, with fireweed dominant 1 1941 1907 1860 1760 Alaska Glacier Bay Kilometers 510150

66. Fig. 54-22-2 Pioneer stage, with fireweed dominant 1 1941 1907 1860 1760 Alaska Glacier Bay Kilometers 510150 Dryas stage 2

67. Fig. 54-22-3 Pioneer stage, with fireweed dominant 1 1941 1907 1860 1760 Alaska Kilometers 510150 Dryas stage 2 Alder stage 3 Glacier Bay

68. Fig. 54-22-4 Pioneer stage, with fireweed dominant 1 1941 1907 1860 1760 Alaska Glacier Bay Kilometers 510150 Dryas stage 2 Alder stage 3 Spruce stage 4

69. Fig. 54-22a Pioneer stage, with fireweed dominant 1

70. Fig. 54-22b Dryas stage 2

71. Fig. 54-22c Alder stage 3

72. Fig. 54-22d Spruce stage 4

73. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Succession is the result of changes induced by the vegetation itself On the glacial moraines, vegetation lowers the soil pH and increases soil nitrogen content

74. Fig. 54-23 Successional stage PioneerDryasAlderSpruce Soil nitrogen (g/m 2 ) 0 10 20 30 40 50 60

75. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Human Disturbance Humans have the greatest impact on biological communities worldwide Human disturbance to communities usually reduces species diversity Humans also prevent some naturally occurring disturbances, which can be important to community structure

76. Fig. 54-24

77. Fig. 54-24a

78. Fig. 54-24b