1. CHAPTER 19 – Communities and Ecosystems

2. KEY PROPERTIES OF COMMUNITIES
A community
Is an assemblage of species living close enough together for potential interaction..

3. Diversity
The diversity of a community is the variety of different kinds of organisms that make up the community
There are two main components:
Species richness, the total number of different species in the community
Relative abundance of the different species..

4. Prevalent Form of Vegetation
The prevalent form of vegetation mainly depends on the terrestrial situation
The types and structural features of plants in a community largely determine the kinds of animals that live in the community..

5. Stability
Community stability - ability to resist change and return to its original species combination after being disturbed
Depends on both the type of community and the nature of disturbances..

6. Trophic Structure
The trophic structure of a community concerns the feeding relationships among the various species making up the community..
Figure 19.4

7. INTERSPECIFIC INTERACTIONS IN COMMUNITIES
Interspecific interactions are interactions between species
Competition between species
Predation
Symbiosis

8. Competition Between Species
Interspecific competition
May occur when two or more species in a community rely on similar limiting resources
May limit population growth of the competing species..

9. Competitive Exclusion Principle
Russian ecologist G. F. Gause studied the effects of interspecific competition in two closely related species of protists..
Separate cultures
Combined cultures
P. aurelia
P. caudatum
Figure 19.5

10. From his research, Gause concluded that two species so similar that they compete for the same limiting resources cannot coexist in the same place
Competitive Exclusion Principle..

11. Testing the competitive exclusion principle..
High tide
Chthamalus
Balanus
Ocean
Low tide
Figure 19.6

12. The Ecological Niche A species’ ecological niche
Is the sum total of a species’ use of the biotic and abiotic resources in its environment
Is the species’ ecological role
Two species cannot coexist in a community if their niches are identical..

13. Resource Partitioning
Is the differentiation of niches that enables similar species to coexist in a community
There are two possible outcomes of competition between species with identical niches
Extinction of one species
Evolution of one species to use a different set of resources..

14. A. ricordii
A. ricordii
A. distichus
A. insolitus
A. aliniger
A. christophei
A. distichus
A. distichus
A. christophei
A. cybotes
A. cybotes
A. etheridgei
A. etheridgei
A. insolitus
Figure 19.7

15. Predation Is when organisms eat other organisms
Identifies the predator as the consumer and the food species as the prey
Includes herbivory, the consumption of plants by animals..

16. Predator Adaptations Most predators have acute senses Many predators
Have adaptations such as claws, teeth, fangs, stingers, or poison to help catch and subdue prey
Are fast and agile..

17. Plant Defenses Against Herbivores
Plants have various types of defenses against herbivores
Chemical toxins
Spines and thorns..

18. Animal Defenses Against Predators
Animals can avoid being eaten
By using passive defenses such as hiding
By using active defenses such as escaping or defending themselves..

19. Behavioral defenses include
Alarm calls
Mobbing..
Figure 19.8

20. Distraction displays
Direct the attention of the predator away from a vulnerable prey to another prey that is more likely to escape..
Figure 19.9

21. Camouflage, or cryptic coloration
Is a passive defense that makes a potential prey difficult to spot against its background..
Figure 19.10

22. Animals with chemical defenses are often brightly colored
Some animals have mechanical or chemical defenses against predators..
Animals with chemical defenses are often brightly colored
This is a caution to predators called warning coloration..
Figure 19.11

23. Mimicry
Is a “copycat” adaptation in which one species mimics the appearance of another
Is used by some species to gain protection..

24. A palatable or harmless species mimics an unpalatable or harmful model..
Figure 19.12

25. Two or more unpalatable species resemble each other..
Figure 19.13

26. Predation and Species Diversity in Communities
Predator-prey relationships
Can actually preserve species diversity..

27. The experiments of Robert Paine
Removed a dominant predator from a community
Provided evidence of the phenomenon of predation..

28. With Pisaster (control)
Without Pisaster
Figure 19.14

29. Paine’s experiments and others
Led to the concept of keystone predators
Keystone predators
Help maintain species diversity by preventing competitive exclusion of weaker competitors..

30. Symbiotic Relationships
Is an interspecific interaction in which one species, the symbiont, lives in or on another species, the host
Parasitism
Mutualism

31. Parasitism Parasitism
Is a symbiotic relationship in which one organism benefits while the other is harmed
The parasite obtains its nutrients by living in or on its host organism..

32. Mutualism Is a symbiosis that benefits both partners
Many mutualistic relationships have evolved from predator-prey or host-parasite interactions..

33. The Complexity of Community Networks
The branching of interactions between species makes communities complex..
Wounding
Detection by plant
Release of volatile attractants
Recruitment
Chemical in saliva
Figure 19.17

34. DISTURBANCE OF COMMUNITIES
Are episodes that damage biological communities, at least temporarily
Destroy organisms and alter the availability of resources
Affect all communities..

35. Ecological Succession
Is the process of community change
Primary succession
Secondary succession..

36. In primary succession
A community arises in a virtually lifeless area with no soil..
Retreating glacier
Barren landscape
Moss & lichens

37. Primary succession from barren soil to a complex community can take hundreds of years..
Shrubs & small trees
Larger, intermediate species
Climax community

38. Secondary succession occurs where a disturbance has destroyed an existing community but left the soil intact..

39. AN OVERVIEW OF ECOSYSTEM DYNAMICS
An ecosystem
Is a biological community and the abiotic factors with which the community interacts..

40. Energy Flow Chemical cycling
Is the passage of energy through the components of the ecosystem
Chemical cycling
Is the use and reuse of chemical elements within the ecosystem..

41. Chemical cycling (C, N, etc.)
Energy
Flows through an ecosystem when consumers feed on producers
Cannot be recycled within an ecosystem, but must flow through continuously..
Chemical cycling (C, N, etc.)
Chemical energy
Light energy
Heat energy
Figure 19.20

42. Energy flow and chemical cycling
Depend on the transfer of substances in the feeding relationships, or trophic structure of an ecosystem
Trophic levels
Divide the species of an ecosystem based on their main sources of nutrition
Trophic relationships
Determine an ecosystem’s routes of energy flow and chemical cycling..

43. Trophic Levels and Food Chains
A food chain
Quaternary consumers
Carnivore
Is the sequence of food transfer from trophic level to trophic level
May have many levels..
Carnivore
Tertiary consumers
Carnivore
Carnivore
Secondary consumers
Carnivore
Carnivore
Primary consumers
Herbivore
Zooplankton
Producers
Plant
Phytoplankton
Figure 19.21
A terrestrial food chain
A marine food chain

44. Herbivores, which eat plants, algae, or autotrophic bacteria, are the primary consumers of an ecosystem
Above the primary consumers, the trophic levels are made up of carnivores, which eat the consumers from the levels below
Secondary consumers include many small mammals, such as rodents, and small fishes that eat zooplankton
Tertiary consumers, such as snakes, eat mice and other secondary consumers
Quaternary consumers include hawks and killer whales..

45. Detritivores, or decomposers
Derive their energy from the dead material left by all trophic levels
Recycle the nutrients locked in organisms..
Figure 19.22

46. Food Webs The feeding relationships in an ecosystem
Are typically not as simple as in an unbranched food chain
Are usually woven into complex food webs..

47. Quaternary,
tertiary, &
secondary consumers
Tertiary &
Secondary &
primary consumers
Primary consumers
Producers (plants)

48. ENERGY FLOW IN ECOSYSTEMS
Food chains cannot be longer than 4 – 5 trophic levels.
What limits food chains?

49. Productivity and the Energy Budgets of Ecosystems
Biomass
Is the amount of organic material in an ecosystem
An ecosystem’s primary productivity
Is the rate at which plants and other producers build biomass..

50. Productivity of different ecosystems..
Percentage of Earth’s surface area
(b) Average net primary productivity (g/m2/yr)
(c) Percentage of Earth’s net primary productivity
Open ocean
Continental shelf
Extreme desert, rock, sand, ice
Desert and semidesert scrub
Tropical rain forest
Savanna
Cultivated land
Boreal forest (taiga)
Temperate grassland
Woodland and shrubland
Tundra
Tropical seasonal forest
Temperate deciduous forest
Temperate evergreen forest
Swamp and marsh
Lake and stream
Estuary
Algal beds and reeds
Upwelling zones

51. Energy Pyramids
When energy flows as organic matter through the trophic levels of an ecosystem, much of it is lost at each link in a food chain..

52. Plant material eaten by caterpillar
100 kilocalories (kcal)
35 kcal
Cellular respiration
50 kcal
Feces
15 kcal
Growth
Figure 19.25

53. An energy pyramid
Is a diagram that represents the cumulative loss of energy from a food chain..

54. Tertiary consumers 10 kcal Secondary consumers 100 kcal
Primary consumers
1,000 kcal
Producers
10,000 kcal
Figure 19.26

55. CHEMICAL CYCLING IN ECOSYSTEMS
Depend on a recycling of chemical elements..

56. The General Scheme of Chemical Cycling
Biogeochemical cycles
Are chemical cycles in an ecosystem that involve both biotic and abiotic components..

57. Three key points to biogeochemical cycles
Each circuit has an abiotic reservoir
A portion of chemical cycling can rely completely on geological processes
Some chemicals require processing before they are available as inorganic nutrients..

58. Generalized scheme for biogeochemical cycles..
Consumers
Producers
Detritivores
Nutrients available to producers
Abiotic reservoir
Geologic processes
Generalized scheme for biogeochemical cycles..

59. Examples of Biogeochemical Cycles
A chemical’s specific route through an ecosystem varies with the particular element and the trophic structure of the ecosystem..

60. Higher-level consumers
The carbon cycle
CO2 in atmosphere
Burning
Wood and fossil fuels
Cellular respiration
Higher-level consumers
Decomposition
Detritivores
Photosynthesis
Producers
Primary consumers
Detritus
Figure 19.29a

61. The nitrogen cycle Detritus Nitrates (NO3– ) Decomposition
Denitrifying bacteria
Assimilation by plants
Nitrogen (N2) in atmosphere
Amino acids and proteins in plants and animals
Detritus
Detritivores
Nitrogen-fixing bacteria in root nodules of legumes
Decomposition
Nitrogen fixation
Nitrogen-fixing bacteria
in soil
Ammonium (NH4+ )
Nitrifying bacteria
Nitrates (NO3– )

62. Precipitated (solid) phosphates Phosphates in solution
The phosphorous cycle
Uplifting of rock
Phosphates in rock
Weathering of rock
Phosphates
in organic compounds
Consumers
Producers
Rock
Precipitated (solid) phosphates
Phosphates in solution
in soil (inorganic)
Detritus
Detritivores in soil
Figure 19.29c

63. The water cycle Net movement of water vapor by wind (36) Solar heat
Precipitation over the sea (283)
Solar heat
Water vapor over the sea
Oceans
Net movement of water vapor by wind (36)
Evaporation from the sea (319)
Evaporation and transpiration (59)
Water vapor over the land
Precipitation over the land (95)
Surface
water and groundwater
Flow of water from land to sea (36)
Figure 19.29d

64. BIOMES
Are the major types of ecosystems that cover large geographic regions of the Earth..

65. How Climate Affects Biome Distribution
Because of its curvature, Earth receives an uneven distribution of solar energy.
Low angle of incoming sunlight
Sunlight directly overhead
Atmosphere
Figure 19.30

66. Cloud formation and rain Ascending moist air releases moisture
The uneven heating causes rain and wind
Heated by the direct rays of the sun, air at the equator rises, then cools, forms clouds, and drops rain..
Cloud formation and rain
Ascending moist air releases moisture
Descending dry air
Tropics
Temperate zone

67. Proximity to large bodies of water and the presence of landforms such as mountain ranges also affect climate..
Wind direction
Pacific Ocean
East
Coast Range
Cascade Range
Figure 19.32

68. Terrestrial Biomes
The distribution of terrestrial biomes depends largely on climate
If the climate in two geographically separate areas is similar, the same type of biome may occur in them..

69. Most biomes are named for major physical or climatic features and for their predominant vegetation..
Figure 19.33

70. Tropical forest..
Figure 19.34a

71. Savanna
Figure 19.34b

72. Desert
Figure 19.34c

73. Chaparral
Figure 19.34d

74. Temperate grassland
Figure 19.34e

75. Temperate deciduous forest
Figure 19.31f

76. Coniferous forest
Figure 19.34g

77. Tundra
Figure 19.34h

78. Freshwater Biomes Aquatic biomes
Occupy the largest part of the biosphere..

79. Lakes and Ponds
Standing bodies of water - range from small ponds to large lakes..
Figure 19.35a

80. The photic (photosynthetic) zone
In lakes and large ponds the communities are distributed according to the depth of water and its distance from shore.
The photic (photosynthetic) zone
Includes the shallow water near shore and the upper stratum of water away from shore
Is named because light is available for photosynthesis
The aphotic zone
Is deeper, where light levels are too low to support photosynthesis
The benthic zone
Is the bottom of all aquatic biomes

81. Rivers and Streams Are bodies of water flowing in one direction
Support quite different communities of organisms than lakes and ponds
Figure 19.35b

82. Marshes, ponds, and other wetlands
Are common in downstream areas
Figure 19.35c

83. Human activities have affected many streams and rivers
Figure 19.36

84. Marine Biomes Oceans Estuaries Cover about 75% of the planet’s surface
Are areas where a freshwater stream or river merges with the ocean
Are one of the most biologically productive environments on Earth
“Nurseries of the
sea”..

85. Major Oceanic Zones Marine life is distributed according to
Depth of the water
Degree of light penetration
Distance from shore
Open water versus bottom..

86. Oceanic zones Intertidal zone Continental shelf Pelagic zone
Benthic zone (seafloor)
Photic zone
Aphotic zone
Pelagic zone
Figure 19.38

87. The intertidal zone Is the area where land meets water
Includes organisms adapted to attach to rocks or vegetation or to burrow..
Figure 19.39

88. The pelagic zone Is the open ocean
Contains phytoplankton and zooplankton
Plankton are organisms that are pushed around because they are too small to resist the ocean currents..

89. The benthic zone Is the ocean bottom or seafloor
Temperature is constant 4o C
May include hydrothermal vent communities..
Figure 19.40