1. Chapter 6 Community Ecology, Population Ecology, and Stability

2. Chapter Overview Questions  What determines the number of species in a community?  How can we classify species according to their roles in a community?  How do species interact with one another?  How do communities respond to changes in environmental conditions?  Does high species biodiversity increase the stability and sustainability of a community?

3. Core Case Study: Why Should We Care about the American Alligator?  Hunters wiped out population to the point of near extinction.  Alligators have important ecological role.

4. Core Case Study: Why Should We Care about the American Alligator?  Dig deep depressions (gator holes). Hold water during dry spells, serve as refuges for aquatic life. Hold water during dry spells, serve as refuges for aquatic life.  Build nesting mounds. provide nesting and feeding sites for birds. provide nesting and feeding sites for birds. Keeps areas of open water free of vegetation. Keeps areas of open water free of vegetation.  Alligators are a keystone species: Help maintain the structure and function of the communities where it is found. Help maintain the structure and function of the communities where it is found.

5. COMMUNITY STRUCTURE AND SPECIES DIVERSITY  Biological communities differ in their structure and physical appearance.

6. Species Diversity and Niche Structure: Different Species Playing Different Roles  Biological communities differ in the types and numbers of species they contain and the ecological roles those species play. Species diversity: the number of different species it contains (species richness) combined with the abundance of individuals within each of those species (species evenness). Species diversity: the number of different species it contains (species richness) combined with the abundance of individuals within each of those species (species evenness).

7. Species Diversity and Niche Structure  Niche structure: how many potential ecological niches occur, how they resemble or differ, and how the species occupying different niches interact.  Geographic location: species diversity is highest in the tropics and declines as we move from the equator toward the poles.

8. TYPES OF SPECIES  Native, nonnative, indicator, keystone, and foundation species play different ecological roles in communities. 1. Native: those that normally live and thrive in a particular community. 2. Nonnative species: those that migrate, deliberately or accidentally introduced into a community.

9. 3. Indicator Species: Biological Smoke Alarms  Species that serve as early warnings of damage to a community or an ecosystem. Presence or absence of trout species because they are sensitive to temperature and oxygen levels. Presence or absence of trout species because they are sensitive to temperature and oxygen levels.

10. 4. Keystone Species: Major Players  Keystone species help determine the types and numbers of other species in a community thereby helping to sustain it.

11. Foundation Species: Other Major Players  Expansion of keystone species category.  Foundation species can create and enhance habitats that can benefit other species in a community. Elephants push over, break, or uproot trees, creating forest openings promoting grass growth for other species to utilize. Elephants push over, break, or uproot trees, creating forest openings promoting grass growth for other species to utilize.

12. Case Study p. 108-109: Why are Amphibians Vanishing?  Frogs serve as indicator species because different parts of their life cycles can be easily disturbed.

13. Case Study: Why are Amphibians Vanishing?  Habitat loss and fragmentation.  Prolonged drought.  Pollution.  Increases in ultraviolet radiation.  Parasites.  Viral and Fungal diseases.  Overhunting.  Natural immigration or deliberate introduction of nonnative predators and competitors.

14. SPECIES INTERACTIONS: COMPETITION AND PREDATION How can species avoid competition or predation? Species can interact through competition, predation, parasitism, mutualism, and commensalism. Species can interact through competition, predation, parasitism, mutualism, and commensalism. Some species evolve adaptations that allow them to reduce or avoid competition for resources with other species (resource partitioning). Some species evolve adaptations that allow them to reduce or avoid competition for resources with other species (resource partitioning).

15. Resource Partitioning  Each species minimizes competition with the others for food by spending at least half its feeding time in a distinct portion of the spruce tree and by consuming somewhat different insect species.

16. Niche Specialization  Niches become separated to avoid competition for resources.

17. SPECIES INTERACTIONS: PREDATION  Some prey escape their predators or have outer protection, some are camouflaged, and some use chemicals to repel predators.

18. (a) Span worm - camouflage

19. (b) Wandering leaf insect - camouflage

20. (c) Bombardier beetle – chemical warfare

21. (d) Foul-tasting monarch butterfly

22. (e) Poison dart frog

23. (f) Viceroy butterfly mimics monarch butterfly – mimicry

24. (g) Hind wings of Io moth resemble eyes of a much larger animal.

25. (h) When touched, snake caterpillar changes shape to look like head of snake.

26. SPECIES INTERACTIONS: PARASITISM, MUTUALISM, AND COMMENSALIM  Parasitism occurs when one species feeds on part of another organism.  In mutualism, two species interact in a way that benefits both.  Commensalism is an interaction that benefits one species but has little, if any, effect on the other species.

27. Parasites: Sponging Off of Others  Although parasites can harm their hosts, they can promote community biodiversity. Some parasites live in host (micororganisms, tapeworms). Some parasites live in host (micororganisms, tapeworms). Some parasites live outside host (fleas, ticks, mistletoe plants, sea lampreys). Some parasites live outside host (fleas, ticks, mistletoe plants, sea lampreys). Some have little contact with host (dump-nesting birds like cowbirds, some duck species) Some have little contact with host (dump-nesting birds like cowbirds, some duck species)

28. Mutualism: Win-Win Relationship  Two species can interact in ways that benefit both of them.

29. (a) Oxpeckers and black rhinoceros

30. (b) Clownfish and sea anemone

31. (c) Mycorrhizal fungi on juniper seedlings in normal soil

32. (d) Lack of mycorrhizal fungi on juniper seedlings in sterilized soil

33. Commensalism: Using without Harming  Some species interact in a way that helps one species but has little or no effect on the other.

34. ECOLOGICAL SUCCESSION: COMMUNITIES IN TRANSITION  New environmental conditions allow one group of species in a community to replace other groups.  Ecological succession: the gradual change in species composition of a given area Ecological succession Ecological succession Primary succession: the gradual establishment of biotic communities in lifeless areas where there is no soil or sediment. Primary succession: the gradual establishment of biotic communities in lifeless areas where there is no soil or sediment. Secondary succession: series of communities develop in places containing soil or sediment. Secondary succession: series of communities develop in places containing soil or sediment.

35. Primary Succession: Starting from Scratch  Primary succession begins with an essentially lifeless are where there is no soil in a terrestrial ecosystem

36. Primary Succession Lichens on rocks Shrubs and grasses grow in cracks created by lichen Each stage accumulates soil and organic material that facilitates the growth of the next stage

37. Volcanic Eruptions Mt. St. Helen’s Pyroclastic Flow area Pre-eruption 1981

38. 1985 1995

39. 2004 25 years after eruption

40. In the blast area 19781981

41. 1985 2004

42. Secondary Succession: Starting Over with Some Help  Secondary succession begins in an area where the natural community has been disturbed.

44. ECOLOGICAL STABILITY AND SUSTAINABILITY  Having many different species appears to increase the sustainability of many communities.  Human activities are disrupting ecosystem services that support and sustain all life and all economies.

45. Changes in Population Size: Entrances and Exits  Populations increase through births and immigration  Populations decrease through deaths and emigration

46. Age Structure: Young Populations Can Grow Fast  How fast a population grows or declines depends on its age structure. Prereproductive age: not mature enough to reproduce. Prereproductive age: not mature enough to reproduce. Reproductive age: those capable of reproduction. Reproductive age: those capable of reproduction. Postreproductive age: those too old to reproduce. Postreproductive age: those too old to reproduce.

47. Limits on Population Growth: Biotic Potential vs. Environmental Resistance  No population can increase its size indefinitely. The intrinsic rate of increase (r) is the rate at which a population would grow if it had unlimited resources. The intrinsic rate of increase (r) is the rate at which a population would grow if it had unlimited resources. Carrying capacity (K): the maximum population of a given species that a particular habitat can sustain indefinitely without degrading the habitat. Carrying capacity (K): the maximum population of a given species that a particular habitat can sustain indefinitely without degrading the habitat.

48. Exponential and Logistic Population Growth: J-Curves and S-Curves  Populations grow rapidly with ample resources, but as resources become limited, its growth rate slows and levels off.

49. Exponential and Logistic Population Growth: J-Curves and S-Curves  As a population levels off, it often fluctuates slightly above and below the carrying capacity. S-Curve

50. Exceeding Carrying Capacity: Move, Switch Habits, or Decline in Size  Members of populations which exceed their resources will die unless they adapt or move to an area with more resources.

51. Exceeding Carrying Capacity: Move, Switch Habits, or Decline in Size  Switch Habits: Over time species may increase their carrying capacity by developing adaptations.  Move: Some species maintain their carrying capacity by migrating to other areas.  So far, technological, social, and other cultural changes have extended the earth’s carrying capacity for humans.

52. Population Density and Population Change: Effects of Crowding  Population density: the number of individuals in a population found in a particular area or volume. A population’s density can affect how rapidly it can grow or decline. A population’s density can affect how rapidly it can grow or decline. e.g. biotic factors like diseasee.g. biotic factors like disease Some population control factors are not affected by population density. Some population control factors are not affected by population density. e.g. abiotic factors like weathere.g. abiotic factors like weather

53. REPRODUCTIVE PATTERNS  Some species reproduce without having sex (asexual). Offspring are exact genetic copies (clones). Offspring are exact genetic copies (clones).  Others reproduce by having sex (sexual). Genetic material is mixture of two individuals. Genetic material is mixture of two individuals. Disadvantages: males do not give birth, increase chance of genetic errors and defects, courtship and mating rituals can be costly. Disadvantages: males do not give birth, increase chance of genetic errors and defects, courtship and mating rituals can be costly. Major advantages: genetic diversity, offspring protection. Major advantages: genetic diversity, offspring protection.

54. Sexual Reproduction: Courtship  Courtship rituals consume time and energy, can transmit disease, and can inflict injury on males of some species as they compete for sexual partners.

55. Reproductive Patterns: Opportunists and Competitors  Large number of smaller offspring with little parental care (r- selected species).  Fewer, larger offspring with higher invested parental care (K-selected species).

56. Reproductive Patterns  r-selected species tend to be opportunists while K-selected species tend to be competitors.

57. Many small offspring Little or no parental care and protection of offspring Early reproductive age Most offspring die before reaching reproductive age Small adults Adapted to unstable climate and environmental conditions High population growth rate (r) Population size fluctuates wildly above and below carrying capacity (K) Generalist niche Low ability to compete Early successional species r-Selected Species Cockroach Dandelion

58. Fewer, larger offspring High parental care and protection of offspring Later reproductive age Most offspring survive to reproductive age Larger adults Adapted to stable climate and environmental conditions Lower population growth rate (r) Population size fairly stable and usually close to carrying capacity (K) Specialist niche High ability to compete Late successional species K-Selected Species SaguaroElephant

60. Case Study: Exploding White-Tailed Deer Populations in the United States  Since the 1930s the white-tailed deer population has exploded in the United States. Nearly extinct prior to their protection in 1920’s. Nearly extinct prior to their protection in 1920’s.  Today 25-30 million white-tailed deer in U.S. pose human interaction problems. Deer-vehicle collisions (1.5 million per year). Deer-vehicle collisions (1.5 million per year). Transmit disease (Lyme disease in deer ticks). Transmit disease (Lyme disease in deer ticks).