1. Environment: The Science behind the Stories
Lecture Outlines
Chapter 6
Environment: The Science behind the Stories
4th Edition
Withgott/Brennan

2. This lecture will help you understand:
Species interactions
Feeding relationships, energy flow, trophic levels, and food webs
Keystone species
The process of succession
Potential impacts of invasive species
Restoration ecology
Terrestrial biomes

3. Case Study: black and white and spread all over
In 1988, Zebra mussels were accidentally introduced to Lake St. Clair
In discharged ballast water
By 2010, they had invaded 30 states
No natural predators, competitors, or parasites
They cause millions of dollars of damage to property each year

4. Species interactions
Species interactions are the backbone of communities
Natural species interactions:
Competition = both species are harmed
Exploitative = one species benefits and the other is harmed
Predation, parasitism, and herbivory
Mutualism = both species benefit

5. Competition
Competition = multiple organisms seek the same limited resources
Food, space, water, shelter, mates, sunlight
Intraspecific competition = between members of the same species
High population density = increased competition
Interspecific competition = between members of 2 or more species
Strongly affects community composition
Leads to competitive exclusion or species coexistence

6. Results of interspecific competition
Competitive exclusion = one species completely excludes another species from using the resource
Zebra mussels displaced native mussels in the Great Lakes
Species coexistence = neither species fully excludes the other from resources, so both live side by side
This produces a stable point of equilibrium, with stable population sizes
Species minimize competition by using only a part of the available resource (niche)

7. Niche: an individual’s ecological role
Fundamental niche = the full niche of a species
Realized niche = the portion of the fundamental niche that is actually filled
Due to competition or other species’ interactions

8. Resource partitioning
Resource partitioning = species use different resources
Or they use shared resources in different ways
Ex: one species is active at night, another in the day
Ex: one species eats small seeds, another eats large seeds

9. Character displacement
Character displacement = competing species diverge in their physical characteristics
Due to the evolution of traits best suited to the resources they use
Results from resource partitioning
Birds that eat larger seeds evolve larger bills
Birds that eat smaller seeds evolve smaller bills
Competition is reduced when two species become more different

10. Exploitation: predation
Exploitation = one member exploits another for its own gain (+/- interactions)
Predation, parasitism, herbivory
Predation = process by which individuals of one species (predators) capture, kill, and consume individuals of another species (prey)
Structures food webs
The number of predators and prey influences community composition

11. Zebra mussel predation on phytoplankton
Zebra mussels eat phytoplankton and zooplankton
Both populations decrease in lakes with zebra mussels
Zebra mussels don’t eat cyanobacteria
Population increases in lakes with zebra mussels
Zebra mussels are becoming prey for some North American predators:
Diving ducks, muskrats, crayfish, flounder, sturgeon, eels, carp, and freshwater drum

12. Effects of predation on populations
Increased prey populations increase predators
Predators survive and reproduce
Increased predator populations decrease prey
Predators starve
Decreased predator populations increase prey populations

13. Predation has evolutionary ramifications
Natural selection leads to evolution of adaptations that make predators better hunters
Individuals who are better at catching prey:
Live longer, healthier lives
Take better care of offspring
Prey face strong selection pressures: they are at risk of immediate death
Prey develop elaborate defenses against being eaten

14. Defenses against being eaten

15. Exploitation: parasitism
Parasitism = a relationship in which one organism (parasite) depends on another (host)
For nourishment or some other benefit
The parasite harms, but doesn’t kill, the host
Some are free-living
Infrequent contact with their hosts
Ticks, sea lampreys
Some live within the host
Disease, tapeworms 15

16. Parasites evolve in response to each other
Parasitoids = insects that parasitize other insects
Killing the host
Coevolution = hosts and parasites become locked in a duel of escalating adaptations
Has been called an evolutionary arms race
Each evolves new responses to the other
It may not be beneficial to the parasite to kill its host 16

17. Exploitation: herbivory
Herbivory = animals feed on the tissues of plants
Widely seen in insects
May not kill the plant
But affects its growth and survival
Defenses against herbivory include:
Chemicals: toxic or distasteful
Thorns, spines, or irritating hairs
Other animals: protect the plant 17

18. Mutualism Two or more species benefit from their interactions
Symbiosis = mutualism in which the organisms live in close physical contact
Each partner provides a service the other needs (food, protection, housing, etc.)
Microbes within digestive tracts
Mycorrhizae: plant roots and fungi
Coral and algae (zooxanthellae)
Pollination = bees, bats, birds and others transfer pollen from one flower to another, fertilizing its eggs 18

19. Pollination
In exchange for the plant nectar, the animals pollinate plants, which allows them to reproduce 19

20. Relationships with no effect on one member
Amensalism = a relationship in which one organism is harmed while the other is unaffected
Difficult to confirm, because usually one organism benefits from harming another
Allelopathy = certain plants release harmful chemicals
Or, is this a way to outcompete another for space?
Commensalism = a relationship in which one organism benefits, while the other remains unaffected 20

21. Ecological communities
Community = an assemblage of populations of organisms living in the same place at the same time
Members interact with each other
Interactions determine the structure, function, and species composition of the community
Community ecologists are people interested in how:
Species coexist and relate to one another
Communities change, and why patterns exist 21

22. Energy passes through trophic levels
One of the most important species interactions
Who eats whom?
Matter and energy move through the community
Trophic levels = rank in the feeding hierarchy
Producers (autotrophs)
Consumers
Detritivores and decomposers 22

23. Producers: the first trophic level
Producers, or autotrophs (“self-feeders”) = organisms capture solar energy for photosynthesis to produce sugars
Green plants
Cyanobacteria
Algae
Chemosynthetic bacteria use the geothermal energy in hot springs or deep-sea vents to produce their food 23

24. Consumers: consume producers
Primary consumers = second trophic level
Organisms that consume producers
Herbivores consume plants
Deer, grasshoppers
Secondary consumers = third trophic level
Organisms that prey on primary consumers
Carnivores consume meat
Wolves, rodents 24

25. Consumers occur at higher trophic levels
Tertiary Consumers = fourth trophic level
Predators at the highest trophic level
Consume secondary consumers
Are also carnivores
Hawks, owls
Omnivores = consumers that eat both plants and animals

26. Detritivores and decomposers
Organisms that consume nonliving organic matter
Enrich soils and/or recycle nutrients found in dead organisms
Detritivores = scavenge waste products or dead bodies
Millipedes, soil insects
Decomposers = break down leaf litter and other non-living material
Fungi, bacteria
Enhance topsoil and recycle nutrients 26

27. Energy, biomass, and numbers decrease
Most energy organisms use is lost as waste heat through cellular respiration
Less and less energy is available in each successive trophic level
Each level contains only 10% of the energy of the trophic level below it
There are also far fewer organisms and less biomass (mass of living matter) at the higher trophic levels
A human vegetarian’s ecological footprint is smaller than a meat-eater’s footprint 27

28. Pyramids of energy, biomass, and numbers

29. Food webs show relationships and energy flow
Food chain = a series of feeding relationships
Food web = a visual map of feeding relationships and energy flow
Includes many different organisms at all various levels
Greatly simplified; leaves out most species 29

30. Some organisms play big roles
Community dynamics are complex
Species interactions differ in strength and over time
Keystone species = has a strong or wide-reaching impact
Far out of proportion to its abundance
Removal of a keystone species has substantial ripple effects
Alters the food chain

31. Species can change communities
Trophic Cascade = predators at high trophic levels indirectly affect populations at low trophic levels
By keeping species at intermediate trophic levels in check
Extermination of wolves led to increased deer populations, which overgrazed vegetation and changed forest structure
Ecosystem engineers = physically modify the environment
Beaver dams, prairie dogs, ants, zebra mussels

32. Communities respond to disturbances
Communities experience many types of disturbance
Removal of keystone species, spread of invasive species, natural disturbances
Human impacts cause major community changes
Resistance = community of organisms resists change and remains stable despite the disturbance
Resilience = a community changes in response to a disturbance, but later returns to its original state
A disturbed community may never return to its original state

33. Primary succession
Succession = the predictable series of changes in a community
Following a disturbance
Primary succession = disturbance removes all vegetation and/or soil life
Glaciers, drying lakes, volcanic lava
Pioneer species = the first species to arrive in a primary succession area (i.e. lichens)

34. Secondary succession
Secondary succession = a disturbance dramatically alters, but does not destroy, all local organisms
The remaining organisms form “building blocks” which help shape the process of succession
Fires, hurricanes, farming, logging
Climax community = remains in place with few changes
Until another disturbance restarts succession

35. Communities may undergo shifts
The dynamics of community change are more variable and less predictable than thought
Conditions at one stage may promote another stage
Competition may inhibit progression to another stage
Chance factors also affect changes
Phase (regime) shift = the overall character of the community fundamentally changes
Some crucial threshold is passed, a keystone species is lost, or an exotic species invades
i.e. overfishing and depletion of fish and turtles has allowed algae to dominate corals

36. Community cohesion
Frederick Clements = viewed communities as cohesive entities, with integrated parts
Its members remain associated over space and time
The community shared similar limiting factors and evolutionary histories
Henry Gleason = maintained that each species responds independently to its own limiting factors
Species join or leave communities without greatly altering the community’s composition
The most widely accepted view of ecologists today

37. Invasive species threaten stability
Invasive species = non-native (exotic) organisms that spread widely and become dominant in a community
Introduced deliberately or accidentally from elsewhere
Growth-limiting factors (predators, disease, competitors, etc.) are removed or absent
They have major ecological effects
Chestnut blight from Asia wiped out American chestnut trees
Some species help people (i.e., European honeybees)

38. Two invasive mussels

39. Controlling invasive species
Techniques to control invasive species
Removing them manually
Applying toxic chemicals
Drying them out
Depriving them of oxygen
Stressing them with heat, sound, electricity, carbon dioxide, or ultraviolet light
Control and eradication are hard and expensive
Prevention, rather than control, is the best policy

40. Altered communities can be restored
Humans have dramatically changed ecological systems
Severely degraded systems cease to function
Ecological restoration = efforts to restore communities
Restoration is informed by restoration ecology = the science of restoring an area to an earlier condition
To restore the system’s functionality (i.e. filtering of water by a wetland)
It is difficult, time-consuming, and expensive
It is best to protect natural systems from degradation in the first place

41. Restoration efforts
Prairie restoration = replanting native species, controlling invasive species
The world’s largest project = Florida Everglades
Flood control and irrigation removed water
Populations of wading birds dropped 90-95%
It will take 30 years and billions of dollars to restore natural water flow

42. Widely separated regions share similarities
Biome = major regional complex of similar communities recognized by
Plant type
Vegetation structure

43. Multiple factors determine a biome
The type of biome depends on abiotic factors
Temperature, precipitation, soil type, atmospheric circulation
Climatographs = a climate diagram showing
An area’s mean monthly temperature and precipitation
Similar biomes occupy similar latitudes

44. Aquatic systems have biome-like patterns
Various aquatic systems comprise distinct communities
Coastlines, continental shelves
Open ocean, deep sea
Coral reefs, kelp forests
Some coastal systems (estuaries, marshes, etc.) have both aquatic and terrestrial components
Aquatic systems are shaped by
Water temperature, salinity, and dissolved nutrients
Wave action, currents, depth, light levels
Substrate type, and animal and plant life

45. Temperate deciduous forest
Deciduous trees lose their leaves each fall
They remain dormant during winter
Mid-latitude forests in Europe, East China, Eastern North America
Even, year-round precipitation
Fertile soils
Forests = oak, beech, maple

46. Temperate grasslands More extreme temperature difference
Between winter and summer
Less precipitation
Also called steppe or prairie
Once widespread, but has been converted to agriculture
Bison, prairie dogs, ground-nesting birds, pronghorn

47. Temperate rainforest Coastal Pacific Northwest
Great deal of precipitation
Coniferous trees: cedar, spruce, hemlock, fir
Moisture-loving animals
Banana slug
Erosion and landslides affect the fertile soil
Lumber and paper
Most old-growth is gone

48. Tropical rainforest
Southeast Asia, west Africa Central and South America
Year-round rain and warm temperatures
Dark and damp
Lush vegetation
Diverse species
But in low densities
Very poor, acidic soils

49. Tropical dry forest Also called tropical deciduous forest
Plants drop leaves during the dry season
India, Africa, South America, north Australia
Wet and dry seasons
Warm, but less rainfall
Converted to agriculture
Severe soil erosion

50. Savanna Grassland interspersed with trees
Africa, South America, Australia, India
Precipitation is only during the rainy season
Animals gather near water holes
Zebras, gazelles, giraffes, lions, hyenas

51. Desert Minimal precipitation Some are bare, with sand dunes (Sahara)
Some are heavily vegetated (Sonoran)
They are not always hot
Temperatures vary widely
Saline soils
Animals = nocturnal, nomadic
Plants = thick skins, spines

52. Tundra Russia, Canada, Scandinavia Minimal precipitation
Extremely cold winters
Permafrost = permanently frozen soil
Melting due to climate change
Few animals: polar bears, musk oxen, caribou, migratory birds
Lichens, low vegetation, few trees

53. Boreal forest (taiga) Canada, Alaska, Russia, Scandinavia
A few evergreen tree species
Cool and dry climate
Long, cold winters
Short, cool summers
Nutrient poor, acidic soil
Moose, wolves, bears, lynx, migratory birds

54. Chaparral Occurs in small patches around the globe
Mediterranean Sea, Chile, California, south Australia
High seasonal biome
Mild, wet winters
Warm, dry summers
Frequent fires
Densely thicketed, evergreen shrubs

55. Altitudes create “latitudinal patterns”
Vegetative communities rapidly change along mountain slopes
The climate varies with altitude
A mountain climber in the Andes
Begins in the tropics and ends on a glacier
Rainshadow effect = air going over a mountain releases moisture
Creating an arid region on the other side
Hiking up a mountain in the southwest U.S. is like walking from Mexico to Canada

56. Conclusion
Biomes and communities help us understand how the world functions
Species interactions affect communities
Predation, parasitism, competition, mutualism
Causing weak and strong, direct and indirect effects
Feeding relationships are represented by trophic levels and food webs
Humans have altered many communities
Ecological restoration attempts to undo the negative changes that we have caused

57. QUESTION: Review Mutualism is a form of species interaction where:
a) Both species are harmed
b) One species benefits, but the other is harmed
c) Both species benefit
d) One species excludes another from a particular area
Answer: c

58. QUESTION: Review
Which of the following is NOT an exploitative interaction?
a) Predation
b) Herbivory
c) Parasitism
d) All of these are exploitative interactions
Answer: d

59. QUESTION: Review An example of resource partitioning would be:
a) One species eating larger berries, another species eating smaller berries
b) One species moving out of an area to find new resources
c) A host species becoming more vulnerable to parasitism
d) A pine tree evolving thicker pinecones to reduce consumption by squirrels
Answer: a

60. QUESTION: Review Which statement is NOT true about trophic levels?
a) Plants are autotrophs and occupy the first trophic level.
b) Detritivores consume waste products or dead bodies.
c) Biomass and energy decrease going up the food chain.
d) There are more predator species than prey species in an area.
Answer: d

61. QUESTION: Review
Primary succession would take place on all of the following EXCEPT:
a) The slopes of a newly formed volcanic island
b) Wetlands in Texas, following Hurricane Rita
c) A receding glacier
d) Vegetation regrowing in a drying lake
Answer: b

62. QUESTION: Review
Because communities can undergo phase (regime) shifts, we must remember that: a) Secondary succession results in a predictable series of stages. b) We can count on being able to reverse damage caused by human disturbance. c) We cannot count on being able to reverse damage caused by human disturbance. d) Changes humans set in motion will not be permanent.
Answer: c

63. QUESTION: Review
All of the following are ways to control invasive species, EXCEPT:
a) Remove individuals from the area
b) Stress them by noise
c) Trap them
d) Encourage them to hybridize with another species
Answer: d

64. QUESTION: Review
Which biome has year-round rain and warm temperatures, is dark and damp, and has lush vegetation?
Tropical rainforest
Temperate grasslands
Chaparral
Taiga
Answer: a

65. QUESTION: Review
Which biome is dominated by a few evergreen species, has long, cold winters, and moose, wolves, bear, and lynx?
Tropical rainforest
Temperate grasslands
Temperate rainforest
Taiga
Answer: d

66. QUESTION: Weighing the Issues
Would you be willing to decrease the amount of meat you consume (e.g., eat lower on the food chain) to decrease your ecological footprint?
a) Yes, if the extra food was sent to countries with starving people.
b) Yes, because it would decrease environmental degradation.
c) I don’t eat meat now.
d) No, I don’t see the need to eat lower on the food chain.
Answer: any

67. QUESTION: Weighing the Issues
Although mustangs are not native to the United States, they exist in several western states on federally owned land. As an introduced species, what should be done with them?
a) As an exotic species, they should immediately be removed and adopted or killed.
b) Although they are an exotic species, they are part of our heritage, and should be allowed to stay.
c) They have been here so long, we should just leave them alone.
d) Many countries eat horse flesh, so we should round them up and export them to horse-eating countries.
Answer: any

68. QUESTION: Interpreting Graphs and Data
What does this figure illustrate?
a) A predator–prey cycle
b) Competitive exclusion
c) Resource partitioning
d) Succession
Answer: c

69. QUESTION: Interpreting Graphs and Data
In this climatograph for Vaigach, Russia, in the tundra biome, winters are:
a) Long and warm
b) Short and cool
c) Long and cold
d) Short and warm
Answer: c