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

4. In 1988, zebra mussels were accidentally introduced
Central Case Study: Black and White and Spread All Over: Zebra Mussels Invade the Great Lakes
In 1988, zebra mussels were accidentally introduced
By 2010, they had invaded 30 states
No natural predators, competitors, or parasites
They cause millions of dollars of damage to property each year

6. Species Interactions Species interactions shape and define communities
Natural species interactions:
Competition = relationship in which both species are harmed
Exploitative = one species benefits and the other is harmed
Predation, parasitism, and herbivory
Mutualism = relationship in which both species benefit

7. Competition can occur when resources are limited
In competition, multiple organisms seek the same limited resources and all competitors suffer (/ interaction)
Food, space, water, shelter, mates, sunlight
Intraspecific competition = occurs between members of the same species
High population density leads to increased competition

8. Competition can occur when resources are limited
Interspecific competition = occurs between members of two or more species
Strongly affects community composition
Leads to competitive exclusion or species coexistence

9. Competition can occur when resources are limited
Competitive exclusion = one species completely excludes another species from using a 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)

10. Competition can occur when resources are limited
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

12. Competition can occur when resources are limited
Resource partitioning = process by which species use different resources or use shared resources in different ways
For example, birds all eating insects, but catching them on different parts of the tree
For example, one species eats small seeds and another eats large seeds

14. Competition can occur when resources are limited
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

15. Several types of interactions are exploitative
Exploitation = process by which 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

16. Predators kill and consume prey
Zebra mussels eat phytoplankton and zooplankton
Both populations decrease in lakes with zebra mussels
Zebra mussels don’t eat cyanobacteria
Cyanobacteria increase in lakes with zebra mussels
Predators may also be prey
Zebra mussels are being eaten by diving ducks, muskrats, crayfish, flounder, sturgeon, eels, carp, and freshwater drum

17. Predators kill and consume prey
Predator–prey interactions can sometimes drive cyclical population dynamics
Increased prey population increases predators
Predators survive and reproduce
Increased predator population decreases prey
Predators starve
Decreased predator population increases prey populations

19. Predators kill and consume prey
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 have evolved elaborate defenses against being eaten

21. Parasites exploit living hosts
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 parasites are free-living
Infrequent contact with their hosts
Ticks, sea lampreys
Some live within the host
Tapeworms
Others cause disease
These are pathogens 21

23. Parasites exploit living hosts
Parasitoids = insects that parasitize other insects
Lay eggs in larva or adults of other species
Kill the host
Coevolution = process in which 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 evolutionarily beneficial to the parasite to kill its host 23

24. Herbivores exploit plants
Herbivory = when animals feed on the tissues of plants
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
Like in parasitism, herbivore–plant interaction can result in coevolution. 24

26. Mutualists help one another
Mutualism = relationship in which 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 = interaction in which bees, bats, birds, and others transfer pollen from one flower to another, fertilizing its eggs 26

27. 27

28. 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:
Which species coexist, and how species relate to one another
How communities change, and why patterns exist 28

29. Energy passes among trophic levels
One of the most important species interactions involves who eats whom.
Matter and energy move through the community
Trophic level = rank in the feeding hierarchy
Producers (autotrophs)
Consumers
Detritivores and decomposers 29

31. Producers
Producers, or autotrophs (“self-feeders”) = organisms that 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 31

32. Consumers 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 (that eat insects) 32

33. Consumers Tertiary consumers = fourth trophic level
Predators at the highest trophic level
Consume secondary consumers
Are also carnivores
Hawks, owls
Omnivores = consumers that eat both producers (plants) and consumers (animals)

34. 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 nonliving material into simpler chemicals that can be used by plants
Fungi, bacteria
Enhance topsoil and recycle nutrients 34

35. Energy, biomass, and numbers decrease at higher trophic levels
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 about 10% of the energy of the trophic level below it
There are also far fewer organisms and less biomass (mass of living matter) at each higher trophic level
A human vegetarian’s ecological footprint is smaller than a meat-eater’s footprint 35

37. Food webs show feeding relationships and energy flow
Food chain = a linear 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
Contains many food chains 37

39. Some organisms play outsized roles in communities
Community dynamics are complex
Species interactions differ in strength
Keystone species = a species that has a strong or wide-reaching impact far out of proportion to its abundance
Removal of a keystone species has substantial ripple effects
Significantly alters the food web

41. Some organisms play outsized roles in communities
Trophic cascade = a phenomenon in which predators at high trophic levels indirectly affect populations at low trophic levels
Predators keep species at intermediate trophic levels in check, allowing growth of species at a lower level
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

42. Communities respond to disturbance in various ways
Disturbance = event that causes rapid changes in the environment that alters the community or ecosystem
Tree falling, opening space in a forest
Removal of keystone species, spread of invasive species
Natural disturbances like tornadoes, hurricanes
Human impacts cause major community changes
Some species become adapted to disturbance
Plants growing in fire-prone regions may have seeds that require fire to germinate

43. Communities respond to disturbance in various ways
Communities have different ways of maintaining themselves when disturbed
Resistance = when a community of organisms resists change and remains stable despite the disturbance
Resilience = when 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

44. Succession follows severe disturbance
Succession = the predictable series of changes in a community following a disturbance
Primary succession = disturbance removes all vegetation and soil life
Community is built from scratch
Glaciers, drying lakes, volcanic lava
Pioneer species = the first species to arrive in a primary succession area (e.g., lichens, mosses)

46. Succession follows severe disturbance
Secondary succession = a disturbance dramatically alters, but does not destroy, all local organisms
The remaining organisms and soil form “building blocks” that help shape the process of succession
Fires, hurricanes, farming, logging
Climax community = community that remains in place with few changes until another disturbance restarts succession

48. Communities may undergo shifts
The dynamics of community change are more variable and less predictable than thought
Competition may inhibit progression to another stage
Chance factors also affect movement between stages
Climax community may not be based on climate alone
Phase (regime) shift = occurs when the overall character of the community fundamentally changes
Some crucial threshold is passed, a keystone species is lost, or an exotic species invades
Human activity may be creating novel or no-analog communities that are new mixtures of species that have not been seen before in nature

49. Invasive species pose new threats to community stability
Invasive species = non-native (exotic) organisms that spread widely and become dominant in a community
Introduced species = species that were deliberately or accidentally brought from elsewhere
Growth-limiting factors (predators, disease, competitors, etc.) are removed or absent
Have major ecological effects
Chestnut blight from Asia wiped out American chestnut trees
Some species help people (e.g., European honeybees)

51. Prevention, rather than control, is the best policy
We can respond to invasive species through control, eradication, or prevention
Techniques to control invasive species
Removing them manually
Applying toxic chemicals
Introducing native predators or diseases
Stressing them with heat, sound, electricity, carbon dioxide, or ultraviolet light
Control and eradication are hard and expensive
Understanding the biology of invasive species can help predict where they will be a problem
Prevention, rather than control, is the best policy

52. 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 (e.g., 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

53. Altered communities can be restored
Prairie restoration involves replanting native species, controlling invasive species
Nearly all tallgrass prairie was converted to agriculture by the 19th century
The world’s largest project is the 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

55. Earth’s Biomes Widely separated regions share similarities
Biome = major regional complex of similar communities recognized by plant type and vegetation structure

57. Climate influences the location of biomes
The type of biome depends on abiotic factors
Temperature, precipitation, soil type, atmospheric circulation
Climatograph = a climate diagram showing an area’s mean monthly temperature and precipitation
Similar latitudes have similar climates
Similar biomes occupy similar latitudes

59. Aquatic and coastal systems resemble biomes
Various aquatic systems comprise distinct communities
Coastlines, continental shelves
Open ocean, deep sea
Coral reefs, kelp forests
Freshwater lakes and rivers
Some coastal systems (estuaries, marshes, etc.) have both aquatic and terrestrial components

60. Aquatic and coastal systems resemble biomes
Aquatic systems are shaped by
Water temperature, salinity, and dissolved nutrients
Wave action, currents, depth, light levels
Substrate type and animal and plant life

61. Temperate deciduous forest
Deciduous trees lose their leaves each fall
They remain dormant during winter
Mid-latitude forests in Europe, eastern China, eastern North America
Even, year-round precipitation
Fertile soils
Dominant forests trees are often oak, beech, maple

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

65. 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
Logged for lumber and paper
Most old growth is gone

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

69. 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 seasonal rainfall and less overall than rainforest
Converted to agriculture
Severe soil erosion

71. 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

73. Desert Minimal precipitation Some are bare, with sand dunes (Sahara)
Some are vegetated (Sonoran)
They are not always hot
Temperatures vary widely during the day
Saline soils
Animals are often nocturnal, nomadic
Plants may have thick skins, spines to protect their water

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

77. Boreal forest Also called taiga Canada, Alaska, Russia, Scandinavia
Extends for large continuous areas
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

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

81. Altitudes create patterns analogous to latitudinal
Vegetative communities change along mountain slopes
The climate varies with altitude in the same way it varies with latitude
A mountain climber in the Andes begins in the tropics and ends on a glacier
Rainshadow effect = phenomenon that occurs when air going over a mountain releases moisture on one side, creating an arid region on the other side
Hiking up a mountain in the southwest U.S. is like walking from Mexico to Canada

83. Conclusion
Biomes and communities help us understand how the world functions
Species interactions affect communities
Predation, parasitism, competition, mutualism
Cause 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

84. QUESTION: Review Mutualism is a form of species interaction where
both species are harmed.
one species benefits, but the other is harmed.
both species benefit.
one species excludes another from a particular area.
Answer: c

85. QUESTION: Review
Which of the following is NOT an exploitative interaction?
Predation
Herbivory
Parasitism
All of these are exploitative interactions.
Answer: d

86. QUESTION: Review An example of resource partitioning is
one species eating larger berries and another species eating smaller berries.
one species moving out of an area to find new resources.
a host species becoming more vulnerable to parasitism.
a pine tree evolving thicker pinecones to reduce consumption by squirrels.
Answer: a

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

88. QUESTION: Review
Primary succession would take place on all of the following EXCEPT
the slopes of a newly formed volcanic island.
a forest in northwest Oregon after it had been logged.
a receding glacier.
a drying lake.
Answer: b

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

90. QUESTION: Review
All of the following are ways to control invasive species EXCEPT
removing individuals from the area.
stressing them by noise.
introducing a predator.
encouraging them to hybridize with another species.
Answer: d

91. 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

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

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

94. 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?
As an exotic species, they should immediately be removed and adopted or killed.
Although they are an exotic species, they are part of our heritage and should be allowed to stay.
They have been here so long, we should just leave them alone.
Many countries eat horse flesh, so we should round them up and export them to horse-eating countries.
Answer: any

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

96. QUESTION: Interpreting Graphs and Data
According to this climatograph for Vaigach, Russia, in the tundra biome, winters are
long and warm.
short and cool.
long and cold.
short and warm.
Answer: c