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Environment: The Science behind the Stories

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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

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