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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

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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

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