© 2012 pearson education, inc. - · pdf file04.09.2012 · 1 © 2012...

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© 2012 Pearson Education, Inc.

Ch. 4 - Species Interactions andCommunity Ecology:• 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


Central Case Study: Black and White andSpread All Over

• In 1988, discharged shipballast water accidentallyreleased zebra mussels intoLake St. Clair

• By 2010, they had spread to30 states– No natural predators,

competitors, or parasites• They cause millions of

dollars of property damageeach year


Species interactions

• Species interactions are the backbone of communities• Effects of species interactions on the participants:

Type of interaction Effect on Species 1 Effect on Species 2

Competition – –

Predation, parasitism,herbivory

+ –

Mutualism + +

“+”: positive effect “–”: negative effect


Competition occurs with limited resources

• Competition: multiple organisms seek the same limitedresource– Food, water, space, shelter, mates, sunlight, etc.

• Intraspecific competition: between members of the samespecies– High population density: increased competition

• Interspecific competition: between members of differentspecies– Strongly affects community composition– Leads to competitive exclusion or species coexistence

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Results of interspecific competition

• Competition is usually subtle and indirect• One species may exclude another from using the resource

– Zebra mussels displaced native mussels in the Great Lakes– Quagga mussels are now displacing zebra mussels

• Or, competing species may be able to coexist– Natural selection favors individuals that use different

resources or shared resources in different ways


Resource partitioning

• Resource partitioning:competing species coexistby specializing– By using different

resources (small vs. largeseeds)

– Or using sharedresources differently(active during day vs.night)


An exploitative interaction: predation

• Predation: process by which individuals of onespecies (predators) capture, kill, and consumeindividuals of another species (prey)

• Exploitation: onemember benefits whilethe other is harmed(+/- interactions)– Predation,

parasitism, herbivory


Predation can drive population dynamics

• Increased prey populations increase food for predators– Predators survive and reproduce

• Increased predator populations decrease prey– Predators starve and their populations decrease

• Decreased predator populations increase prey populations

Insert Fig. 4.4

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Prey develop defenses against being eaten


An exploitative interaction: 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 parasites contact hosts infrequently– Cuckoos, cowbirds

• Some live within the host– Disease, tapeworms

• Some live on thehosts’ exterior

– Ticks, sea lampreys


An exploitative interaction: herbivory

• Herbivory: animals feed on thetissues of plants– Widely seen in insects

• May not kill the plant– But affects its growth and

reproduction• Defenses against herbivory include:

– Chemicals: toxic or distasteful– Thorns, spines, or irritating hairs

• Herbivores may overcome thesedefenses


Mutualists help one another

• Two or more species benefit from their interactions– Each partner provides a service the other needs (food,

protection, housing, etc.)• Symbiosis: a relationship in which the organisms live in

close physical contact (mutualism and parasitism)– Microbes within digestive tracts– Mycorrhizae: plant roots and fungi– Coral and algae (zooxanthellae)

• Pollination: bees, bats, birds, and others transfer pollenfrom one flower to another, fertilizing its eggs

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Pollination

• In exchange for the plant nectar, the animals pollinateplants, which allows them to reproduce


Ecological communities

• Community: an assemblage of populations of organismsliving in the same area at the same time– Members interact with each other– Interactions determine the structure, function, and species

composition of the community• Community ecologists are interested in how:

– Species coexist and interact with one another– Communities change, and why these patterns exist


Energy passes among trophic levels

• One of the most importantspecies interactions– Who eats whom?

• Matter and energy movethrough the community

• Trophic levels: rank inthe feeding hierarchy– Producers (autotrophs)– Consumers– Detritivores and

decomposers© 2012 Pearson Education, Inc.

Producers: the first trophic level

• Producers, or autotrophs (“self-feeders”): organismscapture solar energy for photosynthesis to produce sugars– Green plants– Cyanobacteria– Algae

• They capture solar energy and use photosynthesis toproduce sugars

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Consumers: consume producers

• Primary consumers: second trophic level– Organisms that consume producers– Herbivorous grazing animals– Deer, grasshoppers

• Secondary consumers: third trophic level– Organisms that prey on primary consumers– Wolves, rodents, birds

• Tertiary consumers: fourth trophic level– Predators– Hawks, owls


Detritivores and decomposers

• Organisms that consume nonliving organic matter• Detritivores: scavenge waste products or dead bodies

– Millipedes, soil insects• Decomposers: break down leaf litter and other nonliving

material– Fungi, bacteria– Enhance topsoil and recycle nutrients


Energy, biomass, and numbers

• Most energy that organisms use in cellular respiration islost as waste heat– Less and less energy is available in each successive

trophic level– Each trophic 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 uses less energy and has a smaller ecological footprint than a meat eater


Pyramids of energy, biomass, and numbers

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Food webs show relationships and energyflow

• Food chain: a series offeeding relationships

• Food web: a visual mapof feeding relationshipsand energy flow amongorganisms

Food webs are greatlysimplified and leave out most species


Some organisms play big roles

• Keystone species: has astrong or wide-reachingimpact– Far out of proportion to

its abundance• Removing a keystone

species has substantialripple effects– Alters the food web

• Large-bodied secondaryor tertiary consumers


Species can change communities

• Trophic cascade: predators at high trophic levelsindirectly promote populations at low trophic levels– By keeping species at intermediate trophic levels in check

• Extermination of wolves led to increased deerpopulations …– Which overgrazed vegetation …– Which changed forest structure

• Ecosystem engineers: physically modify the environment– Beaver dams, prairie dogs, ants


Invasive species threaten stability

• Alien (exotic) species: non-native species fromsomewhere else enters a new community

• Invasive species: non-native species that spreadswidely and become dominant in a community– Introduced deliberately or accidentally– Growth-limiting factors (predators, disease, competitors,

etc.) are absent– Major ecological effects– Pigs, goats, and rats have destroyed island species

• But some invasive species (e.g., honeybees) helppeople

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Invasive mussels modify communities


Controlling invasive species

• Techniques to control invasive species include:– Removing them manually– Applying toxic chemicals– Drying them out, depriving them of oxygen– Introducing predators or diseases– Stressing them with heat, sound, electricity, carbon

dioxide, or ultraviolet light• Control and eradication are hard and expensivePrevention, rather than control, is the best policy


Altered communities can be restored

• Humans have dramatically changed ecological systems– Severely degraded systems cease to function

• Restoration ecology: the science of restoring an area toan earlier (presettlement) condition– Tries to restore the system’s functionality (e.g., filtering of

water by a wetland)• Ecological restoration: actual efforts to restore an area

– Difficult, time-consuming, and expensive

It is best to protect natural systems from degradation inthe first place


Examples of restoration efforts

• Prairie restoration: replanting native species, controllinginvasive species, controlled fire to mimic natural fires

• The world’s largest project: Florida Everglades– Flood control and irrigation removed its water– Populations of wading

birds dropped 90–95%– It will take 30 years

and billions of dollarsto restore naturalwater flow

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Widely separated regions share similarities

• Biome: major regional complex of similar communitiesrecognized by:– Plant type– Vegetation

structure

There are about 10terrestrial biomes


Abiotic factors influence biome locations

• The type of biome depends on temperature, precipitation– Also air and ocean circulation, soil type

• Climatographs: a climate diagram showing an area’smean monthly temperature and precipitation

Similar biomes occupysimilar latitudes


Temperate deciduous forest

• Deciduous trees lose theirbroad leaves each fall– They remain dormant during

winter• Midlatitude forests in Europe,

east China, eastern NorthAmerica

• Even, year-round precipitation• Fertile soils• Forests: oak, beech, maple


Temperate grasslands

• More temperature difference– Between winter and summer

• Less precipitation supportsgrasses, not trees

• Also called steppe or prairie• Once widespread, but has

been converted to agriculture• Bison, prairie dogs, ground-

nesting birds, pronghorn

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Temperate rainforest

• U.S. coastal PacificNorthwest

• Heavy rainfall• Coniferous trees: cedar,

spruce, hemlock, fir• Moisture-loving animals

– Banana slug• Erosion and landslides

affect the fertile soil• Most old-growth is gone

as a result of logging© 2012 Pearson Education, Inc.

Tropical rainforest

• Southeast Asia, west AfricaCentral and South America

• Year-round rain and warmtemperatures

• Dark and damp• Lush vegetation• Diverse species

– But in low densities• Very poor, acidic soils

– Nutrients are in the plants


Tropical dry forest

• Also called tropicaldeciduous 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


Savanna

• Tropical grasslandinterspersed with trees

• Africa, South America,Australia, India

• Precipitation occurs onlyduring the rainy season

• Animals gather near waterholes

• Zebras, gazelles, giraffes,lions, hyenas

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Desert

• Minimal precipitation• Sahara: bare, with sand dunes• Sonoran: heavily vegetated• Temperatures vary widely

– Day vs. night, seasonally• Soils (lithosols): high

mineral content, low organicmatter

• Animals: nocturnal, nomadic• Plants: thick skins, spines


Tundra

• Russia, Canada, Scandinavia• Minimal rain, very cold

winters• Permafrost: permanently

frozen soil• Residents: polar bears, musk

oxen• Migratory birds, caribou• Lichens, low vegetation, no

trees• Alpine tundra: on

mountaintops


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


Chaparral

• Occurs in small patchesaround the globe

• Mediterranean Sea, Chile,California, south Australia

• Densely thicketed,evergreen shrubs

• Highly seasonal biome– Mild, wet winters– Warm, dry summers

• Fire-resistant plants

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Conclusion

• Species interactions affect communities– Competition, predation, parasitism, competition,

mutualism– Causing weak and strong, direct and indirect effects

• Feeding relationships are represented by trophic levelsand food webs

• Humans have altered many communities– Partly by introducing non-native species

• Ecological restoration attempts to undo the negativechanges that we have caused

© 2012 pearson education, inc. - · pdf file04.09.2012 · 1 © 2012...

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