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All the organisms in a particular area make upa community
A number of factors characterize everycommunity
Biodiversity
The prevalent form ofvegetation
Response to disturbances
Trophic structure(feeding relationships)
36.1 A community is all the organisms inhabiting aparticular area
Figure 36.1
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Biodiversity is the variety of different kinds oforganisms that make up a community
Biodiversity has two components
Species richness, or the total number of
different species in the community
The relative abundance of different species
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Interspecific competition occursbetween twopopulations if they both require the same
limited resource
A population's niche is its role in thecommunity
The sum total of its use of the biotic and abioticresources of its habitat
36.2 Competition may occur when a sharedresource is limited
STRUCTURAL FEATURES OF COMMUNITIES
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Predation is an interaction where one specieseats another
The consumer is called the predator and the
food species is known as the prey
Parasitism can be considered a form ofpredation
36.3 Predation leads to diverse adaptations in bothpredator and prey
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As predators adapt to prey, sometimes naturalselection also shapes the prey's defenses
This process ofreciprocaladaptation is
known ascoevolution
Example:
Heliconius andthe passionflowervine
Figure 36.3A
Eggs
Sugardeposits
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Prey gain protection against predators througha variety of defense mechanisms
Mechanical defenses, such as the quills of aporcupine
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Chemical defenses are widespread and veryeffective
Animals with effective chemical defenses areoften brightly colored to warn predators
Example: the poison-arrow frog
Figure 36.3B
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Camouflage is a very common defense in theanimal kingdom
Example: the gray tree frog
Figure 36.3C
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A keystone species exerts strong control oncommunity structure because of its ecologicalrole
A keystone predator may maintain communitydiversity by reducingthe numbers of thestrongest competitors
in a communityThis sea star is a
keystone predator
36.4 Predation can maintain diversity in acommunity
Figure 36.4A
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Predation by killer whaleson sea otters, allowing sea
urchins to overgraze on kelp
Sea otters represent thekeystone species
Figure 36.4B
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A symbiotic relationship is an interactionbetween two or more species that live togetherin direct contact
There are three main types of symbioticrelationships within communities
Parasitism
Commensalism
Mutualism
36.5 Symbiotic relationships help structurecommunities
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Parasitism is a kind of predator-preyrelationship
The parasite benefits and the host is harmed inthis symbiotic relationship
A parasite obtains food at the expense of its host
Parasites are typically smaller than their hosts
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In the 1940s, Australia was overrun byhundreds of millions of European rabbits
The rabbits destroyed huge expanses of Australia
They threatened the sheep and cattle industries
In 1950, a parasitethat infects rabbits(myxoma virus)
was deliberatelyintroduced tocontrol the rabbitpopulation
Figure 36.5A
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Commensalism is a symbiotic relationshipwhere one partner benefits and the other is
unaffected
Examples of commensalism
Algae that grow on the shells of sea turtles
Barnacles that attach to whales
Birds that feed on insects flushed out of thegrass by grazing cattle
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A community interacts with abiotic factors,forming an ecosystem
Energy flows from the sun, through plants,animals, and decomposers, and is lost as heat
Chemicals are recycled between air, water,soil, and organisms
36.8 Energy flow and chemical cycling are the twofundamental processes in ecosystems
ECOSYSTEM STRUCTURE AND DYNAMICS
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A terrarium ecosystem
Figure 36.8
Chemical cycling(C, N, etc.)
Lightenergy
Chemicalenergy
Heatenergy
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A food chain is the stepwise flow of energy andnutrients
from plants (producers)
to herbivores (primary consumers)
to carnivores (secondary and higher-levelconsumers)
36.9 Trophic structure is a key factor in ecosystemdynamics
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Figure 36.9A
TROPHIC LEVEL
Quaternaryconsumers
Tertiaryconsumers
CarnivoreCarnivore
Carnivore Carnivore
Carnivore Carnivore
Herbivore Zooplankton
Plant Phytoplankton
Secondary
consumers
Primaryconsumers
Producers
A TERRESTRIAL FOOD CHAIN AN AQUATIC FOOD CHAIN
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Decomposition is the breakdown of organiccompounds into inorganic compounds
Decomposition is essential for the continuationof life on Earth
Detritivoresdecompose wastematter and recyclenutrients
Examples: animalscavengers, fungi,and prokaryotes
Figure 36.9B
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A food web is a network of interconnectingfood chains
It is a more realistic view of the trophicstructure of an ecosystem than a food chain
36.10 Food chains interconnect, forming food webs
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Figure 36.10
Tertiaryandsecondaryconsumers
Secondaryandprimaryconsumers
Primaryconsumers
Producers
(Plants, algae,phytoplankton)
Detritivores
(Prokaryotes, fungi,certain animals)
Wastes anddead organisms
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Biomass is the amount of living organicmaterial in an ecosystem
Primary production is the rate at which
producers convert sunlight to chemical energy
The primary production of the entire biosphereis about 170 billion tons of biomass per year
36.11 Energy supply limits the length of food chains
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A pyramid of production reveals the flow ofenergy from producers to primary consumers
and to higher trophic levels
Figure 36.11
Tertiaryconsumers
Secondaryconsumers
Primaryconsumers
Producers
10 kcal
100 kcal
1,000kcal
10,000 kcal
1,000,000 kcal of sunlight
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Only about 10% of the energy in food is storedat each trophic level and available to the next
level
This stepwise energy loss limits most foodchains to 3 - 5 levels
There is simply not enough energy at the verytop of an ecological pyramid to support anothertrophic level
36 12 C i A i i i
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The dynamics of energy flow apply to thehuman population as much as to otherorganisms
When we eat grain or fruit, we are primaryconsumers
When we eat beef or other meat from herbivores,we are secondary consumers
When we eat fish like trout or salmon (which eatinsects and other small animals), we are tertiaryor quaternary consumers
36.12 Connection: A production pyramid explainswhy meat is a luxury for humans
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Because the production pyramid tapers sosharply, a field of corn or other plant crops can
support many more vegetarians than meat-eaters
Figure 36.12
Secondaryconsumers
Primaryconsumers
Producers
Humanvegetarians
Corn
Humanmeat-eaters
Cattle
Corn
TROPHIC LEVEL
36 13 Ch i l l d b t i
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Ecosystems require daily infusions of energy
The sun supplies the Earth with energy
But there are no extraterrestrial sources ofwater or other chemical nutrients
Nutrients must be recycled between organismsand abiotic reservoirs
Abiotic reservoirs are parts of the ecosystemwhere a chemical accumulates
36.13 Chemicals are recycled between organicmatter and abiotic reservoirs
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There are four main abiotic reservoirs
Water cycleCarbon cycle
Nitrogen cycle
Phosphorus cycle
35 14 W t th h th bi h i
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Heat from the sun drives the global water cycle
Precipitation
Evaporation
Transpiration
35.14 Water moves through the biosphere in aglobal cycle
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Figure 36.14
Solarheat
Precipitationover the sea
(283)
Net movement
of water vaporby wind (36)
Flow of waterfrom land to sea(36)
Water vaporover the sea
Oceans
Evaporationfrom the sea
(319)
Evaporationandtranspiration(59)
Water vaporover the land
Precipitationover the land(95)
Surface waterand groundwater
36 15 Th b l d d h t th i
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Carbon is taken from the atmosphere byphotosynthesis
It is used to make organic molecules
It is returned to the atmosphere by cellularrespiration
36.15 The carbon cycle depends on photosynthesisand respiration
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Figure 36.15
CO2 in atmosphere
Cellular respiration
Higher-levelconsumers
Primaryconsumers
Plants,algae,
cyanobacteria
Photosynthesis
Wood andfossil fuels
Detritivores(soil microbes
and others) Detritus
Decomposition
Burning
36 16 Th it l li h il b t i
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Nitrogen is plentiful in the atmosphere as N2
But plants cannot use N2
Various bacteria in soil (and legume rootnodules) convert N2 to nitrogen compoundsthat plants can use
Ammonium (NH4
+) and nitrate (NO3
)
36.16 The nitrogen cycle relies heavily on bacteria
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Some bacteria break down organic matter andrecycle nitrogen as ammonium or nitrate to
plants
Other bacteria return N2 to the atmosphere
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Figure 36.16
Nitrogen (N2) in atmosphere
Amino acidsand proteins in
plants and animalsAssimilationby plants
Denitrifyingbacteria
Nitrates(NO3
)
Nitrifyingbacteria
Detritus
Detritivores
Decomposition
Ammonium (NH4+)
Nitrogenfixation
Nitrogen-fixingbacteria in soil
Nitrogen-fixingbacteria in root
nodules of legumes
Nitrogenfixation
36 17 The phosphorus cycle depends on the
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Phosphates (compounds containing PO43-
) andother minerals are added to the soil by thegradual weathering of rock
Consumers obtain phosphorus in organic formfrom plants
Phosphates are returned to the soil through
excretion by animals and the actions ofdecomposers
36.17 The phosphorus cycle depends on theweathering of rock
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Figure 36.17
Upliftingof rock
Phosphatesin solution
Weatheringof rock
Phosphates
in rock
Phosphatesin organic
compounds
Detritus
Detritivoresin soil
Phosphatesin soil(inorganic)
Rock Precipitated(solid) phosphates
Plants
Animals
Decomposition
Runoff
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Dams were builtacross streams at
the bottom of eachwatershed tomonitor water andnutrient losses
Figure 36.18A
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In 1966, one of the valleys was completelylogged
It was thensprayed withherbicides for3 years to
prevent plantregrowth
All the original
plant materialwas left inplace todecompose Figure 36.18B
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36 19 Talking About Science: David Schindler
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Eutrophication is a process in which nutrientrunoff from agricultural lands or livestockoperations causes photosynthetic organisms in
ponds and lakes to multiply rapidly
The result is algal bloom
36.19 Talking About Science: David Schindlertalks about the effects of nutrients onfreshwater ecosystems
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Algal bloom can cause a pond or lake to losemuch of its species diversity
Human-caused eutrophication wiped outfisheries in Lake Erie in the 1950s and 1960s
Figure 36.19B
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Dr. David Schindler is an ecologist who workedat the Experimental Lakes Project in northern
Ontario
He performedseveral classic
experiments oneutrophicationthat led to the banon phosphates in
detergents
Figure 36.19A
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According to Dr. Schindler, there are threeserious threats to freshwater ecosystems
Acid precipitation
Climate warming
Changes in land use