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Ch. 45: Community Ecology and Ecosystems
Community Structure
Species Richness = a listing of the various species found in a community
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Ex. Tropical Rain Forests have more different types of species that a coniferous forest
Species Diversity = includes species richness and species abundance
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The greater the species richness and the more even the distribution of those species, the
greater the species diversity
Community Interactions
Habitat = a particular place where a species lives and reproduces
Ecological Niche = the role a species plays in its community
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Includes the resources used to meet energy, nutrient, and survival demands
Fundamental Niche = all the abiotic conditions under which a species could survive with
no adverse biotic conditions (disease, predation, competition)
Realized Niche = the resources a species actually uses
The fundamental niche is always greater than the realized niche
Effect of Competition
Competition occurs when members of different species need to use the same resource that is in
limited supply
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Ex. Paramecium species both flourish if grown separately, but if grown together, one
thrives and the other does not
Competitive Exclusion Principle = no two species can occupy the same niche at the same time
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One will always out-compete the other
To avoid this, organisms use Resource Partitioning = dividing up the use of a limited
resource so that both species can survive
o Ex. Owls and hawks eat same prey, but owls are nocturnal hunters and hawks are
diurnal hunters
By specializing niches, more individuals of each species can avoid competition and have
a reproductive advantage
Character Displacement = when characteristics are more divergent when populations are
found in the same community than when they are alone
o Ex. Finch beaks on Galapagos
Predator-Prey Interactions
Predation = when one living organisms (the predator) feeds on another (the prey)
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Includes Parasitism
Predator and prey both affect the population size of the other, sometimes creating a “boom and
bust” cycle of their populations
Prey Defenses
Include: heightened senses, speed, protective armor, spines, thorns, tails and appendages that
break off, chemical defenses, and camouflage
Cryptic Coloration = ability to blend into background
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Ex. Flounder, walking sticks, toads, etc.
Aposematic (Warning) Coloration = bright colors that stand out to warn of possible danger
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Ex. Poison arrow frogs or skunks
Features to trigger startle responses in predators
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Ex. South American lantern fly
Association with other prey can help protect an individual
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Includes flocks, schools of fish, herds, and mimicry
Batesian Mimicry = when one (harmless) species resembles another that possesses an
overt predation defense
o Ex. Scarlet kingsnake (harmless) looks like a coral snake (venomous)
Mȕllerian Mimicry = when two species that are both harmful resemble each other
o Reinforces their strategy with predators
o Ex. Many stinging bees look alike
Symbiotic Relationships
Symbiosis = when two different species live together, affecting each other
Three Types:
1) Parasitism = parasite benefits while the host is harmed
 Host often provides parasite with food and place to live and reproduce
o Ex. Heart worm and dogs
 May only slightly weaken host or may kill them over time
2) Commensalism = one species benefits while the other is unaffected
 Ex. Clown fish and sea anemones
 Some debate about whether it really exists
3) Mutualism = both species benefit
 Ex. Termites need protozoans in their digestive tract to break down wood
 Ex. Mycorrhizae, root nodules, and lichens are ones you should know
COMMUNITY DEVELOPMENT: Ecological Succession
Succession = change within a community over time
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Usually depends on type of dominant plant life
Primary Succession  occurs in areas where this is no soil formation
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Ex. After volcanic eruptions or glacial retreats
Wind, water, and often lichens begin to break the rock down into soil
Secondary Succession  occurs in areas where soil is already present
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Pioneer Species = First species to live there
Often small, short-lived seed plants  mixed species  large, long-lived species of trees
o Plant life present determines the animal life that can live there
Each group of species prepares the way for the next until you get the climax community
Climax Community = succession always leads to the same type of community in a
particular area
o This community remains until a disturbance happens
 Ex. Tornado, beaver dams, volcanic eruptions, etc.
o Will tend to return to this climax community make-up again
(Our climax community is the beech-maple forest)
DYNAMICS OF AN ECOSYSTEM
Autotrophs (Producers) = produce their own organic food
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Need only inorganic materials and an energy source
Includes cyanobacteria, algae (phytoplankton), and green plants OR chemosynthetic
bacteria
Heterotrophs (Consumers) = must eat other organisms as food
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Herbivores = eat plants or algae (producers)
Carnivores = eat other animals
Omnivores = eat both plants and animals
Detritivores = eat detritus (decomposing organic matter)
Decomposers = break down dead organic matter, including animal wastes
o Critical in nutrient cycling
Energy Flow
Can be shown with diagrams: Food Chains and Food Webs, or Ecological Pyramids
Trophic (feeding) Levels = the level of nutrients within a food web or chain
Food chains and food webs diagram the flow of energy amongst organisms
Food chains typically follow the pattern:
Primary Producers  Primary Consumers  Secondary Consumers  Tertiary Consumers
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Ex. Leaves  Caterpillars  Birds  Hawks
Food Webs = several interconnected food chains
 You need to be able to analyze a food chain or food web and determine how changes in
one population will affect the others.
Ecological Pyramids
Food chains are typically limited to the tertiary consumer level. This is due to the loss of energy
between trophic levels.
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10% Rule: Only 10% of energy is passed to the next level. The other 90% is used by the
organism to drive its metabolism and is eventually lost as heat.
Flow of energy can be shown with an ecological pyramid.
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Other pyramids reflect this loss of energy by showing that the number of individuals that can be
supported by an area decreases as you move through a food chain
Numbers Pyramids = # of each type of organism at each trophic level
Biomass Pyramids = dry weight of each organism
Biogeochemical Cycling = how nutrients are moved from the inorganic world into the organic
world and back again
Water Cycle
Involves: precipitation  evaporation OR precipitation  transpiration/evaporation
Human Impact: Groundwater Mining = when we withdraw more water from aquifers than they
can replace
Freshwater makes up only 3% of the world’s supply, but is considered a renewable resource (for
now)
Carbon Cycle
Involves: CO2 enters through carbon fixation in plants (part of photosynthesis), then is used by
organisms for body functions/parts, then is returned to environment via respiration and more
Human Impacts: More CO2 is being added due to burning fossil fuels and less is being removed
due to deforestation  Greenhouse Effect (N2O and CH4 also play a role) = when these gases
trap heat in the Earth’s atmosphere
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Leads to Global Warming and Climate Change
o Glaciers will melt, sea levels will rise, super-storms will develop
Phosphorus Cycle
Involves: Weathering of rocks, ionizing in soil, being incorporated in plants, move through
organisms, decay back to soil
Human Impact: Fertilizers and detergents contain lots of phosphates, which then enter the water
supply, and result in eutrophication (over-enrichment) of waterways
Nitrogen Cycle (see diagram)
Human Impacts:
1) Fertilizers contain nitrates, which can run-off into lakes and rivers  results in Algal
Blooms
o Cause a sudden overgrowth in algae
o Then they die off and decomposers quickly increase in numbers
o They use up all the O2 in the water
o Results in massive fish kill
2) Contribute to acid rain when nitrogen oxides from fossil fuels (and SO2) react with water
in atmosphere to form acid