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Community Ecology
Chapter 54
Interspecific Interactions
• Competition --/-• Competitive exclusion
• Ecological Niches (Habitat-address; nicheprofession)
• Resource partitioning-allows similar
species to coexist in a community
• Fundamental niche-potential
• Realized niche-actual-may be result of
interspecific competition
Character Displacement
• Tendency for characteristics to diverge
more in sympatric pop of 2 species than in
allopatric pop
Predation +/-• Can be animal eating plant tissues
• Defensive adaptations
– Cryptic coloration
Aposematic colorationwarning
Batesian mimicry-harmless or
palative looks bad
Mullerian mimicry
• 2 unpalatable species look alike
Herbivory +/-Plants have chemical toxins, spines, thorns
ex strychnine, nicotine, selenium toxins
Herbivores-special adaptations
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–
–
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Insect-chemical sensors
Sense of smell
Specialized teeth
Length of digestive systems
Symbiosis
• Parasitism +/-• Mutualism +/+ obligate; facultative
• Commensalism +/0
Facilitation
• Species can have positive effects on the
survival and reproduction of another
species without living in direct or intimate
contact.
• Ex. Juncus grows in salt marshes and
prevents salt buildup-benefits other
species
Species Diversity
• Species richness
• Relative abundance
Shannon diversity (H)
• Index based on species richness and
relative abundance
Trophic structure
• Food Chain
Food Webs (Elton 1920s)
Limits on length of food
chain
• Energetic hypothesis-inefficiency of energy
transfer -10% rule
• Dynamic stability hypothesis-long food
chains are less stable than short onespopulation fluctuations at lower trophic
levels are magnified at higher levels
• Also-carnivores tend to be larger at
successive trophic levels-can’t get enough
food to meet needs
Dominant species
• Most abundant-have the highest biomass
• Exert a powerful control
• Are they are competitively superior in
exploiting limited resources?
• Are they are most successful at avoiding
predation?-would explain effect of invasive
species…
Invasive pressure
• American Chestnut
• Before 1910-40% of US
trees-fungal diseaseChestnut blight-killed all
the trees-oak, hickory
replaced; mammals, birds
ok, but 7 species of moths and butterflies
became extinct
Keystone species
• Sea otters: Sea otters are a keystone species in the kelp forests.
They eat many invertebrates, but especially sea urchins. If there are
too many sea urchins, they will eat too much of the kelp and
destroy it.
• Elephants: By eating small trees, elephants
preserve the grasslands, because the grasses
need plenty of sun to survive. If they were not
there, the savanna would convert to a forest or
scrublands.
• Grizzly bears: As predators, bears keep down the
numbers of several species, like moose and elk.
They also carry and deposit seeds throughout the
ecosystem. Bears that eat salmon will leave their
dropping and the partially eaten remains that
provide nutrients such as sulfur, nitrogen and
carbon to the soil.
Foundation species
• Ecosystem “engineers”
• Affect by causing physical changes in the
environment
• Ex beavers
• Facilitators-may help other species
Models of organization
• Bottom up VH increase of veg-more H
• NVHP
• Top down VH increase in H- less V
• NVHP Trophic Cascade (ex.
Remove top carnivoresprimary
carnivores so upherbivores
decreasephytoplankton goes
upnutrients go down) (Manipulate +/effect
Biomanipulation-prevent algal blooms by
adding consumers rather than chemicals
Disturbance
• Influences species diversity and
composition
• Storms, waves, fires, freezing, drought,
• Moderate disturbance can foster greater
diversity than low or high levels
Ecological succession
• Species are replaced by other species
• Primary
• Secondary
• Climax community
Island Biogeography
• http://www.youtube.com/watch?v=2Ravt
4AqdZI
Island Equilibrium Model
Latitudinal gradients
• Species richness increases as approach
tropics
• Tropics-older; others have repeatedly
started over (glaciers retreating, etc)
• Growing season longer
• Sunlight and precipitation higher
• Evapotranspiration-evap of water for soil
and plants together
• Zoonotic pathogens: transferred to
humans from other animals (vector)
Detritivores
• Return nutrients to the soil
• Law of conservation of mass
Aquatic Ecosystem
• Light limitation
• Nutrient limitation
• Eutrophication
Biomass-dry mass
•*
• *In inverted pyramid, phytoplankton grow,
reproduce, and are consumed so quickly by
the zooplankton that they never develop a
large population size, or standing crop
• Phytoplankton continually replace their
biomass at such a rapid rate, they can
support a biomass of zooplankton bigger
than their own biomass.
• Terrestrial herbivores are held in check by
a variety of factors.
– Mechanical defenses
– Chemicals
The Green World Hypothesis
– Low nutrient concentrations so must consume
large quantities
– Abiotic factors-temp & moisture extremes
– Competition
Productivity
• GPP-gross primary production
• NPP-net primary production
• NPP=GPP – R(autotrophic respiration)
• Primary production
– in aquatic is mostly affected by light and
nutrients-N and P
– Eutrophic-nutrient rich; oligotrophic-nutrient
poor
– On land-temp and water
– evotranspiration
Biogeochemical cycles
Nitrogen cycle
Additional Terms
• Bioremediation-use of organisms to
detoxify polluted areas
• Bioaugmentation-add desirable species
such as nitrogen fixers
• Biodiversity (3 Levels)-genetic diversity,
species diversity and ecosystem diversity
• Threats: habitat loss, introduced species,
over-harvesting, global change
Population conservation
• Focuses on:
– Population size
– Genetic diversity
– Critical habitat
MVP
• Minimum Viable Population
• Extinction Vortex
Landscape and regional
conservation
• Habitat fragmentation
• Movement corridors
• Biodiversity hot spot-small area with an
exceptional concentration of endemic
species
Human Actions
• Agriculture-nutrient cycling-take it out of
soil or too much in water
• Acid precipitation
• Biological magnification
• Greenhouse effect
• Global warming
• Ozone layer
• BIDE birth immigration death
emigration
• Additive growth
• Multiplicative growth
Elements
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