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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
Insect-chemical sensors
Sense of smell
Specialized teeth
Length of digestive systems
• Parasitism +/-• Mutualism +/+ obligate; facultative
• Commensalism +/0
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
• 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
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
Foundation species
• Ecosystem “engineers”
• Affect by causing physical changes in the
• Ex beavers
• Facilitators-may help other species
Models of organization
• Bottom up
• NVHP
• Top down
• NVHP Trophic Cascade
• Biomanipulation-prevent algal blooms by
adding consumers rather than chemicals
• Influences species diversity and
• 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 Equilibrium Model
• Return nutrients to the soil
• Law of conservation of mass
Aquatic Ecosystem
• Light limitation
• Nutrient limitation
• Eutrophication
Biomass-dry mass
• 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.
The Green World Hypothesis
Transitional Page
• 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
– 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
• Minimum Viable Population
• Extinction Vortex
Landscape and regional
• Habitat fragmentation
• Movement corridors
• Biodiversity hot spot-small area with an
exceptional concentration of endemic
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