Transcript File ap notes chapter 53

Chapter 53: Community Ecology
Community
Assemblage of populations of different species living close
enough for potential interaction
Interspecific interactions
Relationship of an organism with other species in its community
Types:
Competition
Predation
Herbivory
Symbiosis
Parasitism
Mutualism
Commensalism
disease
Interspecific interactions are -/-.
 Competitive exclusion: when 2 species compete for a
resource that is in short supply it can lead to the
elimination of one of those species
Ecological niche
 sum total of species’ use of biotic & abiotic resources
in its environment
 Fundamental niche
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Realized niche
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Theoretical resource use
ideal conditions
actual resources use
real conditions of competition & predation included
**2 species cannot coexist with identical niches
Evidence of competition in nature
 Resource partitioning
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Character displacement
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Sympatric species consume slightly different resources such
as food
Tendency for traits to be more divergent in sympatric
populations than in allopatric populations of the same 2
species
Parasitism (+/-)
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Predator lives on or in host but seldom kills host
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Parasitoidism (+/-)
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Endoparasite examples: tapeworm, flukes
Ectoparasite examples: European cuckoos laying eggs in nest of
another species
Parasite kills host
Example: wasp lays eggs in host, larva hatch, feed, &
eventually kill host
Disease (+/-)
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Pathogen=microscopic parasite that causes lethal harm
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Symbiosis: close association between host & symbiont
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Commensalism (+/0)
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Mutualism (+/+)
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Symbiont benefits from host while host is uneffected
Few absolute examples
Cattle egret feeds on insects that grazing cattle flush out of grass
Interaction benefits both species
Examples: nitrogen-fixing bacteria on legumes, cellulose digesting
microorganisms in digestive tracts of termites & cows, specific nectar
pollinating insects of specific flowers
Coevolution
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Change in one species acts as a selective force on another
species
Counter-adaptations of the second species in turn affects
selection in the first species
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Predation & Herbivory (+/-)
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Predator eats its prey
Adaptations for stalking prey:
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Acute senses
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Heat sensors, chemical sensors, sharp eyesight
Structures
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Claws, teeth, fangs, stingers, poisons
Speed & agility
 camouflage
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Prey/Plant defenses include
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Structural
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Thorns, spines
Chemical
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Toxic or bitter taste
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Passive hiding
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Cryptic coloration
 Shape of animal, deceptive markings (i.e. fake eyes)
Aposematic coloration
 Bright coloration as a warning of toxicity
Mimicry
 Batesian- edible species resembles inedible species
 Mullerian- two inedible species resemble each other
 Use by predator to lure prey- example… snapping turtle wags
tongue like a worm to attract fish
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**Community structure is dependant on
species diversity & trophic structure; is also
effected greatly by certain species in the
community
Species diversity
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The variety of different organisms that make up the
community
Components
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Species richness
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Total number of different species in the community
Relative abundance
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Proportion of each species in the community
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Trophic structure
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Food chains
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Food webs
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Feeding relationships between organisms in the
community
Linked food chains
Limits to food chain length
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Energetic hypothesis
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Food chain is limited by inefficiency of energy transfer along the
chain (only 10% passed on to next trophic level)
Dynamic stability hypothesis
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Long food chains are less stable than shorter food chains
a result of the magnification of population fluctuations at higher
trophic levels (top predators more likely to go extinct)
Variable environments=shorter food chains
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Species with a large impact on community
structure
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Dominant species
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Keystone species
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Species in the community with the most biomass or
abundance
Species that play a pivotal ecological role or niche
Foundation species
Species that causes physical changes in the environment
that affects the structure of the community
 Ex. beavers
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Non-equilibrium model
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Communities are constantly changing
Disturbance influences species diversity & composition
Disturbance
event that changes a community through removal of
organisms &/or altering resource availability
 Examples: storm, fire, drought, human activity*
*largest/widespread agent of change
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Intermediate disturbance hypothesis
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Moderate levels of disturbance can create conditions that
encourage species diversity by opening up new niches
low levels of disturbance lower diversity because species are
out-competed
high levels of disturbance reduce diversity because of stress
to species
Ecological succession
 Disturbed area is colonized by a variety of
species which are replaced by other species
which are again replaced….
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Primary succession
Lifeless area without soil begins being inhabited by
variety of species
 Dominant species are often autotrophic prokaryotes,
lichens, & mosses to start replaced by grasses, shrubs,
& trees
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Secondary succession
Existing community is cleared by a disturbance that
leaves the soil intact
 Ex. Species inhabiting a forest after a fire
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Biogeographic features affect community
biodiversity
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Geographic location
Species diversity is higher at equatorial region compared
to seasonally disturbed higher latitudes
 Evapotranspiration rate is higher at equatorial regions
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Size
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Larger geographic areas have a greater number of
species as long as all other factors are equal
Models for community organization
 Bottom-up model
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Suggests alteration of biomass at lower trophic
levels will influence the higher trophic levels
Ex. Adding nutrients to soil increases plants, then
herbivores then carnivores
Top-down model/trophic cascade model
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Postulates that predation controls community
organization
Ex. Removing lake predator increases herbivores
which decreases plants which increases nutrients
Hypothesis for community structure
 Interactive hypothesis
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Community is an assemblage of closely linked species having
mandatory biotic interactions that cause the community to
function as an integral unit
Individual hypothesis
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Community is a chance assemblage of species found in an
area because of similar abiotic requirements
Generally accepted by plant ecologists
Models for individual hypothesis:
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Rivet model
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Most species in a community are associated tightly with others in its
community in a web of life
Redundancy model
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Web of life is loose
Increase or decrease in one species has little effect on other species
because there are redundant species to fill voids