Ch 54 Community Ecology part 1 -...
Transcript of Ch 54 Community Ecology part 1 -...
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Community Ecology BIOL 221
Ch. 54
Overview: A Sense of Community
• biological community
• an assemblage of popula9ons of various species
• living close enough for poten9al interac9on
• interspecific interac<ons
• rela9onships between species in a community
• compe99on, preda9on, herbivory
• and symbiosis
• parasi9sm, mutualism, and commensalism
• Can affect the survival and reproduc9on of each species
• effects can be summarized as posi9ve (+), nega9ve (–), or no effect (0)
Community Interac<ons
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Interspecific Compe<<on • compe<<ve exclusion
• –/– interac9on
• occurs when species compete for a resource in short supply
• Strong compe99on leading to local elimina9on of a compe9ng species
• Compe99ve exclusion principle
• two species compe9ng for the same limi9ng resources
• cannot coexist in the same place
Ecological Niches • ecological niche
• The total of a species’ use of bio9c and abio9c resources
• Can also be thought of as an organism’s ecological role
• Ecologically similar species can coexist in a community
• if there are one or more significant differences in their niches
• Resource par<<oning
• differen9a9on of ecological niches, enabling similar species to coexist in a community
Ecological Niches
A. ricordii
A. insolitus usually perches on shady branches.
A. distichus perches on fence posts and other sunny surfaces.
A. aliniger A. distichus
A. insolitus
A. christophei
A. cybotes A. etheridgei
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• As a result of compe99on
• a species’ fundamental niche may differ from its realized niche
Realized Niches
Ocean
Chthamalus
Balanus
EXPERIMENT
RESULTS
High tide
Low tide
Chthamalus realized niche
Balanus realized niche
High tide
Chthamalus fundamental niche
Low tide Ocean
Character Displacement • Character displacement
• a tendency for characteris9cs to be more divergent
• in sympatric popula9ons of
two species
• than in allopatric popula9ons of the same
two species
• varia9on in beak size
• between popula9ons of two
species of Galápagos finches
Los Hermanos
G. fuliginosa G. fortis
Beak depth
Daphne
G. fuliginosa, allopatric
G. fortis, allopatric
Sympatric populations
Santa María, San Cristóbal
Beak depth (mm)
Perc
enta
ges
of in
divi
dual
s in
eac
h si
ze c
lass
60 40 20
0
60 40 20
0
60 40 20
0 8 10 12 14 16
Preda<on • Preda<on
• +/– interac9on
• one species (predator) kills and eats the other (prey)
• adapta9ons of predators
• claws, teeth, fangs, s9ngers, and poison
• Prey defensive adapta9ons
• Behavioral defenses
• hiding, fleeing, forming herds or schools, self-‐defense, and alarm calls
• Morphological and physiological defenses
• Cryp<c colora<on (camouflage) makes prey difficult to spot
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Aposema<c Colora<on • Aposema<c colora<on
• Animals with effec9ve
chemical defense
• oYen exhibit bright warning colora9on,
called
• Predators are par9cularly cau9ous
• in dealing with prey that display such
colora9on
• In some cases, a prey
species may gain
significant protec9on
• by mimicking the
appearance of
another species
• Batesian mimicry
• palatable or harmless
species mimics an
unpalatable or
harmful model
Batesian Mimicry
Hawkmoth larva
Green parrot snake
• Müllerian mimicry
• two or more
unpalatable species
resemble each
other
Mullerian Mimicry
Cuckoo bee
Yellow jacket
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Herbivory • Herbivory
• +/– interac9on
• refers to an interac9on in which an herbivore eats
parts of a plant or alga
• has led to evolu9on of plant mechanical and
chemical defenses
• and adapta9ons by herbivores
Symbiosis
• Symbiosis
• A mutualism where
two or more species
live in direct and
in9mate contact with
one another
Parasi<sm
• parasi<sm
• +/– interac9on
• Parasite
• derives nourishment from another organism
• Host
• which is harmed in the process
• endoparasites
• live within the body of their host
• Ectoparasites
• live on the external surface of a host
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Mutualism • mutualism
• +/+ interac9on
• interspecific interac9on that
benefits both species
• Obligate
• where one species cannot survive
without the other
• Faculta9ve
• where both species can survive alone
Acacia tree and ants (genus Pseudomyrmex)
Area cleared by ants at the base of an acacia tree
Commensalism
• Commensalism
• +/0 interac9on
• one species benefits
• and the other is apparently unaffected
• hard to document in nature
• because any close associa9on
• likely affects both species
Species Diversity • Species diversity
• The variety of organisms that make up the community
• Two components
• species richness and rela9ve abundance
• Species richness
• Total number of different species in the community
• Rela<ve abundance
• Propor9on each species represents of the total individuals in the community
Community 1 A: 25% B: 25% C: 25% D: 25%
Community 2 A: 80% B: 5% C: 5% D: 10%
A B C D
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Trophic Structure
• Trophic structure
• feeding rela9onships between organisms in a community
• key factor in community
dynamics
• Food chains
• link trophic levels from
producers to top carnivores
Carnivore
Carnivore
Carnivore
Herbivore
Plant
A terrestrial food chain
Quaternary consumers
Tertiary consumers
Secondary consumers
Primary consumers
Primary producers
A marine food chain
Phytoplankton
Zooplankton
Carnivore
Carnivore
Carnivore
Food Webs
• Food web
• Branching food chain with complex trophic
interac9ons
• More realis9c than food
chain
Humans
Smaller toothed whales
Baleen whales
Sperm whales
Elephant seals
Leopard seals
Crab-eater seals
Birds Fishes Squids
Carnivorous plankton
Copepods Euphausids (krill)
Phyto- plankton
Dominant Species • Dominant species
• Those that are most abundant
• or have the highest biomass
• Biomass is the total mass
of all individuals in a
popula9on
• Exert powerful control over the
occurrence and distribu9on of
other species