lecture 37 — biotic interactions
in ecosystems
lecture content
1. competition (niches and character displacement)
2. predation ( regulate prey behaviour as well as number, arms races)
forms of symbiosis:
3. parasitism (one species benefits at cost to the other)
4. commensalism (one species benefits, neutral for other)
5. mutualism (both benefit)
1. competition
arises because of resource limitations
Intraspecific competition: between members of same species
interspecific competition: between species
competitive exclusion principle: If two species compete for exactly the same
resource, one will drive the other to (local) extinction
ecological niche
= the position of a species within the ecosystem
if the habitat a species occupies is its ‘address’ then the niche it occupies is its
‘profession’
lecture 37 — biotic interactions in ecosystems 1
, niche if the sloth is tree-top large herbivore — very successful (sloths make up 50% of
rainforest mammal biomass)
fundamental niche = niche potentially occupied by a species
realised niche = niche actually occupied by a species
difference between these may be due to competition
e.g. the presence of one barnacle species limits the realised niche of another species
e.g. situation where two barnacle species are present results in them having two
different realised niches
removing one species of barnacles means the other can occupy its fundamental niche
can be competition in time as well as space
common spiny mouse and golden spiny mouse both live in deserts in middle east.
when they co-exist (=sympathy), common spiny mouse is nocturnal and golden spiny
mouse is diurnal (=active during day)
when living separately (=allopatry), both are nocturnal
shift in niche proved by experimental removal of common spiny mice
golden ones shift to being nocturnal
character displacement
a tendency for characteristics to be more divergent in sympatric populations (living
together) of two species than in allopatric populations (living separate) of the same two
species
results in reduced competition
e.g. variation in beak size between populations of two species of galapagos finches
lecture 37 — biotic interactions in ecosystems 2
in ecosystems
lecture content
1. competition (niches and character displacement)
2. predation ( regulate prey behaviour as well as number, arms races)
forms of symbiosis:
3. parasitism (one species benefits at cost to the other)
4. commensalism (one species benefits, neutral for other)
5. mutualism (both benefit)
1. competition
arises because of resource limitations
Intraspecific competition: between members of same species
interspecific competition: between species
competitive exclusion principle: If two species compete for exactly the same
resource, one will drive the other to (local) extinction
ecological niche
= the position of a species within the ecosystem
if the habitat a species occupies is its ‘address’ then the niche it occupies is its
‘profession’
lecture 37 — biotic interactions in ecosystems 1
, niche if the sloth is tree-top large herbivore — very successful (sloths make up 50% of
rainforest mammal biomass)
fundamental niche = niche potentially occupied by a species
realised niche = niche actually occupied by a species
difference between these may be due to competition
e.g. the presence of one barnacle species limits the realised niche of another species
e.g. situation where two barnacle species are present results in them having two
different realised niches
removing one species of barnacles means the other can occupy its fundamental niche
can be competition in time as well as space
common spiny mouse and golden spiny mouse both live in deserts in middle east.
when they co-exist (=sympathy), common spiny mouse is nocturnal and golden spiny
mouse is diurnal (=active during day)
when living separately (=allopatry), both are nocturnal
shift in niche proved by experimental removal of common spiny mice
golden ones shift to being nocturnal
character displacement
a tendency for characteristics to be more divergent in sympatric populations (living
together) of two species than in allopatric populations (living separate) of the same two
species
results in reduced competition
e.g. variation in beak size between populations of two species of galapagos finches
lecture 37 — biotic interactions in ecosystems 2
