The Ecological Niche
Niche - the role a species plays in a community;
its total way of life
Habitat - the place in which an organism lives
out its life
Habitat
The type of environment where an organism normally
lives.
lives
(e.g. a stoney stream, a deciduous temperate woodland,
bottomland hardwood swamp, a bayou)
Niche
i h
The niche
Th
i h off a species
i consists
i t of:
f
• Its role in the ecosystem (herbivore,
carnivore, producer etc)
• Its tolerance limits (e.g.
g soil p
pH,,
humidity) – its limiting factors
• Its requirements for shelter, nesting
sites etc., all varying through time
Limiting
i ii
Factors
•
•
•
•
•
Amountt off water
A
t
Amount of nutrients
Temperature
Amount of space
Availability of mates
Biotic
i i and
d Abiotic
bi i Factors
• What is a biotic factor?
– Any biological influence on an organism.
– Includes all other living organisms in the
ecological community.
• What is an abiotic factor?
– Any physical, non-living influence on an
organism.
i
• Both determine survival and growth of an
organism as well as ecosystem productivity.
productivity
The combination of all
the factors that describe
where in a habitat an
organism can live
describes the organism’s
organism s
“fundamental niche.”
Extend to “multidimensional hypervolume” for many factors
For two factors the niche can be
represented a two-dimensional shape
S
Species
i A
Niche represented
by a 2-dimensional
area
Separate niches
i h
Species B
Species A
No overlap of
niches.
niches
So coexistence is
possible
Two species can have overlapping niches
Species
p
B
Species C
Interspecific
competition
occurs where the
niches overlap
Many species have overlapping niches
Species
Habitat
Other foods?
mockingbird
floor
berries, insects
chickadee
canopy
insects
squirrel
q
canopy
py
insects, mushrooms,
fl
flowers,
seeds
d
mouse
floor
seeds, insect larvae
Fundamental and Realized Niches
Species commonly do not exploit their entire niche.
Th utilize
They
ili only
l a portion
i off their
h i niche.
i h The
Th portion
i
they utilize is called their “realized niche.”
Species are often restricted from utilizing their entire
niche due to the presence of other species.
A
Humiditty
H
Humiditty
H
Species A by itself
Species B by itself
T
Temperature
t
H
Humidity
y
Species A and B together
A
B
Temperature
B
T
Temperature
t
The realized niche is
smaller than the
fundamental niche
When species coexist through utilization of different types of
resources or different ranges of a limiting resources it is called
“Resource Partitioning” or “Niche Partitioning”
Anolis lizards in Cuba live in the same area but exploit different
microhabitats
Specialization
p
avoids competition
p
Species C
Species B
Evolution by
natural selection
towards
separate niches
Species B’
Species C’
Specialization into two separate niches
Species under continual competition will sometimes evolve
because of selection against those individuals that suffer the most
severe competition
Finches in the Galapagos
Islands feed on seeds and
their beak size determines
the size seeds they can eat
When found on different
p
) the beak
islands ((allopatric)
sizes are similar
When found on the same island (sympatric) they have divergent
beak sizes - greater difference when sympatric than when
allopatric is called “Character Displacement”
Competition for seeds is highest on intermediate sized seeds - one
species specializes on large seeds, the other on small seeds
Classic example - interaction between barnacles - Chthamalus
and Semibalanus
Chthamalus lives in the
intertidal zone
Semibalanus lives in the
subtidal zone
If Semibalanus
S b l
i removedd
is
Chthamalus also utilizes the
subtidal zone
Semibalanus is unable to live
in the intertidal zone due to
d i ti
desiccation
Semibalanus excludes Chthamalus from the subtidal zone through
its rapid growth - undercuts or crushes Chthamalus
The realized niche is smaller than the fundamental niche for
Chthamalus
A species’
p
role in the
ecosystem can often
be partly described
by the way it
captures energy
Autotrophs
Organisms that synthesize their own complex, energy rich,
organic molecules from simple inorganic molecules
Autotrophs can also be called “producers.”
Heterotrophs
Organisms that obtain complex, energy rich,
organic compounds form the bodies of other
organisms
g
((dead or alive))
Heterotrophs can also be called consumers.
Detritivores
ii
Heterotrophs that ingest dead organic matter.
(e.g. earthworms, woodlice, millipedes)
Detritivores can also be called consumers.
Saprobes
Heterotrophic
p
organisms
g
that secrete digestive
g
enzymes
y
onto dead organic matter and absorb the digested
material. (e.g. fungi, bacteria)
Saprobes can also be called consumers.
Energy available for use decreases through the consumer
levels.