Transcript PowerPoint - Susan Schwinning

ECOLOGICAL NICHES
The way an organisms “makes a living”
is that species niche.

Term first used by Grinnell in 1917 in a paper on the
Californian thrasher. For Grinnell: niche = habitat
requirements.

Elton’s niche (1927): an animal’s place in the community
(who it competes with, who it eats, and by whom it gets
eaten.

Hutchinson’s niche (1957): the set of environmental
conditions, defined by many variables, in which the
species can live.
Elton’s niche: a
place in the food
web:
Elton’s niche: a
place in the food
web:
Hutchinson’s niche:
the total set of all
physical conditions
in which a species
can be found.
Extend to “hypervolume” for many factors
Hutchinson’s niches get smaller when other species
are present:
Humidity
Spc B by itself
A
B
Temperature
Temperature
Spc A and B together
Humidity
Humidity
Spc A by itself
B
A
Temperature
ECOLOGICAL NICHES

Fundamental niche: the full range of conditions
under which an organism can exist.

Realized niche: the portion of the fundamental
niche occupied in the presence of other species.

For all niches: we recognize them only if at least
one species takes them.
WHAT IS SO IMPORTANT ABOUT NICHES?
Because the niche may explain what it takes for a
species to exist in a place, niche theory can
potentially answer many fundamental questions:
 How can so many species stably coexist?
 How does a niche come into being?
 Are all niches occupied?
 Is there any upper limit to how many niches (thus
species) there can be?
How many times can the total available energy (sunlight)
be subdivided to support another species?
Environmental Temperature
EXAMPLES

Fundamental and realized niches in space and time.

What happens to a vacant niche?

Does high diversity prevent invasion by a new species?
Two species of
barnacle
Chthamalus
Balanus
The two species live in different sections of rock:
Desiccation tolerance limits here
Predation tolerance limits here
The two species fundamental niche is where each
organism can settle and thrive in the absence of the other:
Here Balanus outcompetes
Chthalamus
Here Chthalamus outcompetes Balanus
growth
rate
Balanus larvae settle
Chthamalus larvae settle
low
middle
Location in intertidal zone
high
Balanus alone
Balanus
fundamental
niche
growth
rate
Chthamalus alone
Chthamalus
fundamental niche
low
middle
Balanus
realized
niche
growth
rate
high
Balanus and Chthamalus together
Chthamalus
realized niche
low
middle
high
Location in intertidal zone
Coyote (10 – 25 kg)
Food: sheep, poultry, mice, rabbits,
ground squirrels, other small rodents,
insects, reptiles, fruits and berries.
Red fox (4 – 8 kg)
Food: mice, voles, woodchucks, rabbits,
chipmunks, fruits, insects, birds and
eggs, carrion, garbage, amphibians, and
reptiles.
Fundamental Niche
Relative
food
use
Coyote
Red Fox
insects
birds
rodents
rabbits
Food item size
young livestock
Realized Niche
Relative
food
use
Coyote
Red Fox
insects
birds
rodents
rabbits
Food item size
young livestock
Animals trapped as a function of time
Diverse community of tropical rodents in Mexico
Castro-Arellano & Lacher 2009
Some ants forage at different times.
If ants forage at the same times, often not in the same place.
10:30
Vacant niches:
Fish gills have many
parasites.
Numbers vary from 0 to 30.
Fish populations can have up to 30
species of parasites, but most of the
time they have far fewer.
This indicates a missed ecological
opportunity, or empty niches.
Vacant niches, implications:
If every environment or community has many vacant
niches, many more species could share the available
resources.
Thus, it should often be possible to introduce new species
without losing resident ones.
Humans have either intentionally of unintentionally
introduced many species with mixed results.
•
naturalization: species gets added to the local species pool,
adding to local diversity.
•
Invasion: new species take over, replacing many species of
the local species pool, diversity declines.
Some introductions from Europe:
Some other introductions:
Invasive species in the habitat of origin are
harmless:
Invasiveness and invasibility:
What makes some species more aggressive in the new habitat?
Noxious invaders often have the following characteristics:
•
•
•
•
•
Sexual & asexual reproduction
Rapid reproduction
High dispersal
Phenotypic plasticity
Tolerance for environmental conditions (generalist)
Lack of natural enemies in the new environment
Lack of co-evolution with native competitors
What makes a habitat more invasible than others?
Disturbance of the native community
Recent history of ecosystem (generalist)
Low native diversity
More diverse communities often accommodate more exotic
species, however, exotic species may be less invasive in
diverse communities.
Plant species in Australian heath and shrublands
From Levine and D’Anotonio 2000
In controlled experiments, invasive species are indeed less
successful invading high-diversity plots.
Digitaria ischaemum (weedy C4 grass) and Crepis tectorum (weedy composite)
in Minnesota grassland plots:
Naeem et al. 2000
Summary:
1) The niche concept has been around for 100 years and has
had many different interpretations and applications.
2) Ultimately, niches do not explain species diversity (because
the species makes the niche, not the niche the species),
but the concept still makes us ask good scientific questions:
•
What does a species need to persist?
•
How is a species range/activity affected by the presence of other
species?
•
What makes a community vulnerable to invasion?
•
What makes a species a “hostile” or “benign” invader?