Transcript PowerPoint - Susan Schwinning

MUTUALISM (+,+)
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Example: hummingbird
and a hummingbird
pollinated plant:
Species 2
Species 1
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Each population has a positive effect on the other.
d (ln N1 )
d (ln N 2 )
0
0
dN 2
dN1
In interspecific mutualism, species exchange goods
or services beneficial to the other species:
• food for food
• food for services
• services for services
To be a true mutualism, giving up the goods or
services should represent a cost to the organism.
Definitions:
Obligate mutualism: both species would not persist without
the other.
Facultative mutualism: both species can live without the
mutualistic species.
Symbiosis: a very close association between two species
(“living together”).
parasitic symbiosis
mutualistic symbiosis (obligate or facultative)
Plant-pollinator mutualism
(food for services)
One yucca species
can only be
pollinated by one
species of moth.
One species of
yucca moth lays its
eggs only inside
flowers of only one
species of yucca.
An obligate mutualism.
Ant-aphid mutualism
(food for services)
Ants are protecting
aphids from competitors
and predators.
Aphids squirt honeydew
that is eaten by ants.
A facultative mutualism.
Rhizobium-legume mutualism
(food for food)
Plants supply sugars to
the rhizobium bacteria
and shelter against toxic
levels of oxygen.
Rhizobium bacteria fix
nitrogen and export it to
plants roots.
A facultative-obligate mutualism.
Clownfish-sea anemone mutualism
(service-for-service)
Both species protect
the other from their
respective predators.
The clownfish has a
mucus on its skin
that protects from
the anemone’s sting.
A facultative mutualism.
Termite – intestinal flagellate mutualism
(food-for-service)
The flagellate digests wood and transforms it into food for the
termite, the termite provides a livable habitat to the flagellate.
An obligate mutualism.
Also a symbiosis
Müllerian Mimicry
(services for services mutualism)
Unpalatable species
that look alike all
teach their predators
the same message.
Young blue jay is offered the wing of a monarch butterfly.
Blue jay after eating the monarch wing.
Deters predators of both species
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Mutualism:
All toxic look-alikes benefit each other.
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Deters predators of both species
What should the isoclines of a mutualistic
relationship look like?
N2
N2
N1
N1
competition
mutualism
N2
N2
K2
K1
N1
K1
N1
K2
Mutualists always coexist.
Mutualism is facultative: each
species alone has a K.
Both species have higher densities at
the equilibrium when the mutualist is
there than when it is not there.
Negative K’s: neither species can live
on its own. Mutualism is obligate
If the species coexist, it is due to the
stabilizing effect iof competition with
other species.
Both species have a minimal viable
population size due to the mutualism.
N2
K1
N1
K2
Spc 1 can exist without spc 2 but not
vice versa. Mutualism is obligate only
for spc 2, not for spc 1.
Both species coexist or spc 2 goes to
extinction and spc 1 to carrying
capacity.
There is a spc 1-dependent minimal
viable population size only for spc 2.
Theoretical outcomes of two-species mutualism:
Obligate mutualism (neither species can persist on its own):
Coexistence or Extinction, depending on species densities.
Facultative mutualism (both species can persist on their own):
Stable coexistence at densities above each species’ single-species
carrying capacity.
Facultative-obligate mutualism (only one species can persist without the
other):
The obligate mutualist has a chance of going extinct.
Both species coexist if the obligate mutualist maintains high
numbers.
Deters predators of both species
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Mutualism:
All toxic look-alikes benefit each other.
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Deters predators of both species
Batesian Mimicry:
A palatable or harmless mimic exploits a non-palatable or
dangerous model
Monarch butterfly
(dangerous model)
Viceroy butterfly
(harmless mimic)
Monarch caterpillar
The sap of milkweeds contains
a mild toxin: cardiac glycoside
Milkweed
Viceroy
Coral snake (model)
King snake (mimic)
Robber fly (mimic)
Bumblebee (model)
Wasp (model)
Moth mimic
Beetle mimic
Fly mimic
What kind of a species
interaction is this?
Monarch butterfly
(model)
Viceroy butterfly
(mimic)
Prevents the predators from learning to avoid
Exploitation:
The mimic exploits the model
Monarch butterfly
(model)
Viceroy butterfly
(mimic)
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Deters predators of both species
Milkweed (nectar producing)
Lantana (no nectar)
Epidendrum
(no nectar)
Sexual baiting: some
orchids mimic female
wasps: male wasps will
copulate, orchids will get
pollinated and the wasp
will get nothing.
If cheating in a mutualistic relationship can produce an
exploitative relationship,…
and if cheating increases the benefit of the cheater,….
Then why are there so many mutualistic species
relationships?
Occasional cheating also occurs within
mutualisms:
Yucca-moth
mutualism:
sometimes moths
lay too many eggs
into the flower.
Some strains
of rhizobium
bacteria do
not produce
excess
nitrogen.
Why haven’t these mutualisms disappeared long ago?
Cheating must be sanctioned
(so that the cost of cheating exceeds the benefits of cheating.)
Yucca plants abort
fruits with too
many moth larvae.
All larvae die.
Rhizobia
strains that do
not export
nitrogen are
oxygen starved
by the host
plant and die.
Summary:
Mutualism is a mutually beneficial ecological interaction between two
species.
In mutualism, species exchange goods or services, at a cost to both
parties. However, benefits generally outweigh the costs.
Mutualism is obligate, facultative, or obligate-facultative.
Mutualistic relationships can be precarious: if mutually obligate, one
species’ demise leads to the other species’ demise as well.
There is a tendency for cheaters to invade or evolve from within. For a
mutualism to be evolutionarily stable, the cheater must be punished. If
the cheater cannot be effectively punished, the interaction may evolve
into an exploitation.