Transcript Mutualism and Commensalism

Mutualism and
Commensalism/
Coevolution
BIOL400
5 October 2015
Commensalism
and
Mutualism
Commensalism
 Close
association of two species that
benefits one, without benefiting or harming
the other
 Exs:
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Birds nesting in trees
Epiphytic plants (bromeliads, poison ivy, etc.)
Barnacles attached to whale heads
Algae on turtle shells
Mutualism
 Close
association of two species that
benefits both
Mutualism Categories
 1)
Trophic—both species derive nutritional
benefit

Exs:
Ants and acacias (Fig. 12.6 p. 217)
Fungi and algae in lichens
Mycorrhizae and trees
Fig. 12.6 p. 217
p. 217
Figs. 12.21& 12.22 p. 228
Douglas fir seedlings in sterilized
soil, with areas “contaminated”
with fungal spores
Mutualism Categories
 2)
Defensive/Cleaning—one species
benefits from cleaning by another (also
partly trophic)

Exs:
Cleaner fish
Screech owls and blindsnakes
Mutualism Categories
 3)
Dispersive—one species benefits from
dispersal of its reproductive products (also
partly trophic)

Exs:
Pollen
Seeds (fruits, elaiosomes)
Spores (certain mosses, fungi)
Keystone Commensals and
Keystone Mutualists

Species whose roles
in commensal or
mutualistic
interactions greatly
affect community
structure
 “Pulling” the keystone
would cause the
ecosystem to change
dramatically
Gopher Tortoise of SE U.S.
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Up to 100 feet of burrows
maintained by one tortoise
at any time
Periodically abandon
burrows to dig new ones
350 other species use
gopher tortoise burrows

At least one (the indigo
snake) is threatened by
declines in gopher tortoise
numbers
American Alligator
in the Everglades, FL
Dig “gator holes” as retreats during hottest part
of day
 May be only standing water during severe
droughts

Fig Wasps and Fig Trees

Wasps are pollinators
 Numerous species
(such as this emerald
toucanet) rely on fig
masting as periodic
food supply
Coevolution
Coevolution
 Reciprocal
selective forces of two species
on one another
 Evolutionary adaptive responses of each
species to the other
 May concern
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•
Physiology
Anatomy
Behavior
Life-cycle attributes
Fig. 2.11 p. 27
Coevolution in Mutualism
 Coevolution
is a necessary part of
mutualistic interactions


Ex: physiological, anatomical, and behavioral
adaptations of ants and acacias
Ex: same, in a pollination relationship
 Close
examination also demonstrates
antagonism in these interactions

Selection wouldn't have it any other way!
Antagonism in
Coevolved Mutualisms
 Producing
not enough nectar to satiate is
selected, as opposed to producing enough
to satiate
 Delaying fruit ripening until seeds are fully
developed
Species May Take Advantage
of Mutualistic Interactions

Fish that resemble
cleaner fish but
sneak bites from the
mouths of larger fish

Orchids that have
labella that resemble
female bees
Coevolution
and
Competition
Coevolution and Competition
 Species
that compete for limited resources
can coexist if their degree of overlap is
small enough, i.e., by partitioning the
resources
 Character displacement: divergence of
a characteristic related to resource use in
areas of geographic range overlap
Fig. 10.22 p. 182

Clearest when


A) each of the
sympatric species also
has an area of
allopatry
B) the two species are
quite similar in both
resource use and the
character related to it
in their respective
allopatric portions of
their ranges
Fig. 10.23 p. 183
Fig. 10.24 p. 184
HANDOUT—Moen and Wiens 2009
HANDOUT—Losos and de Queiroz 1997
Difficulty in Proving
Character Displacement

Character displacement is an historical process
 Stringent requirements for establishing it has
occurred:
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—At least partial allopatry (no evidence is possible if
sympatry is complete)
—Heritability (often assumed without certainty)
—No other unrelated reason for the divergence in
sympatry
—The two species must actually compete
(resources must be limiting)
Coevolution
and
Predation
Coevolution in
Predator-Prey Relationships
 Often
compared to an arms race, with
adaptation and counter-adaptation
Prey Defenses (Predator Counteradaptations)
 Anatomical
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Thorns
Spicules
Quills
Armors
(Giraffe tongues)
(Hawksbill turtle intestinal
lining)
(Fishers)
(Gulls/bivalves)
(Starfish stomachs/oysters)
(Jaguar jaws/tortoises)
HANDOUT—Meylan 1988
Prey Defenses
 Chemical
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Plant “secondary
compounds”
Bombardier beetle
Skunks
Salamandra
salamandra
Various toads and
frogs
Monarch caterpillar
Fig. 12.1 p. 211 & Table 12.1 p. 212
Fig. 12.3 p. 214

47 tree spp.
in Panama
Fig. 12.4 p. 215

Toxins may be
produced only in
response to
herbivory
 More toxins may
be produced in
most valuable
plant organs
Prey Defenses
 Behavioral
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Hiding
Running
Aggressive defense
Group living
Cryptic Coloration

Coloration that may
make an animal blend
into its environment
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Exs: Peppered moths
Kenyan chameleon
Spring peeper
Disruptive Coloration

Coloration that
confuses predator
against environmental
background

Exs:
Zebras
Garter snakes
Aposematic Coloration

Warning coloration
associated with
toxicity or other
chemical defenses

Exs:
Skunks
Dendrobatid
tree frogs
Mimicry

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Batesian:
Palatable/nonvenomous
species mimic
unpalatable or venomous
species
Mullerian: Similarity
among unpalatable or
venomous species
Eyespots—provide startle
effect
Cryptic mimicry—Prey (or
predator) resembles
inanimate object of its
environment
Fig. 11.22 p. 206
Left: Venomous Micrurus
Right: Nonvenomous Pliocercus
Coevolution
and
Parasitism
Coevolution and Parasitism
 Van
Valen's Red Queen Hypothesis is
another form of the arms-race concept
 Pathogens become more virulent, but
selection rapidly spreads any infection
resistance a host population has
 In the wild, infections tend to be less
virulent over time
Fig. 15.21 p. 277

No evolution of mice


Experimenter used
inbred genetic strain
Typhoid bacterium is
winning a one-sided
arms race