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Coevolution
Coevolution involves the joint
evolution of two or more species as a
consequence of their ecological
interaction.
Interspecific competition is
a powerful ecological
force.
Symbiosis – an ecological coupling of two or more species
in a coevolutionary relationship.
Species A
Benefit (+)
Species B
Benefit (+)
Not Affected (0)
Harmed (-)
Not Affected (0)
Harmed (-)
Mutualism
Commensalism
Predation
Herbivory
Parasitism
Commensalism
No Interaction?
Amensalism
Predation
Herbivory
Parasitism
Amensalism
Competition
Plant-Animal Coevolution
Plants have no
opportunity to
“flee” or to “hide”.
Evolved defenses
reflect that.
Herbivores that attempt to
feed on them may be pierced
by the spines, and perhaps
even infected.
Many plants, particularly
those in arid climates,
produce sharp spines to
protect themselves from
herbivores.
Other plants may produce
chemical defenses.
These are often referred to
as secondary chemical
compounds.
Tobacco plants produce nicotine, which disrupts the metabolism of insects
feeding on the leaves.
Seeds of some morning glories
contain d-lysergic acid.
It is believed that this leads to
increased predation on insects
that feed on the seeds.
Horseradish, and other members of the mustard family, produce mustard
oil. This is a tissue toxin that provides protection from insects.
Milkweed
Milkweed and dogbane
produce cardiac glycosides
which are toxic to insects.
Dogbane
Mutualisms
Interactions can
be favorable to
both species
involved.
Cleaner fish
This small, brightly stripped cleaner fish of the wrasse family is collecting
a meal about the relaxed mouth of a large reef fish, Nassau Grouper,
which benefits from the “cleaning.”
Some ants and aphids
have evolved an
interaction in which
the ants protect the
aphids, and transport
their eggs.
The aphids produce
“honeydew” from tree
sap, which is utilized
by the ants.
Attini ants live in the New World tropics and culture fungus in the
genus Leucocoprini.
Leaf-cutter ants—mutualism
Above ground, ants cut small
pieces of leaves and carry
them to their underground
nests where the chewed
leaves enrich soil. Into this
soil, bits of fungi are planted
that grow and provide food for
the ants.
The ants carry on
their bodies the
bacterium
Streptomyces
which produces
antibiotics to fight a
fungal parasite.
Mutualism—fish
The small Spanish hogfish dashes into the mouth of a willing barracuda where it feeds on
debris and parasites. The hogfish gains a meal and the barracuda gains a cleaning.
Ants and Acacias
Acacia is widely distributed in tropical regions.
In Mexico, Acacia cornigera has a close, mutualistic
association with the ant Pseudomyrmex ferruginea.
FIGURE 10.3 Ants and Acacias-Mutualism
(a) Ants feed off the Beltian bodies produced at the tips of leaves by the acacia tree and off
nectaries along the stems. (b) Ants live in the hollow, swollen thorns of the acacia. The
ants protect the acacia from phytophagous insects and from overgrowth of competing
species of plants.
How could such a close relationship evolve? Perhaps…..
1. Acacias developed thorns for protection from herbivores.
2. Ants began to use acacias as nesting sites.
3. Ants that did not defoliate the host plant would be able to continue
nesting there. In addition, if they attacked neighboring plants of other
species, the host acacia would benefit and so would the ants.
4. Ants would be predisposed to definding their nest sites. This
behavior could easily be extended to defending the host acacia.
5. Finally, any acacia that produced a food supplement (such as
nectaries or Beltian bodies) would support more ants and thus be
favored.
Honeybees and Flowers
A major evolutionary
advance of the
Mesozoic Era was the
appearance of the
flowering plants, or
angiosperms.
While the
gymnosperms that
preceded them relied
largely on the wind for
pollination, many
angiosperms use
animal vectors to
transfer pollen.
Among the best known
flower pollinators are
honeybees.
Honeybees are
attracted to flowers for
nectar and pollen.
They have specialized
“pollen baskets” on
their legs which are
filled with pollen
during flower visits.
In the visits, the
honeybees transfer
pollen from one flower
to another.
Hummingbirds
have a similar
coevolved
relationship with
flowering plants.
Flower of an orchid
Note the
distinguishing
nectar guides,
the spots near
the center of the
flower.
Mutualism—birds and crocodiles
This African crocodile relaxes and holds its mouth open. This signals Egyptian Plovers to
enter and safely feed on fouling parasites and debris. The crocodiles gain a cleaning, and
the plovers a meal.
Mutualism—oxpecker
This red-billed oxpecker forages for parasites on the backs of African ungulates. Here the
oxpecker is working around the neck of domestic cattle. Parasites tend to collect along the
back of the neck where scratching cannot dislodge them. The oxpecker gains a meal, and
its customers get rid of parasites.
Commensalism
In some cases,
interactions are not
symmetric, i.e. one
organisms benefits
while the other is not
impacted.
Large African
herbivores are often
followed by
insectivorous birds
like the cattle egret.
Orchid flowers that
mimics specific
female wasps
The flower’s
mimicry attracts
male wasps that
arrive
attempting to
mate. Instead,
the males only
get doused with
pollen, which
they carry to
the next
expected
amorous
rendezvous.
Skunk cabbage
Rolled within its large
leaves are the
reproductive parts of
the plant. When these
mature, a pungent
odor is released,
drawing in insects that
naturally seek such
odors. In searching
within the flower for
the odor, they become
covered with pollen,
which they carry to
other plants as they
continue their search.
Protective Coloration
Camouflage--stone plants
These plants of dry and desert areas collect water within their tissues and occur in spare
habitats where they could be easily spotted by grazing or browsing herbivores. However,
their unusually rounded shape seems to make them appear like uninteresting stones,
which are overlooked and these plants escape being eaten.
Camouflage—inedible
The resemblance of these insects to inedible plant parts affords them some protection from
prowling insect-eating predators, such as birds.
Camouflage—coloration and shape
This dwarf seahorse (center) is camouflaged within the branches of this colonial sea fan.
Reef, Solomon Islands.
Histrio histrio – the sargassum angler
Brush katydid
Camouflage—arctic hare
This hare depends upon its white color to blend into the snowy background. When
discovered, it turns to speed to make an escape from predators.
Harbor seal pup
The white coat of the harbor seal pup affords some camouflage with the ice and snow upon
which it spends much of its early life when it is especially vulnerable to predators.
Camouflage—predator
This stonefish is encrusted with various creatures of the coral reef, camouflaging it to
unsuspecting prey that cruise by.
Startle response, eyespots on butterfly
Flashed suddenly when approached, the eyespots on the wings of some butterflies are
thought to confuse the insect-eating bird with its own predator, such as an owl, causing the
bird to pause and give the butterfly a chance to escape.
Startle Response - Eyespots
When discovered in its cryptic disguise, some moths and butterflies can
flash eyespots on their wings, startling the predator, and giving it an extra
moment to make its escape. (b) The eyespots are thought to confuse the
insect-eating bird with its own predators, such as an owl, causing the bird to
pause.
Mimicry I
Müllerian
mimicry—Many
bees, yellow
jackets, and wasps
have a common,
bright yellow/black
warning pattern,
which they can all
back up with an
unpleasant sting.
Batesian mimicry—
Harmless syrphid
flies evolved a
similar color
pattern, taking
advantage of the
avoidance of the
yellow/black
pattern.
Mimicry II
a) Batesian mimicry
between toxic
monarch (model) and
harmless viceroy
(mimic), left and right,
respectively. b) An
example of Müllerian
mimicry, where both
ecologically
sympatric pairs are
distasteful, and both
have warning
coloration.
Life-cycle of monarch
Adult monarch
butterflies are
protected from birds
and other predators
by the toxins in their
tissues. These
toxins are
incorporated from
the milkweeds they
feed on as larvae
(caterpillars).
FIGURE 10.11 Blue Jay Learning Aversion to Distasteful Monarch
(a) This hand-reared blue jay, having never eaten a monarch, rips off the wings and
gobbles down the body. (b) The toxins quickly make the blue jay sick, and it spits up the
monarch. Thereafter, even if presented a monarch lacking such toxins, the blue jay refuses
it.
Dodo bird (extinct)
The flightless dodo lived on
the island of Mauritus off the
coast of Africa until the last
bird was killed in 1681. It fed
on plants and seeds, including
the seeds of the Calavaria
tree.
These seeds had evolved
thick coats to survive the
passage through the grinding
gizzard of the dodo. With the
extinction of the dodo, these
seeds no longer made such
an abrading trip through the
digestive tract, the coat
remained thick, and the young
tree embryo could not so
easily germinate.
Flicker Frequency ?
A newborn watersnake shown crawling (a, c) and motionless (b, d). In motion, the
snake’s banding pattern looks evenly gray, as it would when exceeding the flicker
frequency of a predator. (From Pough 1976.)