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among organisms
 Generate stability within an ecosystem
 Are types of density-dependent limiting factors
 Competition
 Predation
 Symbiosis
 Competition
 Orgs. of same
or diff. species
want to use
same resource
@ same
place/time
 Competing for light,
water, space, nutrients
 Competition
 Orgs. of same
or diff. species
want to use
same resource
@ same
place/time
 Predation
 One org.
captures and
feeds on
another org.
 Mud dauber wasps sting and
paralyze spiders. They seal them in
mud nests for their young to feed.
 Predation
 One org. captures and
feeds on another org.

Ladybeetle about to
devour an aphid
 Predation
 One org. captures and
feeds on another org.
Symbiosis
 Two sp. living
closely
together
 Three types…
Symbiosis
 Mutualism:
Both orgs.
benefit from
each other
(+/+)
Symbiosis
 Mutualism:
Both orgs.
benefit from
each other
(+/+)
 Clownfish are frequently found in
the tentacles of sea anemones,
which typically capture their prey by
paralyzing them with discharged
cnidoblasts (nematocysts) , and
then ingesting the animal within the
gastrovascular cavity. Studies have
shown that a component of
clownfish mucus inhibits the
discharge of these cnidoblasts.
© Gregory G. and Mary Beth Dimijian
A remarkable 3-way mutualism appears to have evolved between an ant, a butterfly caterpillar,
and an acacia in the American southwest. The caterpillars have nectar organs which the ants
drink from, and the acacia tolerates the feeding caterpillars. The ants appear to provide some
protection for both plant and caterpillar.
A fly agaric mushroom (Amanita muscaria) and a cone of Eastern White Pine are
side by side on a New Hampshire forest floor in October.
A G.
sapling
of Eastern
Hemlock
© Gregory
and Mary Beth
Dimijian
sends sprays over the mushroom, and wintergreen adds a splash of red. The pine and
fungus form a partnership in which underground filaments of the mycorrhizal fungus
invade the roots of the pine, and both provide essential nutrients to each other. Both
partners have their reproductive structures above ground.
© Gregory G. and Mary Beth Dimijian
Tiny fig wasps reproduce inside unripe figs and can be seen if the fig is cut open at the right
stage. These wasps and fig trees are "obligate mutualists," meaning that they cannot reproduce
without each other. A parasite of the mutualism is seen in the inset, with a long ovipositor with
which she lays her eggs inside the fig.
Symbiosis
 Commensalism:
One species
benefits, the
other is neither
helped or
harmed.
(+/0)

Barnacles on a gray whale
A critical phase in the life cycle of plants is the
proper dispersal of its seeds. Many wonderful or
strange adaptations have evolved to insure this
dispersal. One of these adaptations is the
evolution of recuved spines on the seeds or
seedpods to attach the seeds to the fur of
passing vertebrates who carry the seeds away
from the parent plant. In the case of humans, fur
is replaced by pants, sweaters, socks, and other
pieces of clothing. Plants, therefore, anticipated
the invention of velcro from several million years.
The plant benefits from the relationship by the
dispersal of its seeds. The vertebrates are not affected except, perhaps, by
being annoyed.
One of the most famous examples are the burdocks, common weeds found
along roadsides and in empty lots and fields. The species on the left is the
Great Burdock (Arctium lappa). The seed heads (burs) of burdocks long
spines with hooked tips. The hooked tips catch onto the hair of passing
vertebrates (cows, deer, dogs, humans) and the burs are carried elsewhere
until they finally drop off or are pulled off by the carriers.
The Monarch butterfly (Danaus plexippus) feeds
as a larva on species of milkweeds (Asclepias
spp.). The milkweeds contain a group of
chemicals called cardiac glycosides. Cardiac
glycosides are poisonous to vertebrates
(although not to invertebrates). The larvae store
these cardiac glycosides and the later adult
contains them as well. If a bird (or other
vertebrate such as a mouse or frog) eats a
Monarch it finds them distasteful to begin with
and is later sick. Experimentally birds learn to
avoid Monarchs. The Monarch advertises its
inedibility by a bright orange and black
coloration.
The Viceroy (Limentis archippus) is not
distasteful and does not contain cardiac
glycosides. However by mimicing the the
pattern of the Monarch it is also avoided by
birds and other vertebrates that have learned to
avoid the Monarch. This particular relationship
is called Batesian Mimicry.
The
Demodicid
Demodex
folliculorium
< 0.4mm long
Lives in pores
and hair
follicles, usually
on the nose,
forehead, cheek,
chin, and in
roots of
eyelashes
The
Demodicid
Demodex
folliculorium
Live head down,
feeding on secretions
and dead skin.
Can lay 25 eggs.
They grow, leave to
mate and find other
follicles.
Symbiosis
 Parasitism:
One species
lives on or in its
host, harming
it. (+/-)
 A tomato hornworm is covered with
cocoons of pupating braconid
wasps.
Pediculus humanus (head louse) adult.
Dirofilaria immitis
dog heartworm
Adult Rhodnius prolixus
taking a blood meal
through human skin. The
reduviid insect transmits
the parasites which cause
Chagas disease in feces
deposited near the site of
their bite. Scratching or
rubbing by the person
bitten can transfer the
parasites into the body via
the wound or other sites
such as the eye.
Human tapeworm
tapeworm
 Sheep tapeworm
 Head – called scolex
 Body segments – proglottids
 Each body segment
has ovaries and testes
(hermaphroditic)
 Each segment can reproduce another worm (called
gravid [fertile])