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Species Interactions
• Survival for living organisms is not just
responding to physical environmental factors.
It also involves interactions with other
organisms.
• Two species may interact as predator and
prey or parasite and host. In this interaction,
one species benefits (+) and the other is
negatively (-) affected.
• A predator is typically larger than its prey and
kills it, whereas a parasite is typically smaller
than its host and usually does not kill it or
does not kill it immediately.
PREDATION
PREDATION
• Early observations
indicated that predatorprey relationships were
cyclical. This idea gained
support from analyses of
fur trapping records of
the Hudson's Bay
Company.
• The number of furs
purchased at the
Company's forts was
meticulously recorded,
for well over 100 years.
• An analysis of the numbers of
snowshoe hares, and one of their
main predators, the lynx, shows
predator-prey cycle. Peaks and
valleys can be easily observed at
roughly 8-10 year intervals.
• Predation can be a strong agent of
natural selection.
• Prey defenses can be a stabilizing factor
in predator-prey interactions. Easily
captured prey are eliminated, and prey
with effective defenses (that are
inherited) rapidly dominate the
population.
• Examples include camouflage in the
peppered moth, and prey that are
nocturnal to escape detection.
• Predation can have far-reaching effects
on biological communities.
• A starfish is the top predator upon a
community of invertebrates living in
tidally inundated rock faces in the
Pacific Northwest.
• The rest of the community includes
mollusks, barnacles and other
invertebrates, for a total of 12 species.
• When the the starfish were removed,
an acorn barnacle and a mussel began
to occupy virtually all available space,
out competing other species.
• Species diversity dropped from more
than 12 species to essentially 2. The
starfish was a keystone predator,
keeping the strongest competitors in
check.
• Although it was a predator, it helped to
maintain a greater number of species in
the community. Its beneficial impact on
species that were weak competitors is
an example of an indirect effect.
DEFENSE AGAINST
PREDATORS
With predators always on the lookout
for a meal, prey must constantly avoid
being eaten. Any adaptation the prey
uses adds to the chances of survival for
the species. Some adaptations are
defense mechanisms which can give the
prey an advantage against enemies.
• There are three ways animals avoid
falling prey to a predator.
• The first is very direct and comes
naturally. Animals can use speed as a
very effective means of escaping
predators. You can't eat what you can't
catch!
• A second defense mechanism is
camouflage. One form, cryptic
coloration, allows the animal to blend in
with its environment to avoid being
detected. It is important to note that
predators also use cryptic coloration to
avoid detection by unsuspecting prey.
In the snowy environment of the Arctic, the polar
bear is white to avoid being noticed as it
approaches the seal, and the seal pup is white
to avoid being noticed by the bear.
A female katydid
blends with the
tropical vegetation
in the lowland
Amazon rain forest
of Peru. Her wings
mimic the mottling
of the surrounding
leaves.
A scorpionfish rests immobile on a coral reef in the
Philippines, 60 feet below the surface, camouflaged against
the colorful tapestry of the reef.
• Trickery can also be used as a defense.
False features that appear to be
enormous eyes or appendages can
serve to dissuade potential predators.
Mimicking an animal that is dangerous
to a predator is another effective means
of avoiding being eaten.
Munching on a plant
stem in Costa Rica's
Monteverde Cloud
Forest Reserve, this
Xylophanes
caterpillar has such
tiny eyes that you
would need a hand
lens to see them. The
red "eyes" and
pointed "stinger" are
both fake.
This tasty
nymph of an
insect in the
family Alydidae
assumes the
fraudulent
guise of an ant,
and forages on
plants in open
areas of
tropical rain
forest in Costa
Rica where
birds could
easily find it.
Unless an experienced bird calls its bluff, it
may owe its survival to its anatomical
mimicry of an ant
• The final defense is physical or
chemical combat.
• Some animals' physical features make
them a very undesirable meal.
Porcupines make it very difficult for
predators with their extremely sharp
quills.
• Chemical features can be
just as effective. We all
know what happens when
a skunk is scared!
• The dart frog also uses
chemicals (poisons
secreted from its skin) to
deter attackers. Any
animals that eat these
small frogs are likely to
get very sick or die.
Monarch larvae are
specialist
herbivores,
consuming only
host plants in the
milkweed family.
Milkweed makes
them poisonous to
most vertebrates
and provides
monarchs with an
effective chemical
defense against
many predators.
The Viceroy
butterfly. This is the
well known mimic
of the more
common Monarch
butterfly. Because
they look like the
bad tasting
monarch
butterflies, they are
often avoided by
predators
PARASITISM
This Caribbean soldierfish
is host to the parasitic
isopod attached to its head,
between its eyes. The fish
has no way of removing the
isopod which feeds on his
body tissues.
Human Parasities:
roundworms (intestinal
cavity); Tripanosoma
gambiense causes African
sleeping sickness; Human
liver fluke ( a flatworm)
Lampreys on Great Lake
fish
The opened up hinge area
of the Purple Hinged Rock
Scallop. Cliona celata is a
boring sponge which bores
as a parasite into mollusc
and barnacle shells
Birds are well known for their parental care, patiently
incubating their eggs and then bringing food to their young
until they are old enough to look after themselves. However,
certain birds, known as "brood parasites," lay their eggs in
the nests of other birds and do not provide any parental
care for their own offspring. Care that the "hosts" provide to
the young parasites is care denied to their own young. This
often has a detrimental effect on the reproductive success
of the hosts and may affect their population numbers as
well.
Brown-headed Cowbirds are one of the most well known
examples of a brood parasite. It hosts are species such
as warblers, tanagers, vireos, and thrushes. The populations of
many of these birds have been declining, partly due to
parasitism by cowbirds. Cowbirds affect the breeding success
of their hosts in two ways:
1. female cowbirds remove host eggs from the nest
2.
nestling cowbirds compete with the host nestling. Cowbird
nestlings are usually much larger and more aggressive than
nestlings of host species.
SYMBIOTIC RELATIONSHIPS
MUTUALISM
Mutualism is when two organisms of different species
"work together," each benefiting from the relationship.
One example of a symbiotic relationship is that of the
oxpecker (a kind of bird) and the rhinoceros or zebra.
Oxpeckers land on rhinos or zebras and eat ticks and other
parasites that live on their skin.
The oxpeckers get food and the beasts get pest control.
Also, when there is danger, the oxpeckers fly upward and
scream a warning, which helps the symbiont
Goby fish and shrimp
The shrimp digs and cleans up a burrow in
the sand in which both the shrimp and the
goby fish live.
The shrimp is almost blind leaving it
vulnerable to predators when above ground.
In case of danger the goby fish touches the
shrimp with its tail to warn it of imminent
danger. When that happens both the shrimp
and goby fish quickly retract into the burrow.
Crustose lichens cling to the bare, exposed surface of
metamorphic rock in the Colorado Rockies, where only the
hardiest pioneer organisms can survive
Leafcutter ants carry leaf fragments to their underground
nest in the lowland rain forest of La Selva Biological
Station, Costa Rica. The leaves will become food for the
symbiotic fungi cultivated by the ants, which in turn
provide food for the ants in the form of filaments swollen
with nutrients.
In the tunnels of the nest interior, members of the colony bring leaf
fragments back to feed the fungal garden (light-colored substrate),
and soldiers guard the queen, nearly hidden at right.
Avoiding antibiotic resistance for 50 million years: a
pathogenic fungus, Escovopsis attacks the fungal garden of
leafcutter ants. Some leafcutters carry on their bodies a living
bacterial colony (white patches on ant) which produces an
antibiotic that controls the growth of the pathogen . An
evolutionary "arms race" keeps the antibiotic effective.
Labroides dimidiatus
inspecting the mouth of a
giant moray eel
The anglerfish
uses its
bioluminescent
capability in its
hunt for food. The
fish dangles an
illuminated pod to
lure prey close
enough to be
snatched.
The bioluminescence for the lure is due to presence of
bacteria, that are endosymbionts. In a related adaptation,
anglerfish are dull gray, dark brown or black, and are thus
not visible either in their own light or in that of similarly
luminescent prey.
COMMENSALISM
• Anemone fishes (sometimes called clownfishes)
are tropical, reef fishes from the Pacific and
Indian Oceans.
• These fishes are unusual because they have a
close relationship with sea anemones.
• Sea Anemones consists of a hollow cylinder
surrounded by a crown of tentacles. The
tentacles are equipped with specialized cells
called nematocysts. Nematocysts are shaped
and function like small harpoons and contain a
poison sufficient to paralyze or kill small fish
and other reef inhabitants.
• The anemone fish lives
among the forest of
tentacles of an anemone
and is protected from
potential predators not
immune to the sting of the
anemone.
• The anemone fish is
protected from the sting
of the anemone tentacles
by a substance contained
in the mucous on its skin.
• the anemone treats the
fish as part of itself and
does not sting it
• A critical phase in the life cycle
of plants is the proper dispersal
of its seeds. One adaptation to
increase dispersal is the
evolution of recurved 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.
• The plant benefits from the
relationship by the dispersal of
its seeds. The vertebrates are
not affected except, perhaps, by
being annoyed.
Interspecific competition
• The interactions among species influence the
number and kinds of species that exist within
a community. Competition limits the number
of species that can coexist. Two species that
have similar niches compete very strongly.
The competitive exclusion principle states
that only one of the species can exist; the
other is out-competed and dies out.
Interspecific competition occurs in two ways:
1. Interference competition: involves
actual fighting over resources.
2. Exploitative competition:
consumption of resources by individuals
of one species limits availability to
another species.
RESOURCE PARTIONING
Species that share the same resources can coexist if
their niches are not too similar. Species evolve
differences in what they eat or where they feed such
that coexistence is possible. This is referred to as
resource partitioning.
Character displacement
• Populations of the same species that
compete for the same resources can
decrease competition by exploiting different
parts of their habitat.
• This will often lead to physical changes in
the populations as they become increasingly
adapted to a particular niche.
• This can lead to speciation and increased
biodiversity
• Ants live on acacia trees and are able to
feast on the sugar produced by the tree. The
tree is protected by the ants' attack on any
foreign insects that may harm the tree. This
is an example of :
a) parasitism b) commensalism
c) mutualism d) symbiosis
e) competition
• Which of the following relationships would
be symbiotic?
a) commensalism only
b) mutualism only
c) parasitism only
d) commensalism and mutualism
e) commensalism, mutualism, and
parasitism
• Which of the following is an example of a
mutualistic relationship?
a) Lichen.
b) Barnacles that grows on a rocky surface.
c) Tapeworm in the stomach of a mammal.
d) Cattle egrets feast on insects that are
aroused into flight by cattle grazing in the
insects' habitat.
e) An African bird benefits from sitting in
shade underneath an elephant.
• A form of species interaction in which one
of the species benefits while the other is
unaffected is called
a) parasitism b) mutualism
c) commensalism d) symbiosis
e) competition
• Symbiotic relationships frequently develop
between organisms that live in close
physical proximity to each other.
Female cowbirds often lay their eggs in the
nest of wrens, who unwittingly raise the
young cowbirds as their own,
This relationship is an example of
a) commensalism b) parasitism
c) mutualism d) competition e) nihilism
• Protozoans living in the intestine of a
termite secrete enzymes that digest
cellulose, providing digestive end products
of value to both organisms. This symbiotic
relationship could be described as
a) mutualism b) commensalism
c) parasitism d) saprophytism
e) competition
• The leaves of mistletoe plants
photosynthesize, but the roots of the
mistletoe plant absorb nutrients
from living oak trees. The symbiotic
relationship is best described as
a) mutualism b) commensalism
c) parasitism d) saprophytism
e) competition
• Interaction between two species in which
one feeds on the other is
a) competition b) a community
c) an ecosystem d) predation
e) symbiosis
• Interaction between two species as both
attempts to use the same environmental
resources is
a) competition
b) a community
c) an ecosystem
d) predation
e) symbiosis
• In large natural ecosystems, competition
between two species over time will usually
result in
a) each species occupying a slightly
different niche.
b) equal numbers of each species persisting
for a long time.
c) death of all members of one species
within a short time.
d) hybridization between the two species,
resulting in a third species.
e) None of these are correct.
• Which statement is NOT true about parasitism?
a) The host is generally larger than the parasite.
b) An efficient parasite usually kills its host.
c) Smaller parasites often live as endoparasites
within the body of the host.
d) Ectoparasites are attached to the outside of the
host's body by specialized organs.
e) Some organisms and all viruses are obligate
parasites and must live inside a host
• A keystone species is
a) an organism that acts as a commensal in a
host.
b) a predator that destroys many different
species in a community.
c) a mimic that has the same appearance as
another, poisonous species.
d) a prey species that must be present or the
predator species will die off.
e) a species whose removal causes major
shifts in other species in the community.