Species Interactions

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Species Interactions
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• 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.

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PREDATION
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PREDATION

• Early observations indicated that predator-prey
  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.

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• 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.

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• 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.

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• 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.

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• 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. 

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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.

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• 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!

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• 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.

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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.
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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.
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A scorpionfish rests immobile on a coral reef in
the Philippines, 60 feet below the surface,
camouflaged against the colorful tapestry of the
reef.
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• 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.

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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.
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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
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• 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.

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• 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.

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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.
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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
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PARASITISM
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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.
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Human Parasities roundworms (intestinal
cavity) Tripanosoma gambiense causes African
sleeping sickness Human liver fluke ( a
flatworm)
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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
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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.
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• 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
• female cowbirds remove host eggs from the nest
• nestling cowbirds compete with the host
  nestling.  Cowbird nestlings are usually much
  larger and more aggressive than nestlings of host
  species. 

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SYMBIOTIC RELATIONSHIPS
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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

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Goby fish and shrimp
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• 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.

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Crustose lichens cling to the bare, exposed
surface of metamorphic rock in the Colorado
Rockies, where only the hardiest pioneer
organisms can survive
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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.
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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.
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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.
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Labroides dimidiatus inspecting the mouth of a
giant moray eel  
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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.
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COMMENSALISM
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• 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.

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• 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

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• 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.

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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.

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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.
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• 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

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• 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

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• 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.

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• 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

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• 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

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• 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

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• 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

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• Interaction between two species in which one
  feeds on the other is a) competition    b) a
  community
•    c) an ecosystem    d) predation 
•    e) symbiosis

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• 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

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• 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.

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• 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

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• 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.