Download The phrase symbiotic relationship refers to a close ecological

Unit 7 Reading
“Symbiosis”
The phrase symbiotic relationship simply refers to a close ecological relationship
between two different species. These relationships differ along a spectrum from
positive to negative interactions. If both species benefit from the interaction, the
relationship is considered to be a mutualism. When one species benefits and the
other is not impacted, the relationship is considered to be a commensalism.
When one species benefits and the other species is harmed, the relationship is
considered to be either parasitic or predatory or herbivorous. If both species are
impacted negatively through a competition over limited resources, the
relationship is considered to be competitive.i
Symbiotic relationships can vary in intensity. If the organisms are dependent
upon each other, the relationship is termed obligate. However, when the
organisms can survive with or without this relationship, it is termed facultative.ii
Symbiotic relationships come in many
forms that span the tree of life, and
they can be found in all ecosystems,
from terrestrial to aquatic. One of the
most diverse ecosystems which easily
contains examples of each
relationship type can be found in the
ocean, specifically coral reefs.
Figure 1. Coral reef
Coral reefs are considered to be among the most
ecologically diverse systems in the world. Coral
reefs are created from small coral animals which
are classified in the cnidarian group. As adults,
corals are stationary and are considered sessile.
They have small soft bodies, each protected by a
hard calcium carbonate skeletal structure that is
secreted continuously at the base of the body over
the animal’s lifetime.iii As coral feed, they use their
tentacles to reach out and capture small plankton
and fish. Once a potential threat swims by, the
coral retreat into their protective skeleton. Coral
Figure 2. Coral feeding
animals live in communities, and once old coral
animals die off and new ones settle on top of the dead skeletons, the coral reef
structures will build up substantially over time.iv
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Corals are not the only animals that
live within their reef structures.
Many species of fish, fungi, sea
turtles, algae, sponges, oysters,
clams, shrimp, crabs, sea stars,
urchins, and even other cnidarians
like jellyfish and sea anemones all
call these reefs home.v With such
a diverse assemblage of
organisms, it is easy to see how a
variety of ecological interactions
would evolve over time.
Figure 3. Aerial view of coral reef
In the coral reef system, a classic example
of a mutualistic relationship exists between
clown fish and sea anemones. Made
famous by Pixar’s movie, Finding Nemo,
clown fish often hide within the stinging
tentacles of sea anemones. The clown fish
get protection, while they also scare off
potential predatory fish of the anemone
and therefore provide protection for their
protectors.
Figure 4. Clown fish and anemone
A commensalism exists commonly in the coral reef between glass shrimp and
chocolate chip sea stars. Glass shrimp, as they are named, are almost
completely transparent. To hide from predators, they often hop on the back of a
chocolate chip sea star for camouflage, while the sea star is completely
unaffected.vi
Parasitic interactions are common in any ecosystem, and the
coral reef is no exception. Sea spiders are considered
parasites to table coral. Sea spiders often seek protection
and will pierce the body of the coral (called the polyp) and live
inside them.
Figure 5. Sea spider
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Herbivory is illustrated in coral reefs by several species, including the long-spined
sea urchin as well as herbivorous fish species. These urchins and fish will graze
on algae that are commonly found throughout the reef, which will essentially take
over and negatively impact the community if populations are not kept in check.vii
Predation is also common in these reef
communities, and a classic example involves the
barracuda fish and the
parrotfish. Barracuda fish
are fierce predators and
regularly seek out prey such
Figure 6. Barracuda fish as the colorful herbivorous
parrotfish. Another example, which reveals some
complexity in the coral reef, involves the saddled
butterflyfish and the sea anemone. We mentioned earlier
that clownfish protect the anemone against their predator,
which happens to be a saddled butterflyfish!viii
Figure 7. Saddled butterflyfish
There are many more types of interactions within not only the coral reef
community but in communities all over the world. However, these examples give
a glimpse of the complexity that can arise over a long and complex evolutionary
history!
i
Marietta College, “Symbiosis,” n.d., http://www.marietta.edu/~biol/biomes/symbiosis.htm.
ii
University of Michigan, “Ecological Communities: Networks of Interacting Species,” 2008,
http://www.globalchange.umich.edu/globalchange1/current/lectures/ecol_com/ecol_com.html.
iii
Environmental Protection Agency (EPA), “Coral Reef Protection: What Are Coral Reefs?” n.d.,
http://water.epa.gov/type/oceb/habitat/coral_index.cfm.
iv
ibid.
v
ibid.
vi
Canisius College, Canisius Ambassadors for Conservation, “Mutualism,” n.d.,
http://www.conservenature.org/learn_about_wildlife/great_barrier_reef/mutualism.htm.
vii
The Nature Conservancy, “Coral Reefs,” 2012,
http://www.reefresilience.org/Toolkit_Coral/C3a1_Herbivory.html.
viii
Public Broadcasting System (PBS), “Coral Reef Connections: Predators and Prey,” 2001,
http://www.pbs.org/wgbh/evolution/survival/coral/predators.html.
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Pictures:
Figure 1. Coral Reef
http://upload.wikimedia.org/wikipedia/commons/d/d0/Coral_reef_at_palmyra.jpg
Figure 2. Coral Feeding
http://upload.wikimedia.org/wikipedia/commons/9/90/Lobophyton_%28soft_coral
%29_with_extended_polyps.jpg
Figure 3. Aerial View Coral Reef
http://commons.wikimedia.org/wiki/File:Coral_Reef_aerial.png
Figure 4. Clown fish and Anemone
http://commons.wikimedia.org/wiki/File:Clown_fish_amphiprion.jpg
Figure 5. Sea Spider
http://upload.wikimedia.org/wikipedia/commons/2/27/Sea_spider.jpg
Figure 6. Barracuda Fish
http://commons.wikimedia.org/wiki/File:Barracuda(kok).jpg
Figure 7. Saddled Butterflyfish
http://upload.wikimedia.org/wikipedia/commons/1/16/Saddle_Butterflyfish_1.jpg
Saylor URL: www.saylor.org/BIO102 Subunit 7.4.1
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