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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 Saylor URL: www.saylor.org/BIO102 Subunit 7.4.1 The Saylor Foundation Saylor.org Page 1 of 4 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 Saylor URL: www.saylor.org/BIO102 Subunit 7.4.1 The Saylor Foundation Saylor.org Page 2 of 4 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. Saylor URL: www.saylor.org/BIO102 Subunit 7.4.1 The Saylor Foundation Saylor.org Page 3 of 4 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 The Saylor Foundation Saylor.org Page 4 of 4