Sunday, April 5, 2009
The Chain Reaction
On page 261, Carroll talks about how humans have influenced the destruction of entire ecosystems indirectly and directly. Carroll specifically talked about how overfishing has affected “complex webs of interactions (261). Can you go into more detail of how the disappearance of one species from an ecosystem can affect a complex web? Be sure to include information about trophic levels in the food chain. Also be sure to address the balance preserved by different species i.e. the lynx and the hare. Also address other ways humans have influenced the ecosystem other than overfishing.
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In Carroll's example of eliminating part of the complex webs in the ecosystem on page 261, he uses sea urchins, kelp and cod to explain the problems of over fishing. Since the population of cod have decreased, the amount of sea urchins consumed have decreased. Since the urchins eat the kelp, the kelp has been suffering while the urchins seemingly take over. While eliminating just one species in this relationship, there arise many problems for everyone involved.
ReplyDeleteEcosystems have four main components: the environment, consumers, producers and decomposers. The decomposers obtain energy from wastes or dead organisms and start the flow of energy up to producers and consumers. Each level has its own trophic level and a food chain is the flow of energy between these levels.
Food chains in the ecosystem involve the transfer of energy between producers, consumers, decomposers and the environment. Moving up the chain, less and less energy is transferred to the predator. Therefore, the top of the food chain usually contains the least amount of energy. Even one change in this chain can effect every organism involved.
When studying the populations of the hare and the lynx in comparison, one could see that they are very similar in variation. When the amount of hares increases in a certain area, the population of the lynxes soon increases because of the availability of more food. However, when the population of the hares increase, the lynxes can no longer be supported by the abundance in food and they soon decrease, also. This shows how two different organisms in the same food chain directly affect one another.
Over fishing by humans has created much disturbance in the food chain in the marine ecosystem. However, other behaviors by humans have also caused disturbances. One is deforestation. By eliminating much of the environment that food chains get their energy from, humans have caused many disturbances in forest ecosystems. Organisms lose their homes, protection and energy sources.
Another example of human interference is their involvement with the spreading of non-indigenous organisms. For example, humans, without necessarily knowing it, transfer organisms from their native homes to a foreign place while traveling. The new species being introduced to a new ecosystem and food chain can significantly cause problems. Now, there is more food available for some organisms, and other organisms are preyed on more often. Human activity can inadvertently cause major disturbances in the ecosystem around them.
We have talked about this in biology since day 1 of regular biology in 6th grade! ☺ Basically, the problem with the disappearance of one species from an ecosystem is that all the species that live there rely on each other in one way or another. For example, we rely on spiders to kill mosquitoes. One article stated that “researchers found a jumping spider in East Africa that not only craves on blood full mosquitoes, but specifically on those loaded with the deadly malaria parasite. "These predatory spiders could help control the lethal disease," scientists say.” This is interesting because many people HATE spiders and would rather kill all of them than ever see them again. But, research is now showing that spiders are essential to the protection of human kind. Weird, huh?
ReplyDeleteLikewise, there is an extremely delicate balance between every species and how they interact. The interaction does not necessarily need to be through direct contact, but, like the spiders with the mosquitoes, humans rely on the spiders but do not need to directly interact with them.
The disappearance of one species can be completely detrimental to an entire ecosystem because the species rely on one another. According to an experiment done by the scientists James H. Brown, Thomas G. Whitham, S. K. Morgan Ernest, and Catherine A. Gehring, research has shown “that complex dynamics of species populations reflect interactions with other organisms and fluctuating climate; genotype x environment interactions affect responses of species to environmental change; herbivore-resistance traits of dominant plant species and impacts of "keystone" animal species cascade through the system to affect many organisms and ecosystem processes; and some environmental perturbations can cause wholesale reorganization of ecosystems because they exceed the ecological tolerances of dominant or keystone species, whereas other changes may be buffered because of the compensatory dynamics of complementary species.” This means that many things can affect the delicate balance of an ecosystem and it must not be taken lightly. Species lower on the trophic levels and lower on the food chain are much more important than the higher ones because they essentially start out the whole web. The plants are extremely important because they feed the herbivores who then feed the carnivores who feed the decomposers. If plants were to disappear, the rest of the trophic levels would essentially fall apart. It is possible that some species could slowly adapt to life without a certain species of plant, but the ecosystem would be completely turned upside down.
This experiment also brings me to the fact that humans have much to do with ecosystems and how balanced they are. The fact that we have so many cars letting out so much CO2 into the air is causing major problems in ecosystems everywhere. It is causing the ozone layer to slowly disintegrate in places which is letting more UV rays into the earth and killing many animals, including humans, through cancer. Likewise, it is causing a greenhouse effect, which is starting global warming. This is drastically altering normal ecosystems and causing the extinction of many important species. According to another article, “U.S. autos emit more than 333 million tons of carbon dioxide each year, more than one-fifth of the nation's total carbon dioxide emissions. Any serious effort to fight global warming must include cutting auto emissions.” We must start trying to alter the damage cars do to the environment or else we are going bring the human race to extinction. We need the species that are on earth right now because they allow us to keep the balance we need in our environment to keep us alive. We need food, right? Well if all the animals go extinct, we won’t have much to sustain ourselves with, will we? Therefore, Carroll is right; although he discussed a slightly smaller problem on a smaller scale, it can and will lead us to the same end.
http://news.softpedia.com/news/Killer-Spiders-That-Prey-Only-Blood-Full-Malaria-Mosquitoes-44364.shtml
http://www.sciencemag.org/cgi/content/abstract/293/5530/643
http://www.edf.org/page.cfm?tagID=1126
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ReplyDeleteCorrect maintenance of the food chain is paramount for several reasons. Oxford biologist Charles Elton, in the 1920's, pointed out the length of a food chain is limited to about 4 or 5 trophic levels. Within these 4/5 levels exist two main types of species, the dominant species and the keystone species. The dominant species in a community is the one with the highest overall biomass. The consequences of removing a dominant species from the community actually may not be catastrophic. This has been seen before, as humans have unknowingly been the culprits several times. One example given by Campbell is the American chestnut, which used to make up nearly half of the canopy. Because of the introduction of the a fungal disease called chestnut blight by humans to New York City, the species is now absent in the canopy. While 7 species did become extinct as a result, the overall negative impact was minimal, as other species seemed to have taken over the role as the dominant species. The other major role, as mentioned above, is that of the keystone species. The difference between a dominant and a keystone species is that while a keystone species may not have abundant numbers, it does have a large impact on the community through its various ecological roles. In order to demonstrate the importance of a keystone species, Robert Paine performed an experiment on the west coast of North America. He removed Pisaster ochraceous, a predator of the mussel Mytilus californianus, and then observed. What he recorded was the monopolization of space by the mussel, which because it was left unchecked through the absence of the sea star, was able to exert its dominance over the other species inhabiting the same area, as the species diversity declined to about 5% of what it was with the sea star. Even though the sea star was not particularly numerous, it was crucial to keeping the balance and allowing for greater species diversity. Another terrific example of a keystone species integral to the overall well-being of its community is the sea otter. Once an abundant predator in the North Pacific Ocean, fur trade conducted by the Native Americans and French nearly obliterated the entire population. After recieving protection through an international treaty, the sea otters were able to recover to "very high densities". The sea otter feeds on sea urchins which consequently feed on kelp. Although the populations of both urchin and kelp remained at relatively stable levels while the sea otter was present, after the removal of the sea otter, sea urchin population skyrocketed, while kelp population predictably fell precipitously. This demonstrates that throughout the various communities of the world, it is extremely important to maintain vital species such as the keystone species, while the same cannot be said for the dominant species.
ReplyDeleteHumans, through the introduced species, have influenced the South American ecosystem. The book delves deep into this topic, and one of the species it focuses on is the African Honeybee (1097). It may not have had such negative impact on the Brazilian society had it not been for its aggressive nature. This characteristic led them to drive out the native Italian honeybee, upsetting the balance of things in South America, and eventually North America (it has ventured into Mexico and the Southern United States). The reason for this ferocity stems from the species' upbringing in Africa, where the bee had to fight for its resources (in contrast to American bees, as beekeepers have eased conditions), resulting in the bee being naturally selected for its tenacity and aggressiveness. This has resulted in genetic pollution, a gradual process where the non-native (introduced) species, due to its greater overall fitness, is able to wipe out the native plants and species through reproduction. The weaker organism dies off, while the stronger organism (the African bee in this case) is able to spread (pollute) its own genes.
http://en.wikipedia.org/wiki/Introduced_species
Campbell Textbook