Monday, March 30, 2009
Overfishing and the Domino Effect
On page 261, the domino effect is mentioned. Explain what it is and how it connects to kelp deforestation. Also, mention overfishing and how it can affect the marine ecosystem. Why do/did people believe that the oceans were inexhaustible? Are there any specific examples of overfishing mentioned by Carroll?
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The domino effect is the process in which there is a balanced ecosystem where differing species are dependent on one another for survival. With the addition or subtraction of a single species the entire ecosystem can fall just as the tipping of one domino brings the entire bunch to the ground. In its connection with kelp deforestation, kelp is a primary source of food for sea urchins which then are consumed by otters and ground fish such as cod. The kelp are the primary producers and the otters and ground fish are then primary consumers. Due to overfishing, the population of ground fish has dwindled and fur hunting has caused otters to be killed. By drastically diminishing the number of otters and ground fish there is no way to keep sea urchin population in check. This means that the population of sea urchins will expand and with this expansion there is more consumption of kelp leading to a reduction of kelp until the entire population of kelp may disappear from that ecosystem. With the deforestation of kelp, the ecosystem is not only losing a primary food source but kelp is also used for hiding for smaller fish from predators, and also homes for certain species such as algae, shrimp, and sponges. By hunting a single species, an entire ecosystem may fall to the ground, unable to sustain itself with the loss of a vital player. Fishing may come in play again with the hunting of sea urchins, but even with sea urchin numbers decreasing the kelp will grow back but with no balanced ecosystem to return to.
ReplyDeleteOverfishing is the removal of too many fish to keep an ecosystem at stable state. The reason overfishing is such a large problem is that, due to the “domino effect”, as Carroll calls it, the removal of a large number of only one or a few species can lead to instability and degradation of an entire ecosystem. The reason for such drastic consequences relates to the community hypotheses that we learned about in the ecology unit.
ReplyDeleteThe interactive hypothesis states that a community is composed of species that are closely linked locked into association by mandatory biotic interactions that cause the community to function as an integrated unit. From this definition we can see that if one organism is removed, the link for this bound community has been broken, and as the web unfolds, the entire community is degraded.
People once believed that the Earth’s resources were inexhaustible because 1) the human population was much smaller and 2) our demands on resources were much smaller. As the industrial age came, populations and demands skyrocketed, and it has become a very real situation that many of Earth’s resources are running out, both the living and the nonliving.
To conclude, I would like to re-explain Carroll’s example of overfishing and the domino effect because it serves as a good example of yet another hypothesized model of organization in communities. According to Carroll’s description, the proposed community is a top-down model as we have learned. In a top-down model, predation ultimately controls the organization of a community, and any changes in the highest trophic levels of a community will be magnified throughout the lower trophic levels. In Carroll’s example, the otters and groundfish are the highest trophic levels which feed on the sea urchins, which feed on the kelp. According to the top-down model, a change in the level of otters or ground fish can possibly damage the entire community, an effect more easily referred to the domino effect. This, however, is also a demonstration of the interactive hypothesis, because one change in one species has affected the entire web of the community. When overfishing or excessive hunting occurs, the top two trophic levels of the otters and groundfish are made smaller, and the effect ripples through the lower levels because the level sea urchins increases, which causes the kelp to be consumed much more. With this rippling effect of the top-down model, each trophic level of food chain alternates in increasing and decreasing, however, ultimately every level of the community will harmed, because complimentarily as proposed by the bottom-up model, once the changes in the highest trophic level reaches the bottom, this ripple can be sent back upward, which will ultimately cause every level to be affected negatively.
http://www.un.org/events/tenstories/06/story.asp?storyID=800
Campbell Biology 6th Edition
Eric mentioned trophic levels, and that is exactly what the domino effect is. I would like to add a statistic: 10%. That is the estimated trophic efficiency of most trophic levels. Trophic efficiency is the percentage of production transferred from one trophic level to the next. This means that 10% of energy is transferred from primary producers to primary consumers. A “pyramid of production” is called a pyramid because that is what it looks like. The bottom, of the pyramid, the primary producers, use the most energy. The tertiary consumers at the very top barely use any energy compared to the energy available. The significance of this is huge. Most students in elementary school learn about food chains, with herbivores and consumers and so on. The whole thing is a straight line. In reality, it is more like a food web; a complicated mess of predator and prey, and therefore a complicated mess of energy needs. Due to the trophic efficiency in nature, a small occurrence at one trophic level can lead to a disaster at the opposite end.
ReplyDeleteTake the example of DDT. DDT was released into the water at 0.000003 ppm. In zooplankton it was 0.04 pm. By the time it reached birds, the highest trophic level, it was 22 ppm. There was an increase by 10 million times from the bottom trophic level to the top trophic level. Why is this? It’s how nature works. There is a crucial term for it: biological magnification. That’s essentially what the domino effect is. Biological magnification. Magnification occurs because the biomass at any given trophic level is produced from a much larger biomass ingested from the level below. Therefore a carnivore at the top can be very much affected by the ongoings of the organisms at the bottom of the trophic level.
This was a general overview of what the domino effect is and why it works. The specifics of kelp deforestation were covered by Kimberly and Eric.
Obviously, the domino effect has a lot to do with kelp deforestation, as Eric, Kimberly, and Theodore have all pointed out. However, the domino effect can be with anything, at any point in the chain of dominoes, but is more likely to have a bigger impact at the lower trophic levels, such as kelp and krill, which is another domino that Carroll mentions, with particular reference to the decline of whales, as well as to the decline of his beloved icefish. These species are called the keystone species- the ones at the center of it all, the ones that without the complete structure of the grid would fall apart- mainly due to the trophic level deviation, as Theo touched on. These species need to be at the levels that they are, as otherwise there would not be enough of them to supply the proper amount of energy to the rest of the ocean- when kelp gets cut out, energy has got to come from some where. And that’s how the domino effect starts- it’s actually one of the theories about dinosaur extinction- the dinosaurs, according to Lloyd et all thrived on gymnosperms- who were being out dominated by the angiosperms, better suited to live. Well, the reduction of gymnosperms is much like a reduction on kelp- without them, it’s quite likely that Superorder Dinosauria died due to starvation, unable to digest the angiosperms that were taking over, due to a lack of diversification. This means that the herbivorous dinosaurs in a location would die out- and then, without the herbivores to eat, so would the omnivores and the carnivores.
ReplyDeletePeople most likely believed the oceans were inexhaustible just due to their tremendous size- it’s mind boggling to think how huge our country is along, with its vast differences in climates, and then realize that is a small fraction of the land on earth, and then realize that land on makes up a quarter of the earth’s surface! That’s a lot of water, and it goes down a long ways! Can you really blame any common man, for standing at the beach and not being able to believe that we could deplete the ocean’s resources? It’s so vast and bountiful, yet, somehow, due to improved technology, we can do it, and that’s a horrible sign of how powerful man is- that it could wipe the Earth’s waters of life, without ever realizing that it was doing so in the process!.
The domino effect is a powerful one indeed. Carroll mentions in the future the possibilities of overfishing krill. Krill is another thing, like kelp, that seems near irreplaceable. Humans only fish a minor part of the krill population, but if krill fishing expands and the temperatures continue to rise, the algae which krill eat won’t be there, and then krill fishing will devastate the waters- especially with regards to the icefish, who depends on krill up north where few kelp can grow. Icefish, and other fish of the Arctic, are then in turn eaten by seals or polar bears or other animals of that nature. And eventually, if things like this continue, these animals, which we know so well, as they are taught to the children at a young age, will eventually go the way of the dinosaurs.
http://rspb.royalsocietypublishing.org/content/275/1650/2483
http://en.wikipedia.org/wiki/DInosaurs