Thursday, April 16, 2009
Horny Sheep
On pages 254-256, Carroll discusses the effect of evolution and mutation on the populations of big horned sheep. As humans have hunted away the largest sheep with the biggest horns, the leftovers' childrens' children have become less attractive to their kind and as a result breeding has dropped. Find another example of such a phenomena, where evolution has led to a decrease in proliferation, and actually inhibited an organism from reproducing as it should.
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There are many examples of human impacts that have caused an organism to not be able to reproduce, or reproduction has decreased due to the human impact. Many fish deal with being overfished, meaning that human capture this fish to sell for food. The fishermen aim to catch the bigger and older fish. Since these are the fish being captured the species over time mature faster and can therefore, reproduce less. For instance, the Atlantic cod matured around 8 to 10 years, but this has been reduced to about 6 years. An Atlantic cod may lie between 2.5 and 9 million eggs in a single spawning, and they can spawn as soon as they are mature, but research has shown that the age of maturation in present day is 2 years, but the fish do not spawn till about 7 years. This being seen many fishing has been stopped to restore the fish population. Much time is needed in order for the fish population and maturation to return to its original state. There are now many fish that have early maturation and will pass this along to their next generations, but in order for the maturation period to increase there must be a random mutation. Carroll discusses in the book how this evolution takes a lot of time. But, we hope there are some fish that have late maturation and may reproduce to create more of these fish. By closing off fishing the populations may grow, but as soon as fishing opens again and the larger and more mature fish are targeting we will enter the same problem as before. There is a cycle being formed, but we may just be driving fish to extinction. The smaller fish are easily targeted by predators and they will be decreasing in numbers along with the targeted fish by fishermen. The Atlantic cod is one of many examples that have reduced reproduction because the maturation of this organism has decreased greatly due to human impacts on the environment.
ReplyDeletehttp://www.fao.org/docrep/003/V4865E/V4865E05.htm
http://www.iiasa.ac.at/~dieckman/reprints/BaulierEtal2006.pdf
http://marinebio.org/species.asp?id=206
On page 254, Carroll’s discussion of sheep shows a vivid example of evolution. Because of the human interruptions, there have been less and less big-horned sheep to reproduce. However, big horns are what is looked for during mating. Now, because of their decline, reproduction has also slowed. This has thrown off the population of this species and many others that have been prey or predators.
ReplyDeleteThere have been countless examples when humans have been an influence on the extinction or harm of another species. The two biggest factors that cause extinction are climate changes and human behavior. One of the major types of human behavior that has affected the most animals is deforestation.
Deforestation has been just a huge devastation for animals because of its permanence. Humans have taken away food, hunting grounds and homes from animals. This is a major setback for animals to survive and reproduce. Without a home and food to support themselves, or a family, animals are less likely to reproduce.
A specific example of humans interfering with a specific resource from animals would be elephants. For years, humans have poached elephants for their ivory tusks to make things like piano keys and billiard balls. However, since humans target elephants with bigger tusks, there has been a decrease in the amount of elephants with large tusks. It has been proven that male elephants use their tusks in mating to attract other elephants. Since human behavior has decreased the size of tusks in elephants, there has been decreased reproduction and an overall decrease in the size of elephant’s tusks.
http://www.eleaid.com/index.php?page=elephanttusks
http://en.wikipedia.org/wiki/Extinct
http://berkeley.edu/news/media/releases/2004/09/30_.shtml
What happened to the big horned sheep could be called “Unnatural selection”, as coined by Carroll. Due to the presence of hunters, these big horned will likely be colloquially called the small horned sheep soon. The money from the hunts is used towards conservation of nature because most believe that the eradication of a few rams will not majorly affect the population of rams as a whole. However, this is the opposite of really happened. Because hunters exclusively hunted rams with other the largest horns, the population of large horned rams decreased. Female rams also desired large horned rams as mates. “Mating success increases with dominance rank and horn length” (Carroll 254). Horned rams grow their large horns between the ages of two and four and continues growing more after age six. Unfortunately, many rams are shot before the age of eight years and even before four years. This has significantly reduced the population of rams with very large horns. Natural selection has favored the growth of smaller-bodied, smaller horned rams than their larger counterparts that are killed by hunters.
ReplyDeleteHumans create unnatural selection in the environment; when humans select for particular traits in certain animals, such as the bighorn ram, they inevitably affect the evolution of certain species and thus, affect their population. Another problem is that humans seem to have no perceptible carrying capacity, “the maximum population size that a particular environment can support at a particular time with no degradation of the habitat” (Campbell). However, most all species do have a carrying capacity. Carrying capacity is never a fixed number but varies due to environmental conditions; humans have ingenuity in that they are able to eliminate environmental conditions, such as epidemics of certain diseases such as polio. To solve this problem, Alexander Fleming, a human, discovered penicillin and used it to treat polio. Vaccinations were thus used by humans, with the exclusion of chiropractors and anti-vaccine groups to treat such diseases. This is artificial active immunity and induces the immune system to create memory cells from a weakened or dead pathogen. However, it is also important to note that while the human has grown indefinitely so far, it cannot do so forever. While humans will probably not be hunted, there will be a limited number of resources, such as water, in the (near) future.
A similar happening occurred with the population of cods. Due to technology developed by humans, drying and salting cod made it easier for fishermen to transport large amounts of cod; as a result, with no knowledge of overfishing, fishermen from all of Europe overfished cod from the North Atlantic coast. The cod population dropped 99.9% from its previous population. Humans were the dominant species in this hunter-prey relationship. Humans had the highest biomass, the sum weight of all individuals. Humans affect the ecosystem negatively by activities such as logging, clearing huge swaths of forest for urban development, mining, and farming.
To solve the cod problem, the federal government then started to buy boats to discourage overfishing and created an offshore fishery in hopes of helping the cod population recover from the ecological blow. In spite of this, only smaller fish were ever produced. The oldest and largest fish were favored by fishermen, similar to how hunters favored rams that were larger and had larger horns. When fishermen fished for the largest cod exclusively, these cods were removed from the ecosystem and then natural selection favored the smaller fish. Also, without cod, a sea predator, other predator species experienced a population boom. Cod eggs were rapidly consumed and hurt the cod population; the cods’ reproductive ability was permanently damaged to humans’ previous overfishing of them. By losing large populations of the cod population, 99.9%, making them almost extinct, the ecosystem became less genetically diverse. The cod and its predation of certain species was a limiting factor to those certain species; without that limiting factor, those species experienced a population boom without a population bust. For example, in the case of the snowshoe hare and lynx, there was a cyclic boom and burst series of the populations of both species. The snowshoe hare population would depend on food and predation; when food was abundant, there was a population boom and when predation was high, there was a bust. This happened similarly to the lynx. This boom and bust cycle applies heavily to one-species predation animals. If the cod specifically hunted, there would have been a large boom population growth with no cod population to limit them. If there were other hunters of the prey, then that may have been an eventual limiting factor.
Megan Brasier has also pointed out another species with a human predation problem, causing unnatural selection. She writes, “For years, humans have poached elephants for their ivory tusks to make things like piano keys and billiard balls. However, since humans target elephants with bigger tusks, there has been a decrease in the amount of elephants with large tusks.” This is even more similar to the rams because the length of the elephants’ tusk decreased and thus, so did the reproduction rate as mating became difficult.
When occurring naturally, populations will affect one another. For example, some populations of the stickleback back were induced to change the shape of its spine. Some stickleback fish has reduced pelvises. This was due to different types of predation in its ecosystem. To sticklebacks that populated the surface of the water, long spines protected the fish from being eaten by large predators, like other larger fishes. However, this was the opposite for sticklebacks that lived near the bottom of the ocean floor. Dragonfly larvae hunted stickleback offspring because of their long spine; thus, these sticklebacks eventually favored a reduced pelvis. The reduced pelvis, controlled by Pitx1, probably occurred as a result of a beneficial mutation and natural selection favored stickleback fishes with this mutation.
Humans have had a vast impact on this world we live in. Sometimes we think that our species is the greatest and we should have the right to do whatever we want without regard to the other species that inhabit the earth. They have much right as us to live freely in this world. However, this is not the case as this is the survival of the fittest. Human intervention can be felt in many species. As Megan, Kim, and Jennifer have all talked about deforestation, the overuse of fishing, and the amenities that other animals present such as tusks in elephants. Some more examples of how human intervention is decreasing the reproduction of certain animals is also evident in Rhinos. Rhinos are big animals that are herbivores that have thick protective skin and are commonly found in parts of Africa and Asia. The rhino’s most prized asset is its horn. The horn is composed of keratin, a protein that also makes up our finger nails and hair. The horn is used in traditional Asian medicine and as well as daggers. The powder of the horn was commonly used to treat diseases and other epidemics that were occurred. It is still used in some areas to treat for malaria. While many laws have made it illegal for the hunting of rhinos for the extraction of the horn, poaching still occurs and the horns still get around through the black market. The horn of the Rhino is supposed to represent power, as they use their horns to compete for the right to mate. Only the dominant male gets the right to mate. With out the horns, the Rhino’s have trouble mating because of the lack of the aggressive nature without the horn. The rhino’s have decreased in mating and they are in serious danger of being extinct. The Indian Rhino is down to only 2700 animals left in the wild, and the white rhino only has about 9000 left in the wild.
ReplyDeleteIf we continue to poach these poor rhino’s, these animals which have roamed the Earth for so long will become extinct. Although nature is the survival of the fittest, we should be taking advantage of the fact that we have such complex minds to develop unending technologies to poach and kill rhinos. Every animal has its right to live on this planet, and it should be granted. If this continues, the diversity of our planet will diminish.
http://en.wikipedia.org/wiki/Poaching
http://en.wikipedia.org/wiki/Rhinoceros
http://news.softpedia.com/news/6-Amazing-Things-About-Rhinos-and-their-Horns-79342.shtml
Personally, I think all of the above commenters and the prompt writer misread Carroll’s words- I think that Carroll is implying that if these rams were transplanted into another herd, they wouldn’t get a mate at all. The major reason for this is how bighorn sheep win mates, and that is through head butting fights, quite like deer do. Thus, big horns are necessary- they increase surface area for pushing, and are able to take more damage than thin, weak horns, which will break off after repeated headlong conditions, which would cause the ram to lose. Females are attracted to the winners- so instead of no females reproducing, they are instead most likely settling for the rams that, in other colonies, would lose. Unfortunately, that is what is more likely to cause the fall of the ram- instead of choosing for strength and speed, weak and slow rams are winning mates and by doing so, ensuring that their genes reproduce- which means that the next generation of rams will be slower, and slower, until it reaches the point where the ram just can’t fight off or outrun its predators. Unnatural selection does not select for the fittest, it selects for the weakest to live.
ReplyDeleteHonestly, humans do this all the time, especially when it comes to something like forest animals. If it looks good to us, if it’s strong or has the attributes that a mate would like, the redneck probably values it too, but instead to show off to his buddies the next weekend. Deer are the common example, but as has been mentioned by multiple people, the same happens with elephants, hunted down for their Ivory. Fish are hunted down for their size- in fact, fishing is a competitive sport now- and the biggest fish wins. Of course, this is more because fish are being hunted in record numbers, and overfishing is a risk to several species, but hunting is a risk to the sheep as well as the best of mates being weeded out.
The thing is, as humans, we are burning through out supplies at such a rate that we could be the downfall of ourselves- though no where near our current carrying capacity, our overfishing of the oceans and lakes, as well as hunting for sport and not for food, could have a domino effect of epic proportions, in which we eliminate nearly everything else. While I’m not saying everybody should go out an eat veggies, a moderate stance is the key- people should cut down on the overconsumption and indulgences, especially in times like these, and perhaps we could then stick around a while longer.
http://en.wikipedia.org/wiki/Cod#Breeding
http://en.wikipedia.org/wiki/bighorn_sheep
(last post?)