Oceanic islands provide strong evidence for evolution. Coyne discusses the difference between life on continental islands, such as the British Isles, and oceanic isles, such as Hawaii, on pages 100-109. Recall that continental islands were "once connected to a continent but later separated," but oceanic islands were "never connected to a continent" (Coyne 100). Many mammals, amphibians, reptiles, and fishes never evolved in oceanic islands unless introduced by man. How do oceanic islands differ from continental islands and support the theme of evolution? Think about the different adaptive radiations and why life on these islands is unbalanced. Site specific examples of these adaptations, and explain why they relate to evolution.
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Oceanic islands don't sit on continental shelf and the majority of these islands are formed from volcanoes. Unlike oceanic islands, continental islands lie on a continental shelf. The fact that many species on the oceanic islands are never evolved supports the theme of evolution. On islands far from continents there is less predation and many natural resources rarely exploited by human interaction. The lack of predation allows the animals to survive without selective advantages that would otherwise help them adapt, survive, and reproduce. Furthermore on an isolated island, no new species on being introduced into the environment, so every animal has a very secure niche. Because of it is hard to have adaptive radiations, which are caused by a new organism occupying a vacant niche. For example, on Lake Victoria, "over 300 species of cichlid fish adaptively radiated from one parent species in just 15,000 years (Source A)." Adaptive Radiation can also be cause by innovation. For instance if a species evolves and creates new ecological niches, this would allow for adaptive radiation, but since, many species on oceanic islands don't evolve this does not often happen.
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ReplyDeleteI disagree with Jessica and Anika when they say that evolution does not occur on oceanic islands. Coyne gives several examples of animals that have evolved on oceanic islands like the Galapagos finches and the Hawaiian honeycreepers. Both the finches and honeycreepers are found on oceanic islands and hve shown great evolution. On the Galapagos islands there are fourteen species of finches all filling a different ecological role. The same goes forthe honeycreepers of Hawaii.
ReplyDeleteBut to answer the question about the lack of mammal, amphibian, and reptile evolution on oceanic islands, well we can just look in the book. Coyne clearly addresses this issue. Land mammals, reptiles, and amphibians cannot reach an oceanic island through long-distance dispersal like birds, plants, and insects can. On continental islands, one can find many land animals because the island was once connected to a cotinent. But on an oceanic island, the only way for organisms to arrive is by flying or swimming in the ocean. Most mammals (with the exception of bats) cannot fly and therefore cannot inhabit an oceanic island, unless previously introduced by humans. Birds on the ther hand are "capable of flying great distances over the sea, carrying with them not only their own eggs but also seeds of plants they've eaten (which cangermibate from their droppings), parasites in their feathers, and small organisms sticking to mud on thir feet" (104). Reading Coyne's explanation, it seems pretty logical that land animals would not be present on oceanic islands, causing such an unbalanced biodiversity. The organisms present on oceanic islands also closely resemble those present on the nearest shore.
The whole idea of oceanic islands makes sense only when viewed through the lens of evolution. Creationism cannot explain why mammals, reptiles, and amphibians are missig on oceanic islands or why the organisms thtdo inhabit oceanic islands are so similar to those on the nearest shore. Evolution, however, makes sense. Accidental dispersal is the key. Coyne says: "the inhabitants of oceanic islands descended from earlier species that colonized the islands, usually from nearby continents, in rare events of long-distance dispersal" (108). In this statement Coyne says it all. Accidental dispersal is a major component of evolutionary theory and completely refutes creationism; for that reason, oceanic islands give great evidence of evolution.
A reason that many mammals, reptiles, and amphibians didn't evolve in oceanic islands could be that there wasn't a need to. The animals already living on oceanic islands were able to reproduce and survive without changing their genetic material. Like Jessica said, there are no predators on the island that required the organisms on the island to evolve into mammals, reptiles, and amphibians because there was no benefit into evolving to those exact animals. The animals on oceanic islands evolved into something that would provide with some advantage that ensures their survival on the oceanic island. Evolving into mammals, reptiles, and amphibians don’t give that animals an advantage on the oceanic island. Mr. Coyne has said on page 101 that introduced species by humans wiped out and endangered the native species. Because there was no need for the animals to evolve into mammals, reptiles, and amphibians, the animals already living there couldn’t defend themselves against the introduced mammals, reptiles, and amphibians because they had never experienced anything like those animals before and therefore didn’t have the right genetic material to survive against the introduced animals.
ReplyDeleteIn continental islands there is a need for animals to evolve into mammals, reptiles, and amphibians. Because of the different climate on continental islands compared to oceanic islands there is a natural selection to evolve into amphibians, reptiles, and mammals. Each these new animals possess a new natural selection may it be wings to fly way from predators or being able to go into both aquatic and land areas (http://www.springerlink.com/content/u1174111j6476782/). Evolving into amphibians, reptiles, and mammals help the survival of the species in the continental environment. For example, mammals, the latest type of animals, has evolved to have hair and have mammary glands which produce milk for their young (Campbell 720). Animals evolved into mammals because the new traits of hair and mammary glands were beneficial to them in their environment. The hair protects the animal from the cold and the mammary glands help nourish the young when they are too young to be able to get food for themselves. These traits however don’t benefit the animals on oceanic islands because of the different environments.
This prompt is an example of the theme interdependence in nature. Animals always evolve but what new organisms it evolves into depends on its environment and surrounding. The oceanic island environment determines the advantages an animal should have to survive in its environment. The continental islands environment determines the advantages an animal should have to survive in its environment. Since the islands are different, the advantages are going to be different so different animals are going to be able to survive each different environment.
Let me get this straight: Anika Ghosh is proposing that mammals, reptiles and amphibians evolved many times over and over again in different places where there was some sort of environmental need for them?
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