Coyne covers speciation and divergent evolution in Chapter 7: "Speciation is a splitting event, in which each ancestral branch splits into two twigs, which themselves split later, and so on as the tree of life ramifies. This means that the number of species builds up exponentially, although some branches are pruned through extinction" (Coyne 179).
Relate the concepts of speciation and divergent evolution to specific terms we learned over the summer when studying community ecology (Chapter 54 of Campbell). In other words, how do the community dynamics we've discussed, for instance responses to competition within a niche, lead to speciation? Answers may refer to the "splitting event" or the eventually "prun[ing] through extinction [of some branches]" (or both), and all responses should include an example scenario.
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Coyne’s point about “some branches [being] pruned through extinction” (179) relates to the concept of competitive exclusion. If there is a limited resource that two (or more) species are competing for, the species can’t coexist. One species will beat out the other because of a reproductive advantage. Campbell states that “in the absence of disturbance, one species will use the resources more efficiently and thus reproduce more rapidly than the other,” (1199) which will eventually lead to “local elimination of the inferior competitor,” (1199)
ReplyDeleteA good example scenario of this is seen in studies done by ecologist G. F. Gause. He took two closely related protists, Paramecium aurelia and Paramecium caudatum (blog won’t allow italics?). Putting both groups in stable conditions with the same amount of food being added each day, the species grew exponentially and leveled off at carrying capacity when grown separately. Then, when Gause cultured both groups together, P. caudatum went extinct because P. aurelia had a competitive edge in getting food. (http://www.biologyreference.com/Ce-Co/Competition.html) In this way, natural selection favored the species that had the edge, and the other species couldn’t migrate, didn’t adapt, and ended up dying. Competitive exclusion is an example of a mechanism that leads to the ‘pruning’ of the tree. This relates to the theme of interdependence in nature, because this competition between species is what leads to stability in an ecosystem- one species for every niche.
In addition to what the above poster has said, competitive exclusion caused by one species also influences the development of other, separate species. This is because that exclusion causes the superior species to become the dominant species, "the species in a community that are the most abundant or have the highest collective biomass" (Campbell, 1207). Furthermore, Campbell states that, "as a result, dominant species exert a powerful control over the occurrence and distribution of other species" (1207). Because, as the Campbell definition states, the dominant species is the most abundant species, that species also passively affects the development of other species that are able or not able to develop mutualistic relationships with the dominant species. An example given in the Campbell book is the American Chestnut tree. When a disease was accidently introduced that killed all the chestnut trees, several species of moths and butterflies that fed on the tree went extinct as well.
ReplyDeleteWhile dominant species can be caused by one species having a natural competitive advantage, there are many cases in the world where a dominant species is caused by an invasive species, where a species is transplanted from its native habitat into a new one. One such case is the introduction of the European Red Fox ([i]Vulpes vulpes[/i]) to Austrailian wildlife (http://www.environment.gov.au/biodiversity/invasive/publications/pubs/european-red-fox.pdf). Unlike the introduction of european honeybees to japan mentioned in Chapter 5 of Coyne's book, the red fox quickly asserted itself as one of Australia's dominant predators, which in turn severely reduced many native species that did not have adaptions to protect themselves from the fox.
In both of these cases, dominant species contribute to the pruning and branching of species. As stated earlier, dominant species influence the speciation of other species. Other organisms must develop adaptations to live with or protect from this species. Those species that cannot live mutualistically become extinct and are 'pruned.' Likewise, the loss of a dominant species is responsible for the pruning of organisms dependant on the dominant species, while also allowing other species that were inhibited by the dominant species to develop further.
An organisms may split and diverge once the species aren't able to share the same niche anymore. Once there isn't enough food or there isn't enough space in the previous spot for everyone to live on, someone has to change how they live or their niche. Once an organism is able to change niche, they are splitting or diverging from their original specie. Also if there is a limited supply of resources for the organisms living in the same place, one specie could wipe out the other like Radhe has said previously in her post. Either way no same organism can have the same niche because there aren't enough resources for all the organisms to survive and reproduce (http://www.tutorvista.com/ks/divergent-evolution-examples).
ReplyDeleteFor example the A. distichus(italics) and the A. insolitus(italics) are both lizards that eat the same insects. There is a lot of competition for food that there is no way that both species of lizards could live in the same area. As a result the A. distichus(italics) lives on sunny fence posts, and the A. insolitus(italics) lives on shady branches. As a result of the difference in niches the A. insolitus(italics) and the A. distichus(italics) don't have to compete over food. The lizard species had to diverge and split because there wasn't enough food for all the individual organisms (Campbell 1199).
I agree with what Kevin had said about species having to diverge and split if an invasive specie comes. The organism need to find a way to survive and reproduce and branching for a specie always them to do so. By branching away and forming a new niche, the new specie doesn't have to compete as much as before for resources essential to surviving and reproducing.