Monday, April 12, 2010
Evolution and Interdependence in Nature
In the chapter titled “What is Evolution?” Coyne discusses the history of life in terms of a tree “with all species originating from a single trunk” (7). This statement is saying that all species diverged from one common ancestor, implying that all species are somewhat related. Organisms are also related in the ways they interact with each other: symbiosis, predation, parasitism, competition, etc. Different relationships can either prove or even cause evolution, and so evolution goes hand in hand with the theme of interdependence in nature. Assess the validity of this statement. Do you feel that these two biological themes are at all related? If so, then how are they related? Give examples—using the book, Campbell, or any outside sources—of how interdependence in nature has caused or gives proof of evolution.
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I do feel that the biological theme of interdependence in nature and evolution are inter-related. I believe that the interdependence in nature is what causes some of the evolution of species.
ReplyDeleteThe theme of interdependence in Nature refers to competition, herbivory, or predation between organisms in nature. Interdependence in Nature is how organisms interact with one another in their ecosystem and community.
The interdependence in nature can increase the fitness of a species, such as in mutualism. For example, nitrogen fixation by bacteria in the root nodules of legumes is an example of a positive interdependence in nature, mutualism; the legumes benefit by getting the nitrogen they need to produce proteins and amino acids while the bacteria also benefit by getting food and energy from the plants.
According to Campbell, positive interdependence in nature can cause evolution; "mutualistic relationships sometimes involve the evolution of related adaptation in both species" (Campbell 1203). To support this statement, Campbell uses the example of flowering plants having the adaptation of nectar or fruit to attract animals that "function in pollination or seed dispersal" (1203).
The interdependence in nature can also decrease the fitness of a species, such as in parasitism (being the victim of a parasite) and predation (being the prey). For example, if a lion preys on an antelope, then the fitness of the antelope is decreased because it is food and not able to survive and reproduce.
As we know, evolution is a battle to survive and reproduce in an environment. If an organism is the victim of a negative relationship in nature, then its chances of surviving and reproducing are lowered. Through natural selection, those organisms who are able to overcome the negative pressures will survive, and those who cannot will die.
Therefore, interdependence in nature and evolution are related. Certain interactions between organisms in nature whether positive like mutualism or negative like parasitism will cause species who can best survive under those relationship circumstances to survive and reproduce.
I agree with Frank that the theme of interdependence in nature is related to evolution.
ReplyDeleteCompetitive exclusion and resource partitioning are two concepts that relate to the theme of interdependence in nature because the two concepts describe interactions between species that allow the species to either become extinct or survive and reproduce.
According to the principle of competitive exclusion, “Two species cannot coexist permanently in a community if their [ecological] niches are identical” (Campbell et al., 2008, p. 1,199). Of course, competitive exclusion is generally true because two species with the same niche must compete for the same components (i.e. food, shelter, gases, water, etc.) of the niche, and the two species are not equally fit to obtain the components of the niche. The more fit species will proliferate, while the less fit species will decline. Eventually, the less fit species will become extinct, as the species's population dwindles to zero. One way for the less fit species to survive and reproduce coexisting with the more fit species is by resource partitioning (i.e. changing niches). Natural selection will generally force one of two species with identical niches to undergo resource partitioning as an adaptation to a place where another species has the same niche; therefore, “evolution by natural selection can result in one of the species using a different set of resources” (p. 1,199).
It would be logical for two very similar species to have the same ecological niche if the two species live in different ecosystems. Therefore, the fact that, in the same ecosystem, two species that would have the same ecological niche if the two species were in different ecosystems would prove that the two species underwent resource partitioning and evolved niche differentiation.
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ReplyDeleteAs Frank and Yiding's responses suggest, an interdependence in nature is prominent in many aspects of evolutionary theory. To add on to their examples, this concept can also be seen in two types of speciation: allopatric and sympatric.
ReplyDeleteAccording to Campbell, "in allopatric speciation [...] gene flow is interrupted when a population is divided into geographically isolated subpopulations" (492). Coyne provides an example of allopatric speciation on page 175; a geographically isolated subgroup of a flowering plant will evolve to accomodate local pollinators, ceasing the possibility of interbreeding with its sister species. Here, new species in an environment depend on surrounding organisms to determine the effectiveness of new adaptations and to drive evolution of the new species.
In this example, the accomodation of local pollinators demonstrates the theme of interdependence in nature; the geographic location of flowering plants and the presence of other organisms in that area determines the flower's fate because of their close relationship, with the pollinators aiding reproduction in plants.
Sympatric speciation, on the other hand, "occurs in populations that live in the same geographic area" and is "less common than allopatric speciation" (Campbell, 494).
In this case, interdependence in nature is in fact the cause of the scarcity of sympatric speciation compared to allopatric speciation. As Coyne puts it, "the number of times that sympatric speciation has not occured given the opportunity [is surprising]" (185). Using the logic for speciation due to geographic isolation, a species in the same geographic location would not usually diverge because most of the time all members of the population would undergo similar adaptations since the surrounding environment and organisms on which the species depends are the same. Though some scientists are not convinced of its occurence, there is some evidence of the sympatric speciation of three-spined stickleback (http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/S/Speciation.html).