A primary succession occurs when the change in species composition than in a previous uninhabited environment. This means no soil exists when the primary succession starts. An example of a primary succession is recently formed lava from a volcano or bare rock surfaces. Therefore, in the ecosystem animation it, is a secondary succession. I say this because a secondary succession happens after a disturbance of some sort.
An example of a secondary succession would be an abandoned farmland, a forest fire, or even a place that has human activity. After the disturbance occurs, it destroys the vegetation and the soil is still intact. Question from Chapter 6- Critical and Creative Thinking: Although most salamanders have four legs, the aquatic salamander shown below resembles an eel. It lacks hind limbs and has very tiny forelimbs.
Propose a hypothesis to explain how limbless salamanders evolved according to Darwin’s theory of natural selection. According to Darwin there needs to be four characteristics for animals and plants to evolve. Number one is they need to be isolated. Number two is that reproduction needs to be involved, so there needs to be more than one, a boy and a girl. Number three is that natural selection needs to occur, meaning that animal does whatever it is that they need to do to survive, even if they have no limbs.
And Number four is they need to be fit sexually meaning that there should be no missing parts that will not be able to let them reproduce. So in this particular case, it seems that a salamander eventually become isolated by water resulting in them not using any of his limbs. After that these salamanders kept reproducing, and those with the longer legs could survive predators in that area. http://en. wikipedia. org/wiki/On_the_Origin_of_Species http://www. spaceandmotion. com/Charles-Darwin-Theory-Evolution. htm