Question

Compare and contrast the three major modes of speciation, giving examples of each using the same organisms in different environments. Be specific and discuss 2 different species concepts in your examples.

Answer 1

The three modes of speciation are:

Allopatric: In this kind of speciation a population is divided in 2 by a physical barrier, it might actually something like a mountain or a water body (for example) but they might only be dsitributes in different locations, the main point is to physically separate 2 populations. The independent existance of both populations make them take different evolutionary paths, one population will mutate and transfer alleles in a manner and the other one in its own manner. In terms of the biological concept of species, eventually the populations will form different reproductive mechanisms, leading to 2 different species that cannot interbreed. In terms of the evolutionary concept of species, each population already formed different species since they formed different lineages with their own evolutionary forces acting differently on them, even when they had the ability to hybridize.

Example: A mouse species population is disrupted due to the construction of a new dam, one subpopulation to the south and one to the north. Each population is exposed to a bit different environmental conditions, natural selection acts differently in each population because of it, and the effects of genetic drift leads to fix different alleles in the northern population compared to the southern population, many years later the populations seems quiet different, one of them developed a mating behavior that is not found in the other, so interbreeding is never seen.

Peripatric: In this case the only difference is the size of the fragmented populations, a small population get separated from a bigger population.

Example: A mouse population lives in certain region, some travelers observed the mice in nature and really loved them so they take some of them, around 10, to bring them to their ranch at the other side of the country. The original population takes its own path, while the 10 mice taken away succesfully reproduce in live in the ranch. genetic drift rapidly eliminates some alleles for some genes, producing a population that (with only a few generations) seems different to the original population. Eventually, after many years, they are considered different species, they and act look different

Parapatric: In this mode of speciacion, there is no physicall separation between the populations, in a same area, 2 populations start to differentiate, this starts by finding a mechanism to isolate reproduction. This is a non common mode, it normally occurs due to specialization to exploit certain different resources in the habitat, this means they start to occupy different niches in the habitat. This could occur due to avoiding competition, as the fitness of both subpopulation tends to increase if they find a way to specialize to different resources. The biological concept of species is closely related to this kind of speciation because reproduction plays a major role in stablishing the initial real differentiation. Along with such reproductive isolation comes the differentiation of lineages, and only then we can talk about the evolutionary concept, 2 different lineages that evolve separately with their own isolated inheritance of genes.

Example: The mice species in its habitat feeds from roots and vegetables in general, but they started to grow a lot and the resources are starting to not be just as enough as they used to be. Mice start to violently fight when they find other mice exploiting a food resource. Some mice start to eat only leaves and roots from acquatic plants, they strongly compete for these plants and start to decrease the frequency of fights for terrestrial plants. The rest of the mice constantly more frequently start to exploit the terrestrial plants because they find less fights when taking them. Eventually a population specializes to eating terrestrial plants, while the others eat acquatic plants