Question

Pick two of the mechanisms listed and compare and contrast them. Remember that compare and contrast means to explain how they are similar and how they are different.

Geographic Isolation: The geography of an ecosystem can change over time. Forests shrink while grasslands expand. Rivers can erode valleys into mountains. Lakes can dry up, separating into two bodies of water instead of just one. These geographic changes can create barriers that are difficult if not impossible for different populations of the same species to cross. When this happens, the two populations become reproductively isolated. Over time, the combination of reproductive isolation and evolution creates such a difference between the genetic makeup of the two populations that it is not possible for the two populations to interbreed and create fertile offspring. At that point, the two populations have become separate species. For example, there are two closely related species of antelope squirrel that live in the Grand Canyon region, but they are separated by the canyon. Based on DNA analysis, the two species are very closely related, and most evolutionary biologists believe they started off as two populations of the same species that were isolated by the formation of the Grand Canyon.

Habitat Isolation: Populations that live in the same ecosystem can also become isolated when the populations choose to live in different habitats ecosystem. For example, in one ecosystem, you have a forested area that surrounds a lake. One population settles within the forest while the other population tends to live near the edges of the lake. Over time, this preference for habitats causes the two populations to isolate reproductively and evolve different characteristics. Once the two populations can no longer breed together and produce fertile offspring, they have become different species. One of the classic examples of this include the big cats in Africa. Lions and tigers can mate and produce offspring called ligers. These offspring are sterile and cannot produce offspring of their own. Therefore, lions and tigers are considered separate species. Evolutionary biologists believe that these two species evolved from the same species with populations that preferred different habitats. In the case of the populations that eventually evolved into lions, these individuals preferred the grasslands, whereas the populations that would eventually evolve into tigers preferred the jungles.

Answer 1

Answer & Explanation:

Geographic Isolation and Habitat Isolation are two mechanisms that contribute to the formation of new species through reproductive isolation and evolution. Both mechanisms involve the separation of populations, which leads to the development of different characteristics over time, ultimately resulting in speciation. However, the primary factors driving the separation in each mechanism are distinct.

In Geographic Isolation, the separation of populations is due to physical barriers created by changes in the geography of an ecosystem, such as the formation of mountains or the drying up of lakes. These barriers hinder or prevent gene flow between the populations, causing them to evolve independently. A prime example of this is the antelope squirrel species in the Grand Canyon region, where the formation of the canyon isolated two populations of the same species, leading to speciation.

In contrast, Habitat Isolation occurs when populations within the same ecosystem choose different habitats to live in, which causes reproductive isolation. The separation is not due to physical barriers, but rather the preferences of populations for specific habitats within the ecosystem. For instance, the African big cats, lions and tigers, evolved from the same ancestral species, with one population preferring grasslands and the other preferring jungles. This habitat preference led to reproductive isolation and eventually speciation.

In summary, both Geographic Isolation and Habitat Isolation contribute to speciation through reproductive isolation and evolution. The key difference between the two mechanisms is the factor driving the separation of populations: physical barriers in Geographic Isolation and habitat preferences in Habitat Isolation.