Powerpoint: Feb 5

• Explain how new species arise in response to new niches
• Differentiate among and give examples of convergent evolution, divergent evolution (or adaptive radiation) and speciation.

Speciation: occurs when a population diverges and begins to evolve into different species.

Speciation can occur via any number of evolutionary mechanisms. All the mechanisms operate at different times, different places and with different intensity to produce new species.

Species: A distinct, identifiable group of populations whose members can interbreed. Generally distinct from other species in appearance, behaviour, habitat, ecology, genetic characteristics and etc.

Niches: The particular habitat requirements of a certain species and the role that species plays in the ecosystem

The important thing to know about niches is that they represent an environment (food, abiotic factors, predators etc.) that can then lead to the evolution of new species. Recall that in the case of natural selection, the environment impacts the evolution of species. In the population, where there are a variety of traits, some traits will be better adapted for survival and reproduction. These traits (and the alleles associated with them) will be selected for and likely increase in frequency.

Genetic drift and a lack of gene flow can also contribute to speciation. Genetic drift (founder effect) leads to the geographic isolation of species. The geographic isolation of the species reduces gene flow (exchange of alleles via mating) in the old and new population. Therefore, the differences between the populations can continue.

Let’s take a look at an example:

On the island of Anguilla, an isolated island thousands of miles away from any form of land, researchers found populations of iguanas. They noticed that the iguanas existed in two distinct populations, one lived on land (mainland iguanas) and the second lived in and next to the sea (marine iguanas). The researchers hypothesized that the two types of iguana are descended from the green iguanas of South America, and must have been blown out to sea from South America during the storms and established at Anguilla. 

Given your knowledge of evolution, how did the two types of iguana (mainland and marine) arise from the original Green iguana population?

As with any case in speciation, there are multiple possible evolutionary forces that could have contributed to it. Here is one way that it may have happened:

• Genetic Drift (founder effect): The green iguanas that were shipwrecked on Anguilla were probably genetically and maybe morphologically different from their counterparts in South America. Therefore, the allele frequencies has already changed and evolution has happened, though that alone would not make a new species.
• Natural Selection: Natural selection occurs where species that are unable to adapt to the environment (or their niche) are less likely to survive and reproduce. In this case, however, there may have been two very different niches for the iguanas to adapt to: the marine one and land one. Therefore, some green iguanas who were able to adapt to land were more successful, while the ones who adapted to the sea were more successful. Each population began to adapt to their respective environments.
• Gene Flow (LACK OF GENE FLOW): Because the iguana populations were geographically distinct, they may have not interacted as much. Therefore, gene flow was reduced and exchange of alleles would reduce. The genetic (and morphological) differences between the two populations increase and the two diverge.
• Mutations: mutations will always play a role in adding new traits to a population. However, since the iguanas are in a different environment, different traits will give the iguanas different success. As a simplified example, if a mutation in the marine iguana population were to cause them to be able to stay under the water for longer periods of time, the trait would be very beneficial. The trait would then lead to the successful survival and reproduction of the individuals who have it and become increasingly common in the population. Such a trait may not be as useful in the land iguanas and may not be selected for.

Please note that the scenarios are NOT representative of what you will see on the test. The scenarios are for you to think more deeply about natural phenomenon and critically think about the mechanisms of evolution.

Handouts: 

Scenario Activity – Speciation – DOES NOT represent the test. For thinking more deeply about natural phenomenon.

Speciation – Review Worksheet (finish for Wednesday please). It’s a short one 🙂