Answers to exploration questions: biodiversity and the tree of life

If you are wondering where the suggested answers came from, you can review the videos and article in this tutorial.

1.     After watching the videos in this tutorial, your friend is confused about the scenario in which local government agencies were trying to decide which of three lakes (Lakes A, B, and C) should be protected. Your friend says, “If all three lakes have the same species richness, then it doesn’t matter which lake is protected, because each lake has the same amount of biodiversity.” In few sentences, explain why it would be better to protect the Lake C ecosystem rather than A or B. Be sure to include an explanation of the type of information that helped shape this decision.

Answer: A complete explanation would mention that the decision was made using more criteria than just species richness. The decision also took into account evolutionary lineages as depicted by phylogenetic trees. Scientists used molecular and morphological data to construct phylogenetic trees for the fish living in Lakes A, B and C to determine the evolutionary relationships of the different fish species. They found that the four species in Lake A were more closely related to each other than they were to any of the other fish species in the other lakes. The tree also showed that the four species in Lake B were also more closely related to each other than to fish in the other lakes. But one species from Lake C was more closely related to those in Lake A, and another species in Lake C was more closely related to the Lake B species. Lastly, the two remaining species from Lake C were closely related to each other, but formed a group that was only distantly related to the species in either Lake A or Lake B.

Although the lakes had equal species richness (four unique species in each lake), biodiversity exists at other levels beside just species richness. Evolutionary lineages are another important aspect of biodiversity, and Lake C has the greatest evolutionary diversity. So the government agencies focused their conservation efforts on protecting the Lake C ecosystem.

2.     After you and a friend have watched the videos in this tutorial, your friend asks you a couple of questions about the sea urchin cladogram shown in one of the videos.

Briefly answer your friend’s questions in a few sentences.

Answer: A complete explanation would mention that the two species of sand dollars are more closely related to each other than they are to sea urchins. They share a common ancestor, which is represented by the black dot at the branch point that connects the lines of the two species of sand dollars. A unique character, or evolutionary novelty, that distinguishes sand dollars from sea urchins is that sand dollars have flat bodies, which is an adaptation for living on sandy beaches. Sea urchin bodies, on the other hand, are high-bodied and round -- almost ball-shaped. The flat-body trait of the sand dollars can be indicated by the black rectangular box below the common ancestor dot. This is one of the unique traits that connects all of the sand dollars to the exclusion of the sea urchins.