Question

4 Conditions for Natural Selection Problem 1: There are two species of freshwater shrimp that are introduced to a pond. The first species, Caridina cantonensis, is brightly colored with red and white stripes. The second species, Caridina multidentata, is more mottled drab in coloration. Fish have an easier time finding and eating Caridina cantonensis due to their bright colors. When each of these species reproduce they produce about 100 offspring, but only 30% Caridina cantonensis offspring survive to reproductive age, while 75% Caridina multidentata offspring survive to reproductive age. In this situation what is natural selection selecting for? In this situation what is natural selection selecting against? How do you predict this population will evolve? Identify how each of the listed conditions from the above scenario that influence natural selection. Population must have variation. Some variations are favorable More offspring are produced than survive Those that survive have favorable traits Differential reproductive success Problem 2: There are two types of aliens on Kepler-20e (a distant earth like planet). Both aliens eat from the same extremely tall trees in the local forests. Alien A is able to eat the leaves, bark, and fruit that are produced by these trees. Alien B is only able to digest the fruit from the trees, as they lack an important enzyme that breaks down the tough material in the leaves and bark. One year a new disease prevents all of the trees from growing any fruits. Both of these alien species have babies year round but each year some of each species die due to larger alien predators. In this situation what is natural selection selecting for? In this situation what is natural selection selecting against? How do you predict this population will evolve? Identify each of the listed conditions from the above scenario that influence natural selection. Population must have variation Some variations are favorable More offspring are produced than survive Those that survive have favorable traits Differential reproductive success

Answer 1

1. In this scenario, trait (color) that is favorable is mottled drab. This is because species with this trait are more “protected” from the fish. So, natural selection is selecting for Caridina multidentata color and their offspring will have a higher survival rate. This is an example of differential reproductive success (one trait is more conducive to a species' continued survival).  

2. Populations of aliens have variation, in this case different kinds of nutrition due to presence/absence of enzymes. Some of those variations are favorable, in this case Alien A and its ability to eat the leaves, bark, and fruit. So, when disease which prevents fruit growth occurs, this type of Alien and its offspring will survive.