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Biology LibreTexts

Lab 2: Natural Selection

  • Page ID
    24388
  • Natural Selection:

    Predators often make very complex decisions when it comes to foraging behavior such as selecting prey items. Although small prey items are often abundant and easy to handle, a predator may have to eat a significant number to meet their nutritional needs and expend a great deal of energy collecting them. Larger prey items may be more rare or difficult to handle but can provide a good, filling meal. Prey items use many strategies to avoid being eaten by predators. Some preys are fast, while others come out only at night to avoid detection. Some organisms exhibit cryptic coloration to blend in with their surroundings. This camouflage can help prevent an organism from being eaten by a predator and allow them to survive and reproduce.

    Dr. DesRochers has made some observations about the actions of primate predators on Quadratus daltonii. Q. daltonii is a four-sided, bilaterally compressed organism with a green and white dappled coloration. These organisms are sessile and match their green and white dappled habitat almost perfectly and can be very difficult to see. They reproduce annually via sexual reproduction. In his observations in the field, Dr. DesRochers observed that larger Quadratus daltonii were consumed more often than smaller individuals. In order to model this predator-prey relationship in the lab, we will be using physical models of the organisms and their environment. Humans can serve as the primate predator in this experiment.

    Luckily, Dr. DesRochers and his team have already developed a hypothesis for you to test. They hypothesize that larger Quadratus daltonii are eaten more often because they are easier to see.

    As a group, you should come up with a detailed method that you would use to test the team’s hypothesis. Each group has one simulated environment and a bag of Quadratus daltonii models with which to test their hypothesis. Remember, a good method needs to be detailed and repeatable by other scientists. Please make sure you consider the details when you develop your method. For example, rather than say “we will use small, medium, and large squares” you should say “we will use 3 cm, 5 cm, and 7 cm squares”. By quantifying the size of the squares you used, another scientist could repeat your experiment. There are many details to consider! Once each group has developed a test for this hypothesis, we will discuss as a class and come up with a joint method for all to use.

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    Please clearly explain your group's method below:

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    Once the class has decided on a common method, each group will collect data and report it on the board. Please record the class-wide data below.

     

     

     

     

     

     

     

     

     

    Graph the class-wide data using the type of graph that you feel best presents the information you gathered.

     

     

     

     

     

     

     

     

     

    Follow-up Questions:

    1. Do the data that the class collected supports the initial hypothesis? If not, why?

     

     

     

     

     

    2. Develop an alternate hypothesis that may explain the initial observation that larger Quadratus daltonii are being eaten more often by primate predators (this needs to be a hypothesis that could be tested in the lab with models).

     

     

     

     

     

    3. Based on Dr. DesRochers’ observations in the field that the larger Q. daltonii are consumed more often, what form of natural selection would you expect to see in this population after several generations? What type of Q. daltonii would be most abundant? Least abundant?