Name:________________________________________ Period:____________________

 

Types of Natural Selection

 

Determine the type of selection (stabilizing, directional, or disruptive) each statement describes. Draw a graph to show the distribution of phenotypes in the population after the selection has occurred.

 

  1. Members of a population of tree frogs vary in leg length and hop from tree to tree in the rain forest to search for food. Environmental changes cause massive destruction of the forest, resulting in fewer trees. Over several generations, scientists discover that mostly long-legged frogs remain.
  1. Which variation(s) is/are selected for? Why?

 

 

  1. Which variation(s) is/are selected against?

 

 

  1. Which type of selection is described?

 

 

  1. Draw the graph that represents this type of selection:

(donít forget to label the x- axis and yĖaxis)

  


 

                                                                                                         

 

 

 

 

 

 

 

  


     
  1. Members of a population of grasses range in length from 8 cm to 28 cm. The 8-12 cm blades receive little sunlight, and the 20-28 cm blades are eaten quickly by grazing animals.

      a. Which variation(s) is/are selected for? Why?

 

 

b. Which variation(s) is/are selected against?

 

 

c. Which type of selection is described?

 

 

 

d. Draw the graph that represents this type of selection:

(donít forget to label the x- axis and yĖaxis)

  


 

                                                                                                             

 

 

 

 

                                                                                                                 Normal variation

 

 

 

 

  1. Members of a population of sea urchins vary in length of their spines. Short-spined sea urchins are camouflaged easily on the sea floor. Long-spined sea urchins present a tough defense against predators.

a. Which variation(s) is/are selected for? Why?

 

 

b. Which variation(s) is/are selected against?

 

 

c. Which type of selection is described?

 

 

d. Draw the graph that represents this type of selection:

(donít forget to label the x- axis and yĖaxis)

  


 

                                                                                                         

 

 

 

 

 

 

 

 

 

 

 

 

  1. Small spiders have a difficult time catching prey. Large spiders are easy for predators to see and capture.

a. Which variation(s) is/are selected for? Why?

 

 

b. Which variation(s) is/are selected against?

 

 

c. Which type of selection is described?

 

d. Draw the graph that represents this type of selection:

(donít forget to label the x- axis and yĖaxis)

  


 

                                                                                                         

 

 

 

 

 

 

 

 

 

 

 

 

  1. Woodpeckers with long beaks are better able to reach insects inside the tree bark then woodpeckers with short beaks.

a. Which variation(s) is/are selected for? Why?

 

 

b. Which variation(s) is/are selected against?

 

 

c. Which type of selection is described?

 

 

d. Draw the graph that represents this type of selection:

(donít forget to label the x- axis and yĖaxis)