2. Saving the Eagles. The pesticide DDT was especially threatening to bald eagle

Question

2. Saving the Eagles. The pesticide DDT was especially threatening to bald eagles because they are at the top of their food chain. Below are data on the productivity of the eagle population in northwestern Ontario, Canada. The Eagles nest in an area free of DDT but migrate south and eat prey contaminated with the pesticide. DDT was banned at the end of 1972. The researcher observed every nesting area he could reach every year between 1966 and 1981. He measured productivity by the count of young eagles per nesting area. The count of young eagles per nesting area 0.0 Yoar .(a) Does the time plot support the claim that banning DDT helped save the eagles? Explain why? (b) It appears that the overall pattern can be described by two straight lines. Visualize the least-squares line for 1966 to 1972 (pre-ban) and also the least-squares line for 1975 to 1981 (allowing a few years for DDT to leave the environment after the ban). What can you say about the strength and direction of the relation between the productivity (count of young eagle per nest) and year for the pre-ban and post-ban data? .(c) How does the direction of the correlation relate to the effect of banning DDT on eagle productivity?

Explanation / Answer

a) Yes banning DDT helped to save the eagles because from the graph we can see that the count of young eagles is increasing, and before that when DDT used it was decreasing.

b) For pre-ban years, we can see the data is not exactly linear, slightly curved. So, the least-squares line for 1966 to 1972 may not be a very good model. If we fit a least-squared line we will get a downward straight line which says as time is going if we are continuing the use of DDT then the count will going to decrease.

For post-ban years, we can see the data is strongly linear. So, the least-squared model will be a good model. Here if we fit the model we will find a straight line with positive slope and it also implies that after banning DDT the count of the birds is increasing in a linear trend.

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