Question

use the graphs below to answer questions 11 - 13.

1. describe what happened to beaver colonies after 1995 (when wolves were reintroduced). then describe the relationship between the number of beaver colonies and the willow tree ring area.
2. after about 1999, the willow tree ring area started to decrease again. what might account for this decrease?

Explanation:

For Question 11:

1. After 1995 (wolf reintroduction), the number of beaver colonies remained low until around 2000, then began a steady, significant upward trend through 2010.
2. As beaver colonies increased starting in 2000, the willow tree ring area (a measure of tree growth) first increased, then decreased. The initial increase aligns with reduced herbivory from elk (due to wolf presence), while the later decrease corresponds to beavers willow consumption.

For Question 12:

The decrease in willow tree ring area after 1999 is most likely due to the growing number of beaver colonies. Beavers rely on willow trees for food and building materials, so as their population increased, they consumed more willows, limiting the trees' growth (and thus reducing the annual ring area).

Answer:

1. After 1995, beaver colonies stayed low until ~2000, then rose steadily through 2010. As beaver colonies increased, willow ring area first increased (from reduced elk browsing) then decreased as beavers consumed more willows.
2. The growing beaver colony population, which feeds on and uses willow trees for resources, likely caused the decrease in willow tree ring area after 1999.