Final answer:
Beavers are ecosystem engineers which build dams and affect their surrounding environments and wildlife habitats. They also transport plant propagules, shaping the spread of aquatic plants. Historically, the demand for beaver pelts has impacted their populations and influenced human fashion.
Step-by-step explanation:
Beavers have a significant impact on their ecosystems, both as ecosystem engineers and through their role in wildlife habitats. The passages provided give insights into the behavior and habitats of beavers—how they create their homes by building dams and lodges, and how their activities can shape the environment. Beavers are known to transport plant propagules which can help in the spreading of aquatic plant species. Moreover, their ability to alter landscapes makes them a keystone species, as they can change the flow of streams and create wetlands, which are beneficial for numerous other wildlife species.
In historical context, the beaver has had a strong impact on human culture and economies as well, particularly illustrated by the beaver hat styles from 'Castrologia, Or, The History and Traditions of the Canadian Beaver', indicating that the demand for beaver pelts has had a significant effect on these animals' populations and, by extension, on the environments they engineer.