When Wolves Were Returned to Yellowstone National Park in 1995

When wolves were returned to Yellowstone National Park in 1995, they immediately began feeding on elk, reducing their numbers. This allowed aspen trees to increase in abundance, which ushered in the return of beaver populations. As beaver populations dammed streams, they slowed water flow and stabilized streambanks. The stabilization of streambanks increased riparian habitat in which songbirds could nest, and the ponds provided breeding habitat for amphibians. Explain this story using the concepts of top-down and bottom-up control.