Two decades later, bringing wolves to the park remains as controversial as ever with local ranchers and hunters. And while researchers agree that wolves have significantly changed Yellowstone, there’s debate on how much other factors are at work too. Wolves aren’t the only thing that’s changed the park since 1995. Droughts have affected the rivers, trees, and animal life. Yellowstone has become more popular, leading to more development in the area. Bears seem to have developed more of a taste for elk. And while top-down trophic cascades are more intuitive (add a predator at the top, and you affect their prey, which affects their food, which affects their food…), ecologists are taking a closer look at “bottom-up” trophic cascades and how plants shape ecosystems. Some recent efforts are examining herbivores and trophic cascades that move from the center out. To summarize a room full of journal articles: Each player has a unique and important role in the health of its ecosystem. So yes, when an apex predator like the wolf is taken away, the whole ecosystem suffers. But the same was true two hundred years ago when beavers were decimated by trapping. Losing any one species hurts the whole. To update Paul’s “many parts, yet one body” metaphor in 1 Corinthians 12, the bison cannot say to the beaver, “I have no need of you.