"When we try to pick out anything by itself,
we find it hitched to everything else in the Universe."
John MuirI don't know whether you've seen the film A river runs through it directed by Robert Redford. It's a Brad Pitt vehicle but the running thread is the relationship between boys and water; in particular their love of fishing. "I am haunted by waters". It is all wet and nostalgic, of course, but shows that people could live beside a river and not destroy it. I hope it's on Netflix for you, if you haven't seen it. Here's another gorgeous-to-view impact-on-river video that you might well have seen last year when it came out How wolves Change Rivers narrated by eco-journo George Monbiot. More? Try a more didactic and lupocentric bit of National Geographic propaganda. I've just finished a great longish-form essay Lessons from the wild side on the complex web of ecological relationships in Yellowstone which is behind the Science paywall for academics only. Shame! I'll have to abstract some nuggets for you.
The story of Yellowstone is a tale of trying to find the way to manage a 'natural' ecosystem which isn't quite big enough. Anything smaller than the planet isn't big enough. The park is surrounded by sparsely populated communities that have an agenda that must be reconciled with the federal reserve next door Sheep farmers don't really want to have wolves dodging back into a safe-haven across an invisible dotted line on a map in Washington. In 1886, the US army was drafted into protect the livestock from poachers and took out all the wolves as part of their brief to protect the large herbivores. Large eating machines like elk Cervus canadensis went through the river valleys like combine harvesters, eating grass and shrubs and saplings voraciously and indiscriminately. Without topside growth the roots holding riverside banks together died off and the rivers started to erode any remaining soil which might support some shrubs and trees. Insanely, the rangers resorted to shooting thousands of elk to give everything else some space. That introduced a lot of lead into the environment, but nobody mentions that. In 1995, some bright spark had the idea to reintroduce wolves which were quieter and more efficient than guns and quickly drove the elk and other large herbivores into less accessible refuges within the park. That allowed shrubs to thrive which provided habitat for nesting birds which brought in a lot more twitchers with cameras and binoculars.
Grizzly bears Ursus arctos horribilis also find board and lodging in the park and attract their own share of rubber-necking tourists. In the Spring of the year, the bears used to gorge on cut-throat trout Oncorhynchus clarkii when they returned to shallow gravelly streams to spawn. In the late 1980s some imbecile introduced lake trout Salvelinus namaycush which was esteemed as a game-fish. This invasive species out-competed the cut-throats for food but spawned in a different bear-inaccessible part of the environment. The grizzlies turned to baby elk for calories which had an effect on elk densities. As John Muir, the supreme environmentalist and philosopher, says at the top of this piece, we are all connected in quite surprising ways.
Another interesting story is the relationship between beavers Castor canadensis and willows Salix spp. Although the 5 minute telling says that wolves cause the regeneration of riparian willows, it's not so simple. Willows thrive in damp soils but that means that they much prefer soils that are always wet and beaver-dams are an important driver in raising the local water-table so that willow roots never dry out. But willows are an essential component for dam-engineering. How to break this log-jam without some dorky human intervention ("Let's make concrete dams, boys") is a bit of a poser. But it's certainly true that if humans would just bug out of trying to manage things, some sort of equilibrium would emerge. It might not happen in the lifetime of the current government, though: ecology is a long game. And it's important not to impose out own aesthetic on the view. There's more to ecology than pandas Ailuropoda melanoleuca and tigers Panthera tigris: parasitic wasps deserve a place in the sun, too.
Further thoughts on the same theme: Whales cause (beneficial, naturally, whales being so cuddly) climate change. Rather than reducing the concentration of krill and small shoal fish by their predations, whales seem to increase oceanic biomass by mobilising limiting resources [fecal plume is the technical term] like iron and nitrogen, and so increasing the amount of photosynthetic phyto-plankton at the base of the food pyramid. This acts as a carbon sink as the micro-plants convert atmospheric C02 into sugars and save the planet from our insane consumption of fossils fuels.