The Man Who Threw Starfish Into the Sea
In 1963, on a rocky stretch of shore in Washington State, an ecologist called Robert Paine started an experiment that still sounds faintly mad. At low tide he would climb down to the rock pools, prise the starfish off with a crowbar, and hurl them as far out into the Pacific as he could throw. Then he’d come back and do it again. And again, for years.
What he found is that the starfish played a unique role in those mini ecosystems; it ate mussels. And when Paine took it away, the mussels started to take over. They smothered the bare rock, crowded out the barnacles, the limpets, the anemones, the seaweeds. Within a couple of years a shore that had held fifteen or so species held about half that. The whole rich, tangled community had unravelled. All because one animal, not even a particularly abundant one, was quietly holding it together.
Paine gave that kind of animal a name; he called it a keystone species. It’s a term we now use everywhere.
Sat, waiting for dusk – and hopefully, beaver – on a bank of the River Otter
#BeaversWithoutBorders
Here’s the uncomfortable thing about applying Paine’s idea to Britain, we’ve already lost many of our keystone species, one by one. The lynx was gone by around 1,300 years ago. The wolf hung on longer but was hunted to extinction too. The beaver we trapped and wiped out for its fur by the 1700s. These are three of Britain’s lost keystone or ecosystem-shaping species. Others such as wild boar, bison, elk and wild horses also played major ecological roles.
Fortunately there are more and more projects each year championing the reintroduction of keystone species.
We first camped on Knepp in September 2022, not long after they’d brought beavers back to the estate. Alongside free-roaming horses and, to some extent, cattle, Knepp has been running Paine’s experiment in reverse. Instead of removing keystone species and watching an ecosystem unravel, they’ve been putting them back and watching nature respond. Beavers are the ultimate ecosystem engineers, who don’t just live in a landscape, they rebuild it.
Amber went back this summer with her Hunter & Gather colleagues and got to see their years of dam-building and lodge-work turning a fenced experiment into something that looks genuinely wild. Despite the success of many fenced beaver enclosures, for years we had only one completely wild population of beavers, on Devon’s River Otter.
Fast forward to February 2025 and the government finally legalised licensed wild release and beavers can now legally return to English rivers on purpose, for the first time in four hundred years.
”The lynx is going to take more time to build up steam, and more importantly it is going to need space.
A rare sight that would have once been commonplace throughout Britain
Lynx Next?
The lynx is where it gets more interesting. A lynx is a shy, solitary, forest cat that goes out of its way to avoid people. There is no record of a wild one killing a human. Sheep, maybe. But their presence also puts pressure on foxes who also predate on sheep. But the main reason for the lynx is for what it can do to thin out our wildly overpopulated deer, which, along with the sheep, are quietly eating the future of British woodland by stripping out every sapling before they grow.
The public seems to agree. In the Missing Lynx consultation, around 72% of people backed a reintroduction. Scotland has been running proper public sessions since the start of 2026. And yet the only lynx to actually touch British soil recently were four cats dumped illegally in the Cairngorms in early 2025, one of which died after being recaptured.
The lynx is going to take more time to build up steam, and more importantly it is going to need space.
Flakes of wood created by a beavers front teeth
Wolves and Trophic Cascades
And then there’s the wolf, one of the most powerful drivers of ecological change in an ecosystem. Reintroduction of the grey wolf to Yellowstone has been seen for a long time as one of the best examples of trophic cascade, which is a term used to describe what can happen to an ecosystem when a keystone species is removed or added. While scientists still debate exactly how much of Yellowstone’s recovery can be credited to wolves alone, there is broad agreement that their return fundamentally changed how the ecosystem functioned. For example, before wolves, elk could linger for longer in winter, spending more time near rivers and browsing heavily on young willow, which made it tougher for the beaver, who rely on willow during winter. With wolves, elk had to keep on the move, so they couldn’t as intensely graze the willow.
But the truth is, the wolf is barely on the British agenda anyway, at least there’s no serious programme, just the occasional fenced private proposal. So the argument for bringing our predators home now is really a lynx argument. The wolf is a much longer, much harder conversation, and maybe it’s alright that we’re not ready to have it yet.
”Britain has just proved it can put a keystone back, but the beaver was the easiest one.
The question is how brave we are about the next.
I’ve slept out in the New Forest, in the dark, under the trees. It’s one of the quietest, most grounding things I know. But I’ll admit that the whole experience would be a different and far more serious proposition if there were wolves and bears moving through those trees. I can understand why we are not ready to have that conversation yet.
But look at any of the rewilded beaver landscapes, from Sussex to Scotland and you can see what just one missing keystone species can do. Britain has proved it can bring one back. The beaver was the easiest one. The question now is how brave we’re willing to be about the next.
If you want to learn more about keystone species from around the world, I hugely recommend The Serengeti Rules (a book by Sean B Carroll or the film by Nicolas Brown).
