Predators shape ecosystems more by fear than killing

A ground-breaking study has caused a dramatic rethink of the process by which predators control ecosystems, and it’s turning classic ecology on its head.

Crab in mudIn the gleaming salt marshes of Georgia’s Sapelo Island, US, Dr John Griffin was unleashing terror. An ecologist, he had emptied an army of mud crabs into the sediment to see what would happen to their prey.

Dr Griffin, a lecturer at Swansea University, had his eye on the little marsh periwinkles. These snails like to feast on the leaves of the green and precious cordgrass that dominates the marshes. Mud crabs ought to gobble up myriads of snails — and give the grasses a reprieve.

It is classic ecology you may have been taught at school: predator eats prey, prey eats plants, so more predators mean more plants. What happened, though, did not fit the models: the snails actually flourished under the assault of the mud crabs — and the vivid green of the marshes became dotted with circles of dead grass.

The result of the experiment was unexpected, and the explanation is profound. It challenges assumptions about how species respond to each other and it may mean that we have underestimated their ability to cope with changes in the environment. Read more.