The streams of Trinidad and Tobago are home to the most unexpected of landscape gardeners. They’re guppies – tiny and beautifully coloured fish, just an inch or so long. Without tools or plans, they shape the environment around them, tweaking everything from the numbers of different species to the nutrients in the water.
The guppies are quick to adapt to different environments and particularly to which predators are around. The number and types of predators affect the guppies’ lifespan, how big they get and when they become sexually mature. This, in turn, affects what they eat, and that influence ripples across the entire stream.
We’re used to the idea that environments can shape the bodies and behaviour of living things, as species evolve adaptations that allow them to thrive in their surroundings. But the opposite also happens. Living things are both the product and the architects of their environment, with evolution and ecology affecting each other in a grand cycle. This whole process rests on the idea that evolution, though often assumed to move at glacial pace, can happen at rapid speed on a small scale. And the guppies are clear proof of that.