Guppies (Poecilia reticulata) are one of those species of fish that really are all over the place. Walk into just about any pet store with live fish for sale, and you’ll probably find a display of guppies. Go snorkelling in a freshwater stream somewhere near the Equator, and you may find guppies there, too. Take a close look at one of Rio de Janeiro’s sewers, and you’ll find that guppies even live there quite happily!
But even though these are the same species of fish, they may have very different traits. For example, they might have different breeding patterns or different diets. Let’s look at how and why this happens.
Guppy traits depend on their environment
Guppies are abundant and widespread. In other words, there’s a lot of them, and they live in a lot of different places and environments. Guppies in different environments need specific characteristics, or traits, to deal with those environments.
The development of these differences is a process that ecologists call local adaptation. Local adaptation is based on the idea that species adapt to their environment in a way that it will survive. This is driven by the process of evolution.
For example, some guppies live in the same streams as their predators. Others don’t. Ecologists (scientists who study interactions between organisms and their environment) have found that these two categories of guppies have different traits.
One guppy predator is a type of fish called a cichlid. The guppies that live alongside cichlids start reproducing earlier. They also have more offspring faster and in a shorter period of time. They do these things to make sure their species survives. With cichlids around, individual guppies are less likely to survive to maturity.
Did you know? Some cichlids that live alongside guppies have features that make them voracious predators. For example, they have long bodies that let them swim quickly. They also have strong, fast-moving jaws that can protrude to grasp prey.
Guppies that live alongside cichlids also impact their environment differently than those who don’t. That’s because these two categories of guppy have different diets.
Guppies that coexist with (live with) cichlids usually do not live near many other guppies. This way, they do not have to compete with many other guppies for food. So guppies that coexist with cichlids get to access the best quality food, like midges and other invertebrates.
Pike Cichlid: A voracious guppy predator. Source: Wikimedia Commons
Meanwhile, guppies that don't coexist with cichlids live at much higher densities. They do have to compete for food. This means that they can't be as picky, so they have a much broader diet that also includes microorganisms and decomposing organisms.
This is really cool, because it means that predator-prey interactions can change the traits of a population, and vice versa. In other words, ecological and evolutionary processes affect each other. This is exciting to biologists, who thought for many years that ecological processes happened very quickly while evolutionary processes happened slowly.
Aquatic midge larvae: guppy food Source: Wikimedia Commons
Did you know? Can you think of examples of variation within a species closer to home? Here is one: populations of American black bear in British Columbia's Great Bear Rainforest. They contain variation in fur colour. Some have black fur, while others have white fur.
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