Fish & Flowers

Fish & Flowers

Fish and flowers sound like they go together like pickles and ice cream. But in some environments, they have a surprisingly close relationship.


Six degrees of pollination. I'm Bob Hirshon and this is Science Update.

We all know rain makes the flowers grow – but sometimes fish help too. That’s according to University of Florida ecologist Robert Holt.

He and his colleagues studied eight freshwater ponds. There, bees pollinate nearby flowers, while dragonflies prey on the bees. But fish control the dragonfly population by eating their larvae. Holt’s team compared the flora around ponds with fish to ponds without.


Ponds that had fish in them tended to have fewer larval dragonflies, and fewer adult dragonflies …

…which meant more bees, and more frequent pollinations. Plants around fishless ponds, on the other hand, were more likely to be pollen starved. The study suggests one way that the effects of overfishing may ripple onto land. I'm Bob Hirshon, for AAAS, the science society.

Making Sense of the Research

According to the UN’s Food and Agriculture Organization, over 70 percent of the world’s fish species have been overfished or nearly wiped out. That’s trouble for humans, since hundreds of millions of people depend on fish as a central part of their diet. However, the consequences of overfishing can reach far beyond the human food supply, as this study shows.

Holt’s team studied a relatively controlled environment: the University of Florida’s Ordway Nature Preserve. Some of the ponds in this preserve were stocked with fish, while others weren’t. The flowers near the ponds with fish not only had more bees in the immediate area, but also had been pollinated more frequently than the flowers near fishless ponds. What’s more, flowers near fishless ponds were significantly more likely to be “pollen starved.”

So, while fish don’t actually pollinate flowers, they have a strong indirect influence in this environment. This doesn’t mean that fish in general influence the flower population worldwide, but it does suggest that waterside plants in certain ecosystems could be affected by a drop (or rise) in the fish population.

And what happens next? Flowers aren’t just decorations; they’re reproductive organs. If a plant’s flowers aren’t sufficiently pollinated, it won’t produce seeds, which means the next generation of plants will be lost. If plants disappear from the banks of ponds or other bodies of water, that could affect animals that depend on those plants for food or shelter. The loss of those animals, in turn, could affect other animals that live further inland. In short, what starts as the loss of a few fish could potentially ripple far beyond the water.

Incidentally, the common name for one species of dragonfly is the “bee butcher.” These are fierce predators of most flying insects, including other dragonflies. They’re able to eat an insect as large as themselves (imagine eating a meal as big as you are)! So it’s quite possible that changes in the fish population that affect dragonflies could have many other effects on the local insect population.

Now try and answer these questions:

  1. In the ponds that Holt’s team studied, how do fish influence pollination?
  2. How might this impact the environment in other ways?
  3. Can you infer, from this study, that a loss of salmon in saltwater streams would affect nearby flowers? Why or why not?


For Educators

In the Access Excellence lesson Symbiosis and Co-Evolution, students investigate a symbiotic relationship in the lab setting and carry out research into symbiotic relationships.

The long-term Ecology and Biome Unit, also from Access Excellence, is an in-depth exploration of biomes, environmental communities, and human ecology.

For an example of a similar chain of ecological relationships, see the National Geographic magazine article Bats and Cecropias, which discusses how rainforests in French Guiana rebound after logging. The forests return with the help of tough little fruits from Cecropia trees and some beneficial bats who spread the tree's seeds.

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