Does every organism matter?

Does every organism in a community really matter, even a small fish or an insect? Activity 12.3 follows a real study with a surprising answer.

Researchers looked at how fish in ponds affect seed production in the plants nearby. They compared two ponds:

How could fish in the water change the flowers on the bank? Compare the dragonflies, bees and butterflies at each pond first. Pond A, with fish, had fewer dragonflies than Pond B.

Here's why. Fish eat dragonfly larvae (baby dragonflies), so a pond with fish raises fewer dragonflies to adulthood.

Dragonflies in turn eat flies, bees and butterflies. With fewer dragonflies about, more bees, flies and butterflies survive around Pond A.

And those insects are pollinators: they carry pollen from flower to flower nearby, helping the plants make seeds. So flowers near a pond with fish may produce more seeds than flowers near a pond without.

The chain runs fish → dragonflies → pollinators → seeds. The fish's effect on the flowers is indirect: it works through two other kinds of organism. The study shows biotic parts (fish, dragonflies, pollinators, plants) and abiotic parts (temperature, water, nutrients) all affecting one another. Now try the harder question: if people overfished the pond, fish would fall, dragonflies would rise, pollinators would fall, and the plants would make fewer seeds. One change upsets the whole balance.