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Ecosystems

River and pond life

Animal and plant life in a slow-moving riverAnimal and plant life in a slow-moving river Rivers hold a very small proportion of the Earth’s water, but they are extremely important habitats for many kinds of animals—both above and below the water's surface. A fast-flowing stream is too rough for all but the hardiest plant species, but in gentler, deeper water, plants can take root in a muddy riverbed. They provide food, shelter and nesting sites for many animals. Worms and snails living in the mud are food for fish, which, in turn, are eaten by otters and diving birds such as the kingfisher. Mayflies and other insects living at or near the water’s surface are preyed upon by other insects, such as dragonflies, as well as by birds, fish and frogs.

Brook trout in a coldwater streamBrook trout in a coldwater stream
Brown bears prey on sockeye salmon.Brown bears prey on sockeye salmon.

Upper reaches

At their source, usually in the mountains, rivers are fast-flowing, and few plants can root themselves in the river bed. The main source of food for invertebrates, such as water-living snails, leeches and fly larvae, is decaying plant material. This is washed downstream from vegetation that overhangs the river, and is filtered from the water by the invertebrates as they cling to the rocky river bed. Birds and strong-swimming fish then feed on the invertebrates.

 

When alarmed, toads produce tiny, harmless amounts of bufotoxins—a poison 20 times stronger than cyanide.

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