Characteristics
One of the most important features of ponds is the presence of standing water, which provides habitat for wetland plants and animals. Familiar examples might include water-lilies, frogs, turtles and herons. Often, the entire margin of the pond is fringed by wetland, and these wetlands support the aquatic food web, provide shelter for wildlife, and stabilize the shore of the pond. Some grazing animals like geese and muskrats consume the wetland plants directly as a source of food. In many other cases, however, the pond plants fall into the water and decay. A large number of invertebrates then feed on the decaying plants, and these invertebrates provide food for wetland species including fish, dragonflies and herons. The open water may allow algae to grow, and these algae may support yet another food web that includes aquatic insects and minnows. A pond, therefore, may have combinations of three different food webs, one based on larger plants, one based upon decayed plants, and one based upon algae. Hence, ponds often have a large number of different animal species using the wide array of food sources. They therefore provide an important source of biological diversity in landscapes.
Vernal ponds are ponds which dry up for part of the year. Naturally occurring vernal ponds do not usually have fish. They are called vernal ponds because they are typically at their peak depth in the spring ("vernal" means to do with the spring). The absence of fish is a very important characteristic, since it provide amphibians with breeding locations free from predation by fish. Hence, introducing fish to a pond can have serious detrimental consequences. In some parts of the world, such as California, the vernal ponds have rare and endangered plant species. On the coastal plain, they provide habitat for endangered frogs such as the Mississippi Gopher Frog.
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