Introduced Species
Introduced species are a major threat to Bay wetland habitats. An introduced species is a plant or animal that has not historically lived in a particular habitat, but has been brought here by some other means, usually by humans. One very common introduced species in the Bay Area is the eucalyptus tree, which was brought here from Australia because it grew quickly and provided Bay Area residents with a quick and easy source of lumber.
All plant and animal species grow and reproduce as much as possible to ensure their survival. In native habitats or balanced ecosystems, uncontrolled growth or reproduction of a single plant species is prevented because many other native plants are equally well adapted to grow and compete for the same area. The same rule applies to animal species. Almost every animal gets eaten by some other animal, and this natural predator-prey relationship keeps the population in balance. It also ensures biodiversity, which means that lots of different plant and animal species live in a given place.
Occasionally, when a new species is brought to an area where it would not normally live, it dies because it is not adapted to live or reproduce in the new habitat. Often, the species survives, but stays contained in a very small area, such as a garden or yard. Sometimes, the species takes a strong hold in the new habitat, reproducing at a fast rate. Without natural predators or competitors around to curb its population growth, this species gradually begins to take over the new habitat, competing with and often killing off the native plants and animals that have lived there for centuries. An introduced species that invades and takes over a native habitat is called an invasive species.
Non-native plants and animals are not bad species -- each one plays a critical role in its natural habitat. Outside of their natural habitats, and in the absence of natural predators and competitors, these species do disrupt and sometimes harm the ecosystem.
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