House sparrows from England were released in the United States. They have competed with native bluebirds. These house sparrows are .

House sparrows from England were released in the United States. They have competed with native bluebirds. These house sparrows are invasive species.

Explanation:  

House sparrows are invasive species that were introduced in the United States and once established these birds started to compete with native species and managed to displace many native birds. They seriously affected farmlands. Now they are everywhere always associated with human being presence.  

Biologic Invasive species: It refers to new species that disperse and establish in a new area far or out of their original distribution range. Once established, these species expand their distribution from the first invaded spot and overgrows. As they expand, they compete with other species for resources, such as food sources, water, shelter, radiation, exposure, among others. Species are considered to be invasive because of their high reproductive rate, population growth, and interaction with native species, which provokes huge damages in the native ecosystems. It is very common for these species to scape and start new populations in the new area, where they have less environmental pressure and better conditions than in their origin area -fewer predators, more resources, better nitches-, and these factors favor their establishment.

There are some typical steps in an invasion process:

1) Introduction or dispersion to the new area,

2) Naturalization. The new species establishes in the new area. It can grow, reproduce, and make use of resources.

3) Overgrowth and uncontrolled expansion.

4) Interaction with other species.

5) Stabilization.

In some cases biologic invasions are natural processes, that occur in small groups of individuals that can expand to other ecosystems, and the appearing or despairing of barriers promotes their expansion. But these biologic invasions have been accelerated by human beings, referring to this as "human-assisted invasions".

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