Introduction

An invasive or exotic species is a non-native species to a particular ecosystem that is likely to cause environmental or economic harm or be detrimental to human health (www.invasivespeciesinfo.org). Invasive species can be found in most environments on earth. Additionally, the term invasive species not only applies to animals, but also applies to plants, fungi, and even microorganisms.

Invasive species can be introduced to a new ecosystem in a variety of fashions. For instance, humans have introduced exotic species to new areas throughout history. In some cases, humans have done so accidentally via ships or other forms of transportation. Additionally, humans have purposely introduced exotic species into new ecosystems in order to raise them for food or even just for sport. Organisms, themselves, have also migrated to new ecosystems.

Invasive species can cause damage to an ecosystem in a variety of ways. In fact, invasive species impact almost half of all the threatened and endangered species in the United States (www.invasivespeciesinfo.org). Oftentimes, many invasive species have no natural predator when they move into a new ecosystem. Thus, they are able to exploit the new environment and, consequently, their population thrives. Additionally, invasive species compete with and, many times, outcompete native species for important resources, which causes a decline in the native species. The effects of an invasive species do not only span to their direct competitors, but can have a lasting effect throughout the different trophic levels of the ecosystem.

The next few pages will display a few invasive species that have had a large impact on the northeastern United States: the zebra mussel, the hemlock woolly adelgid, and the common reed.

Here are a few other examples of invasive species that impact the northeastern United States.