Many different factors contribute to the destruction of biodiversity on Earth.
From clear cutting ancient forests in the Pacific Northwest to the pollution that runs into our streams, human activity has had devastating effects on many habitats around the world. Due to the delicate balance of nature, when a new plant or animal is taken from its natural environment and introduced into a new ecosystem, the effects can be drastic. Humans sometimes introduce new species into an environment by accident. For instance, the European zebra mussels hitched rides on cargo and cruise ships and now pose a great threat to the health of the Great Lakes and other northeastern United States lakes. Native mussels have been nearly eliminated from the western basin of Lake Erie by the zebra mussels.