An invasive species is a species that causes harm to its non-native environment. In the deserts of Arizona, there is an invasive grass called Cenchrus ciliaris, otherwise known as buffelgrass. Buffelgrass was brought to the Americas from Africa, with the intent of using it as a grass that livestock could graze on. However, in the desert, this plant competes for the limited water, and it doesn’t leave any for similar sized plants. Buffelgrass can also tolerate droughts and can create fires, which in turn kill many other plants.
A threatened species is a species that may become endangered in the near future. The Mexican spotted owl, or Strix occidentalis lucida, is currently a threatened species. The owl has suffered habitat loss due to human collection of timber and wildfires.
An endangered species is a species that may become extinct in the near future, meaning there would be no more left in existence. The Mexican gray wolf (Canis lupus baileyi) population is very low in numbers. The wolf created a problem with human livestock and human civilization, so it was hunted.