Habitat Loss—a habitat refers to the home of any organism. This may be a coral reef, mangrove forest, upland forest, mudflat, seagrass bed, rainforest and many more. Habitat loss is the greatest cause of species endangerment. Examples of this include the construction of roads, homes or buildings etc.
Disease—diseases come naturally however sometimes humans introduce diseases and problems into a species that threatens their survival. An example of this is the effect of insecticides or pesticides that causes changes in the genetic makeup of an organism. In the United States, the introduction of the insecticide DDT (Dichloro-Diphenyl-Trichloroethane), which was found in waterways and soil, eventually worked its way up the food chain from small water feeders to the fish who ate the plant life in the water and the animals and humans who ate the fish. When DDT was left in the water it eventually broke down and became DDE (dichlorodiphenylethylene). These toxic substances (along with others like PCB’s) caused eagles and peregrine falcons to produce eggs that had shells so thin that they broke just from the mother sitting on them.
Addressing the Problem
The very best way are parks. Protected parks that are protected by hired people to keep illegal poachers and loggers. You can't just protect the species, you have to protect the whole ecosystem. Take the blue poison dart frog for example. You have to protect the Bromilliad flower which it lives in, which means you have to protect the trees the bromilliad lives in as well. you also need to protect the natural predators the frog has, so it doesn't get an out of control population. You have to protect the poison dart frog's natural prey, insects which live in the ecosystem, which means you have to protect where the insect lives, and so on. Everything is connected, so to really protect a species, you have to protect it's whole ecosystem. Chances have it that another species in it's ecosystem is threatened or endangered as well. Heck, all species are going to be endangered at the rate us humans are going.