This species should be considered the most invasive due to the fact that it was introduced to many parts of the world. It even took  over a large part of the continent of Australia. This was due to the introduction of the cane toad in Australia because of the success in Hawaii and the Philippines. The wanted to clear out the pests that were inhabiting their crops. 

These cane toads are very well suited to be an invasive species. This is in part due to the fact that they profusely breed. Females lay a clump of spawns with thousand of eggs. The toad's tadpoles are highly toxic, and this allows them to grow to adulthood. Adults have poison glands to ward of any attackers.

These Lemurs are especially endangered due to the fact that they are endemic to Madagascar. Unlike many animals that have different species in different areas, all the species of Lemur are all on this island. Madagascar is is slowly being degraded by hunting, loss of habitat, and introduction of new species.

There were other species of Lemurs, but due to human interaction many of these have become extinct. Though there is interest in preserving Madagascar there are still things threatening it. There are laws against hunting lemurs, and although this is true, it continues and they are considered a delicacy and are eaten. Some people kill lemurs due to their belief that they bring death. 

The lemurs are constantly threatened by habitat deforestation. This due to constant need and want for lumber. Also, there was an introduction of new species that threaten the lemurs. These species include dogs, cats and mongooses.

I believe this is a good candidate due to the fact that is helps many other species, by simply fending for itself. It is a keystone species because it helps other species thrive. It does this through being a predator and doing things to make it easier to hunt. 

Their hunting keeps prey numbers. This allows other species to thrive and not overpopulate. They also push back much vegetation to create gator holes. During the dry season, these gator holes are still full of water. These become a refuge for many of the animals.

I believe that blue whale is a candidate due to the massive amounts of its prey it eats daily. A blue whale eats about 3500 kg of food daily.  It uses baleen plates in their back of its throat to filter out the food from the water. It barely has to do any work to feed upon its prey. It simply gulps in sea water and pushes back out. 

Blue whales also are found in many of the world's oceans. This fact helps them get prey from different parts of the world and their supply of food is practically unlimited. There  main food supply is called krill. These are tiny shrimp that live together in large masses. Also, its blue gray color allows it to hunt because it blends in. 

This has the coolest prey adaptation because of its tentacles. Each tentacle is covered in stinging organelles called nematocysts. The are paired with capsules filled with a  coiled filament that stings.These tentacles aren't used for anything but to defend the jellyfish.  They do not sting anything unless the jellyfish is being harmed.. When they do sting however, the coiled filaments are released and make contact with the target and inject toxins into it.

When in contact with humans, jellyfish stings are very painful. Depending on the species, they can very toxic and kill humans. Generally, however, jellyfish are not dangerous to humans.