40-60% of all bird and reptile extinctions are due to the invasion of rats because of their ability to successfully inhabit islands. The Aleutian Islands in Alaska provide homes, important breeding conditions, and adaptable climates for seabirds; and the brown rats have invaded on nearly ten of them. Because of the Brown Rat invasion the seabird rates are suspiciously low, implying there is a connection between the seabirds and the rats(1).
According to a global analysis, brown rats have been invading and feeding on a quarter of the seabird species, severely disrupting the seabird's living conditions. The brown rats feed on the nests and unborn eggs, and even attack the adult seabirds. Over a hundred different seabird species are considered threatened by the rats due to their invasion being on the top of the bird's danger list. The rats go up to adult birds as well and have even been known to leave a bird nearly headless. (2)
Seabirds are important factors in the ocean ecosystem, and 30% are in danger of extinction. Certain birds are more vulnerable to the rat invasions then others, however almost all birds suffer from the rats. The smaller seabird species who create their nests and lay their eggs in more rat-prone areas are more susceptible to the rat attacks(2).

Beginning in the 1900's, Tigers population size has gone down by nearly ninety-five percent, as well as there habitats. Tigers, however, are not becoming extinct due to natural causes, but because of humans. Poachers, or someone who illegally hunts game, continue to hunt and kill (by poisoning their drinking water, or by setting traps) these magnificent animals for their skins, and/or body parts for the Chinese medicine. Even after twenty years of attempts to stop tiger hunting, still three of the original eight subspecies of tigers have become extinct in the last twenty years. 
In the 1900's there were as many as 100,000 tigers wondering around in the world, a dramatic drop in 1970 when there became only 40,000 left, and now there are known to be only under 8,000 tigers left. Of the eight original subspecies the only give that remain are the Bengal, IndoChinese, Siberian, South China, and the Sumatran Tigers(3).
Of the five species left the order of the population size, largest to smallest, goes like this: Bengal with a little less than 2,000 remaining, then the Sumatran, IndoChinese, Siberian and lastly the South China all decreasing slowly with under 500 tigers in each species. In fact, the South China may have gone extinct for one has not been spotted in years(4). 

Several scientists believe that Grizzlies are very important, essential species to ecosystems in North America because of their ability to regulate prey, and disperse seeds(such as blueberries and buffaloberies). However Grizzlies do much more for their environments than just disperse these seeds. When Grizzlies fish for the salmon, they take their fish and eat it in the forests; when they finish they just leave the salmon's carcasses there where the plants and trees absorb the nitrogen from it. When the Grizzlies dig for roots and other things they help mix the soil, keeping the nutrients mixed and rich, which again is an essential in their ecosystem(10)

Snow leopards are not only adapted in order to successfully attack their prey, but also to survive and hunt in their environment as well. The leopards have light colored fur, and spots in order to become camouflaged in their environment, making it easier for them to be able to sneak up on their prey. They also have very large front paws which allows them to manuvure about the rocks, they also have very thick skin on these paws to keep them from becoming freezing during winter when there is feet of snow covering the ground.
The adaptations that they have to help adapt to their environment are also very important to their surivival, such as the thick fur on the bottom of their stomach, which can reach up to three inches thick in order to keep the cat warm during the cold winters. They also have small ears that are very easy to flatten, making it easier to hide behind a rock without being spottted, and it also allows less heat to escape from the animals. 
These animals have very muscular legs which helps them jump about the rocks without getting hurt, and allows them to pounce on their prey with ease, and to do it silently. Snow leopards are very fast, have keen eye sit(they can see eight times better than humans can), and a precise sense of smell(in which their nose changes the cold air to warm air before it reaches their lungs) in order to smell their prey and accurately pounce(13)

Puffer fish, also known as blowfish, are very clumsy, slow swimmers. Many biologists believe that they obtain the adaptations that they do because their swimming style makes them very susceptible to predators. Pufferfish have very elastic stomachs and have the ability to inhale water or air within a split second in order to turn into a ball, becoming inedible. Specific species of puffer fish have spines on their back, so when they become a ball, not only are they impossible to swallow, but painful as well.
Blowing up into a nearly inedible, painful to eat ball is not the only adaptation that puffer fish have. Nearly all puffer fish contain a chemical called, tetrodotoxin; this causes the puffer fish to taste bitter(if able to be eaten in the first place), and it usually is toxic to fish as well. If humans consume this tetrodotoxin it is very toxic, in fact one puffer fish has enough tetrodotoxin in it to kill 30 people, and there is no anecdote. Some puffer fish have bright colors in order to attract their prey, where as other puffer fish have earthy tones in order to blend in better(8).
Puffer fish also have very good eyesight, which is another defense mechanism they use to outsmart their prey. They use their pectoral, dorsal, anal, and caudal fin to move which allows them to have very precise movement, and when they need it, they can have a sudden burst of speed to get away from their predators. Puffer fish have the ability to move their eyes independently without moving their entire head and some species have the ability to change their skin to blend in with their surroundings(9).