Animals with no natural enemies are known as apex predators. They are, as far as science is concerned, at the top of their respective food chains. This does not mean they are invulnerable to predation by non-natural predators; it means they are predators with no natural predators of their own. Predation in the context of "no natural predators" excludes parasites and bacteria.
The largest living cats on Earth, tigers are at the top of their food chain, which ranges from wild boars and goats to deer, yaks and water buffaloes. Tigers usually hunt solo, by stalking and ambushing their prey. Tigers primarily, but not always, hunt nocturnally, as their feline eyesight is better at night than most other animals'. Using powerful leaping ability, the tiger attacks and pulls down its prey before killing it with bites to the throat.
Also known as the Indo-Pacific crocodile, the saltwater crocodile is the biggest living reptile on the planet. Saltwater crocodiles eat almost anything that moves. Typically their diet consists of fish, crustaceans, birds and watering mammals, although they have been known to kill and eat other predators as well. These savvy reptiles ambush their prey from a relatively deep section of water and throw their immense body weight into a roll, drowning their victims before swallowing them whole. In the case of larger prey, the salt-water crocodile will rip large chunks to eat.
Not all apex predators are bloodthirsty killers. The whale shark, the largest fish in water, does not hunt prey, per se. Instead, it uses a filter feeder mouth that is up to 5 feet in width. With this filtering mouth, the whale shark consumes algae, plankton, krill and fish eggs. Filter pads along the teeth separate food from vast quantities of water that are expelled through the gills. The whale shark is gentle; it has been known to play with human divers.
Some creatures are apex predators even though they lack the great size that put other apex predators at the tops of their respective food chains. Take the electric eels, which generates severe electric shocks up to 600 volts -- strong enough to paralyze and possibly kill a human. Electric eels possess no natural enemies simply because none can withstand the powerful jolts. Electric eels are not true members of the eel family; they are actually invertebrate fish.
- PBS: Glossar (Apex Predator)
- Academia.edu: Tropical Ecology, Volume 53: Status of Large Carnivores and Their Prey in Tropical Rainforests of South-Western Ghats, India; Kannadasan Narasimmarajan
- Panthera Wild Cat Conservation: Food Habits of Amur Tigers
- National Geographic: Salt Water Crocodile
- Zoology; Feeding Anatomy, Filter-Feeding Rate, and Diet of Whale Sharks (Rhincodon typus) During Surface Ram Filter Feeding off the Yucatan Peninsula, Mexico; Phillip Motta
- National Aquarium: Electric Eel