The undisputed top predator of the Amazon River ecosystem is the Black Caiman (Melanosuchus niger). While many people immediately think of the Green Anaconda or the Piranha, the Black Caiman is the largest member of the Alligatoridae family and can reach lengths of over 16 feet. It is an apex predator that preys on a wide variety of animals, including fish, turtles, birds, and even large mammals like capybaras or tapirs that come to the water's edge. Unlike the piranha, which is largely a scavenger or a school-hunter of smaller prey, the caiman has no natural predators once it reaches maturity. Another contender for the title is the Giant River Otter, often called the "river wolf" due to its aggressive group-hunting tactics that can even drive away caimans. However, in a one-on-one scenario, the sheer size and crushing jaw force of the Black Caiman make it the king of the river. The Bull Shark also enters the upper Amazon, but it is a transient visitor compared to the resident caiman, which dominates the complex food web of the world's largest river system.