If it killed the top level of an ecosystem it would damage the whole ecosystem because it's connected. An organism depends on that top organism which would mean that is that organism dies it would affect the organism that depends on it.
Lying generally between the foot of acontinental rise and a mid-ocean ridge,abyssal plains cover more than 50% of the Earth's surface. the zone of theocean floor that separates the thinoceanic crust from thick continentalcrust. ... the slope between the outer edge of the continental shelf and thedeep ocean floor.
Endocrine system is the answer
Cat (Australia); lots of cats became feral and they reproduce very fast. They became the apex predator and the native species have no defense system for them, so the cats brought tens of species on the verge of extinction (mainly placental mammals).
Fox (Australia); became an apex predator in the lack of competition, and damages the populations of native small placental mammals.
Hair (Australia); reproduces much quicker than the native species of mammals, increased significantly in numbers, and out competes the native species for the food sources.
African bee (the Americas); much more aggressive and stronger than the native bees and systematically kills their populations.
Grey squirrel (Britain); reproduces quicker than the red squirrel, is bigger, and out competes for food, brought it on the verge of extinction.
Yes they are alive in numbers today and they are known as one of the most top shark killers there are, other than the great white shark and killer whales. *there is a pic below of the shark, I take no credit for it, I just found it off google.