|Carnivore | Deposit feeder | Herbivore | Omnivore | Parasite | Scavenger | Suspension feeder|
Predators are either carnivores or omnivores. The difference between a predator and a parasite is that for a predator killing the prey is necessary for consuming it, but for parasites it is not even desirable because a parasite lives on or in its host.
Herbivores also consume other species, but generally only in part, leaving the organism alive. However, where the prey consists of single-celled algae, the activities of the herbivorous grazer is generally of the same nature as that of a carnivore. As often in ecology there is seldom consensus on the distinctions; some ecologists prefer functional definitions like the one outlined above, others rather look at the ecological dynamics the relationships between the species create. The Volterra-Lotka equations describe a simple mathematical model of the interaction between predators and their prey.
There may be hierarchies of predators; for example, though small birds prey on insects, they may in turn be prey for snakes, which may in turn be prey for hawks. A predator at the top of its food chain (that is, one that is preyed upon by no organism) is called an apex predator; examples include the great white shark, tiger and crocodile and even omnivorous humans (although, given the chance, some predators such as the Australian salt water crocodile will prey on humans). Such predators may have a profound influence on the balance of organisms in a particular ecosystem; introduction or removal of this predator, or changes in its population, can have drastic cascading effects on the equilibrium of many other populations in the ecosystem.
Specialists and generalists
Many predators specialize in hunting only one species of prey. Others are more opportunistic and will kill and eat almost anything. The specialists are usually particularly well suited to capturing their preferred prey. The prey in turn, are often equally suited to escape that predator. This is called an evolutionary arms race and tends to keep the populations of both species in equilibrium.
There is a full spectrum of specialization. Some predators specialize in certain classes of prey, not just single species. Almost all will switch to other prey (with varying degrees of success) when the preferred target is extremely scarce.
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