The term carnivore is used in a variety of ways. The general ecological definition of a carnivore is an organism that feeds on animals, as opposed to feeding on plants (herbivores) or dead organisms (detritovores). Often, specialist carnivores are defined by the type of animal that they consume. For example, insectivores feed on insects, piscivores feed on fish, and vermivores feed on worms. In practice, the term “carnivore” is often applied, in the narrow sense, to organisms that consume meat, for example a lion feeding on a zebra or a fox feeding on a hare. There are carnivorous animals, plants and fungi. By definition carnivores lie at trophic level 3 or higher on the ecological food pyramid, since they consume other animals, who in turn are consumers of an even lower trophic level.
The term carnivore can also be applied to members of the Mammalian order Carnivora which includes dogs, cats, bears, weasels, skunks and seals.
Cheetah displaying teeth, an effective tool for snaring prey, eastern Namibia. @ C.Michael Hogan Carnivorous animals devour other animals to gain both energy and nutrients. Carnivorous animals may kill their food directly (predators) or they may eat animals that have either been killed by other predators or died naturally (scavengers). Carnivorous animals are found in terrestrial, marine, and freshwater habitats. Carnivores range greatly in size. Some carnivores can be quite large, including the blue whale, the largest animal on Earth, whereas others, such as predatory nematodes in the soil, can be quite small.
Predatory carnivores have adaptations that allow them to capture and eat their animal prey including crypsis, speed, size and strength, sharp teeth and claws, and poisons.
Carnivores can play important roles in ecosystems through their control of the population size of species in lower trophic levels. Carnivores at the top of the food chain, apex predators, can have profound effects on the trophic levels below them (see Top down control). There are many examples where the removal of top predators, e.g., overharvesting of sharks in the seas, or the reintroduction top predators, e.g., returning wolves to Yellowstone National Park, has had wide-ranging effects on the ecosystem. Carnivorous scavengers play an important role in nutrient cycling.
Venus fly trap consuming faunal prey. Source: Botanical Society of America Some plants that live in low nutrient soil environments capture and digest animals in order to obtain nutrients. Insects are the most common prey of carnivorous plants, but some plants may capture frogs and small mammals. Some carnivorous plants occur in bogs where the high moisture and sunlight availability makes it likely that photosynthesis is nutrient limited. There are over 600 species of carnivorous plants spread across nine plant families.
Carnivorous plants use a variety of strategies for trapping their prey including pitfall traps (pitcher plants), sticky traps (sundews and butterworts), snap traps (venus flytraps), suction traps (bladderworts), and lobster-pot traps (corkscrew plants).
Fungus capturing a nematode. Scanning Electron Micrograph N. Allin and G.L. Barron
Most fungi obtain their energy and nutrients by digesting dead matter. However, some fungi that live in the soil obtain additional nutrients by capturing and ingesting microscopic organisms such as bacteria, nematodes, amoeba, and collembolans. These fungi have evolved both active and passive mechanisms to capture their prey. There are over 200 species of carnivorous fungi spread across three phyla.
Members of this order are technically know as "carnivorans" but sometimes are referred to as carnivores. The Order Canivora contains 0ver 286 species spread across 15 families. Although many members of this order are ecological carnivores, eating meat is not the defining characteristic of this group. Instead members of this order share characteristics of their skulls and teeth.