Predation refers to a flow of energy between two organisms, predator and prey. In this interaction, the prey loses energy, and the predator gains energy.
The word ‘predation’ derives from the Latin word praedari, meaning ‘to plunder’.Predation includes carnivory, as well as interactions like grazing, parasitism, and symbiotic mutualism. The process of eating seeds and eggs is also considered a form of predation.
Types of Predation
There are four major types of predation:
Carnivorous predators kill and eat their prey. The common perception of carnivory involves a large animal, such as a shark, tiger, or wolf hunting smaller animals like rabbits or deer. However, carnivorous predation is widespread in the animal world and carnivores can come in a variety of sizes – from sea otters hunting sea stars to blue whales consuming zooplankton, each carnivore is adapted to its mode of feeding.
Herbivorous predation involves the consumption of autotrophs, such as plants or photosynthetic algae. Unlike carnivory, not every herbivorous interaction leads to the death of the plant. Occasionally, herbivory can benefit the plant as well.
Fruit seeds are dispersed over wide areas as the herbivore moves. Tough seed coatings are removed in the digestive tract of the herbivore, and its dung fertilizes the soil, providing an ideal environment for seed germination.
Parasitism is a form of predation where the host supplies essential nutrients for the sustained survival and reproduction of the parasite. In many successful parasitic interactions, the host suffers a loss of energy, falls sick, or loses access to nutrients. However, unlike carnivory, the host is not always killed. In most cases, the parasite is much smaller than the host.
Mutualism involves the interaction between two organisms where the host provides the nutrition and space for the growth and reproduction of another species. However, the host is not harmed and the interaction is mutually beneficial.
Examples of Predation
Wolves are large canines that primarily hunt large herbivores such as deer, elk, and sheep. They are particularly well-adapted hunters, with strong jaws, heightened senses, and powerful bodies, they can identify and chase prey at high speeds.
Carnivorous predation can also be an interaction between two groups of organisms. While many carnivores hunt prey that is much smaller than themselves, some cooperate with other individuals of their species to bring down larger prey.
For example, lions coordinate in groups to ambush and take down large herbivores such as zebra and rhinos. A pack of Asiatic wild dogs can pursue and hunt large bison that is nearly 10 times the size and weight of a wild dog.
Carnivorous predation is also seen in the plant kingdom, among insectivores such as pitcher plants and Venus flytraps. Insectivores are often found in regions where the soil is not rich in nutrients. One exceptional and unusual form of carnivorous predation is cannibalism, where individuals consume members of their own species.
Grazing is a form of herbivory where the plant regenerates the parts that were eaten by the herbivore. Herbivores are adapted to their mode of feeding. For example, elephants have large flat teeth to grind tough plant material. They also contain microorganisms in their gut to digest plant-based carbohydrates.
Plants have been known to develop defenses against grazing. When giraffes feed on acacia trees, the trees release a toxic substance into their leaves that forces the giraffes to move away from them. In addition, the acacias also release ethylene gas, which signals to trees in the vicinity to pump toxins into their own leaves. The herbivores usually move around 300 feet (91 meters) away to resume feeding.
In marine environments, krill are small crustaceans that feed on the primary photosynthetic organism of the ocean – phytoplankton. Krill are crucial to the health of the ecosystem because they are the main natural food source for many fish as well as large mammals like blue whales.
The parasite that causes malaria, Plasmodium, infects a wide variety of animal hosts, including reptiles, birds, and mammals. The infection and causes cyclical rounds of high fever and chills, and can even kill the host.
Tapeworms are common human parasites that can cause malnutrition, especially in young children. Filarial worms are parasites that cause skin, eye, and lymphatic diseases.
Parasitism is also seen in the plant kingdom. Strangler figs are common tropical plants that behave like parasites. Many belong to the genus Ficus. Their seeds germinate in the crevices of other trees, and they derive their nutrition by dropping roots into the bark of the host tree, rather than into the soil. Over time, the host tree dies and the strangler fig appears as a tree with a hollow central column.
The interaction between humans and their gut flora is a classic case of mutualism. The bacteria aid in digestion and provide protection against the invasion of pathogenic bacteria. Recent research suggests that the collection of all gut bacteria in an individual can have a widespread impact on the host’s metabolism, immunity, and well-being.
Similarly, the root nodules of leguminous plants, such as chickpea and soybeans, play host to nitrogen-fixing bacteria. The bacteria fix atmospheric nitrogen, thereby increasing nutrient availability for the plant. In turn, the plant provides a rich sugar solution to the bacterium.
Trophic levels refer to the hierarchical stages in a food chain, starting from autotrophs and moving towards primary, secondary, and tertiary consumers. An organism that is a predator at one trophic level can become the prey at a higher trophic level. For example, krill are predators of phytoplankton but are also the prey of higher predators, penguins. At the next trophic level, penguins are the prey of sharks.
Animals at the top of the food chain are called apex predators. They have no known predators. Often, they play a key role in maintaining the biodiversity of the ecosystems and are considered keystone species. Any changes to their population or density have a wide range of effects on the relationships present in the entire ecosystem.
It is estimated that only 10% of the energy available at one trophic level is available to the predator at the next level. Therefore, most food chains and webs do not have more than three or four trophic levels.