An organism that captures and survives by feeding on other organisms is called as predator.
The predator gains energy to sustain life and encourage its reproduction on the cost of an organism being eaten, the prey. Predators sit at the top of the food chain and consume its prey perched one trophic level below, which in return eats plants, the basis of the ecosystem (Hairston et al. 1960). Predator plays a very crucial role in framing the ecosystem structure and function. Predator-prey interactions change the community structure, arbitrate trophic cascades, and influence biodiversity and species invasions. Moreover, the prey population dynamics can be controlled by predators by affecting features such as survival, behavior, growth, size, structure, and distribution over an area. Besides animals, carnivorous/insectivore plants like the Venus fly trap and pitcher plant which feed on insects also show predation. These plant species grow in nitrogen-deficient soil. Pitcher plants seize their prey in a cavity containing liquid with digestive enzymes; in contrast, the Venus fly trap catches an insect within the leaf lobes, and the insect is sealed inside. The required nutrients are absorbed by the plants from these insects. Microorganisms like protozoa and bacteria also ingest their prey through phagocytosis. These microbes play very crucial role in balancing population size in microbial communities, which in turn stimulate the diversity of microbes and provide a stable community structure. Predators not only involve the fanged animal that consumes primary consumers but also include organism feeding on those organism which are smaller or of the similar size or even larger like grazing animals whether the grazed organisms can be plankton or mats of microbes (Bengtson 2002). Sometimes seed consumption is also considered as predation as seeds are thought as organisms. Under ideal conditions, seeds emerge to become a complete plant, although, consuming a seed terminate the plant before it can originate, making seed consumption an example of predation (Janzen 1971). Seed predators are limited mainly to mammals, birds, and insects and are present in nearly all terrestrial ecosystems (Hulme and Benkman 2002). Likewise, consumption of egg is also considered in the category of predation as it also causes the death of an entire organism before its growth (Nilsson et al. 1985). Egg predators comprise of some snakes, birds, and mammals, for example, red fox as they opportunistically eat the egg (Hanssen and Erikstad 2013). There are some nematophagous fungi that feed on nematodes which use either active traps in the form of constricting rings or passive traps with adhesive hyphal structures (Pramer 1964). There are a number of microbes like bacteria and protozoa that prey on other microorganisms and hence play very significant role in regulating population sizes in these microbial communities promoting diversity of microbes and stable community structure (Velicer and Mendes-Soares 2009; Stevens 2010a).
Adaptations which make predator highly specialized for killing the prey include sharp teeth, claws or jaws to hold the prey, and venom. Moreover, predators are adapted with highly specialized acute senses such as vision, hearing, or smell. Other adaptations include stealth and aggressive mimicry that improve hunting more efficient. Predation has a powerful selective effect on prey, and the prey develops antipredator adaptations such as warning coloration, alarm calls and other signals, camouflage, mimicry of well-defended species, defensive spines, chemicals, etc.
Classification of Predators
Predators can be classified in two ways: (1) taxonomical classification and (2) functional classification (Begon et al. 2006). Taxonomical classification consists of carnivores consuming plant-eating herbivores. The functional classification includes four types of predators: true predators, grazers, parasites, and parasitoids. True predators more or less kill their prey right after attacking them. Some examples of true predators are most of the carnivorous animals like lion, tiger, eagles, and snake and some carnivorous plants such as pitcher plant and so are seed-eating rodents and ants, plankton-consuming aquatic animal, and so on. Grazers are organisms that partially consume their prey and are hardly lethal. It attacks large number of organism (prey) in their life span. Grazing differs from true predation in the way that the organism being grazed is not killed. The vertebrate herbivores like cattle and sheep are the most common examples of grazers. Parasites feed on parts of their prey (their host) and are rarely lethal in short span of time. Examples of parasites are tapeworm, liver flukes, many pathogenic bacteria, fungi viruses, etc. Parasitoids are the organism that lives in association with their host bodies where they feed, grow, and ultimately kill their host.
Adaptations for Predation
Predators are key driving factors in structuring ecological communities and processes. A predator’s utmost important task is to find or search, chase, and kill its prey to feed. Once predator locates its prey, it must evaluate either to pursue it or to wait for a better option. If the prey organisms are large in number and are mobile, in that case, the sit-and-wait method is the most appropriate method of foraging (Bell 2012). If preys are inactive and scantly distributed, in that case, foraging requires more energy. Predators catch their prey either by pursuing potential prey or by ambushing them. Predation affects the fitness of prey and predators both. To survive and reproduce, organisms must both feed and protect themselves from being eaten. Genetically determined traits that improve an organism’s ability to sustain and reproduce will be transferred to next generation. Traits related with improved predation for predators and escaping predation for prey inclined to be positively selected by natural selection. Predators exhibit a variety of adaptations like sharp teeth, claws, speed, and venom that strengthen their capability to catch food. They also own extremely vital sense organs which help them to detect potential prey. To sustain life, predators must be capable to outsmart their prey and use their acute senses, as well as evolved physical adaptations such as sharp teeth and claws, with various hunting tactics.
Predators have fine sense of smell, vision, and hearing which tend to be very curious regarding their surroundings.
Predators have forward-facing eyes placed on the front of their head providing them three-dimensional binocular visions, whereas eyes of the prey are placed on the sides of their head. Forward-facing eyes allow predator a more restricted view of the surrounding than prey and make it easier to determine distance and see each and every detail from far distance. Apart from binocular vision, predators also have big eyes which help them to pick up light signals easily and are therefore able to spot quick movements.
While predators depend greatly on their sight to locate the prey, they also possess a well evolved sense of smell. Almost all animals release some chemicals into the environment, which are by-products of metabolism. Many predators have the capability to detect these chemicals to find the animals releasing them (Conover 2007). There are some animals such as fox, wolves, and coyote that rely on their sense of smell rather than their vision. These animals possess longer snout which has chemically sensitive cells. For example, foxes are very sensitive to smell such that they can smell their prey lying even two feet under the soil or snow. Reptiles also bear acute sense of smell and can detect smells in very different manner. They stick out their tongues to sense smell in the air. A special organ, Jacobson’s organ, present on top of the reptiles mouth, allows them to smell chemicals present in the air and detect food present nearby.
Predatory animals have a very sharp sense of hearing. They have a special feature of rotating their ears forward and backward to locate the direction from where the sound is coming. The most common example is the bat, which has very sensitive hearing. They have large ears as their primary means of finding prey. Bats produce high-pitched ultrasonic sound waves which are above the upper limit of human hearing. Whenever these sound waves hit something it produces echo. These echoes are heard by bats and they can locate the object. This process of echolocation is used by bats to find their prey. Dolphins also echolocate their prey.
Predators have developed different methods of locating and killing their prey. Some of these strategies include stalking, chasing, sit and wait, etc.
Predatory animals that stalk and follow their prey have very well-developed features which assure that they are able to sneak on their prey undetected. For example, soft padded and retractable paws of cats help them to walk silently. Animals stalking for their prey must have quick reflexes to ensure that their prey is caught.
Sit and Wait
This sit-and-wait strategy requires less energy. The animal that employs this strategy to kill its prey generally has some form of camouflage. They blend in with their surroundings to avoid detection and wait for their prey. The sit-and-wait method of foraging is suitable if preys are densely populated and mobile, and predators require less energy.
Some predators hunt their prey in groups. The advantage of group hunting is that the large number of predators kills prey animals much larger than themselves. For example, this type of hunting strategy is often seen in wolf packs which have very systematic way of hunting.
Apart from various hunting strategies, the predatory animals have adapted different traits such as sharp teeth, jaws, claws, and venom that increase their capability to catch food.
Teeth and Claws
Predatory animals possess long, sharp claws and teeth particularly for tearing, shearing, and cutting the prey. Predatory birds such as hawks, eagles, and falcons have special long curved claws called talons, which help these birds to grasp their prey easily.
Jaws of predatory animals are very strong which enables them to hold and kill the prey as well as tear them to feed themselves. The jaws move up and down which enables the predator to cut through flesh. Snake’s jaw is adapted in order to swallow whole prey.
Many predatory animals possess some specialized body parts that help them to catch and consume their food. Frogs bear long tongues that help them to capture insects, and long sharp beak of great blue herons helps them to catch fish. Likewise, otters have webbed feet and distinctive oils which make them waterproof and help them swim easily and catch food. These specialized characters have been adapted according to environment and feeding conditions.
Predatory animals are more intelligent than the prey. Their intelligence helps them to outsmart their prey. Crows and raven are among the most intelligent birds. They can even copy various sound such as cat meows and whistles.
To avoid predation, prey animals must escape from the predators to survive. The aim of feeding is to locate and capture food without being caught by the other animal. Lots of prey animals have developed and adapted to protect themselves from predators: camouflage, senses, warning signals, different types of defensive weapons like chemical defense, behavioral adaptations like bluffing, hiding, and living in groups. In order to survive, prey animals use these kinds of adaptation against predators.
Coevolution of Predators
Predator-prey interactions are very prevalent in nature. Predator and prey are adapted in such a way that they can counter each other. For example, bats uses echolocation system to detect their prey, and in return, insects have adapted various defenses to counter bats including the capability to hear the echolocation call. Likewise the land predators such as wolves have evolved long limbs to run after prey. These types of adaptation have been characterized as an evolutionary arms race, an example of the coevolution of two species. When a predator pursues a potential prey, the predator is chasing its food, and the prey is running to save its life. If in any case predators fail to catch the prey, it remains starving, but as a consequence of this interaction, it will not suffer a large decline in fitness. In contrary, if the prey is captured by the predator, the seized animal loses opportunity to reproduce in the future. This “life-dinner principle” arranges an evolutionary arms race between the two species (Dawkins and Krebs 1979). In this evolutionary race, the prey undergoes strong selective pressure to evolve better to prevent predation. At the same time, for survival and reproduction, predators must capture sufficient food, and they are put through selective pressure for traits that allow them to hunt successfully. Because of this arms race, the prey has been capable to avoid capture, and predators become able to catch prey efficiently. In some of the examples explained so far, some of the prey species possess bright coloration. Such aposematic coloration helps prey animals from predation by signalling predators that the brightly colored individual is toxic (Stevens 2010a). All the vivid colorations exhibited by the species are not truly toxic. In some species patterns and colors have evolved to mimic those of toxic species. Batesian mimicry is one of such examples, which includes the exceptional polymorphic Papilio dardonus swallowtail butterfly in Southern Africa and Madagascar (Salvato 1997). Female of this species presents in a wide variety of physical appearances among which most of them mimic distasteful species of the Danaus and Amauris genera with which they co-occur.
Dynamics of Predation
Population of species is not everlasting. The number of individuals in a population keeps changing from one time period to the next. Such fluctuations are regulated by the resource availability. When the resources are limited, population declined as organism competed for the limited resources. This process of bottom-up control helped to regulate the population about carrying capacity. Recently, scientist has found that predator population can affect the prey population size by acting as top-down control. If predators are not present, the population of species grows exponentially till it reaches the carrying capacity of the environment (Neal and Dick 2004). Predators often control the growth of prey species both by consuming them and by changing their behavior (Nelson et al. 2004). Actually, the interaction between these two patterns of population control efforts together to operate changes in population over the time. Some other factors like parasite and disease can further influence the population dynamics.
Role of Predators in Ecosystem
Predators play a very important role in the trophic cascades. They are connecting link between nutrient cycling. They can affect the genetic makeup, morphology, physiology, and behavior of prey species. They regulate and control the population of the prey.
Role in Food Chain
Predators are at the top of the food chain and they play an important role in linking the nutrient cycles in the ecosystem. In the absence of predators, herbivores began to overgraze many plant and grass species, hence, affecting the area’s plant population. In a decisive study on the effects of predators on the environment, William Ripple and Robert Beschta (2009) of Oregon State University found that the presence of large predators is important in sustaining native plant communities in both upland and riparian (stream or river) settings because plants contribute to a wide range of “ecosystem services” such as floodplain functioning, soil development, and stream bank/channel stability.
Selective Impact on Prey
Predators are very selective in choosing the prey species. Predation on larger prey often demands substantial threat to the predator and always demands a significant investment of energy. Accordingly, the predators always select the convenient prey, sick, young, and weak.
Biodiversity Management by Predators
Biodiversity of different communities may be increased by predators. By preventing single species from becoming dominant, predators manage the biodiversity. Such predators are called keystone species and can have acute effect in balancing the organisms in a particular ecosystem (Bond 2012). Introducing or removing this predator by changing its population density can result in drastic cascading effects on the equilibrium of many other populations in the ecosystem. For example, in grassland ecosystem, grazers may control the single dominant species from becoming most influential (Botkin and Keller 2003).
Predators are important in maintaining a healthy ecosystem. Predators are important not only because they create biodiversity but also because they indicate biodiversity. In addition to regulating natural systems as described above, predators (especially large predators) serve as a measure of the health of communities around them. Top predators are associated with high biodiversity value because they are sensitive to ecosystem dysfunctions, such as pollution and habitats.
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