Predator – Prey Relationships

The relationship between predators and their prey is an intricate and complicated relationship; covering a great area of scientific knowledge. This paper will examine the different relationships between predator and prey; focusing on the symbiotic relations between organisms, the wide range of defense mechanisms that are utilized by various examples of prey, and the influence between predators and prey concerning evolution and population structure. Symbiosis is the interaction between organisms forming a long term relationship with each other.

Many organisms become dependent on others and hey need one another or one needs the other to survive. Symbiotic interactions include forms of parasitism, mutualism, and commensalism. The first topic of discussion in symbiosis is parasitism. Parasitism is when the relationship between two animal populations becomes intimate and the individuals of one population use the other population as a source of food and can be located in or on the host animal or animal of the other population(Boughey 1973). No known organism escapes being a victim of parasitism(Brum 1989).

Parasitism is similar to preditation in the sense that the parasite derives ourishment from the host on which it feeds and the predator derives nourishment from the prey on which it feeds(Nitecki 1983). Parasitism is different from most normal predator prey situations because many different parasites can feed off of just one host but very few predators can feed on the same prey(1973). In parasite-host relationships most commonly the parasite is smaller than the host. This would explain why many parasites can feed off of one single host.

Another difference in parasite-host relationships is that normally the parasite or group of parasites do not kill the host from feeding, whereas a predator will kill it prey(1983). Efficient parasites will not kill their host at least until their own life cycle has been completed(1973). The ideal situation for a parasite is one in which the host animal can live for a long enough time for the parasite to reproduce several times(Arms 1987). Parasites fall under two different categories according to where on the host they live. Endoparasites are usually the smaller parasites and tend to live inside of the host(1973).

These internal parasites have certain physiological and anatomical adaptations to make their life easier(1987). An xample of this is the roundworm, which has protective coating around its body to ensure that it will not be digested. Many internal parasites must have more than one host in order to carry out reproduction(1989). A parasite may lay eggs inside the host it is living in, and the eggs are excreted with the hosts feces. Another animal may pick up the eggs of the parasite through eating something that has come into contact with the feces. The larger parasites tend to live on the outside of the host and are called ectoparasites(1973).

The ectoparasites usually attach to the host with pecial organs or appendages, clinging to areas with the least amount of contact or friction(1973). Both endo and ectoparasites have the capability of carrying and passing diseases from themselves to hosts and then possibly to predators of the host(1973). One example of this is the deer tick which can carry lyme disease and pass it on to humans or wildlife animals. The worst outbreaks of disease from parasites usually occur when a certain parasite first comes into contact with a specific population of hosts(1975).

An example of these ramifications would be the onset of the plague. Many parasites are unsuccessful and have a difficult time finding food because appropriate hosts for certain parasites may be hard to find(1987). To compensate for low survival rates due to difficulty in finding a host, many parasites will lay thousands or millions of eggs to ensure that at least some of them can find a host and keep the species alive(1987). The majority of young parasites do not find a host and tend to starve to death. Parasites are also unsuccessful if they cause too much damage to their host animal(1987).

Parasites are what is called host specific, this means that their anatomy, etabolism, and life-style is adapted to that of their host(1973). Some parasites react to the behavior of their hosts, an interaction called social parasitism(1989). More simply put a parasite might take advantage of the tendencies of a particular species for the benefit of its own. An example of this is the European Cuckoo. In this case the grown cuckoo destroys one of the host birds eggs and replaces it with one of its own(1991).

The host bird then raises the cuckoo nestling even when the cuckoo is almost too large for the nest and much bigger than the host bird(1991). This is a case where the parasite uses the host to perform a function and making life and reproduction easier on itself. Parasite and host relationships hold an important part of homeostasis in nature. (1975). Parasitism is an intricate component in the regulation of population of different species in nature. Mutualism is another topic at hand in discussing predator-prey relationships. Mutualism is a symbiotic relationship in which both members of the association benefit(1989).

Mutualistic interaction is essential to the survival or reproduction of both participants involved(1989). The best way to describe the relationships of mutualism is through examples. We will give examples of mutualism from different environments. Bacteria that lives inside mammals and in their intestinal tract receive food but also provide the mammals with vitamins that can be synthesized(1975). Likewise termites whose primary source of food is the wood that they devour, would not be able to digest the food if it was not for the protozoans that are present in their intestinal tract(Mader 1993).

The protozoans digest the cellulose that the termites cannot handle. Mycorrhizae which are fungal roots ave a mutualistic symbiotic relationship with the roots of plants(1989). The mycorrhizae protect the plants roots and improve the uptake of nutrients for the plant, in exchange the mycorrhizae receives carbohydrates from the plant. Mutualistic partners have obtained many adaptations through coevolution. Coevolution has led to a synchronized life cycle between many organisms and through mutualism many organisms have been able to coincide together as a working unit rather than individuals.

Commensalism is a relationship in which one species benefits from another species that is unaffected(1975). For instance several small organisms may live in the burrows of other larger organisms at no risk or harm to the larger organisms. The smaller organisms receive shelter and eat from the larger organisms excess food supply. An example of commensalism is a barnacles relationship with a whale. The barnacles attach themselves to the whale and they are provided with both a home and transportation. Another example are the Remoras which are fish that attach themselves to the bellies of sharks by a suction cup dorsal fin.

The Remora fish gets a free ride and can eat the remains of a sharks meals. Clownfish are protected from predators by seeking refuge in the tentacles of sea anemones. Most other fish stay away because the anemones have poison that does not affect the clownfish, therefore the clownfish is safe. Commensalism consists of dominant predators and opportunistic organisms that feed off of the good fortune of the larger predators. Another topic concerning predator prey relationships is the defense mechanisms that are necessary for prey to outwit their predators.

In order for an animal to sustain life, it must be able to survive among the fittest of organisms. An animals anti-predatory behavior determines how long it can survive in an environment without becoming some other animals prey. Some key antipredator adaptations will be described and examined . Perhaps the most common survival strategy is hiding from ones enemies(Alcock,1975). Predators are extremely sensitive to movement and locate their prey by visual cues. By getting rid of these key signals, enemies(predators) are forced to invest more time and energy looking for them.

This may increase the time a prey has to live and reproduce(1975). Hiding is generally achieved through cryptic coloration and behavior(1975). How effective an organisms camouflage is depends on how long an organism can remain immobile for a long amount of time. Animals can resemble a blade of grass, a piece of bark, a leaf, a clump of dirt, and sand or gravel. In less than 8 seconds, a tropical flounder can transform its markings to match unusual patterns on the bottom of their tanks in the laboratory(Adler,1996).

When swimming over sand, the flounder looks like sand, and if the tank has polka dots, the flounder develops a coat of dots(1996). Without any serious changes, the flounder can blend surprisingly well with a wide variety of backgrounds Ramachandran, 1996). Behavioral aspects of camouflage in organisms include more than just remaining motionless. An organism will blend into its background only if it chooses the right one. When the right one is chosen, the organism will position itself so that its camouflage will match or line-up with the background.

Despite the fact that an organism may be beautifully concealed, it may still be discovered at some point by a potential consumer(Alcock,1975). Detecting a predator is another antipredator adaptation that is very useful. Some prey species have an advantage over other prey species by being ble to detect a predator before it spots them or before it gets to close to them. In order to detect enemies in good time to take appropriate action, prey species are usually alert and vigilant whenever they are at all vulnerable(Alcock,1975).

A test was conducted in the early 1960s at Tufts University dealing with ultrasonic sound wave that bats give off, and the way moths can detect these soundwaves(May,1991). In most cases bats are blind, so they rely only on their sense of hearing to help them maneuver and hunt while flying in the dark. Also flying in the dark/nighttime, are insects, moths in his case. In a laboratory, bats and moths were observed, and every time a moth would come close to a bat giving off an ultrasonic signal, the moth would turn and go the opposite way(1991).

When the moth would become too close to the bat, it would perform a number of acrobatic maneuvers such as rapid turns, power dives, looping dives, and spirals(1991). Detection by groups of animals will usually benefit the whole group formation. By foraging together several animals may increase the chance that some individual in the herd, flock, or covey will detect a predator before it is too late(Alcock,1975). Each individual benefits from the predator detection and alarm behavior of the others, which will increase the probability that it will be able to get away.

There is always a chance that prey will be chased by a predator. Evading predators is sometimes necessary for an organism to employ, to make sure they will not be captured when being pursued. Outrunning an enemy is the most obvious evasion tactic(Alcock,1975). When a deer or antelope is being chased, they dont just run in one direction to flee, they alter their flight path. The prey will demonstrate erratic and unpredictable movements(1975). The deer or ntelope may zig and zag across a savanna to make it more difficult for the predator to capture them.

Repelling predators is a strategy that can either be last chance tactic or the primary line of defense for an organism. This attack on the predator is used drive it away from the prey. These adaptations can be classified as (1)mechanical repellents, (2)chemical repellents, (3)and group defenses(Alcock,1975). An example of a mechanical repellent is sharp spines or hairs that make organisms undesirable. Some chemical repellents involve substances that impair the predators ability to move or cause a predator to etreat due to undesirable odor, bad taste, or poisonous properties.

Groups of organisms can also repel predators. Truly social insects utilize many ingenious group defenses(1975). For example, soldier ants posses an acidic spray and a sticky glue to douse their enemies with(1975). They can also chop and stab their enemies with their sharp jaws. One of the last types of antipredator behaviors/adaptations is mimicry. An organism that is edible but looks like it is a bad tasting organism is known as a Batesian mimic. A good example of this mimicry works is how birds at first ere more likely to go after the more conspicuous looking items rather than those that didnt stand out(Adler,1996).

If too many mimics exist, more predators will consume them, and soon they will become a primary food source. Organisms that share the same style of coloration take part in Mullerian mimicry. An example of this is the yellow and black stripes on bees and wasps. The symbiont states that this single look helps bird-brained predators to learn which organisms to avoid. This warning coloration in turn saves the organisms life as well as helps the predator to avoid a distasteful, maybe even toxic meal.

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