Predator - Prey Relationships

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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 they 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 nourishment 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' s 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 example of this is the roundworm, which has protective coating around it's 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 host's 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 special 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...
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