Predator - Prey Relationships The relationship between predators and their prey is an intricate and complicated one; cover a vast field of scientific knowledge. This article will examine the different relationships between predator and prey; focusing on the symbiotic relationships between organisms, the wide range of defense mechanisms used by various prey examples, and the influence between predators and prey regarding evolution and population structure. Symbiosis is the interaction between organisms that form a long-term relationship with each other. Many organisms become dependent on others and need each other or each needs the other to survive. Symbiotic interactions include forms of parasitism, mutualism, and commensalism. The first topic of discussion in symbiosis is parasitism. Parasitism occurs when the relationship between two animal populations becomes intimate and individuals from one population use the other population as a food source and may be in or on the host animal or the animal from the other population (Boughey 1973) . No known organism escapes being a victim of parasitism (Brum 1989). Parasitism is similar to prediction in that the parasite derives nourishment from the host it feeds on and the predator derives nourishment from the prey it feeds on (Nitecki 1983). Parasitism is different from most normal predator prey situations because many different parasites can feed on a single host, but very few predators can feed on the same prey (1973). Parasite-host relationships: Most commonly the parasite is smaller than the host. This would explain why many parasites can feed on a single host. Another difference in the parasite-host relationship is that normally the parasite or group of parasites does not kill the host while feeding, whereas a predator kills its prey (1983). Efficient parasites will not kill their host at least until their life cycle has been completed (1973). The ideal situation for a parasite is one in which the host animal can live long enough for the parasite to reproduce several times (Arms 1987). Parasites fall into two different categories depending on where they live on the host. Endoparasites are usually the smallest parasites and tend to live inside the host (1973). These internal parasites possess some physiological and anatomical adaptations that make their life easier (1987). An example of this is the roundworm, which has a protective coating around its body to ensure it is not digested. Many internal parasites must have more than one host in order to reproduce (1989). A parasite can lay eggs inside the host it lives in, and the eggs are expelled in the host's feces..