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 ití
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 itís 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 hostís 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 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,
metabolism, 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 itís 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 itís 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