Symbiotic
relationships among species are a bit rarer. That is, a truly symbiotic
relationship in which two species have adapted their interaction behavior such
that both benefit from the relationship is not terribly common. Certain species
of ants, for example, will maintain farms of aphids. The ants provide food and
protection for the aphids, and the aphids in turn produce an excess of sugar
laced honeydew that the ants gather for food. In this relationship, both
species derive a direct benefit from the others’ behavior; one species is not a
direct predator of the other.
Parasitic
interactions connect different species through relationships in which one
species derives some essential benefit from the other species without providing
a reciprocal benefit in return. In many instances, a parasite may well be
detrimental to its host species, but perhaps not to the extent of causing the
death of the host. Thus, the relationship can last over multiple generations of
the two species. Large vertebrate species carry invertebrate parasites within
their digestive or cardiac circulatory systems.
Finally, we come
to the predatory relationships that define much of our conceptualization of
nature. Many ecosystems have evolved complex food chains that encompass the
interaction types that we are discussing. Throughout such food chains we might
well observe a variety of predatory relationships and their subsequent
interaction types. We’re well aware of the predatory nature of large carnivores
given the innate fear that most members of the human species have for them; “Lions
and tigers and bears; Oh my!” But, predators and prey exist at all levels
within ecosystems, as the poem, usually attributed to Jonathan Swift, says:
Big bugs have little bugs
Upon their backs to bit’em.
And little bugs have littler bugs,
And so ad infinitum.
Within a
physical ecosystem, success of a species may be measured by the number of
members of that species found. To achieve that number, there are no a priori limits on the actions or
behavior of members of any specific species in their interactions with members
of other species. Eat or be eaten is
probably a pretty good catch phrase for operating within such an ecosystem.
However, the interactions among species and within species are replete with
examples of sacrifice and behavior that we view as altruistic when we give it
an anthropomorphic guise.
A mother bear
will challenge much larger male bears if she feels they are threatening her
cubs. Male penguins sit for months without eating in order to incubate an egg
in the frozen reaches of Antarctica. And birds, both mothers and fathers,
will work incessantly to forage for food to feed their nestlings. However, such
higher-order behaviors are subject to the satisfaction of lower-order needs. A
mother gazelle may abandon her young if it is unable, perhaps due to injury or
illness, to keep up with the movement of the herd from which the mother derives
protection and support. Many other counter examples to apparent altruistic
behavior exist as well. Some species will actually eat their young if they
encounter them following their birth. Male bears are known to attack cubs in
some instances. And, sometimes birds will abandon their nests for yet unknown
reasons. Such examples serve to illustrate that full understanding of inter-
and intra-species interactions is not warranted; however, a variety of models
have been suggested for various species. Since the primary objects of our
interest are humans, computers, their groupings and their interactions, we will
concentrate our discussion in these areas.
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