Predation is an ecological factor of almost universal importance for the
biol- ogist who aims at an understanding of the habits and structures of
animals. Despite its pervasive nature opinions differ as to what
predation really is. So far it has been defined only in negative terms;
it is thought not to be par- asitism, the other great process by which
one organism harms another, nor filter-feeding, carrion-eating, or
browsing. Accordingly, one could define predation as a process by which
an animal spends some effort to locate a live prey and, in addition,
spends another effort to mutilate or kill it. Ac- cording to this usage
of the word a nudibranch, for example, that feeds on hydroids would be a
predator inasmuch as it needs some time to locate col- onies of its prey
which, after being located, scarcely demand more than eating, which
differs little from browsing. From the definition just proposed
consumption of the prey following its capture has been intentionally
omit- ted. Indeed, an animal may be disposed of without being eaten.
Hence the biological significance of predation may be more than to
maintain nutrition- al homeostasis. In fact, predation may have
something in common with the more direct forms of competition, a facet
that will be only cursorily touched upon in this book.