Nonequilibrium in communities - Nonequilibrium Ecology - page 27

Figure 2.1. The trematode Syncoelium filiferum from the gill arches of the teleost fish
Seriolella brama in New Zealand. It is one of the very few (if not the only) species of
trematode infecting the gills of fish, most others occurring in the digestive tract and
associated organs. It is attached by means of a very large ventral sucker to the spines of
the bony gill arches. From Rohde, Roubal, and Hewitt ( 1980 ). Reprinted by
permission of the Royal Society of New Zealand.
''insensitive to the presence or absence of other species.'' With regard to
interspecific competition, patterns found in many communities may be
explained by competition, but also by alternative hypotheses.
The following example of a very simple community of gill parasites
shows the difficulties or, in the absence of fossil data, even the impossi-
bility of making a decision as to whether the individualistic or structured
hypothesis is correct. It also shows that the possibility should not be
disregarded that a community may be composed partly of individualistic-
ally assembled and partly of interacting species. Nineteen Seriolella brama,a
small to medium sized teleost fish, were examined at a locality in New
Zealand (Rohde et al. 1980 ). The gill parasite community consisted of
three species, the digenean trematode Syncoelium filiferum (Figure 2.1 ) ,
and the monogeneans Eurysorchis australis (Figure 2.2 ) and Neogrubea
seriolellae (Figure 2.3 ). The first species is an opportunistic parasite
which infects a wide range of marine teleosts, whereas the other two
are, on present knowledge, specific to two species of Seriolella. A pre-
requisite for successful infection with Syncoelium is presence of spines on
the bony gill arches to which it can attach by means of its ventral sucker.
Eurysorchis inhabits the bony gill arches, pseudobranchs and mouth cavity,
attached to these flat surfaces by means of its large flattened clamps which
act as suckers. Neogrubea is always attached by means of its clamps to the
gill filaments, which are ''grasped'' by the two valves of the clamps. All
three species have clear morphological adaptations to their microhabitats