Biology Reference
In-Depth Information
likely that species richness is even greater, since the Australian studies are
based on small sample sizes, and other authors had already recorded one
species of monogenean and three species of digeneans from Australian
eels, not found by Kennedy. The component community richness of
intestinal helminths was 3-9, and the infracommunity richness 1.2-3.6,
with a maximum of seven species.
The studies by Hine (
1980a
,
1980b
) and Hine and Francis (
1980
)of
parasites of 839 Anguilla australis and 459 A. dieffenbachi from 34 localities
in New Zealand recorded a total of 21 metazoan species of parasites, of
which about 18 are from the digestive tract, including 11 species occur-
ring at high prevalences of infection in both hosts, and 7 at low (
10%)
prevalences. Of the latter, one was found only in A. dieffenbachi, and
four were found only in A. australis. No distinction is made between eel
specialists and generalists. However, Kennedy (
1995
) has shown that very
few of the rare species and most of the common species in Australia are
eel specialists. Therefore, as an approximation, about 11 species can
be considered to be specialists; 8 species, including 4 common ones,
were trematodes. Data on infra- and component community richness
were not given.
According toMarcogliese and Cone (
1998
), differences in the numbers
of specialist species between Britain/Canada on the one hand and
Australia on the other are significant: only 7 out of 12 species in Nova
Scotia and 8 out of 25 species in Britain were eel specialists, compared
with 15 out of 27 species in Australia. This shows that Atlantic eels
have much poorer parasite communities than A. reinhardti in Australia,
particularly with regard to specialist parasites. New Zealand eels share
ten helminth genera with Australian eels (Kennedy
1995
), but total
parasite richness and total richness of intestinal helminths, in particular
of species occurring at high prevalences of infection and therefore pro-
bably eel specialists, are smaller in New Zealand than in Australian
A. reinhardti.
How can the differences be explained? The fact that both component
communities of parasites and infracommunities are richer in Australia,
suggests that ''supply side ecology'' may be an explanation, and that
infracommunities are not limited by competition between species within
them, as suggested by Kennedy and Gu´gan (
1996
). Rohde (
1998b
) has
used computer simulations to show that a curvilinear relationship
between component and infracommunity richness may be a consequence
of differential colonization rates and life spans of species in the commu-
nities (Figure
4.1
). It is not necessary to invoke interspecific competition,
