Biology Reference
In-Depth Information
Examples of communities without evidence of competition
Rathcke (
1976a
,
b
), Strong et al.(
1979
), Strong (
1981
), and Price (
1980
)
give examples of communities in which there is no evidence of compe-
tition (see also some contributions in Esch et al.
1990
). For insects of
Pteridium aquilinum, which are among the best studied communities (see
Lawton
1999
), and for other phytophagous insects (see Strong et al.
1984
) there is little or no evidence of interspecific competition.
Kennedy (
1990
) concluded that helminth communities of freshwater
fish, on the whole, are chance and ''isolationist'' assemblages rather than
structured communities, and Aho (
1990
) concluded that helminth
communities of amphibians and reptiles are depauperate and non-
interactive. According to Pence (
1990
), little is known about helminths
of mammals but, although some mammals may have an interactive
community of helminths (see Haukisalmi and Henttonen
1993a
,
b
),
in other mammalian hosts indirect evidence indicates that their
helminth communities are isolationist and non-interactive (see also
pp. 121-127). Combes (
2001
, pp. 411-413, references therein)
briefly discusses a number of examples with clearly unsaturated infra-
communities, i.e., isolationist communities of parasites with little or
no evidence of interspecific competition. They include helminths of
eel in Britain and Italy, trout, four species of the teleost Lepomis,
Mediterranean sparid and labrid fishes, four species of salamanders,
ectoparasites of Alaskan birds, some gull species, a swan in Poland, and
bats. Some examples of interactive communities include intestinal hel-
minths of lesser scaup (Asythia affinis) in Canada, and the coot Fulica atra
in Poland. Combes gives more examples of isolationist than of inter-
active communities, and even some of the examples for interactive
communitiesgivenbyhimaredoubtful.Thus,hereferstoastudyof
Kennedy and MacKinnon who have shown that two species of the
nematode Thelazia ''show distinct preferences in their locations within
the eyes of cattle (eyelids, various glands, etc.), indicating that they also
form an interactive community.'' No evidence that competition is
responsible for the habitat segregation is given, which may also be due
to random selection of habitats or reinforcement of reproductive bar-
riers. (see pp. 39-47 and Chapter
5
).
Some authors have used the asymptotic relationship between
local and regional species richness as evidence for species saturation
and the effects of interspecific competition, as discussed in the
following.
