Concepts and problems - Nonequilibrium Ecology - page 6

competition) are not considered worthy of publication. Furthermore,
''many scientists feel compelled to fit data into some existing body of
theory, and do not feel equally compelled to falsify theory.'' Thus, very
little of the supposed evidence for interspecific competition has been
tested objectively (see Connell 1980 , and pp. 64-65). Price ( 1984 ) there-
fore proposes that ecologists should test several hypotheses (''paradigms'')
to elucidate simultaneously processes determining community structure.
These hypotheses include the null hypothesis that species respond indi-
vidualistically to selection pressures, without competing for resources,
simply living where conditions are favourable (Gleason 1926 , Ramensky
1926 ); the resource heterogeneity hypothesis, that the number of species
in a community is positively correlated with the number of resources, and
their abundance with the abundance of the resources needed by the
species; the island or patch size hypothesis, according to which area
alone determines the number of species; the time hypothesis, according
to which species numbers are determined by (ecological or evolutionary)
time; and the enemy impact hypothesis, which says that enemies (e.g.,
parasites or predators) limit population sizes below the level at which
resources become limiting. But not only should the relative importance
of the various hypotheses be examined, but also the mechanisms
involved. Hypotheses may be difficult to test for many communities
and under many conditions. Price ( 1984 , p. 374) lists characteristics of
communities that make them suitable for hypothesis testing.
Price ( 1980 ) devotes a large chapter in his Evolutionary Biology of
Parasites to ''nonequilibria'' in populations and communities, and other
chapters also contain relevant information on this subject. In particular,
the chapter on ''Ecological niches, species packing, and community
organization'' gives a comprehensive discussion of nonequilibrium in
parasite communities. Equilibrium is a population state in which birth
and death rates are equal, i.e., where there is no population growth
(MacArthur and Wilson 1967 , May 1973 ), or - more realistically in
stochastic environments - where population size fluctuates around an
average with steady average variance (May 1973 ). If variance is high,
systems are unstable, if it is low, they are stable. Price ( 1980 ) draws
attention to the difference between parasites and predators or browsers:
a parasitic individual typically spends much of its life in a single or perhaps
two patches (host individuals), whereas the latter search many patches.
Globally, for parasites, there may be equilibrium, i.e., the proportion of
patches occupied may remain stable, but within a patch, nonequilibrium
conditions are highly likely (e.g., orange mites studied by Huffaker 1958 ).