PATTKRN A N 0 I’KOCESY 1N COI\1PETITLON
27
resulting in a strong tendency for the species of any genus to be
distributed as ecckypes in different habitats, or if not, to be unable to
coexist permanently on the same area of the same habitat.”
Williams (1947) argues that it is insufficient to show that the species
per genus is smaller in smaller communities than in larger, as this is a
mathematical result of taking a smaller sample from a larger group. It
is necessary to show that the species/genus frequency in the smaller
communities is different from expectation in a randomized sample of
the same number of species, selected without reference to generic
relationships from the smaller or larger fauna. Using an index of
diversity Williams (1947) conc~ludcd that Hlton’s data could have been
obtained from a random sample and that the cvidcnce in fact indicates
natural selection in favor of more rather than fewer species in the same
genus in small communities.
Williams (1 951) reiterated his earlier conclusions after analysing
Moreau’s (1948) records of East African bird communities. He showed
an excess of‘congeneric groups with two or more species above what
would be expected by selection without reference to generic relationships, and further that the excess seems to increase as the number of
congeneric species increases. Williams ( 195 1) concluded from this analysis that (1) competition between closely related species is probably on
the average greater than between less closely related species, and (2)
that closely related species are probably more suited to similar physical
environments and, therefore, similar extra-generic competition.
Bagenal (1951) examined the evidence presented by Elton and
Williams and concluded that many of the communities analysed by
Elton (1946) were unsuitable Serause they were often very heterogeneous, were sampled by a variety of methods and the community
was often sampled over a long period of time. Hutchinson’s (1957)
distinction between homogeneously dicerse and heterogeneously diverse
environments implies that we cannot expect species-abundance distributions to behave in the same way under both conditions, a fact
which is relevant to community surveys. As this classification is related
to the free paths of animals in relation to the mosaic of structural and
microenvironmental features of a habitat, it follows that comparisons
between species with different powers of dispersal and daily activity
will also be suspect. Elton and Williams gave different meanings to
“habitat” and the term is used especially broadly by Williams. Bageiial
(1951) states “From this standpoint &Iton’s conclusions appear to be
correct, though based on unsuitable data, and Williams, far from contradicting Gause and Elton, has provided the corollary that related
species are more likely to occur in similar, though not identical, habitats
than are unrelated ones.”
27
resulting in a strong tendency for the species of any genus to be
distributed as ecckypes in different habitats, or if not, to be unable to
coexist permanently on the same area of the same habitat.”
Williams (1947) argues that it is insufficient to show that the species
per genus is smaller in smaller communities than in larger, as this is a
mathematical result of taking a smaller sample from a larger group. It
is necessary to show that the species/genus frequency in the smaller
communities is different from expectation in a randomized sample of
the same number of species, selected without reference to generic
relationships from the smaller or larger fauna. Using an index of
diversity Williams (1947) conc~ludcd that Hlton’s data could have been
obtained from a random sample and that the cvidcnce in fact indicates
natural selection in favor of more rather than fewer species in the same
genus in small communities.
Williams (1 951) reiterated his earlier conclusions after analysing
Moreau’s (1948) records of East African bird communities. He showed
an excess of‘congeneric groups with two or more species above what
would be expected by selection without reference to generic relationships, and further that the excess seems to increase as the number of
congeneric species increases. Williams ( 195 1) concluded from this analysis that (1) competition between closely related species is probably on
the average greater than between less closely related species, and (2)
that closely related species are probably more suited to similar physical
environments and, therefore, similar extra-generic competition.
Bagenal (1951) examined the evidence presented by Elton and
Williams and concluded that many of the communities analysed by
Elton (1946) were unsuitable Serause they were often very heterogeneous, were sampled by a variety of methods and the community
was often sampled over a long period of time. Hutchinson’s (1957)
distinction between homogeneously dicerse and heterogeneously diverse
environments implies that we cannot expect species-abundance distributions to behave in the same way under both conditions, a fact
which is relevant to community surveys. As this classification is related
to the free paths of animals in relation to the mosaic of structural and
microenvironmental features of a habitat, it follows that comparisons
between species with different powers of dispersal and daily activity
will also be suspect. Elton and Williams gave different meanings to
“habitat” and the term is used especially broadly by Williams. Bageiial
(1951) states “From this standpoint &Iton’s conclusions appear to be
correct, though based on unsuitable data, and Williams, far from contradicting Gause and Elton, has provided the corollary that related
species are more likely to occur in similar, though not identical, habitats
than are unrelated ones.”