32
RICHARD 9. MILLER
evidence that suggests that many of the birds that became extinct in
New Zealand and the Hawaiian Islands were the victims of diseases
introduced by the invaders (Mayr, 1963). Again, it is necessary that
successful invasions and the extinction of members of the native fauna
be carefully documented with supporting evidence of niche relationships
before they are classed as evidence of competition.
In summary we may assign the Werent types of evidence for
competition in nature to four principal categories, all of which contain
elements of spatial relationships:
1. Mutually exclusive spatial distributions without supporting evi2. Mutually exclusive spatial distributions with supporting evidence
3. Observed or inferred ecological displacement (usually correlated
4. Induced changes in distribution pattern.
Udvardy (1952) and Andrewartha and Birch (1954) are critical of
the use of competition to explain any aspect of variation and distribution
of animals. After a review of examples from Lack’s (1944) article on
species formation in passerine birds, Andrewartha and Birch (1954)
concede that closely related birds either seem to live in different places
or use different foods, but they note that “this is true, only more so,
of distantly related species; but no one seriously suggests ‘competition’
as a cause for this.” They ask “Why then should it be necessary t o
invoke competition to explain the same phenomenon among closely
related species, especially when there is no empirical evidence for it?”
Brown and Wilson (1956) agree that the evidence for competition
in nature is scanty indeed, but they also suggest that Andrewartha and
Birch (1954) have failed to appreciate the amount of evidence that does
exist. The tendency for closely related species to inhabit different areas
or to exploit different niches may in many cases originate from causes
quite different from competition (Elton and Miller, 1954), and careful
analysis of the critical variables in fundamental and realized niches is
an obvious requirement in evaluating the role of competition in species
interactions, as the preceding examples have shown. Statistical tests
such as those for specieslgenus frequency, index of diversity, or species
abundance distributions provide estimates which are more quantitative
but are not necessarily more informative than direct observation, and
they cannot be used to either prove or disprove the existence of competition in nature. Mutually exclusive distributions do not necessarily
depend on competition, even when this seems to be the most immediate
explanation. It is unfortunate, in this connection, that Mayr (1963)
dence of a competitive interaction.
of a competitive interaction.
with character divergence) in sympatric populations.
RICHARD 9. MILLER
evidence that suggests that many of the birds that became extinct in
New Zealand and the Hawaiian Islands were the victims of diseases
introduced by the invaders (Mayr, 1963). Again, it is necessary that
successful invasions and the extinction of members of the native fauna
be carefully documented with supporting evidence of niche relationships
before they are classed as evidence of competition.
In summary we may assign the Werent types of evidence for
competition in nature to four principal categories, all of which contain
elements of spatial relationships:
1. Mutually exclusive spatial distributions without supporting evi2. Mutually exclusive spatial distributions with supporting evidence
3. Observed or inferred ecological displacement (usually correlated
4. Induced changes in distribution pattern.
Udvardy (1952) and Andrewartha and Birch (1954) are critical of
the use of competition to explain any aspect of variation and distribution
of animals. After a review of examples from Lack’s (1944) article on
species formation in passerine birds, Andrewartha and Birch (1954)
concede that closely related birds either seem to live in different places
or use different foods, but they note that “this is true, only more so,
of distantly related species; but no one seriously suggests ‘competition’
as a cause for this.” They ask “Why then should it be necessary t o
invoke competition to explain the same phenomenon among closely
related species, especially when there is no empirical evidence for it?”
Brown and Wilson (1956) agree that the evidence for competition
in nature is scanty indeed, but they also suggest that Andrewartha and
Birch (1954) have failed to appreciate the amount of evidence that does
exist. The tendency for closely related species to inhabit different areas
or to exploit different niches may in many cases originate from causes
quite different from competition (Elton and Miller, 1954), and careful
analysis of the critical variables in fundamental and realized niches is
an obvious requirement in evaluating the role of competition in species
interactions, as the preceding examples have shown. Statistical tests
such as those for specieslgenus frequency, index of diversity, or species
abundance distributions provide estimates which are more quantitative
but are not necessarily more informative than direct observation, and
they cannot be used to either prove or disprove the existence of competition in nature. Mutually exclusive distributions do not necessarily
depend on competition, even when this seems to be the most immediate
explanation. It is unfortunate, in this connection, that Mayr (1963)
dence of a competitive interaction.
of a competitive interaction.
with character divergence) in sympatric populations.