PATTERN AND PROCESS IN COMPETITION
G 1
interference element in their competitive interactions. The plains pocket
gopher, Geomys bursarius, can subsist on certain grasses which will not
sustain individuals of the mountain pocket gopher, Thomomys talpoides
(Myers and Vaughan, 1963), so that what has been referred to as an
“included niche” for G. bursarius contains elements outside the niche
of T. talpoides; but both species can survive on such a wide variety of
foods that it is unlikely that food is a critical factor in their habitat or
geographic distribution or in competition between them (Miller, 1964a),
and their aggressive, territorial behavior indicates that competition for
space overrides this source of ecological differentiation. Thus the critical
factors of soil depth and texture determine the suitability of such
space for the different species, and therefore the outcome of competition
between them. Similary, while the salamander Plethodon dunni can
tolerate somewhat lower temperatures than P. vehiculum, the niche of
P . dunni is included within the niche of P. vehiculum in the critical
range of temperature and humidity between the preferred cool and
humid conditions and the suboptimal conditions of high temperature
and low humidity. Thus, the included niche is an adequate description
of interspecies relationships as long as it accounts for the critical range
of factors that govern competition and survival, and in this sense we
should be prepared to accept reasonable approximations. It should also
be emphasized, however, that we cannot assume that intersection between fundamental niches will inevitably lead t o competitive exclusion
-this is an outcome which should first be demonstrated or, in the
absence of direct evidence, only inferred when it is the most reasonable
explanation of observed events.
Given that the examples in this section are of competitive exclusion
under the conditions of an included niche in which N, is the proper
subset of N, and the realized niche of 8, is the difference subset N, - N,,
we can examine the properties of these interactions with respect to:
(1) the characteristics of the competition process, (2) the factors which
give the more specialized species S, its competitive advantage and
(3) the factors which allow the less specialized species S, to survive
competition from S,. I n each of the preceding examples the process of
competition involved a form of interference which led to competitive
exclusion within the niche space of the intersection subset, and the
competition was for some kind of space or a structural feature within
a given space. The space requirements of different taxonomic groups
are obviously different, depending on their specific needs, and we may
infer that the factors affecting the form of interference also were different or had different values, but whatever these factors and mechanisms
may be they apparently lead t o comparable end results through a
similar set of general conditions.
O*
G 1
interference element in their competitive interactions. The plains pocket
gopher, Geomys bursarius, can subsist on certain grasses which will not
sustain individuals of the mountain pocket gopher, Thomomys talpoides
(Myers and Vaughan, 1963), so that what has been referred to as an
“included niche” for G. bursarius contains elements outside the niche
of T. talpoides; but both species can survive on such a wide variety of
foods that it is unlikely that food is a critical factor in their habitat or
geographic distribution or in competition between them (Miller, 1964a),
and their aggressive, territorial behavior indicates that competition for
space overrides this source of ecological differentiation. Thus the critical
factors of soil depth and texture determine the suitability of such
space for the different species, and therefore the outcome of competition
between them. Similary, while the salamander Plethodon dunni can
tolerate somewhat lower temperatures than P. vehiculum, the niche of
P . dunni is included within the niche of P. vehiculum in the critical
range of temperature and humidity between the preferred cool and
humid conditions and the suboptimal conditions of high temperature
and low humidity. Thus, the included niche is an adequate description
of interspecies relationships as long as it accounts for the critical range
of factors that govern competition and survival, and in this sense we
should be prepared to accept reasonable approximations. It should also
be emphasized, however, that we cannot assume that intersection between fundamental niches will inevitably lead t o competitive exclusion
-this is an outcome which should first be demonstrated or, in the
absence of direct evidence, only inferred when it is the most reasonable
explanation of observed events.
Given that the examples in this section are of competitive exclusion
under the conditions of an included niche in which N, is the proper
subset of N, and the realized niche of 8, is the difference subset N, - N,,
we can examine the properties of these interactions with respect to:
(1) the characteristics of the competition process, (2) the factors which
give the more specialized species S, its competitive advantage and
(3) the factors which allow the less specialized species S, to survive
competition from S,. I n each of the preceding examples the process of
competition involved a form of interference which led to competitive
exclusion within the niche space of the intersection subset, and the
competition was for some kind of space or a structural feature within
a given space. The space requirements of different taxonomic groups
are obviously different, depending on their specific needs, and we may
infer that the factors affecting the form of interference also were different or had different values, but whatever these factors and mechanisms
may be they apparently lead t o comparable end results through a
similar set of general conditions.
O*