PATTERN AND PROCESS IN COMPETITION
55
activity rhythms and distribute their use of the environment over
somewhat different times of the 24-hour cycle (Miller, 1955). I n winter,
however, when movements of the bank vole are most severely restricted,
food resources are less abundant, population numbers are high, and
interspecies competition becomes more critical (Kikkawa, 1964). I n
order for C. glareolus to survive as it does in a niche included within
the larger fundamental niche of A . sylvaticus it must have some competitive advantage. Kikkawa’s observations on aggressive behavior and
dominant-subordinate relations show that voles are especially aggressive
and tend to form dominance hierarchies and probably do interfere with
access by mice to areas occupied by the voles.
B. RTRDS
In spite of a vast literature on birds it is difficult to find well-documented information on their habitat requirements and interspecies
interactions. Nevertheless, certain observations suggest that included
niches occur commonly between many species. Snow (1954) concluded
that most members of the Poecile group of titmice in Europe are
separated by habitat and that the local absence of one member of a
closely related pair has not been found to affect the habitat preference
or size of the other, except in the case of Parus palustris and P. atricapillus, which are more similar than are any other sympatric Palearctic
species of this genus. There is evidence that P. palustris has replaced
P. atricapillus in four out of five instances, while in three cases where
P. palustris is absent and its habitat available P. atricapillus has not
extended into it.
This is in striking contrast to the situation in North America where,
with the exception of P. hidsonicus which overlaps widely with P.
atricapillus, all of the Poecile group replace one another geographically,
with some rather narrow zones of overlap (Snow, 1954). The system of
relationships among the Paridae of North America indicates a possible
system of included niches. P. atricapillus has the widest range, across
the whole of the northern part of the continent, but is replaced in the
southeast by P. carolinensis, in the Rocky Mountains by P. gambeli,
on the western seaboard by P. rufescens and in the mountains of Mexico
by P. schteri. Detailed studies of competitive relationships among
these species have not been made, but where the ranges of these forms
are contiguous or overlap they are separated by habitat differences,
and Snow (1954) concludes that “The fact that no two species of the
same genus overlap widely, except for P. hudsonicus and P. atricapillus,
suggests a more recent, less complex evolutionary history for the genus
in North America, a suggestion which receives support from the fact
that on the whole differences between species are not nearly so great
55
activity rhythms and distribute their use of the environment over
somewhat different times of the 24-hour cycle (Miller, 1955). I n winter,
however, when movements of the bank vole are most severely restricted,
food resources are less abundant, population numbers are high, and
interspecies competition becomes more critical (Kikkawa, 1964). I n
order for C. glareolus to survive as it does in a niche included within
the larger fundamental niche of A . sylvaticus it must have some competitive advantage. Kikkawa’s observations on aggressive behavior and
dominant-subordinate relations show that voles are especially aggressive
and tend to form dominance hierarchies and probably do interfere with
access by mice to areas occupied by the voles.
B. RTRDS
In spite of a vast literature on birds it is difficult to find well-documented information on their habitat requirements and interspecies
interactions. Nevertheless, certain observations suggest that included
niches occur commonly between many species. Snow (1954) concluded
that most members of the Poecile group of titmice in Europe are
separated by habitat and that the local absence of one member of a
closely related pair has not been found to affect the habitat preference
or size of the other, except in the case of Parus palustris and P. atricapillus, which are more similar than are any other sympatric Palearctic
species of this genus. There is evidence that P. palustris has replaced
P. atricapillus in four out of five instances, while in three cases where
P. palustris is absent and its habitat available P. atricapillus has not
extended into it.
This is in striking contrast to the situation in North America where,
with the exception of P. hidsonicus which overlaps widely with P.
atricapillus, all of the Poecile group replace one another geographically,
with some rather narrow zones of overlap (Snow, 1954). The system of
relationships among the Paridae of North America indicates a possible
system of included niches. P. atricapillus has the widest range, across
the whole of the northern part of the continent, but is replaced in the
southeast by P. carolinensis, in the Rocky Mountains by P. gambeli,
on the western seaboard by P. rufescens and in the mountains of Mexico
by P. schteri. Detailed studies of competitive relationships among
these species have not been made, but where the ranges of these forms
are contiguous or overlap they are separated by habitat differences,
and Snow (1954) concludes that “The fact that no two species of the
same genus overlap widely, except for P. hudsonicus and P. atricapillus,
suggests a more recent, less complex evolutionary history for the genus
in North America, a suggestion which receives support from the fact
that on the whole differences between species are not nearly so great