PATTERN AND PROCESS IN COMPETITION
11
territory or defended space. A question pertinent to this discussion is
the extent to which such behavior is effective between species, as well
as within species, and how interspecific dominance is established and
maintained. Direct, physical contests require no special methods of
species recognition in order to be effective. The barnacle Balanus
balanoides merely overruns its competitor Chthmalus stellatus, crushing
or grinding its way into the niche space it seeks to occupy (Connell,
1961). Taxonomic aEnity in such cases functions mainly to bring two
species into competition, in that closely related species are more liable
to have similar niche requirements. When more elaborate behavioral
mechanisms are present, however, taxonomic affinity assumes greater
importance. The meadowlarks Sturnella magna and S. neglecta tolerate
intrusion into their territories by species outside this genus, but defense
and display between these two competing species are as frequent and
intense as within species, resulting in complete segregation of their
territories (Lanyon, 1956). Where the plovers Charadrius dubius, C.
hiaticula and Leucopolius alexandrinus occur together they defend and
maintain distinct territories, spaced in such a way that they occupy
three contiguous areas (Sluiters, 1954; Simmons, 1956). Territory is
advertised by the patrolling behavior of the male as he curves in a
“butterfly” display flight, slowly backwards and forwards, singing all
the while. These display flights obviously require that visual and song
signals be recognized in order to be effective interference mechanisms,
and it is evident that relatively elaborate behavior elements that are
found in one species are present in, and recognized by, closely related
competitors. Moore (1964) also notes that interspecific encounters are
more frequent and are more effective between dragonflies that resemble
each other, e.g. he found that Anax irnperator invariably drove Aeshnu
juncea from small ponds but the presence of other, less similar species
did not provoke aggressive attacks. Interestingly enough the motivation
for interspecific encounters among dragonflies might be aggressive or
sexual, e.g. an attacking male might assume a copulatory position on
contact with another male, but the result is the same in that interference
is successful and only one male remains within the territory.
In each of these and other examples, interference between species
almost invariably involves a behavioral element that is present and
effective within the species. Thus, if intraspecific mechanisms are lacking, it is unlikely that competitive exclusion will operate through interference between species. Closely related species are not only more likely
to have similar ecological requirements and, hence, overlapping or
included niches, but are also more able to evolverecognizable, formalized mechanisms of interspecific interference with less dependence on
harmful physical contests.
11
territory or defended space. A question pertinent to this discussion is
the extent to which such behavior is effective between species, as well
as within species, and how interspecific dominance is established and
maintained. Direct, physical contests require no special methods of
species recognition in order to be effective. The barnacle Balanus
balanoides merely overruns its competitor Chthmalus stellatus, crushing
or grinding its way into the niche space it seeks to occupy (Connell,
1961). Taxonomic aEnity in such cases functions mainly to bring two
species into competition, in that closely related species are more liable
to have similar niche requirements. When more elaborate behavioral
mechanisms are present, however, taxonomic affinity assumes greater
importance. The meadowlarks Sturnella magna and S. neglecta tolerate
intrusion into their territories by species outside this genus, but defense
and display between these two competing species are as frequent and
intense as within species, resulting in complete segregation of their
territories (Lanyon, 1956). Where the plovers Charadrius dubius, C.
hiaticula and Leucopolius alexandrinus occur together they defend and
maintain distinct territories, spaced in such a way that they occupy
three contiguous areas (Sluiters, 1954; Simmons, 1956). Territory is
advertised by the patrolling behavior of the male as he curves in a
“butterfly” display flight, slowly backwards and forwards, singing all
the while. These display flights obviously require that visual and song
signals be recognized in order to be effective interference mechanisms,
and it is evident that relatively elaborate behavior elements that are
found in one species are present in, and recognized by, closely related
competitors. Moore (1964) also notes that interspecific encounters are
more frequent and are more effective between dragonflies that resemble
each other, e.g. he found that Anax irnperator invariably drove Aeshnu
juncea from small ponds but the presence of other, less similar species
did not provoke aggressive attacks. Interestingly enough the motivation
for interspecific encounters among dragonflies might be aggressive or
sexual, e.g. an attacking male might assume a copulatory position on
contact with another male, but the result is the same in that interference
is successful and only one male remains within the territory.
In each of these and other examples, interference between species
almost invariably involves a behavioral element that is present and
effective within the species. Thus, if intraspecific mechanisms are lacking, it is unlikely that competitive exclusion will operate through interference between species. Closely related species are not only more likely
to have similar ecological requirements and, hence, overlapping or
included niches, but are also more able to evolverecognizable, formalized mechanisms of interspecific interference with less dependence on
harmful physical contests.