452
JAMES E. DEACON AND W. L MINCKLEY
in condition of the predators. The scanty fauna of such special habitats appears insufficient to maintain their populations at any but a minimal level,
and the lack of evolutionary experience by the native fish obviously negated their capability for maintaining populations under the stress of
prédation. Parasitism, like prédation, is self-limiting as soon as host populations decline.
Johnson and Soong (1965) presented evidence suggesting that exotic
species find it difficult or impossible to successfully invade and establish
populations in Malaya where a large and diversified fauna holds forth. In
habitats simplified or modified by man, exotic species may, and do, become
established. Elton (1958) emphasized this same principle in his "Ecology
of Invasions." Generally, the species that do succeed when introduced into
a faunally saturated area are those with amazingly wide spectra of tolerances, such as the carp or mosquitofish. On the other hand, when one or
a few fish species occupy a given habitat, such as in most desert waters,
exotic species may establish readily, and with various results.
In relatively pristine desert habitats, those uncontaminated by alien
fishes, there is a marked segregation of species into different niches. In
addition, only three families comprise the bulk of the fish fauna of western
North America, yet in only a few instances are two species of the same
genus sympatric (in the geographic sense), and when this occurs they are
typically ecologically allopatric.
An excellent example of the last situation occurred in the minnow genus
Gila (Section IV,A, 1) prior to suppression of diversity in the Colorado
River system by man's activities. In Aravaipa Creek, Arizona, seven native
species coexist, five minnows and two suckers. In addition to having markedly different ranges within the stream (Fig. 6), their local habitats, behavior, periods of reproduction, and food habits scarcely overlap (Barber
and Minckley, 1966; Barber et al., 1970; unpublished data). This type
of order also seems to exist in larger, diversified springs. For example,
in the Cuatro Ciénegas area, 10-14 kinds of fishes coexist in large springheads (lagunas), and they also seem segregated quite highly in various
aspects of their life histories. In that area, a local race of largemouth bass
is naturally sympatric with Cyprinodon bifaciatus, and both exist in reasonably stable, viable populations. Fewer species exist in Nevada and
California springs, but where more than a single kind is present, niche
segregation or different spatial habitats are evident. Single-species populations typically exploit all of their available habitats.
Changes with time, in climate, geology, and so on, obviously effected
decimation of the desert fishes—there are fewer kinds in all of western
North America, for example, than in many states (or single rivers) of the
more mesic eastern United States. However, a substantial number per-
JAMES E. DEACON AND W. L MINCKLEY
in condition of the predators. The scanty fauna of such special habitats appears insufficient to maintain their populations at any but a minimal level,
and the lack of evolutionary experience by the native fish obviously negated their capability for maintaining populations under the stress of
prédation. Parasitism, like prédation, is self-limiting as soon as host populations decline.
Johnson and Soong (1965) presented evidence suggesting that exotic
species find it difficult or impossible to successfully invade and establish
populations in Malaya where a large and diversified fauna holds forth. In
habitats simplified or modified by man, exotic species may, and do, become
established. Elton (1958) emphasized this same principle in his "Ecology
of Invasions." Generally, the species that do succeed when introduced into
a faunally saturated area are those with amazingly wide spectra of tolerances, such as the carp or mosquitofish. On the other hand, when one or
a few fish species occupy a given habitat, such as in most desert waters,
exotic species may establish readily, and with various results.
In relatively pristine desert habitats, those uncontaminated by alien
fishes, there is a marked segregation of species into different niches. In
addition, only three families comprise the bulk of the fish fauna of western
North America, yet in only a few instances are two species of the same
genus sympatric (in the geographic sense), and when this occurs they are
typically ecologically allopatric.
An excellent example of the last situation occurred in the minnow genus
Gila (Section IV,A, 1) prior to suppression of diversity in the Colorado
River system by man's activities. In Aravaipa Creek, Arizona, seven native
species coexist, five minnows and two suckers. In addition to having markedly different ranges within the stream (Fig. 6), their local habitats, behavior, periods of reproduction, and food habits scarcely overlap (Barber
and Minckley, 1966; Barber et al., 1970; unpublished data). This type
of order also seems to exist in larger, diversified springs. For example,
in the Cuatro Ciénegas area, 10-14 kinds of fishes coexist in large springheads (lagunas), and they also seem segregated quite highly in various
aspects of their life histories. In that area, a local race of largemouth bass
is naturally sympatric with Cyprinodon bifaciatus, and both exist in reasonably stable, viable populations. Fewer species exist in Nevada and
California springs, but where more than a single kind is present, niche
segregation or different spatial habitats are evident. Single-species populations typically exploit all of their available habitats.
Changes with time, in climate, geology, and so on, obviously effected
decimation of the desert fishes—there are fewer kinds in all of western
North America, for example, than in many states (or single rivers) of the
more mesic eastern United States. However, a substantial number per-