V I I . DESERT FISHES
451
ones and are reciprocally influenced (Johnson, 1970). Similar effects may
well occur in desert fishes, but their protracted spawning, and other factors,
make the patterns less easily discernible. Species capable of survival under
a wide spectrum of environments are furthermore less likely to exhibit
clear-cut competitive relationships than more specialized kinds, and further
complication arises since flexibility in growth rates tends to dampen out
effects of competition.
Numerous experimental examples exist of one fish species causing
sharp reductions in abundance of another (Ivlev, 1961). It is notable
that many such examples involve closely related forms, or in the cases
of transfers of alien animals to new areas, the interacting species quite
often are ecologically similar although taxonomically distant in relationships. A few instances of apparent breakdown of the Gaussian hypothesis
(Ross, 1957; Fryer, 1959; Weatherley, 1963b) have been attributed in
part to a superabundance of food, but even under more typical circumstances, demonstration of actual competition between species in nature is
very difficult and has rarely been accomplished (Larkin, 1956; Ivlev,
1961). Larkin attributes this to the fact that freshwater habitats are geologically short-lived (see, however, Minckley, 1963 relative to streams),
highly diversified, and subject to very rapid ecological succession. All of
these tend to favor generalization rather than specialization, in fishes at
least. It seems reasonable, and concordant with our observations, that behavioral interactions ( = competition) at the interspecific level may induce
adjustments allowing coexistence of species where a single kind of environment exists over a sufficient period of time. Similar reinforcement of
isolating mechanisms between closely related species was proposed by
Dobzhansky (1940) (see, however, Dobzhansky et al., 1968). When such
systems are disrupted either at the physicochemical or biological environment levels, substantial changes accrue.
Predators presumably are limited in their population sizes by food supply (prey), and at the same time impose limitations on their prey through
cropping. In some instances this fails, as indicated by the lack of ability
of largemouth bass to control some prey species in artificial ponds (Bennett, 1962).
On the other hand, at least two instances of extinction of desert fish
populations are known certainly to have resulted from introduction and
establishment of largemouth bass (Deacon, 1968b; Deacon and Bunnell,
1970). Other such occurrences involving the centrarchid, other fishes, or
even bullfrogs (Rana catesbiaena) (Miller and Hubbs, 1960) have resulted in declines or extinction also. In the two instances studied by us
in Nevada, extinction of the native fish populations (Crenichthys baileyi
and Cyprinodon nevadensis mionectes) was followed by a marked decline
451
ones and are reciprocally influenced (Johnson, 1970). Similar effects may
well occur in desert fishes, but their protracted spawning, and other factors,
make the patterns less easily discernible. Species capable of survival under
a wide spectrum of environments are furthermore less likely to exhibit
clear-cut competitive relationships than more specialized kinds, and further
complication arises since flexibility in growth rates tends to dampen out
effects of competition.
Numerous experimental examples exist of one fish species causing
sharp reductions in abundance of another (Ivlev, 1961). It is notable
that many such examples involve closely related forms, or in the cases
of transfers of alien animals to new areas, the interacting species quite
often are ecologically similar although taxonomically distant in relationships. A few instances of apparent breakdown of the Gaussian hypothesis
(Ross, 1957; Fryer, 1959; Weatherley, 1963b) have been attributed in
part to a superabundance of food, but even under more typical circumstances, demonstration of actual competition between species in nature is
very difficult and has rarely been accomplished (Larkin, 1956; Ivlev,
1961). Larkin attributes this to the fact that freshwater habitats are geologically short-lived (see, however, Minckley, 1963 relative to streams),
highly diversified, and subject to very rapid ecological succession. All of
these tend to favor generalization rather than specialization, in fishes at
least. It seems reasonable, and concordant with our observations, that behavioral interactions ( = competition) at the interspecific level may induce
adjustments allowing coexistence of species where a single kind of environment exists over a sufficient period of time. Similar reinforcement of
isolating mechanisms between closely related species was proposed by
Dobzhansky (1940) (see, however, Dobzhansky et al., 1968). When such
systems are disrupted either at the physicochemical or biological environment levels, substantial changes accrue.
Predators presumably are limited in their population sizes by food supply (prey), and at the same time impose limitations on their prey through
cropping. In some instances this fails, as indicated by the lack of ability
of largemouth bass to control some prey species in artificial ponds (Bennett, 1962).
On the other hand, at least two instances of extinction of desert fish
populations are known certainly to have resulted from introduction and
establishment of largemouth bass (Deacon, 1968b; Deacon and Bunnell,
1970). Other such occurrences involving the centrarchid, other fishes, or
even bullfrogs (Rana catesbiaena) (Miller and Hubbs, 1960) have resulted in declines or extinction also. In the two instances studied by us
in Nevada, extinction of the native fish populations (Crenichthys baileyi
and Cyprinodon nevadensis mionectes) was followed by a marked decline