VII. DESERT FISHES
433
of intense sunlight coupled with high primary productivity. At night, however, conditions may be otherwise.
Bottom muds of many desert habitats have relatively high concentrations
of hydrogen sulfide, as based on olfaction after they are disturbed. Pupfishes, and apparently some other cyprinodontids, spend relatively long
periods of time, especially in winter, within such sediments. Toxicity sometimes must be near-lethal. Martin (1968) suggested possible damage to
sheepshead pupfish exposed to hydrogen sulfide from a bottom agitated
by collecting activities. Minckley (in Hubbs and Miller, 1965) reported
a total kill of fish (Cyprinodon atrorus) resulting from agitation of a deep
silt bottom in a hot (41.5°C), drying pool. However, factors other than
hydrogen sulfide certainly could have been involved under such severe
conditions. It seems entirely probable, however, that Cyprinodon and its
relatives may have evolved a physiological means of coping with hydrogen
sulfide in their severe habitats.
IV. Biological Responses to Desert Water Conditions
A. DISPERSION RELATIVE TO ENVIRONMENT
Fishes native to deserts, almost without exception, have their distributions limited either by geographic barriers, or by a need (or tolerance)
for some special environmental feature. Only one of the 200 or so native
fishes in western North America, the speckled dace, may be considered
widespread (Miller, 1959), and it consists of a myriad of local, variously differentiated forms that may well represent a species-flock rather
than a polymorphic, single entity. The relatively depauperate nature of this
western fauna, resulting from long years of vast geologic and climatic
change, makes it particularly instructive. The relationships of morphology
and environment are perhaps more clearly seen here than in places where
speciose faunas saturate the habitat, and biotic factors obscure biologicenvironmental interrelations.
1. Stream-Dwelling Fishes
Under relatively stable conditions of discharge, or as an average over
a period of time, fishes and other organisms in the linear system provided
by a stream tend to distribute themselves into different sections according
to their requirements or preferences. Many factors other than current,
temperature, substrate, competition from other organisms, and so on, may
be involved, especially in situations such as streams fed by springs. But
the physical gradient, to which current is intimately related, is the factor
against which distributions of fishes are usually compared (Minckley,
433
of intense sunlight coupled with high primary productivity. At night, however, conditions may be otherwise.
Bottom muds of many desert habitats have relatively high concentrations
of hydrogen sulfide, as based on olfaction after they are disturbed. Pupfishes, and apparently some other cyprinodontids, spend relatively long
periods of time, especially in winter, within such sediments. Toxicity sometimes must be near-lethal. Martin (1968) suggested possible damage to
sheepshead pupfish exposed to hydrogen sulfide from a bottom agitated
by collecting activities. Minckley (in Hubbs and Miller, 1965) reported
a total kill of fish (Cyprinodon atrorus) resulting from agitation of a deep
silt bottom in a hot (41.5°C), drying pool. However, factors other than
hydrogen sulfide certainly could have been involved under such severe
conditions. It seems entirely probable, however, that Cyprinodon and its
relatives may have evolved a physiological means of coping with hydrogen
sulfide in their severe habitats.
IV. Biological Responses to Desert Water Conditions
A. DISPERSION RELATIVE TO ENVIRONMENT
Fishes native to deserts, almost without exception, have their distributions limited either by geographic barriers, or by a need (or tolerance)
for some special environmental feature. Only one of the 200 or so native
fishes in western North America, the speckled dace, may be considered
widespread (Miller, 1959), and it consists of a myriad of local, variously differentiated forms that may well represent a species-flock rather
than a polymorphic, single entity. The relatively depauperate nature of this
western fauna, resulting from long years of vast geologic and climatic
change, makes it particularly instructive. The relationships of morphology
and environment are perhaps more clearly seen here than in places where
speciose faunas saturate the habitat, and biotic factors obscure biologicenvironmental interrelations.
1. Stream-Dwelling Fishes
Under relatively stable conditions of discharge, or as an average over
a period of time, fishes and other organisms in the linear system provided
by a stream tend to distribute themselves into different sections according
to their requirements or preferences. Many factors other than current,
temperature, substrate, competition from other organisms, and so on, may
be involved, especially in situations such as streams fed by springs. But
the physical gradient, to which current is intimately related, is the factor
against which distributions of fishes are usually compared (Minckley,