450
JAMES E. DEACON AND W. L. MINCKLEY
throughout the water column following establishment of Poecilia latipinna
and Gambusia affinis in Jackrabbit Spring. A similarly uniform distribution
is also evident in Big Spring, Nevada, but data prior to establishment of
exotic species at that locality are lacking.
6. Biotic Interactions, Man-Induced and Otherwise
Because of the relative simplicity of aquatic habitats in deserts, studies
of their fishes may yield important insight into inter- and intraspecific interactions. Man's activities in the past few years have provided numerous
experiments in nature which pertain to such problems. Competition ot
one form or another is generally considered to be of importance in control
of population sizes in freshwater fishes (Larkin, 1956), but other factors
may sometimes become more critical. There appear three distinct schools
of thought: (1) competition is of primary importance (Nicholson, 1933,
1954); (2) prédation and parasitism are more important than competition
(Utida, 1953; Larkin, 1956); and (3) climatic factors far outweigh biotic
factors in influencing population sizes (Bodenheimer, 1938; Andrewartha
and Birch, 1954).
We have examined the above views with reference to fishes of desert
waters, with special emphasis on the influences of man-induced changes
which have occurred and are occurring. The last view, that of climatic
control of population sizes, has been repeatedly discussed in earlier sections [assuming that an aquatic "climate," the averages and range of
"under-water weather" (Minckley, 1963), is acceptable to the reader], and
is not again covered.
Larkin (1956) defined competition as ". . .the demand, typically at
the same time, of more than one organism, for the same resources of the
environment . . ." This was offered in a discussion of interspecific competition, but seems to apply equally well to intraspecific interactions, and
would imply that competition for food between individuals of a single
species would be most intense. Such does not seem to be the case, according
to Ivlev (1961). The apparent reduction in competitive intensity within a
species seems due to a diversity of behavioral responses (Wynne-Edwards,
1962). Different-sized individuals of various fish species notoriously inhabit
different habitats, displaying an ontogenic change by moving from place to
place with increases in size; food habits may change radically with size, season, and so on, and territoriality also is highly developed in some groups,
and is sometimes of a complex nature (reviewed in part by Liu, 1969).
Segregation by sex also is highly developed in some desert fishes (Minckley
and Carufel, 1967; Arnold, 1970; Barber et al, 1970; Rinne, 1970).
Intraspecific competition obviously does exist, however, such as in the
prolific threadfin shad where older year classes suppress growth of younger
JAMES E. DEACON AND W. L. MINCKLEY
throughout the water column following establishment of Poecilia latipinna
and Gambusia affinis in Jackrabbit Spring. A similarly uniform distribution
is also evident in Big Spring, Nevada, but data prior to establishment of
exotic species at that locality are lacking.
6. Biotic Interactions, Man-Induced and Otherwise
Because of the relative simplicity of aquatic habitats in deserts, studies
of their fishes may yield important insight into inter- and intraspecific interactions. Man's activities in the past few years have provided numerous
experiments in nature which pertain to such problems. Competition ot
one form or another is generally considered to be of importance in control
of population sizes in freshwater fishes (Larkin, 1956), but other factors
may sometimes become more critical. There appear three distinct schools
of thought: (1) competition is of primary importance (Nicholson, 1933,
1954); (2) prédation and parasitism are more important than competition
(Utida, 1953; Larkin, 1956); and (3) climatic factors far outweigh biotic
factors in influencing population sizes (Bodenheimer, 1938; Andrewartha
and Birch, 1954).
We have examined the above views with reference to fishes of desert
waters, with special emphasis on the influences of man-induced changes
which have occurred and are occurring. The last view, that of climatic
control of population sizes, has been repeatedly discussed in earlier sections [assuming that an aquatic "climate," the averages and range of
"under-water weather" (Minckley, 1963), is acceptable to the reader], and
is not again covered.
Larkin (1956) defined competition as ". . .the demand, typically at
the same time, of more than one organism, for the same resources of the
environment . . ." This was offered in a discussion of interspecific competition, but seems to apply equally well to intraspecific interactions, and
would imply that competition for food between individuals of a single
species would be most intense. Such does not seem to be the case, according
to Ivlev (1961). The apparent reduction in competitive intensity within a
species seems due to a diversity of behavioral responses (Wynne-Edwards,
1962). Different-sized individuals of various fish species notoriously inhabit
different habitats, displaying an ontogenic change by moving from place to
place with increases in size; food habits may change radically with size, season, and so on, and territoriality also is highly developed in some groups,
and is sometimes of a complex nature (reviewed in part by Liu, 1969).
Segregation by sex also is highly developed in some desert fishes (Minckley
and Carufel, 1967; Arnold, 1970; Barber et al, 1970; Rinne, 1970).
Intraspecific competition obviously does exist, however, such as in the
prolific threadfin shad where older year classes suppress growth of younger