466
JAMES E. DEACON AND W. L MINCKLEY
abundance or availability. Species in larger, more diversified habitats, such
as permanent lakes, larger creeks, and rivers, usually have a greater diversity of foods available as a more stable resource. More kinds of fishes
typically are present in larger habitats, and feeding niches often are arranged so as to partition the food supplies. Partitioning of niches in smaller
habitats is both impossible because of food limitations and is unnecessary
because of a lack of diversity in the fishes themselves. Feeding periodicity
usually corresponds with the most active periods of the diel activity cycle
either in mono- or polyspecific populations (Darnell and Meierotto, 1965;
Leser and Deacon, 1968).
Many fish species, especially those achieving large sizes, show marked
changes in foods ingested during different periods of their lives. For example, Vanicek and Kramer (1969) found diets of the Colorado squawfish to change from microcrustaceans and chironomid dipterans at total
body lengths of less than 50 mm, to mostly insects between 50 and
100 mm, and to primarily and then exclusively fishes at lengths greater
than 100 and 200 mm, respectively. Bonytail and roundtail chubs shorter
than about 200 mm ate chironomid dipteran larvae and Plecoptera
nymphs; individuals longer than 200 mm mostly ingested terrestrial insects—beetles, ants, and grasshoppers—plus plant debris taken mostly
from the surface.
Dietary changes determined by stomach analysis often may be accompanied by (or occur as a function of) changes in morphology. A critical
stage in the life history of the white sucker (Catostomus commersoni) occurs when the antero-dorsal mouth of the larva migrates to become ventral,
as it is in the adult (Stewart, 1926). This also occurs in other catostomids
of western North America, and is marked by a distinct shift in feeding
from surface and mid-water debris and invertebrates, to benthic organisms
(plant and animal), plus detritus. At a more advanced level, Arnold
(1970) demonstrated a correlation in Cyprinodon bifasciatus between
lengthening of the alimentary tract and a shift from primarily animal foods
(up to a total length of about 29 mm) to mostly bottom ooze rich in
diatoms (at larger sizes). Leser and Deacon (1968) detected no such
diet-related morphological changes in C. n. nevadensis.
Seasonal changes in diets of Nevada pupfish were, however, quite evident (Leser and Deacon, 1968). Frequency of occurrence of the various
food items indicated dominance of algae and amphipod crustaceans in the
spring months, algae in the summer, gastropod molluscs in the autumn,
and gastropods plus coleopteran larvae in the winter. Organic and inorganic debris were important throughout the year, but significantly more
so in the summer. Many of the ingested algae did not appear digested
and may therefore have contributed little as a source of energy. Martin
JAMES E. DEACON AND W. L MINCKLEY
abundance or availability. Species in larger, more diversified habitats, such
as permanent lakes, larger creeks, and rivers, usually have a greater diversity of foods available as a more stable resource. More kinds of fishes
typically are present in larger habitats, and feeding niches often are arranged so as to partition the food supplies. Partitioning of niches in smaller
habitats is both impossible because of food limitations and is unnecessary
because of a lack of diversity in the fishes themselves. Feeding periodicity
usually corresponds with the most active periods of the diel activity cycle
either in mono- or polyspecific populations (Darnell and Meierotto, 1965;
Leser and Deacon, 1968).
Many fish species, especially those achieving large sizes, show marked
changes in foods ingested during different periods of their lives. For example, Vanicek and Kramer (1969) found diets of the Colorado squawfish to change from microcrustaceans and chironomid dipterans at total
body lengths of less than 50 mm, to mostly insects between 50 and
100 mm, and to primarily and then exclusively fishes at lengths greater
than 100 and 200 mm, respectively. Bonytail and roundtail chubs shorter
than about 200 mm ate chironomid dipteran larvae and Plecoptera
nymphs; individuals longer than 200 mm mostly ingested terrestrial insects—beetles, ants, and grasshoppers—plus plant debris taken mostly
from the surface.
Dietary changes determined by stomach analysis often may be accompanied by (or occur as a function of) changes in morphology. A critical
stage in the life history of the white sucker (Catostomus commersoni) occurs when the antero-dorsal mouth of the larva migrates to become ventral,
as it is in the adult (Stewart, 1926). This also occurs in other catostomids
of western North America, and is marked by a distinct shift in feeding
from surface and mid-water debris and invertebrates, to benthic organisms
(plant and animal), plus detritus. At a more advanced level, Arnold
(1970) demonstrated a correlation in Cyprinodon bifasciatus between
lengthening of the alimentary tract and a shift from primarily animal foods
(up to a total length of about 29 mm) to mostly bottom ooze rich in
diatoms (at larger sizes). Leser and Deacon (1968) detected no such
diet-related morphological changes in C. n. nevadensis.
Seasonal changes in diets of Nevada pupfish were, however, quite evident (Leser and Deacon, 1968). Frequency of occurrence of the various
food items indicated dominance of algae and amphipod crustaceans in the
spring months, algae in the summer, gastropod molluscs in the autumn,
and gastropods plus coleopteran larvae in the winter. Organic and inorganic debris were important throughout the year, but significantly more
so in the summer. Many of the ingested algae did not appear digested
and may therefore have contributed little as a source of energy. Martin