468
JAMES E. DEACON AND W. L. MINCKLEY
Most fishes are less efficient at cropping food animals within dense vegetation. However, Danielson (1968) obtained data indicating a greater suppression of mosquito populations by C. n. nevadensis in areas with cover
than in open waters.
Partitioning of foods, mentioned before, is marked in certain habitats.
Fryer (1959) demonstrated extensive partitioning of food niches by
cichlid fishes in Lake Nyassa, Africa. But he also found some species using
essentially identical niches, the latter presumably because of the large habitat and a superabundance of foods (see also, Section IV,A,6). Prédation
in that lake may also have limited populations of potential herbivore competitors, at levels below those of interaction.
Three undescribed cichlids in the Cuatro Ciénegas basin appear to
have differentiated at least in part through nutritional specialization (Taylor
and Minckley, 1966; Minckley, 1969b). One has fine, delicate teeth
on its fragile pharyngeal arches and feeds principally on bottom debris. A second has thick bones and molariform teeth used in crushing
shells of its molluscan foods. A third has elongated teeth on the pharyngeal
bones, and elongated head, jaws, and body, and appears mostly piscivorous. The assumed ancestor of this small species flock, Cichlasoma
cyanogutattum, has modifications of its feeding apparatus that encompass
almost all the three types, with sharp, elongated teeth on the pharyngeal
bones grading medially to molariform ones. Its feeding is similarly
generalized.
The fauna of Aravaipa Creek, discussed before (Section IV,A,6; Fig.
6), shows a marked partitioning of niche with respect to foods, space, and
so on. The top carnivore is the Colorado chub. As an adult it feeds upon
young of all larger species and even upon adults of smaller species, plus
larger invertebrates. Adults of all carnivorous forms feed on larvae of all
other fishes, but this depredation has not been adequately assessed. A midwater species of pools, the spikedace, feeds on terrestrial and aquatic drift
(principally invertebrates). Speckled dace, semi-midwater in slightly
swifter places and on deeper riffles, also eats drift, but it principally feeds
from the bottoms. Loach minnows, discussed before, are almost monophagus on Simuliidae and baetid mayflies. The other minnow, Agosia chrysogaster, lives on broad, slow, sandy areas, and feeds upon finely divided
organic materials, algae, and micro-invertebrates. Two catostomids partition even more markedly, with Pantosteus clarki exclusively using encrusting algae (and associated materials) scraped from bottoms in riffles, while
Catostomus insignis lives on bottom invertebrates extracted from sand
and gravel substrates. It is notable that the feeding activities of both suckers stir bottoms severely, and this causes a dislodgment of a large proportion of the foods used by midwater fishes of the brook.
JAMES E. DEACON AND W. L. MINCKLEY
Most fishes are less efficient at cropping food animals within dense vegetation. However, Danielson (1968) obtained data indicating a greater suppression of mosquito populations by C. n. nevadensis in areas with cover
than in open waters.
Partitioning of foods, mentioned before, is marked in certain habitats.
Fryer (1959) demonstrated extensive partitioning of food niches by
cichlid fishes in Lake Nyassa, Africa. But he also found some species using
essentially identical niches, the latter presumably because of the large habitat and a superabundance of foods (see also, Section IV,A,6). Prédation
in that lake may also have limited populations of potential herbivore competitors, at levels below those of interaction.
Three undescribed cichlids in the Cuatro Ciénegas basin appear to
have differentiated at least in part through nutritional specialization (Taylor
and Minckley, 1966; Minckley, 1969b). One has fine, delicate teeth
on its fragile pharyngeal arches and feeds principally on bottom debris. A second has thick bones and molariform teeth used in crushing
shells of its molluscan foods. A third has elongated teeth on the pharyngeal
bones, and elongated head, jaws, and body, and appears mostly piscivorous. The assumed ancestor of this small species flock, Cichlasoma
cyanogutattum, has modifications of its feeding apparatus that encompass
almost all the three types, with sharp, elongated teeth on the pharyngeal
bones grading medially to molariform ones. Its feeding is similarly
generalized.
The fauna of Aravaipa Creek, discussed before (Section IV,A,6; Fig.
6), shows a marked partitioning of niche with respect to foods, space, and
so on. The top carnivore is the Colorado chub. As an adult it feeds upon
young of all larger species and even upon adults of smaller species, plus
larger invertebrates. Adults of all carnivorous forms feed on larvae of all
other fishes, but this depredation has not been adequately assessed. A midwater species of pools, the spikedace, feeds on terrestrial and aquatic drift
(principally invertebrates). Speckled dace, semi-midwater in slightly
swifter places and on deeper riffles, also eats drift, but it principally feeds
from the bottoms. Loach minnows, discussed before, are almost monophagus on Simuliidae and baetid mayflies. The other minnow, Agosia chrysogaster, lives on broad, slow, sandy areas, and feeds upon finely divided
organic materials, algae, and micro-invertebrates. Two catostomids partition even more markedly, with Pantosteus clarki exclusively using encrusting algae (and associated materials) scraped from bottoms in riffles, while
Catostomus insignis lives on bottom invertebrates extracted from sand
and gravel substrates. It is notable that the feeding activities of both suckers stir bottoms severely, and this causes a dislodgment of a large proportion of the foods used by midwater fishes of the brook.