An Experimental Study of Vertical Habitat Use and Habitat Shifts in ...

native species pairs were partially segregated, species in syntopy interacted as a mixedgroup
without interspecific antagonistic behavior. Based on the concept of competitive
displacement and depending on a species’ generality of habitat use, one would expect a
reduced range of water-column distribution of a native species following the introduction
of a closely-related species (Pielou 1972). However, competitive displacement is not a
general rule in the ecology of fishes, and many studies have demonstrated coexistence of
closely-related species, as well as benefits of mixed-species shoals (Magurran and Pitcher
1983, 1987).
Water depths during normal flows within the upper Greenbrier River system are
greater than those available within the study aquaria, and therefore allow additional space
for segregation between the study species. Species integration, however, likely results
during periods of reduced water column depths during dry summers (Gorman 1988).
Thus, vertical position patterns may change during the low flows of summer, during a
time of competitive crunch (Wiens 1977). Our results suggest that within a water column
space of 51cm, N. scabriceps and N. telescopus rarely used space within 17 cm of the
surface. Therefore, these two species may be in close association during low and high
flows, although direct observational studies (such as snorkeling) are needed to quantify
interactions between the study species within the Greenbrier River drainage. Both C.
spiloptera and C. galactura used the upper water column position in the study aquaria,
and separation between these two species may increase within deeper habitats of the
Greenbrier River.
Vertical segregation between species in this experiment, consistent with a large
body of literature (Baker and Ross 1981, Gorman 1988, Chipps et al. 1993a), supports a
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