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

N. telescopus had modes in the lower-pelagic zone, and both species shared modal
numbers in the lower pelagic zone during a single trial.
For both Notropis species, vertical distributions differed significantly (P < 0.05)
between allotopic and syntopic trials (Table 1, Figure 3). The magnitude of difference
between allotopic and syntopic trials was largest for N. scabriceps. Specifically, N.
scabriceps was primarily benthically-positioned during allotopic trials (within benthic
and near benthic zones), but expanded its vertical position in the presence of N.
telescopus to include 17 and 5 percent of its occupancy within the lower pelagic and
pelagic zones, respectively. Vertical distribution expanded for N. scabriceps and
contracted in groups of N. telescopus. Hence, the two species shifted habitat and
integrated during syntopic trials. Despite integration during syntopy, the high power of
Chi-square tests supported significant separation of the two Notropis species.
Cyprinella Congeners
Cyprinella spiloptera and C. galactura differed in vertical distributions during
allotopic trials and segregated in 7 of 9 syntopic trials. For allotopic trials, vertical
distributions of C. spiloptera were found in significantly lower (P < 0.05) categories than
those of C. galactura (Table 2, Figure 1). During allotopic trials, C. spiloptera polarized
vertical distributions with the mode in the benthic zone (53% of individuals) and the
remaining majority (27%) in the surface-pelagic area (Figure 1). Cyprinella galactura
also had a modal peak in the benthic zone (60% of individuals) during the allotopic trials,
but had the next highest percent occurrences in the near benthic (21%) and pelagic (12%)
zones. In 7 of the 9 syntopic trials, vertical positions of C. spiloptera were significantly
38