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Variation in horizontal zooplankton abundance in mountain lakes: shore avoidance or fish predation? 总被引:1,自引:0,他引:1
Hypothesizing that fish predation, active shore avoidance and outlet stream
avoidance may be separately affecting horizontal zooplankton distribution,
the effects of fish presence, sampling location (midlake, outlet and
non-outlet shore) and time (day or night) on zooplankton abundance and body
size were tested. Statistically significant horizontal zooplankton
abundance gradients occurred in both fish-present and fish-absent lakes.
Fish may strengthen zooplankton spatial patterns common to both
fish-present and fish-absent lakes, as abundance differences among
locations were often greater in fish-present systems compared to
fish-absent systems. Horizontal zooplankton abundance gradients differed
through a diel cycle, but were species specific with some species
exhibiting gradients only during the day, while others exhibit gradients
only during the night. Avoidance of the outlet over and above active shore
avoidance appeared to take place in Daphnia sp. Other
taxa provided equivocal support of active outlet avoidance with most
showing no significant difference between shore and outlet abundance (seven
of nine), one taxa showing a significant decrease and one a significant
increase in outlet compared to shore abundance. No gradients in zooplankton
body size were found.
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