Coexistence of two similar copepod species, <Emphasis Type="Italic">Eudiaptomus gracilis</Emphasis> and <Emphasis Type="Italic">E. graciloides</Emphasis>: the role of differential predator avoidance |
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Authors: | Email author" target="_blank">C?D?JamiesonEmail author |
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Institution: | (1) Department of Statistics, University of Wyoming, P.O. Box 3332, Laramie, Wyoming 82071-3332, USA |
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Abstract: | Habitat choice in relation to environmental factors of two coexisting calanoid copepod species, Eudiaptomus gracilis and E. graciloides, was studied in a mesotrophic lake and in large indoor mesocosms. Both species and sexes showed pronounced diel vertical
migration (DVM) in the field. In 12 m deep mesocosms with free ranging fish DVM was observed and species increased day depth
over time. No changes were observed in copepod day depth over time in experiments with fish kairomone. It is hypothesized
that fish kairomone acts as an early warning system to copepods which respond by moving deeper, but only as far as the thermocline.
For full DVM, a nearby mechanical stimulus is necessary. Thus, as fish go deeper to feed, copepods retreat. The response of
copepods to fish predation, in the presence of low and high numbers of Daphnia,shows that copepods effectively use Daphniaas living shields to avoid predation. The two species adopt different vertical migration strategies depending on whether there
are high or low numbers of Daphniapresent. A dominant feature of mesocosm experiments was the night time aggregating (lekking) of E. gracilis males at the surface. When the spring and autumn percentages of risk takers in the epilimnion were compared, E. gracilis, particularly males, suffered the greatest cost. |
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Keywords: | DVM fish predation lekking diaptomid selection |
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