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Fluctuations in water level and the dynamics of zooplankton: a data-driven modelling approach

Authors


Gideon Gal, Kinneret Limnological Laboratory, Israel Oceanographic & Limnological Research, PO Box, 447, Migdal 14950, Israel. E-mail: gal@ocean.org.il

Summary

1. The zooplankton in Lake Kinneret (Israel) have undergone large fluctuations in recent decades, which have been linked to both biotic and abiotic processes.

2. By applying a data-driven modelling approach to a long-term database, and focusing on key abiotic (lake-level change) and biotic (prey abundance) variables, we attempted to identify the possible factors impacting the lake’s zooplankton community.

3. We hypothesised that changes in the predatory zooplankton (adult cyclopoids) assemblage are driven by changes in lake level during years of large changes. We further postulated that lake-level changes would have a similar impact on the herbivorous zooplankton (cladocerans and cyclopoid copepodites) but an opposite effect on the microzooplankton. In the years of moderate changes to lake level, however, the abundance of predatory zooplankton would determine the size of the herbivore and microzooplankton populations rather than their food sources, that is, top-down control.

4. The resulting decision trees supported the hypotheses stressing the importance of the annual rate of lake-level change in shaping the zooplankton community in the lake. In addition, and in contrast to expectations, bottom-up processes seem to play a role in determining zooplankton abundance.

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