What is it about?
Contrasting physiological mortality with predator-induced mortality is of tremendous importance for the population dynamics of many organisms but is difficult to assess. This is especially true for tiny organisms, such as ciliates and other protists, which do not leave any carcasses behind. I performed a meta-analysis using planktonic ciliates as model organisms to estimate the maximum physiological mortality rates across pelagic ecosystems in relation to environmental and biotic factors.
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Why is it important?
Ciliates are significant players in virtually all planktonic food webs in the sea and inland waters. in the ocean, physiological mortality is more critical for controlling ciliate population size than ciliate losses imposed by microcrustacean predation, but in many lakes, the opposite holds. Resting cyst formation is an effective ciliate trait to cope with the high mortality of motile cells upon starvation. The median physiological mortality rate of planktonic ciliates was 0.62 per day and did not differ between marine and freshwater species.
Perspectives
My analysis casts doubt on the conventional wisdom that predation is the primary source of ciliate mortality in aquatic ecoystems. Temperature did not affect the ciliate mortality rates, but this finding requires more research with contrasting ciliate species. Because ciliates' specific growth rates increase with temperature, the lack of a temperature effect on their mortality rates would have important implications in the context of global warming. Planktonic ciliates may take advantage of rising ocean and lake temperatures if the temperature is unimportant for ciliate mortality.
Univ.Prof. Dr. Thomas Weisse
Universitat Innsbruck
Read the Original
This page is a summary of: Physiological mortality of planktonic ciliates: Estimates, causes, and consequences, Limnology and Oceanography, January 2024, Wiley,
DOI: 10.1002/lno.12503.
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