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Egestion Versus Excretion: A Meta-Analysis Examining Nutrient Release Rates and Ratios across Freshwater Fauna

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School of Biological, Environmental, and Earth Sciences, University of Southern Mississippi, 118 College Dr. #5018, Hattiesburg, MS 39402, USA
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Department of Biology, University of Central Arkansas, 180 Lewis Science Center 201 Donaghey Ave., Conway, AR 72035, USA
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Department of Biological Sciences, University of Alabama, 2109 Bevill Building, Tuscaloosa, AL 35487, USA
*
Author to whom correspondence should be addressed.
Diversity 2019, 11(10), 189; https://doi.org/10.3390/d11100189
Received: 28 June 2019 / Revised: 17 September 2019 / Accepted: 24 September 2019 / Published: 3 October 2019
(This article belongs to the Special Issue Ecological Stoichiometry for Aquatic Ecosystem Studies)
In aquatic settings, animals directly affect ecosystem functions through excretion of dissolved nutrients. However, the comparative role of egestion as an animal-mediated nutrient flux remains understudied. We conducted a literature survey and meta-analysis to directly compare nitrogen (N), phosphorus (P), and N:P of egestion compared to excretion rates and ratios across freshwater animals. Synthesizing 215 datasets across 47 animal species (all primary consumers or omnivores), we show that the total N and P egestion rates exceed inorganic N and P excretion rates but not total N and P excretion rates, and that proportions of P egested compared to excreted depend on body size and animal phylum. We further show that variance of egestion rates is often greater than excretion rates, reflecting greater inter-individual and temporal variation of egestion as a nutrient flux in comparison to excretion. At phylogenetic levels, our analysis suggests that Mollusca exhibit the greatest rates and variance of P egestion relative to excretion, especially compared to Arthropoda. Given quantitative evidence of egestion as a dominant and dynamic animal-mediated nutrient flux, our synthesis demonstrates the need for additional studies of rates, stoichiometry, and roles of animal egestion in aquatic settings. View Full-Text
Keywords: consumer-driven nutrient dynamics; stoichiometry; biogeochemistry; rivers/streams; lakes/ponds consumer-driven nutrient dynamics; stoichiometry; biogeochemistry; rivers/streams; lakes/ponds
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Halvorson, H.M.; Atkinson, C.L. Egestion Versus Excretion: A Meta-Analysis Examining Nutrient Release Rates and Ratios across Freshwater Fauna. Diversity 2019, 11, 189.

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