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Leveraging differences in multiple prey traits allows selective copepods to meet their threshold elemental ratios
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  • Emily Herstoff,
  • Cédric Meunier,
  • Maarten Boersma,
  • Stephen Baines
Emily Herstoff
The College of New Jersey
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Cédric Meunier
Alfred-Wegener-Institut
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Maarten Boersma
Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung
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Stephen Baines
Stony Brook University College of Arts and Sciences
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Abstract

Foraging based on prey elemental content could be more pronounced if consumers leveraged differences in physical traits among stoichiometrically distinct prey to ingest more favorable food, allowing consumers to meet their threshold elemental ratios (TER). We offered the marine copepod, Acartia tonsa, different combinations of large and small diatom congeners, grown to be either stoichiometrically replete or nitrogen-deficient. When offered each diatom alone, A. tonsa exhibited compensatory grazing on large diatoms, and ingested more nitrogen-deficient cells. When offered diatoms that differed in both size and stoichiometry, copepods mixed their diets to achieve a C:N close to their independently estimated optimal TER. When offered pairs of different-sized diatoms of similar stoichiometry, A. tonsa preferred larger cells, suggesting evolutionary constraints drive choice when stoichiometric differences are minimal. Experiments describing selectivity on single traits may seriously underestimate how precisely copepods can optimize their dietary stoichiometry when feeding on a diverse natural prey assemblage.