Sympatric red, grey, and flying squirrels trophically partition niche space via mycophagy

Authors: PAULI, JONATHAN - University Of Wisconsin; MANLICK, PHILIP - University Of Wisconsin; DHARAMPAL, PRARTHANA - University Of Wisconsin; CHIKARAISHI, YOSHITO - Hokkaido University; NICCOLAI, LAURA - University Of Wisconsin; GRAUER, JENNIFER - University Of Wisconsin; BLACK, KRISTINA - University Of Wisconsin; GARCES RESTREPO, MARIO - University Of Wisconsin; PERRIG, PAULA - University Of Wisconsin; WILSON, EVAN - University Of Wisconsin; MARTIN, MARIE - University Of Wisconsin; RODRIGUEZ CURRAS, MAURIEL - University Of Wisconsin; BOUGIE, TIFFANY - University Of Wisconsin; THOMPSON, KIMBERLY - University Of Wisconsin; SMITH, MATTHEW - University Of Wisconsin; Steffan, Shawn

Submitted to: Biology Letters
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/30/2019
Publication Date: 9/16/2019
Citation: Pauli, J., Manlick, P.J., Dharampal, P.S., Chikaraishi, Y., Niccolai, L., Grauer, J.A., Black, K., Garces Restrepo, M., Perrig, P.L., Wilson, E.C., Martin, M.E., Rodriguez Curras, M., Bougie, T., Thompson, K.L., Smith, M.M., Steffan, S.A. 2019. Sympatric red, grey, and flying squirrels trophically partition niche space via mycophagy. Biology Letters. Vol21. https://doi.org/10.1016/J.FOOWEB.2019.E00124.
DOI: https://doi.org/10.1016/J.FOOWEB.2019.E00124

Interpretive Summary: Forest mammals such as squirrels are largely omnivorous, due to their consumption of fungi. Different squirrel taxa actively cultivate fungi within buried pine cones. Evidence of purposeful niche partitioning among squirrels, and further evidence of a mutualism between squirrels and forest fungi is important to the scientists who investigate the functioning of agro-ecosystems. They will benefit because understanding the roles of microbes within the food-chain will dramatically improve our understanding of how food-webs (whether agricultural or non-managed) function.

Technical Abstract: Quantifying how competitors partition resources is central to understanding food web and community dynamics. The analysis of bulk stable isotopes (d13C and d15N) is routinely used to estimate niche characteristics and trophic position (TP). Compound specific isotope analysis, especially of amino acids, has emerged as a new approach to estimate consumers’ TP. However, compound-specific TP estimates are rarely applied to free-ranging terrestrial vertebrates, or in conjunction with bulk isotope mixing models. Herein, we used both approaches to test how three common, syntopic competitors – grey (Sciurus carolinensis), red (Tamiasciurus hudsonicus), and flying (Glaucomys sabrinus) squirrels – partition trophic niche space. Our complementary analyses revealed that squirrels effectively partitioned niche space and TP. Bulk isotopes showed that, while these three species consume the same foods, their dependency on each differed: grey squirrels consumed mast, augmented with fungi and animal matter; red squirrels consumed mast, fungi and animal matter evenly, and flying squirrels consumed fungi and mast. TP estimates from compound-specific analysis fell as predicted and in accordance with our bulk dietary estimates: mast TP = x, fungi and grey squirrels TP = 2, and flying and red squirrels consistently TP > 2. Our findings reveal a mechanism behind the apparent stable co-occurrence of these competitors. This work supports that d15Nglu and d15Nphe have great potential for the estimation of TP across food webs, and provides a powerful framework to quantify partitioning of organisms across ecological communities.