Quantifying niche partitioning and multichannel feeding among tree squirrels

Quantifying resource partitioning is central to community and food web ecology and of increasing interest in an era of rapid global change disrupting biotic interactions. Multichannel feeding – consuming resources from both green and brown food webs – can be a stabilizing force in communities. While multichannel feeding has been well-documented in invertebrate and aquatic systems, it has been relatively under-studied in terrestrial vertebrate populations. Applied ecologists are seeking approaches to assess niche partitioning and cryptic trophic pathways, like multichannel feeding, which have been difficult to quantify, especially among vertebrates. Using both bulk (δ¹³C and δ¹⁵N) and compound specific stable isotope ratios (δ¹⁵N glutamic acid and phenylalanine), we tested how three common and competing tree squirrel partition resources. Our complementary analyses revealed that squirrels partitioned niche space and, because of differences in multichannel foraging, possessed different trophic identities. While all squirrels consumed food items from green and brown food webs, their dependence on each differed, revealing an important, yet cryptic, mechanism behind apparent stable co-occurrence of these competitors. Our work supports multichannel feeding as a potential mechanism promoting coexistence in this guild of terrestrial vertebrates, and provides a framework to quantify resource partitioning in other ecological communities.