Functional traits and environmental conditions predict community isotopic niches and energy pathways across spatial scales

Abstract

Despite ongoing research in food web ecology and functional biogeography, the links between food web structure, functional traits and environmental conditions across spatial scales remain poorly understood. Trophic niches, defined as the amount of energy and elemental space occupied by species and food webs, may help bridge this divide. Here, we ask how the functional traits of species, the environmental conditions of habitats and the spatial scale of analysis jointly determine the characteristics of trophic niches. We used isotopic niches as a proxy of trophic niches, and conducted analyses at spatial scales ranging from local food webs and metacommunities to geographically distant sites. We sampled aquatic macroinvertebrates from 104 tank bromeliads distributed across five sites from Central to South America and compiled the macroinvertebrates’ functional traits and stable isotope values (δ15N and δ13C). We assessed how isotopic niches within each bromeliad were influenced by the functional trait composition of their associated invertebrates and environmental conditions (i.e., habitat size, canopy cover [CC] and detrital concentration [DC]). We then evaluated whether the diet of dominant predators and, consequently, energy pathways within food webs reflected functional and environmental changes among bromeliads across sites. At last, we determined the extent to which the isotopic niches of macroinvertebrates within each bromeliad contributed to the metacommunity isotopic niches within each site and compared these metacommunity‐level niches over biogeographic scales. At the bromeliad level, isotopic niches increased with the functional richness of species in the food web and the DC in the bromeliad. The diet of top predators tracked shifts in prey biomass along gradients of CC and DC. Bromeliads that grew under heterogeneous CC displayed less trophic redundancy and therefore combined to form larger metacommunity isotopic niches. At last, the size of metacommunity niches depended on within‐site heterogeneity in CC. Our results suggest that the trophic niches occupied by food webs can predictably scale from local food webs to metacommunities to biogeographic regions. This scaling process is determined by both the functional traits of species and heterogeneity in environmental conditions. A http://onlinelibrary.wiley.com/doi/10.1111/1365-2435.13142/suppinfo is available for this article.

Niches in the Anthropocene: passerine assemblages show niche expansion from natural to urban habitats

“…Isotopic niches, particularly δ 13 C and δ 15 N, offer a reliable proxy of niche use and provide a solid framework for hypothesis testing (Bearhop et al 2004, Newsome et al 2007, Layman et al 2012, Rodríguez and Gerardo Herrera 2013. They are representative of both trophic level and habitat use and thus integrate a reliable estimate of realized niches at both species and assemblage levels (Jackson et al 2011, Cucherousset and Villéger 2015, Dézerald et al 2018.…”

Responses of zooplankton body size and community trophic structure to temperature change in a subtropical reservoir

“…In an increasingly human‐modified world, there is a growing urgency to understand how the trophic structure and biotic interactions are influenced by global warming (Dézerald et al, ; Rosenblatt & Schmitz, ). By the mid‐21st century, global surface temperature is predicted to increase by 2°C (Pachauri et al, ).…”

“…Niches represent the integration of all the interactions (e.g., trophic) with other species (Newsome, Martinez del Rio, Bearhop, & Phillips, ). They have been used to enhance our understanding of biotic interactions and many aspects of community structure (Dézerald et al, ; Layman et al, ; Newsome et al, ).…”

“…The multivariate space given by δ 13 C and δ 15 N can be termed “isotopic niche” (Newsome et al, ), which is a low‐dimensional specification of Hutchinson's niche (Hutchinson, ; Yeakel, Bhat, Elliott Smith, & Newsome, ). The isotopic niche is increasingly used as a powerful proxy for assessing ecological niche in freshwater ecosystems (Dézerald et al, ; Lemmens et al, ).…”

“…Both intraspecific and interspecific variation can alter community trophic structure and dynamics (Bolnick et al, ; Dézerald et al, ; Griffiths, Petchey, Pennekamp, & Childs, ; Newsome et al, ). For example, a study by Lemmens et al () found that the differences in community isotopic niche space of fish were largely determined by intraspecific variation.…”