Spider webs, stable isotopes and molecular gut content analysis: Multiple lines of evidence support trophic niche differentiation in a community of Hawaiian spiders

Susan Kennedy (1, 2) , Jun Ying Lim (1, 3) , Joanne Clavel (4, 5, 1) , Henrik Krehenwinkel (1, 6) , Rosemary Gillespie (1)

1 UC Berkeley - University of California [Berkeley]
2 Okinawa Institute of Science and Technology Graduate University
3 UvA - University of Amsterdam [Amsterdam] = Universiteit van Amsterdam
4 LADYSS - Laboratoire Dynamiques Sociales et Recomposition des Espaces
5 CNRS - Centre National de la Recherche Scientifique
6 Trier University

1. A pressing question in community ecology is how multiple closely related species are able to coexist. When these species occupy the same guild, competition for limited resources is expected to lead to niche partitioning. Understanding the ways in which ecologically similar species can coexist together requires a close examination of fine-scale ecological differences among the species. 2. We tested for the possibility of ecological niche partitioning in a community of Hawaiian Tetrag- natha spiders, which are members of an adaptive radiation across the Hawaiian islands. Using nine sympatric Tetragnatha species belonging to two different clades - one web building and the other actively hunting - we tested the hypothesis that trophic niches would differ significantly both 1) among species within a clade, indicating food resource partitioning, and 2) between the two clades, corresponding with their differences in foraging strategy. 3. To assess trophic niches of the spider species, we measured a) web architecture (the structure of the hunting tool), b) site choice (the physical placement of the web in the habitat), c) stable isotope signatures of carbon and nitrogen in the spiders’ tissues, and d) gut content of spiders based on metagenomic data. Web architecture and isotopic data were used to generate niche hypervolumes for each species, and pairwise hypervolume overlaps were measured for each pair of species. We then tested for correlations between hypervolume overlap of web architecture and stable isotopes, and gut content beta diversity. 4. We found significant differences in web architecture, site choice, stable isotope signatures, and taxonomic composition of gut contents among the nine species. In addition, we found a trend toward correlation between 1) web hypervolume overlaps and isotopic hypervolume overlaps; 2) web hypervolume overlaps and gut content beta diversity; and 3) isotopic hypervolume overlaps and gut content beta diversity. 5. Our results indicate significant differences in trophic niche among these spiders. Given that these spiders are members of an adaptive radiation, our findings raise the intriguing question of what role trophic niche differentiation may have played in the diversification of this lineage.

Domaines: Sciences de l'Homme et Société; Etudes de l'environnement; Sciences de l'environnement; Ecologie, Environnement; Biodiversité et Ecologie

Susan Kennedy, Jun Ying Lim, Joanne Clavel, Henrik Krehenwinkel, Rosemary Gillespie. Spider webs, stable isotopes and molecular gut content analysis: Multiple lines of evidence support trophic niche differentiation in a community of Hawaiian spiders. Functional Ecology, 2019, 33 (9), pp.1722-1733. ⟨10.1111/1365-2435.13361⟩. ⟨halshs-02935396⟩