Abstract
BackgroundThe use and partitioning of trophic resources is a central aspect of community function. On the ground of tropical forests, dozens of ant species may be found together and ecological mechanisms should act to allow such coexistence. One hypothesis states that niche specialization is higher in the tropics, compared to temperate regions. However, trophic niches of most species are virtually unknown. Several techniques might be combined to study trophic niche, such as field observations, fatty acid analysis (FAA) and stable isotope analysis (SIA). In this work, we combine these three techniques to unveil partitioning of trophic resources in a tropical and a temperate community. We describe patterns of resource use, compare them between communities, and test correlation and complementarity of methods to unveil both community patterns and species’ niches.MethodsResource use was assessed with seven kinds of bait representing natural resources available to ants. Neutral lipid fatty acid (NLFA) profiles, and δ15N and δ13C isotope signatures of the species were also obtained. Community patterns and comparisons were analyzed with clustering, correlations, multivariate analyses and interaction networks.ResultsResource use structure was similar in both communities. Niche breadths (H′) and network metrics (Q and H2′) indicated similar levels of generalization between communities. A few species presented more specialized niches, such as Wasmannia auropunctata and Lasius fuliginosus. Stable isotope signatures and NLFA profiles also indicated high generalization, although the latter differed between communities, with temperate species having higher amounts of fat and proportions of C18:1n9. Bait use and NLFA profile similarities were correlated, as well as species’ specialization indices (d′) for the two methods. Similarities in δ15N and bait use, and in δ13C and NLFA profiles, were also correlated.DiscussionOur results agree with the recent view that specialization levels do not change with latitude or species richness. Partition of trophic resources alone does not explain species coexistence in these communities, and might act together with behavioral and environmental mechanisms. Temperate species presented NLFA patterns distinct from tropical ones, which may be related to environmental factors. All methods corresponded in their characterization of species’ niches to some extent, and were robust enough to detect differences even in highly generalized communities. However, their combination provides a more comprehensive picture of resource use, and it is particularly important to understand individual niches of species. FAA was applied here for the first time in ant ecology, and proved to be a valuable tool due to its combination of specificity and temporal representativeness. We propose that a framework combining field observations with chemical analysis is valuable to understand resource use in ant communities.
Highlights
The use and partitioning of trophic resources is a central aspect of community functioning
Our main findings in this work are: (1) patterns of resource use are similar in both communities, the role of oligosaccharides is distinct; (2) both communities are generalized in resource use, regardless of species richness; (3) temperate ants present higher amounts of fat and more homogeneous Neutral lipid fatty acid (NLFA) compositions; (4) composition and specialization in resource use and NLFAs are correlated, and are related to species’ trophic position; (5) some species show specialized behaviors that can be better understood by method complementarity
Our work is not an explicit test of this hypothesis, but several results agree with the view that specialization does not necessarily increase with higher richness toward the tropics: despite the different number of species, network metrics of resource use and niche breadths were generalized in both communities; fatty acid compositions were highly generalized, in this case in different level, possibly due to other factors; cluster analysis of resource use showed similar patterns between communities and both species clusters and stable isotopes indicated strong overlap inside each community
Summary
The use and partitioning of trophic resources is a central aspect of community functioning. MacArthur (1972) suggested that specialization increases in tropical communities and, as a result, more species can coexist This idea was put in question by recent studies (Schleuning et al, 2012; Morris et al, 2014; Frank et al, 2018). The use of food resources itself is surprisingly understudied, and trophic niches of most species remain poorly known This is evident in rich tropical communities (Rosumek, 2017), and true for some temperate species (Lanan, 2014). Bait use and NLFA profile similarities were correlated, as well as species’ specialization indices (d′) for the two methods. Partition of trophic resources alone does not explain species coexistence in these communities, and might act together with
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