Spatial variability of hosts, parasitoids and their interactions across a homogeneous landscape

Abstract

Species assemblages and their interactions vary through space, generating diversity patterns at different spatial scales. Here, we study the local-scale spatial variation of a cavity-nesting bee and wasp community (hosts), their nest associates (parasitoids), and the resulting antagonistic network over a continuous and homogeneous habitat. To obtain bee/wasp nests, we placed trap-nests at 25 sites over a 32 km 2 area.We obtained 1,541 nests (4,954 cells) belonging to 40 host species and containing 27 parasitoid species. The most abundant host species tended to have higher parasitism rate. Community composition dissimilarity was relatively high for both hosts and parasitoids, and the main component of this variability was species turnover, with a very minor contribution of ordered species loss (nestedness). That is, local species richness tended to be similar across the study area and community composition tended to differ between sites. Interestingly, the spatial matching between host and parasitoid composition was low. Host β-diversity was weakly (positively) but significantly related to geographic distance. On the other hand, parasitoid and host-parasitoid interaction β-diversities were not significantly related to geographic distance. Interaction β-diversity was even higher than host and parasitoid β-diversity, and mostly due to species turnover. Interaction rewiring between plots and between local webs and the regional metaweb was very low. In sum, species composition was rather idiosyncratic to each site causing a relevant mismatch between hosts and parasitoid composition. However, pairs of host and parasitoid species tended to interact similarly wherever they co-occurred. Our results additionally show that interaction β-diversity is better explained by parasitoid than by host β-diversity. We discuss the importance of identifying the sources of variation to understand the drivers of the observed heterogeneity. K E Y W O R D Sbeta-diversity, homogeneous habitat, host-parasitoid food web, local scale, spatial variation, species interactions, trap-nests | 3697 TORNÉ-NOGUERA ET Al.

Nesting biology of Trypoxylon petiolatum Smith, 1858 (Crabronidae), a cavity-nesting solitary wasp new to Europe

“…None of the nests was T. petiolatum. Five extensive trap-nesting studies have been conducted in Catalonia near Olot (20 km from Beuda; 14 sites), Montseny (43 km from Girona, 42 sites), Garraf (115 km from Girona, 25 sites), Aigüestortes (160 km from Girona, 9 sites) and Lleida (190 km from Girona; 50 sites) in 1991, 2016, 2011, 2008and 2016, respectively (Barril-Graells et al 2012Osorio et al 2015Osorio et al , 2018Hernández-Castellano 2020;Torné-Noguera et al 2020). Altogether, these studies produced more than 1000 Trypoxylon nests (including T. figulus (Linnaeus, 1758), T. clavicerum Lepeletier de Saingt Fargeau et Audinet-Serville, 1828, T. minus de Beaumont, 1945, T. scutatum Chevrier, 1867, and T. deceptorium Antropov, 1991, but no nests of T. petiolatum were recovered.…”

“…Trypoxylon spp. are frequent hosts of Melittobia acasta in NE Spain (Osorio et al 2015;Torné-Noguera et al 2020).…”

Species turnover increases ant–trophobiont interaction dissimilarities along a geographical gradient

“…Most mutualist interactions are context-dependent and can vary in terms of specificity and function according to biotic and abiotic factors (Chamberlain & Holland, 2009), which often play different roles over a spatial gradient (Trøjelsgaard et al, 2015). For example, while habitat structure and interspecific interactions are usually leading factors at smaller spatial scales (Poisot et al, 2017), the landscape configuration and the dispersal limitation of organisms are often more important at larger spatial scales (Torné-Noguera et al, 2020). Nonetheless, determining which factors are acting at different spatial scales is challenging, and different factors may be prominent in distinct ecological contexts and spatial gradients (Poisot et al, 2012).…”

Ecosystem type might mask the effect of ecosystem recovery on parasitoids’ biodiversity quality

“…Other indicators may provide more useful information. Beta diversity (i.e., species turnover between habitats) may be more helpful: even in apparently homogeneous landscapes, beta diversity may vary significantly in parasitoids (Torné-Noguera et al 2020). A recent approach proposes using a set of biodiversity indices to give a comprehensive understanding of the assemblage's functionality in a changing environment (Feest et al 2010).…”