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 km2 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.
Highlights
Diversity patterns we observe in nature are the outcome of multiple biotic and abiotic factors and the interactions occurring among them
Whittaker (1960) was the first to propose a partitioning of diversity across three different spatial scales: α-diversity, that is, species richness in a particular locality, γ-diversity, a measure of regional species richness, and β-diversity, a measure of species composition dissimilarity between localities. β-diversity provides a measure of community spatial variability, reflecting historical processes, and revealing information on population dynamics and species responses to habitat modifications such as environmental gradients and perturbations (Cavender-Bares, Kozak, Fine, & Kembel, 2009; Graham & Fine, 2008)
Host dissimilarity increased with geographic distance, whereas parasitoid dissimilarity did not show a distance decay pattern
Summary
Diversity patterns we observe in nature are the outcome of multiple biotic and abiotic factors and the interactions occurring among them. Because parasitoids necessarily depend on their hosts and usually have relatively narrow host ranges (Hawkins, 1994; Jeffs & Lewis, 2013; Poulin et al, 2011), we hypothesize (H2) a strong match in species composition across space and similar distance decay patterns for both groups. We expect higher heterogeneity in interactions than in species composition (Poisot et al, 2017,2015), and because we work in a spatial (as opposed to temporal) gradient, we hypothesize (H3) a higher contribution of species turnover than rewiring to overall interaction dissimilarity. Interaction turnover is often dependent on variation of the lower trophic level (Carstensen et al, 2014; Norfolk et al, 2015; Novotny, 2009; Simanonok & Burkle, 2014), we hypothesize (H4) that interaction β-diversity will be better predicted by host β-diversity than by parasitoid β-diversity
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