Abundance, not diversity, of host beetle communities determines abundance and diversity of parasitoids in deadwood.

Andreas Prinzing,Heinz Bußler,Simon Thorn,Sebastian Vogel,Stefan Schmidt,Jörg Müller

doi:10.1002/ece3.7535

Abstract

Most parasites and parasitoids are adapted to overcome defense mechanisms of their specific hosts and hence colonize a narrow range of host species. Accordingly, an increase in host functional or phylogenetic dissimilarity is expected to increase the species diversity of parasitoids. However, the local diversity of parasitoids may be driven by the accessibility and detectability of hosts, both increasing with increasing host abundance. Yet, the relative importance of these two mechanisms remains unclear. We parallelly reared communities of saproxylic beetle as potential hosts and associated parasitoid Hymenoptera from experimentally felled trees. The dissimilarity of beetle communities was inferred from distances in seven functional traits and from their evolutionary ancestry. We tested the effect of host abundance, species richness, functional, and phylogenetic dissimilarities on the abundance, species richness, and Shannon diversity of parasitoids. Our results showed an increase of abundance, species richness, and Shannon diversity of parasitoids with increasing beetle abundance. Additionally, abundance of parasitoids increased with increasing species richness of beetles. However, functional and phylogenetic dissimilarity showed no effect on the diversity of parasitoids. Our results suggest that the local diversity of parasitoids, of ephemeral and hidden resources like saproxylic beetles, is highest when resources are abundant and thereby detectable and accessible. Hence, in some cases, resources do not need to be diverse to promote parasitoid diversity.

Highlights

Most species worldwide are natural enemies of other species, as exemplified by parasitoids and parasites
To calculate mean nearest taxon distance (MNTD), we first calculated the cophenetic distances between co- occurring species using the function “cophenetic” from the R package “stats.” Because MNTD values can decrease as the number of species in a community increases, an abundance-weighted null model was applied to compare the observed MNTD values with those of 999 randomly generated communities containing the same number of species by using the function “ses.mntd” from the R package “picante” (Cavender-Bares et al, 2006; Kembel et al, 2010)
This procedure resulted in a standardized effect size of MNTD that reflected the mean MNTD, that is, the phylogenetic dissimilarity of a beetle community standardized by species numbers

Summary

| INTRODUCTION

Most species worldwide are natural enemies of other species, as exemplified by parasitoids and parasites. Increasing phylogenetic or functional dissimilarity of host communities is thought to increase the species diversity of their enemies in a community (Schuler et al, 2015; Vialatte et al, 2010). Parasitoid Hymenoptera mainly attack the eggs, larvae, and pupae of saproxylic beetles and exhibit a clear preference for one developmental stage over the others (Strand & Pech, 1995; Wegensteiner et al, 2015) Many of these and other functional properties are phylogenetically conserved (Seibold et al, 2015). We investigated communities of saproxylic beetle hosts and their associated parasitoid Hymenoptera Both groups of insects were reared from experimentally felled trees during the early succession of deadwood.

| MATERIALS AND METHODS

| DISCUSSION