Plant-caterpillar interaction matrices of temperate broadleaf forests

1. Assemblages of insect herbivores are structured by plant traits such as
nutrient content, secondary metabolites, physical traits, and phenology.
Many of these traits are phylogenetically conserved, implying a decrease
in trait similarity with increasing phylogenetic distance of the host
plant taxa. Thus, a metric of phylogenetic distances and relationships can
be considered a proxy for phylogenetically conserved plant traits and used
to predict variation in herbivorous insect assemblages among co-occurring
plant species. 2. Using a Holarctic dataset of exposed-feeding and
shelter-building caterpillars, we aimed at showing how phylogenetic
relationships among host plants explain compositional changes and
characteristics of herbivore assemblages. 3. Our plant–caterpillar network
data derived from plot-based samplings at three different continents
included >28,000 individual caterpillar-plant interactions. We
tested if increasing phylogenetic distance of the host plants leads to a
decrease in caterpillar assemblage overlap. We further investigated to
what degree phylogenetic isolation of a host tree species within the local
community explains abundance, density, richness and mean specialisation of
its associated caterpillar assemblage. 4. The overlap of caterpillar
assemblages decreased with increasing phylogenetic distance among the host
tree species. Phylogenetic isolation of a host plant within the local
plant community was correlated with lower richness and mean specialisation
of the associated caterpillar assemblages. Phylogenetic isolation had no
effect on caterpillar abundance or density. The effects of plant phylogeny
were consistent across exposed feeding and shelter-building caterpillars.
5. Our study reveals that distance metrics obtained from host plant
phylogeny are useful predictors to explain compositional turnover among
hosts as well as host-specific variations in richness and mean
specialisation of associated insect herbivore assemblages in temperate
broadleaf forests. As phylogenetic information of plant communities is
becoming increasingly available, further large-scale studies are needed to
investigate to what degree plant phylogeny structures herbivore
assemblages in other biomes and ecosystems.