Caterpillars, chemicals and evolutionary history: Predicting assemblage structure in a lowland rainforest from phylogeny and ecology

Background/Question/Methods

Plants and their insect herbivores represent a large proportion of all terrestrial biodiversity and both groups contribute greatly towards ecosystem function. Understanding how such incredible diversity has been generated and maintained has been a key aim of ecology for decades, especially when considering the species rich wet tropics. Central to understanding diversification, co-existence and assemblage structure within clades of phytophagous insects is variation in host-specificity. The observed range and identity of the host plants utilized by phytophagous insects is shaped in part by contemporary ecological interactions, evolutionary labile and conserved plant and insect traits, and diffuse co-evolutionary dynamics. We aim to integrate a food-web derived from 130 plant species spread across 41 families and 161 phytophagous insect species from three families with species level phylogenies, plant defensive trait data and parasitism rates. This data will be used to predict wider interactions in an exhaustively sampled hectare of lowland rainforest in Papua New Guinea. As part of ongoing work we present our findings based on food web and phylogenetic data and discuss how other variables might improve our predictions.

Results/Conclusions

The family Geometridae and the superfamily Pyraloidea contribute 9,661 individuals (48%) to the larval leaf chewing guild and have effective specialization values of 0.39 and 0.30 respectively (guild mean: 0.29). Pyraloid host use demonstrates moderate levels of phylogenetic signal through the insect phylogeny and low to moderate levels of phylogenetic signal through the host phylogeny. Plant species are occasionally utilized by several distantly related pyraloid species and the majority of pyraloid species utilize a few con-generic plant hosts. However, within a given insect clade one can find ‘super-generalists’ that spread across many plant families. As such pyraloid host use is reasonably predictable based solely on insect phylogeny. Our analyses for the family Geometridae show that three plant clades link the majority of insect taxa, with distantly related geometrids converging on each clade. Indeed, the level of phylogenetic signal through the plant phylogeny is moderate for this family, but lower through the insect phylogeny. In addition to phylogeny potentially labile plant traits (e.g. certain secondary metabolites), and contemporary ecological interactions may contribute to pyraloid host use. In contrast, conserved host traits (e.g. nitrogen content and exudate presence) may be more important for predicting geometrid host use.