COS 124-5 - Interaction specialization and turnover across scales in a tropical-subtropical plant-insect mutualism

Abstract: Understanding the assembly of local communities from regional species pools is a central goal in ecology. Species interaction networks provide a means to characterize the role of species and their interactions in community assembly. The intertwined coevolutionary and ecological dynamics of highly specialized interactions pose challenges to our understanding of how such communities are assembled and persist over macroevolutionary timescales. Critical to understanding these processes are the questions of what are the architectures of local networks formed by such organisms; whether this structure is conserved between local and regional scales; and to what extent species interaction turnover among local communities results from species composition turnover or changes in interaction patterns. Here, we examine these phenomena using a highly specialized and co-dependent plant-insect mutualism between leafflower trees (Phyllanthaceae: Glochidion) and their pollinating leafflower moths (Lepidoptera: Gracillariidae: Epicephala) across eight sites in tropical and subtropical China. Past work has shown that this mutualism is often extremely species-specific, resulting in local networks that are significantly reciprocally specialized and modular in most cases. We find that significant reciprocal specialization is conserved at both the local and regional scale in these networks, but we also find local-regional discrepancies in whether networks are significantly modular, especially on the island of Hainan, resulting in adjacent local networks that differ in network architecture. We find that local networks are not significantly nested, but the regional network formed by the entire dataset is significantly nested, a surprising and novel result given the extreme level of specialization in this mutualism. Finally, we find that interaction turnover is almost entirely driven by species turnover rather than by interaction rewiring, at the scale of this study. These patterns indicate that some aspects of the architecture of local networks simply reflect those of the regional species interaction pool from which they are assembled; however, other architectural aspects are likely governed by other—potentially local—processes. The fact that some regional networks are not significantly modular and can be nested—even in this highly specialized interaction—suggests consequences for both community assembly and an explanation for the macroevolutionary persistence of such specialized mutualisms.