The effect of species composition dissimilarity on plant–herbivore network structure is not consistent over time

Abstract

The structural organization of several antagonistic networks has been demonstrated to be largely conserved through time and space even when species beta-diversity is high. This might occur either because species are replaced by others that fulfill similar network roles or because interaction probabilities are given by species relative abundances rather than by their functional traits. Alternatively, if species-specific traits are important drivers of realized interactions, any change in species composition should promote a certain degree of network structural dissimilarity. Here, we used a spatial-temporal system comprising asteraceous plants and flower head herbivores from remnants of Brazilian Cerrado to investigate whether the relationship between spatial beta-diversity of species and network structural dissimilarity changes over time. We measured species beta-diversity using Sørensen's dissimilarity index (βsor) and its components of species replacement (β-3) and richness differences (βrich). Network structural dissimilarity was estimated using three different metrics: connectance, modularity, and web asymmetry. We show that, in general, the effect of species beta-diversity on network structure was time-dependent: While some periods presented a positive relationship between spatial beta-diversity and network structural dissimilarity, others presented no significant relationship. This indicates that functionally similar species may present different turnover rates at distinct periods, and different non-exclusive processes affect plant–herbivore network organization across time.