Community level individual-based plant-pollinator networks unveil pollen flow dynamics and plant reproductive success

Abstract

Plant-pollinator networks are a widely used tool to understand the dynamics of such ecological communities. However, while most mutualistic networks have been defined at the species level, ecological processes, such as pollination, take place at the individual level. This recognition has led to the development of individual plant-level networks, yet current approaches only account for individuals of a single plant species due to conceptual and mathematical limitations. Here, we introduce a mechanistic multilayer framework based on the frequency of insect visits to plant individuals belonging to different species. It is designed to depict from the network structure the potential conspecific and heterospecific pollen flows among plant individuals. Pollen transfer is modeled as a transport-like system, where pollen grains are represented as random-walkers that diffuse on an ensemble of bipartite layers of conspecific plants and their floral visitors that are coupled through shared visitors. With this physical conceptualization, we investigate how the number of developed seeds of plant individuals is affected by the multilayer structure (network-level), as well as by their local network properties (motif- and node-level). We apply this multiscale analysis to a dataset of nine plant-pollinator networks from a Mediterranean grassland. At the network-level we show a highly modular structure, with insect visitors effectively connecting individuals of the same and different plant species. Interestingly, the network structure is critical for modulating individual plant reproduction for the three most attractive species. In particular, the motif-level, represented by the number of homospecific and heterospecific motifs, is the best descriptor of plant reproductive success, as it integrates local heterospecific and conspecific interactions. We provide a simple, but robust set of metrics to scale down network ecology to functioning properties at the individual level, where most ecological processes take place, hence moving forward the description and interpretation of multitrophic communities across scales.