Patterns of pollination interactions at the community level are related to the type and quantity of floral resources

Edy Fantinato,Gabriella Buffa,Péter Török,Judit Sonkoly

doi:10.1111/1365-2435.13915

Abstract

Abstract A fundamental question in community ecology is how the quantity of floral resources affects pollinator activity and how this relates to the structure and robustness of pollination networks. The issue has been mainly addressed at the species level, while at the community level several questions are still open. Using a species‐rich semi‐natural grassland as model ecosystem, we explored the relationship between community‐level quantity of floral resources, the number of flower visits at community level and descriptors of the structure and robustness of pollination networks. To assess whether patterns of pollination interactions were consistent when using different types of floral resources, we measured three types of floral resources, namely the volume of nectar, the number of pollen grains and the number of flowers. Community‐level pollinator visitation rate showed a hump‐shaped relationship with the quantity of floral resources. Results were consistent among models employing different measures of floral resources as independent variables. The relationship between the quantity of floral resources and the structure and robustness of the network was not consistent among different types of floral resources; only intermediate levels of nectar volume were associated with high levels of network robustness. The pattern we found is in contrast with some former studies which reported positive linear relationships between the community‐level visitation rate of pollinators and the quantity of floral resources. Rather, the observed hump‐shaped pattern resembles the relationship previously found between the quantity of floral resources of a given plant species and its visitation rate per flower. Our results highlighted that, by using specific types of floral resources (e.g. the volume of nectar and the number of pollen grains), it is possible to reveal ecological processes that would be masked by using the number of flowers as the sole measure of floral resource. A free Plain Language Summary can be found within the Supporting Information of this article.

Highlights

Plant–pollinator interactions are crucial for maintaining the biodiversity and functionality of terrestrial ecosystems
By using specific types of floral resources, it is possible to reveal ecological processes that would be masked by using the number of flowers as the sole measure of floral resource
Our results revealed that the number of flowers can be a reliable proxy for the quantity of floral resources when assessing its relationship with pollinator visitation rate, supporting the reasoning of Hegland and Totland (2005), and justifying studies in which floral resources were quantified by counting the number of flowers (e.g. Benadi & Pauw, 2018; Bergamo et al, 2020)

Summary

| INTRODUCTION

Plant–pollinator interactions are crucial for maintaining the biodiversity and functionality of terrestrial ecosystems. The contradictory findings may be related to the degree of generalisation of the plant community (Bergamo et al, 2020), the range and spatial distribution of floral resource quantity (Essenberg, 2012; Totland & Matthews, 1998) and the pollinator abundance (Ye et al, 2014), which can all influence pollination interactions, possibly leading to different relationships between pollinator visitation rate and the quantity of floral resources. We explored pollination interactions in a species-rich grassland ecosystem to determine how the quantity of different types of floral resources (i.e. the total volume of nectar, the total number of pollen grains and the total number of flowers) relates to pollinator visitation rate, descriptors of network structure (i.e. connectance, complementary specialisation, weighted nestedness and quantitative modularity) and network robustness (based on the topological co- extinction model; TCM; Memmott et al, 2004). We addressed three questions: (a) How does the community-level quantity of floral resources influence the visitation rate of pollinators? (b) How does the community-level quantity of floral resources influence network structure and robustness? and (c) Do different measures of floral resources show consistent relationships with pollinator visitation rate and network structure and robustness?

| MATERIALS AND METHODS

| DISCUSSION

Findings

| CONCLUSIONS