Experimental loss of generalist plants reveals alterations in plant-pollinator interactions and a constrained flexibility of foraging

Paolo Biella,Jan Klecka,Asma Akter,Jeff Ollerton,Sam Tarrant,Jana Jersáková,Štěpán Janeček

doi:10.1038/s41598-019-43553-4

Abstract

Species extinctions undermine ecosystem functioning, with the loss of a small subset of functionally important species having a disproportionate impact. However, little is known about the effects of species loss on plant-pollinator interactions. We addressed this issue in a field experiment by removing the plant species with the highest visitation frequency, then measuring the impact of plant removal on flower visitation, pollinator effectiveness and insect foraging in several sites. Our results show that total visitation decreased exponentially after removing 1–4 most visited plants, suggesting that these plants could benefit co-occurring ones by maintaining high flower visitor abundances. Although we found large variation among plant species, the redistribution of the pollinator guild affected mostly the other plants with high visitor richness. Also, the plant traits mediated the effect of removal on flower visitation; while visitation of plants which had smaller inflorescences and more sugar per flower increased after removal, flower visitors did not switch between flower shapes and visitation decreased mostly in plants visited by many morpho-species of flower visitors. Together, these results suggest that the potential adaptive foraging was constrained by flower traits. Moreover, pollinator effectiveness fluctuated but was not directly linked to changes of flower visitation. In conclusion, it seems that the loss of generalist plants alters plant-pollinator interactions by decreasing pollinator abundance with implications for pollination and insect foraging. Therefore, generalist plants have high conservation value because they sustain the complex pattern of plant-pollinator interactions.

Highlights

Overall community-level dynamics and ecosystem services are often disproportionately affected by a subset of the local species pool[1,2]
The aim of our experiments was to test whether removal of generalist plants (1) led to a decrease in the overall visitation i.e., the abundance of pollinators in the sites; (2) caused changes of the visitation of individual plant species related to the similarity of floral traits with the removed species, overlap in the flower visitor community, and their level of specialisation, and (3) whether pollination effectiveness and the amount of used nectar resources (“standing crop”) changed as a consequence of plant removal
Visitation to Knautia arvensis did not increase over the study period when compared with a model without treatment variable (χ2 = 3.60, df = 1, p = 0.06)

Summary

Introduction

Overall community-level dynamics and ecosystem services are often disproportionately affected by a subset of the local species pool[1,2]. A pilot project in the United Kingdom experimentally manipulated a plant-pollinator community by removal of the most generalist plant (from here on called the “pilot study”) This provided a proof-of-concept and suggested ways in which the pollinator assemblage might react to such perturbation. The aim of our experiments was to test whether removal of generalist plants (1) led to a decrease in the overall visitation i.e., the abundance of pollinators in the sites; (2) caused changes of the visitation of individual plant species related to the similarity of floral traits with the removed species, overlap in the flower visitor community, and their level of specialisation, and (3) whether pollination effectiveness (determined by the number of pollen tubes grown in the pistils after visitation) and the amount of used nectar resources (“standing crop”) changed as a consequence of plant removal

Objectives

Methods

Results

Conclusion