Frequency of flower visitors and achene production increase with rising population size in the self-incompatible herb Centaurea scabiosa (Asteraceae)

Stefan Abrahamczyk,Mirjam Thielen,Maximilian Weigend

doi:10.1007/s11258-021-01129-1

Stefan Abrahamczyk, Mirjam Thielen + Show 1 more

Open Access

https://doi.org/10.1007/s11258-021-01129-1

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Journal: Plant Ecology	Publication Date: Mar 22, 2021
Citations: 3	License type: open-access

Affiliation: University of Bonn, Institute for Biodiversity

Abstract

Self-incompatible, non-clonal plant species are especially dependent on the activity of flower visitors for seed production. Therefore, populations of these plants are vulnerable to a reduced flower visitation rates, but also to increased isolation by extinction of local populations. To study how local populations of Centaurea scabiosa, a self-incompatible, bee-pollinated herb species changed over time in the region of Bonn, we collected historical population records in the area and investigated their current status. We found that more than half of the subpopulations mentioned in the literature between 1950 and 2012 (38 of 65) have since disappeared. Small populations were most vulnerable, whereas medium to large populations increased in size. In a second step, we studied visitation frequencies and achene production and weight across 14 extant populations. We found that both flower visitation frequency and achene production were positively related to population size. Achene weight was neither related to the frequency of flower visitors nor to achene production. These results clearly indicate that reduced pollen transfer and lower pollination rates may contribute to local extinction in small populations of Centaurea scabiosa. Overall our results call for an intensified monitoring of the populations of self-incompatible plant species.

Highlights

In the past decades, the diversity and abundance of flower-visiting insects has dramatically decreased in many Central European habitats due to habitat loss, fragmentation, a reduced food availability and the massive application of pesticides in agriculture (e.g. Biesmeijer et al 2006; Brittain et al 2010; de Palma et al 2016; Abrahamczyk et al 2020)
Reduced seed production necessarily leads to population decline and may even result in local extinction because small populations are increasingly unattractive to pollinators, which often prefer species with large populations
We investigated changes in population size of Centaurea scabiosa in the region of Bonn and the possible correlations between population size and reproductive success

Summary

Introduction

The diversity and abundance of flower-visiting insects has dramatically decreased in many Central European habitats due to habitat loss, fragmentation, a reduced food availability and the massive application of pesticides in agriculture (e.g. Biesmeijer et al 2006; Brittain et al 2010; de Palma et al 2016; Abrahamczyk et al 2020). Self-incompatible species, dependent on active pollen transfer and high outcrossing rates for successful seed production (Jennersten 1988; Agren 1996) are expected to be vulnerable. These plant species commonly have large, attractive flowers with high pollination reward (nectar and/or pollen) and are, important food resources for many species of flower visitors. If more and more populations of a species go extinct within a region, the remaining populations become increasingly isolated This fragmentation reduces gene flow and reduces seed production (Ghazoul 2005). In turn, can only maintain gene flow if appropriate adaptations exist and dispersal vectors are functional (Ghazoul 2005)

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