Effective Long-Distance Pollen Dispersal in Centaurea jacea

Matthias Albrecht,Martin K Obrist,Bernhard Schmid,Peter Duelli,David Kleijn,Jane Catherine Stout

doi:10.1371/journal.pone.0006751

Abstract

BackgroundAgri-environment schemes play an increasingly important role for the conservation of rare plants in intensively managed agricultural landscapes. However, little is known about their effects on gene flow via pollen dispersal between populations of these species.Methodology/Principal FindingsIn a 2-year experiment, we observed effective pollen dispersal from source populations of Centaurea jacea in restored meadows, the most widespread Swiss agri-environment scheme, to potted plants in adjacent intensively managed meadows without other individuals of this species. Potted plants were put in replicated source populations at 25, 50, 100 m and where possible 200 m distance from these source populations. Pollen transfer among isolated plants was prevented by temporary bagging, such that only one isolated plant was accessible for flower visitors at any one time. Because C. jacea is self-incompatible, seed set in single-plant isolates indicated insect mediated effective pollen dispersal from the source population. Seed set was higher in source populations (35.7±4.4) than in isolates (4.8±1.0). Seed set declined from 18.9% of that in source populations at a distance of 25 m to 7.4% at 200 m. At a distance of 200 m seed set was still significantly higher in selfed plants, indicating long-distance effective pollen dispersal up to 200 m. Analyses of covariance suggested that bees contributed more than flies to this long-distance pollen dispersal. We found evidence that pollen dispersal to single-plant isolates was positively affected by the diversity and flower abundance of neighboring plant species in the intensively managed meadow. Furthermore, the decline of the dispersal was less steep when the source population of C. jacea was large.ConclusionsWe conclude that insect pollinators can effectively transfer pollen from source populations of C. jacea over at least 200 m, even when “recipient populations” consisted of single-plant isolates, suggesting that gene flow by pollen over this distance is very likely. Source population size and flowering environment surrounding recipient plants appear to be important factors affecting pollen dispersal in C. jacea. It is conceivable that most insect-pollinated plants in a network of restored sites within intensively managed grassland can form metapopulations, if distances between sites are of similar magnitude as tested here.

Highlights

Habitat fragmentation has been recognized as a major threat to the survival of local populations of plants and animals [1,2]
In the present study we examined the effects of isolation distance from source populations of Centaurea jacea L. in restored meadows on pollinator activity and effective pollen dispersal to single-plant isolates placed into adjacent intensively managed meadows
We addressed the following questions: (1) Is there effective pollen dispersal from source populations of C. jacea in restored meadows to single-plant isolates in adjacent intensively managed meadows and (2) how does distance from the source population affect this dispersal of pollen? (3) Which pollinator groups are responsible for effective pollen dispersal in C. jacea? (4) How does source population size and the flower abundance and diversity of co-flowering plant species influence effective pollen dispersal?

Summary

Introduction

Habitat fragmentation has been recognized as a major threat to the survival of local populations of plants and animals [1,2]. In insect-pollinated plants, pollen dispersal is generally the main component of gene flow [8,9] This pollen-mediated gene flow may be largely driven by ecological factors that determine the availability and foraging behaviour of the involved pollinators [10,11]. These factors may include the ‘‘direct’’ effects of lifehistory traits or taxon-specific foraging behaviour of the pollinators [12], and effects of habitat variables that ‘‘indirectly’’ affect pollen dispersal by altering the availability and foraging behaviour of pollinators, such as the physical distance between plant patches [e.g. 10,13,14], plant population size and density [7,11,15] and the surrounding flowering environment, including conspecific and heterospecific co-flowering plants [13,16,17]. Little is known about their effects on gene flow via pollen dispersal between populations of these species

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Conclusion