Scale-dependent effects of conspecific flower availability on pollination quantity and quality in an invasive shrub
Pollen limitation can strongly influence reproduction of pollinator-dependent plants. Flower abundance can affect pollination ‘quantity’ and ‘quality’ due to its influence on pollen availability and foraging patterns of pollinators, ultimately impacting on seed production. We complemented individual-based measurements with landscape-level metrics to assess the influence of conspecific flower availability at different spatial scales on the quantity and quality components of pollination, and their impact on seed production in the invasive shrub Cytisus scoparius. In 2013–2014, we sampled 40 C. scoparius populations in Nahuel Huapi National Park, Patagonia (Argentina). In each population, we estimated the proportion of tripped flowers, fruit- and seed-set in five randomly selected individuals. The proportion of tripped flowers and the proportion of them setting fruit were used as proxies of pollination quantity and quality, respectively. Conspecific flower availability at distinct spatial scales (5–1000 m) was estimated as the area covered by flowering C. scoparius from color aerial photographs. Flower availability influenced seed output due to contrasting scale-dependent effects on pollination quantity and quality. Increasing flower availability at the landscape-scale reduced pollination quantity, whereas at the neighborhood-scale it increased pollination quality. The overall positive effect of flower availability on seed output at the neighborhood scale was slightly higher than the overall negative effect at the landscape scale. Moreover, pollination quality had a higher positive effect on seed output than pollination quantity. Our results demonstrate that pollination quality may severely limit plant reproduction. Pollination quality limitation can act independently of pollination quantity limitation because these factors operate at different spatial scales.
KeywordsCytisus scoparius Floral display Pollination limitation Reproductive success Spatial scale
We thank Matías Carruitero and Mailén Latorre for helping with fieldwork, Gustavo Santamaria for providing the aerial photographs and Anabella Fantozzi for digitalization of aerial photographs. Gabriela Gleiser, Vanina Chalcoff and José Vesprini provided valuable comments and suggestions on an earlier draft. We also thank the National Park Administration of Argentina (APN) for allowing us to work in Nahuel Huapi National Park. This study was funded by PICT 2012-3015 to CLM and MAA. LC, CLM, JHG and MAA are researchers at the National Research Council of Argentina (CONICET). AMC was supported by a JAE-predoc fellowship and by an Alien Challenge COST-Action Short Term Scientific Mission.
Author contribution statement
LC, CLM and MAA conceived the ideas and designed methodology; LC and AMC collected the data; LC and JHG analysed the data; LC, CLM and MAA led the writing of the manuscript. All authors contributed critically to the drafts and gave final approval for publication.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.
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