Abstract
Seed production is critical to the persistence of most flowering plant populations, but may be strongly pollen limited. To what extent long-lived plants can compensate pollen limitation by increasing future reproduction is poorly understood. We tested for compensation in two Dactylorhiza species that differ in reproductive investment by experimentally reducing and increasing pollination in two independent annual cohorts and monitoring demographic responses in the subsequent 2 years for the 2014 cohort and in 1 year for the 2015 cohort. Demographic rates in the second year were significantly affected by pollination treatment in both species, but specific responses differed both between species and years. There was no effect of pollination treatment on demographic responses in the third year. In sum, effects were too weak to make up for the lost reproduction; total fruit production across all 3 years was by far highest in the increased pollination treatment in both species. These results show that long-lived plants do not necessarily compensate for pollen limitation by increasing future reproduction. It further suggests that even periodic declines in pollination rates may have severe demographic consequences, particularly in populations where germination is not density dependent. This has implications for predicting plant population viability in response to changes in pollination intensity.
Highlights
Pollen availability can be a strong limiting factor of many plant species’ reproduction (Burd 1994; Larson and Barrett 2000; Ashman et al 2004; Knight et al 2005), and is expected to become an increasingly important issue in light of global decreases in overall abundance and condition of pollinators (Biesmeijer et al 2006; Potts et al 2010)
In species with multiple reproductive events, reproductive failure in a single year may be compensated by increased future reproductive output or by increased vegetative growth and probability of survival (Obeso 2002; Sletvold and Ågren 2011, 2015a, b)
In line with our predictions, the species with a shorter life span and higher flower production, D. incarnata, tended to show a higher ability to compensate for reduced reproductive output than D. lapponica
Summary
Pollen availability can be a strong limiting factor of many plant species’ reproduction (Burd 1994; Larson and Barrett 2000; Ashman et al 2004; Knight et al 2005), and is expected to become an increasingly important issue in light of global decreases in overall abundance and condition of pollinators (Biesmeijer et al 2006; Potts et al 2010). In species whose population growth is limited by seed input, increasing strength and variability of pollen limitation may lead to population declines and local extinctions, if selfing or clonal reproduction is absent (cf Lennartsson 2002; Biesmeijer et al 2006). It is crucial to understand how plant populations respond demographically to changes in pollination rates and, in particular, to years of low pollination success
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