Although practitioners aim to reconstruct grasslands for pollinator services, we know relatively little about how fine-scale plant community components affect pollinator visitation and resulting plant seed set. We asked whether pollinator visitation to reconstructed grassland communities was affected by the spatial relationships of the resident forbs and whether these factors affected plant seed set in Ratibida columnifera (hereafter RC). We test the hypothesis that increasing RC association would increase pollinator visitors and plant reproductive output. In summer 2014, using the SPaCE (Species Pattern and Community Ecology) research site in North Dakota, we assessed pollinator visitation during peak RC flowering and the distribution, abundance, and seed set of RC within experimental plots (1 x 1 m; n = 34).
Results/Conclusions
Pollinator diversity was lower when RC patches were more contiguous (F3,30 = 3.521, p < 0.05) and positively affected by RC abundance (F3,30 = 3.521, p < 0.05). Pollinator diversity was marginally positively affected by the overall plot diversity (F3,30 p = 0.0950, R2 = 0.1865). Seed set was reduced in plots with more contiguous RC patches (F1,32 = 14.41, p < 0.001, R2 = 0.2889). Results suggest that fine scale plant association affects pollinator services and resulting plant recruitment in reconstructed grasslands. However, effects of plant association are contrary to our initial hypothesis. Three possible explanations we propose are: 1. Increased plant competition decreases resources available for seed production in larger RC patches 2. RC flowers that are isolated are pollinated more efficiently simply because they lack competition for pollinators from other inflorescences. 3. Pollinators foraging in contiguous patches for RC may decrease time spent at each flower, resulting in less efficient pollination. Studies such as these can be used to inform planting practices used to increase grassland pollinator services.