Pollinator-mediated reproductive consequences of altered co-flowering under climate change conditions depend on abiotic context

Climate change is altering patterns of temporal co-occurrence among species, such as the degree of co-flowering among plant species. Although much is known about how co-flowering affects pollination and plant reproduction, how these interactions are mediated by changes in abiotic conditions is unclear. Using a short-term field experiment based on a long-term flowering phenology dataset, we examine how changes in co-flowering between Linum lewisii and Potentilla pulcherrima affect the pollination and reproductive success of Linum in control and water addition scenarios. Linum is co-flowering less than it used to with Potentilla as the climate changes. We therefore removed Potentilla flowers to alter the degree of co-flowering from 0 to 100%; half of these plots received additional water to relieve drought stress. Linum plants experiencing less overlap with Potentilla had a higher proportion of conspecific pollen on their stigmas in both watered and unwatered plots. Plants experiencing less overlap also produced more seeds per plant, but only in the watering treatment. There was no evidence of pollen limitation of reproduction, but watered plants produced more seeds. These results show that plants that co-flowered to a lesser extent with Potentilla had enhanced reproductive output, probably because they received a higher proportion of Linum pollen, but these biotic effects were only detectable when the plants were less water-limited. This study provides empirical evidence that climate-driven changes in co-flowering can alter reproduction via competition for pollination, and that these biotic effects can be mediated by abiotic conditions.