Local ecological conditions can determine whether species interactions drive evolutionary and community structural change. We investigated whether pollinator-mediated interactions between co-flowering plants varied with plant density, co-flowering neighbor identity, and flowering season. We conducted a field experiment, in which flowering time and floral neighborhood were manipulated in a factorial design. Early- and late-flowering Clarkia unguiculata plants were placed into arrays with Clarkia biloba neighbors, non-congeneric neighbors, additional conspecific plants, or no additional plants as a density control. We compared whole-plant pollen limitation of seed set, pollinator behavior, and pollen deposition among treatments.
Results/Conclusions
Interactions mediated by shared pollinators depended on the identity of the neighbor and possibly changed through time, although flowering-season comparisons were not as robust due to low Early-season plant survival. Interactions with conspecific neighbors were likely competitive late in the season. Interactions with C. biloba appeared to involve facilitation or neutral interactions. Interactions with non-congeners were more consistently competitive. The community composition of pollinators varied among treatment combinations. Pollinator-mediated interactions involved competition and likely facilitation, depending on co-flowering neighbor. Experimental manipulations helped to reveal context-dependent variation in indirect biotic interactions.