Fig. 3.

Patterns of conspecific (CP) tubes/grain versus heterospecific pollen (HP) received on stigmas of spent flowers and potential drivers of variation in these patterns. Potential drivers are CP quality and HP interference with CP, with positive interaction noted in green and negative ones in red for emphasis. In (A) increasing interference or decreasing quality of CP can lead to a negative linear CP tubes/grain–HP relationship, which can be interpreted as forms of competitive interaction. In (B) positive linear interaction between CP–HP or increasing quality of CP can lead to a positive CP tubes/grain–HP relationship, which can be interpreted as a facilitative interaction. In (D) and (E) threshold effects of HP load size on the stigma are driving non-linear patterns and no CP quality effects are at play. Dotted lines reflect the threshold number of HP grains required to cause a competitive (D, E, inference only at large or small HP load sizes, respectively) or facilitative (F, mentoring at high HP) effects.