Fig. 2.

Patterns of conspecific pollen (CP) versus heterospecific pollen (HP) receipt that can be observed on stigmas of spent flowers and potential drivers of variation in these patterns. Potential drivers include variation in pollinator visitation (A, B) or variation in the pollinator pool and floral morphology (C–E). (A, B) Patterns that result from variation in quantity of pollinator visits. In (A), when visitation rate for the focal species is higher (>) or lower (<) in the presence of coflowering species, the pattern can reflect facilitation (green) or competition (red), respectively. However, in (B) lower visitation rate is accompanied by a pollen-transport trade-off leading to a negative CP–HP relationship. (C–E) CP–HP relationships when variation in pollinator pool and floral avoidance mechanisms exist regardless of visitation differences (blue for emphasis of mechanism). (C) Uneven pollinator pools combined with or without floral avoidance can lead to non-linear negative CP–HP relationships. (D) Uneven pollinator pools or presence of floral avoidance can lead to non-linear positive CP–HP relationships. (E) Extremely uneven pollinator pools or perfect floral avoidance of HP represent forms of plant–pollinator specialization and lead to the lack of a CP–HP relationship.