Conclusions
The drivers of variation discussed here may not be exhaustive, however,
they illustrate the high potential for geographic variation in the
intensity and effects of HP transfer interactions as well as in the
evolutionary responses to HP receipt. So far, the study of
pollinator-mediated plant-plant interactions has been almost entirely
dominated by studies of pre-pollination interactions even though their
outcomes are influenced by plant-plant interactions that take place on
the stigma after pollen has been deposited. Therefore, it is paramount
that we fully evaluate the causes, consequences and context-dependency
of HP transfer interactions in order to gain a more complete
understanding of the role that plant-pollinator interactions play in
generating and organizing plant biodiversity. It is also important to
acknowledge that the number of studies documenting patterns of HP
receipt is still limited and strongly biased towards temperate systems
(Arceo-Gómez et al. 2019a; Fig. 3). Studies on HP transfer dynamics in
highly diverse regions such as in Africa and South America are largely
underrepresented (Fig. 3; Arceo-Gómez et al 2019a). Biases in studies of
HP receipt are not only geographical but also phylogenetic as large
groups of plants have also been poorly represented in these studies
(e.g. monocotyledons; Arceo-Gómez et al. 2019a). Thus, there is an
urgent need to evaluate patterns of variation in HP receipt at larger
spatial and phylogenetic scales. Knowledge of wide-scale patterns of HP
receipt may help uncover its potential role in shaping patterns of plant
diversity at a global scale.