Is heterospecific pollen receipt the missing link in understanding pollen limitation of plant reproduction?

How will anthropogenic changes (species invasions/extinctions, land‐use conversion, and climate change) influence the pollination and reproductive success of the world's angiosperms, 85% of which require animal pollination (Ollerton et al., 2011)? Answering this question requires understanding the mechanisms that cause pollen limitation of seed production. Pollen limitation (PL) is widespread (Bennett et al., 2018) and occurs when pollinators fail to deliver adequate quantity or quality of pollen to stigmas (Ashman et al., 2004). It is thought to primarily occur when there are few pollinators visiting the plants or when the pollinators that visit do not bring enough conspecific pollen (CP) or bring CP that is of low quality (e.g., self pollen that comes from a different flowers on the same plant) (Ashman et al., 2004; Aizen and Harder, 2007). Often left out of the conversation on PL, however, is that pollinators can also transfer heterospecific pollen (HP) among species (but see Jakobsson et al., 2009; McKinney and Goodell, 2010).