Conclusion and future directions
In virtually all communities, species vary widely in their abundance. In
this article, I demonstrate that this variability could explain a part
of the angiosperms’ remarkable floral diversity. The model presented
here offers a potential framework to understand the evolution toward
different pollination systems. According to this model, the optimal
pollination system is a function of the pollinator assemblage (which
varies geographically according to the Grant-Stebbins model), the plant
community in which a species is embedded, and its floral abundance. This
more holistic view integrating the plant community context with
selection exerted by different pollinators promises to improve our
understanding of the ecological processes involved in flower
diversification.
Future studies should investigate how this mechanism operates in natural
systems. In support of the model, some studies have shown that the
strength of selection on floral traits can be affected by floral density
(see Eisen et al. 2020 and references therein). An important next step
would be to investigate how floral abundance affects the strength and
direction of selection exerted by different pollinators. Such studies
should be performed at the scale of whole populations to encompass
representative variation in the pollination processes affected by floral
abundance. Studies investigating how different pollination systems are
associated with distinct floral abundances could also be very
informative, although such studies would require careful consideration
of historical contingency and spatiotemporal variation in species’
abundances.
ACKNOWLEDGMENTS
I thank Jessica Forrest, Colleen Smith, Lydia Wong and the members of
the Forrest laboratory for valuable comments on the manuscript.
Financial support was provided through a doctoral scholarship from the
Natural Sciences and Engineering Research Council of Canada.
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Table 1. Description of the parameters and parameter values
used in the mathematical model