Figure 1. Importance of different pollination processes for
plant pollination success as a function of floral abundance, as
determined by the mathematical model. Comparison of pollination success
expected for low, medium and high values of A) pollinator abundance, B)
pollinator specialization, C) pollen removal and D) carryover at
variable floral abundance (see Table 1 for parameter values). E)
Importance of the quantity component of pollination, represented by
pollinator abundance, and the quality component, determined by
pollinator specialization and carryover as a function of floral
abundance (measured as the average between the importance of pollinator
specialization and carryover). F) Hypothetical representation of the
pollination systems offering the highest pollination success at
different floral abundance. Specialization on pollinators with high
pollen carryover and level of specialization is favoured at low floral
abundance (hypothetical examples; hawkmoths and hummingbirds). At
intermediate abundance, specialized pollination by more abundant
pollinators (hypothetical example; bees) is favoured. At high floral
abundance, most pollinators are not sufficiently abundant to remove most
pollen grains and generalization becomes more advantageous. When floral
abundance is too high for the pollinator community to remove most pollen
grains, reliance on abiotic pollen vectors is expected.
Figure 2. Plant-pollinator networks resulting from simulated
communities of different plant species and pollinator attributes. A, B)
At intermediate average flower abundance (500 flowers), plant-pollinator
networks formed with plant species of variable floral abundance result
in variable levels of generalization among plant species while C, D)
networks formed with plant species of the same floral abundance result
in similar levels of generalization. E, F) Networks composed entirely of
low-abundance plant species (100 flowers) result in high level of
specialization. G, H) Networks composed entirely of high-abundance plant
species (1000 flowers) result in widespread generalization. In A, C, E
and G, the thickness of the links represents the number of visits of a
pollinator to a plant species. In B, D, F and H, grey squares denote
interaction between a plant and a pollinator and darker shades represent
higher number of interactions.
Figure 3 . Effect of interspecific variation in abundance in
simulated plant communities on A) variation in degree of generalization,
B) number of shared partners, C) plant-pollinator network nestedness and
D) connectance at different average flower abundances. High average
flower abundance corresponds to 1000, intermediate high corresponds to
500, intermediate low corresponds to 250 and low corresponds to 100.
Symbols and error bars represent mean and standard error.
Figure 4. Degree of
generalization and attributes of the pollinators on which a plant
species colonizing simulated plant communities evolved as a function of
its floral abundance. The parameter values represent the average values
of pollen carryover capacity, specialization and abundance of the
pollinators on which the new colonist evolved and degree of floral
generalization of the new colonist. The parameter values on the y-axis
were normalized so that the minimum value corresponds to 0 and the
maximum value corresponding to 1. The standard error of the mean
parameter values among the 100 simulations is presented as the shaded
area around the mean values.
Figure 5 . The three
processes generating floral diversification according to the model.
Following dispersal by a plant colonist (the red tubular flower species)
from a community (represented in A) to new communities, shifts in
pollination system can occur as a result of either B) change in the
abundance of the new colonist, C) change in plant community composition
(change in abundance of the other community members), or D) change in
pollinator assemblage. C, E, G) Effect of different amounts of variation
in C) abundance of the new colonist, E) community composition and G)
pollinator assemblage between communities on variation in evolved
pollination systems between species for simulated plant clades
colonizing 20 new communities. Variation in evolved pollination systems
was measured as the standard deviation of the average attributes values
and degree of generalization between species of the plant clade. The
parameter values on the y-axis were normalized so that the minimum value
corresponds to 0 and the maximum value corresponding to 1. Panel E) do
not show values of pollinator specialization (measured as the total
flower abundance of all the species it pollinates) and panel G) do not
show values of pollinator abundance because those parameters were
purposely varied between communities and hence variability was expected
for those parameters even in the absence of shift in pollination system.
Illustration by Florence Jean and Sébastien Rivest.