2.2 Reproductive aspect
Seasonal synchronisation of flowering is often closely linked to
vegetative phenology. This has several obvious benefits, apart from
those incidental to optimal timing with respect to climatic factors.
Among the benefits, close synchronisation helps assure adequate pollen
when the female structures are receptive. Also, by all occurring early
enough, this assures sufficient time for fruits and seeds to develop and
mature before either summer drought or autumn cold disrupt such
processes. Moreover, brief but differentiated flowering seasons can also
provide reproductive barriers between species that are interfertile but
whose hybrids may not be ecologically fit; however, such barriers have
broken down in some eucalypt species grown as exotics where their
flowering seasons differ from those in native habitats (Eldridge et al.
1993). This synchrony can mean very seasonal food supplies for animal
pollinators, but very short seasons can be made good by other, sympatric
species having differentiated flowering seasons − as with various
eucalypt species (Eldridge et al. 1993). A further but probably very
incidental benefit of flowering synchrony may be creating a brief
superabundance for herbivores, which we will consider later.
Masting, namely heavy flowering and seed production in some years, with
little or none in between (e.g. Kelly 1994; Kelly and Sork 2002), is a
phenomenon involving the timing of flowering. Its postulated biotic
significance is as a means of alternating between occasional predator
satiation and more frequent predator avoidance. However, it is not
actually a seasonal phenomenon, nor really ontogenetic, so it is not
considered further.
Timing of flowering has been reported as a minor factor in complex
interactions involving transmission of pathogens by pollinators (Biere
and Antonovics 1996; McArt et al. 2014), but is not considered further
in this connection.
Pathogens as putative drivers
The role of pathogens as potential evolutionary drivers of seasonal
phenology appears to have been especially under-researched. Cases we
consider involve: potential roles of pathogens in governing the
deciduous growth habit; the seasonal timing of spring flushing in a
widely distributed conifer; two closely related Pinus species
with overlapping distributions but markedly different seasonal timing of
vegetative and reproductive processes; and an oak species in what is
effectively an altitudinal transect. Briefly considered also is how
pathogens can modify phenotypically some processes that are normally
parts of seasonal phenology.