The role of biotic interactions in shaping plant flowering phenology has long been controversial; plastic responses to the abiotic environment, limited precision of biological clocks and inconsistency of selection pressures have generally been emphasized to explain phenological variation. However, part of this variation is heritable and selection analyses show that biotic interactions can modulate selection on flowering phenology. Our review of the literature indicates that pollinators tend to favour peak or earlier flowering, whereas pre-dispersal seed predators tend to favour off-peak or later flowering. However, effects strongly vary among study systems. To understand such variation, future studies should address the impact of mutualist and antagonist dispersal ability, ecological specialization, and habitat and plant population characteristics. Here, we outline future directions to study how such interactions shape flowering phenology.
"Patterns of floral phenology are considered to reflect evolutionary compromises in response to a set of selective forces, including the availability of water (David et al. 2012) and gene dispersers (pollinators and seed dispersers, Ranieri et al. 2012). The onset of flowering i.e. the transition from leaf to flower production, is often stimulated by a combination of internal (plant age or size) and external factors (day/ night length, low temperature, fire and/or the presence of water ; Erwin 2006, Elzinga et al. 2007). Thus the knowledge of phenological patterns across neighbouring populations and geographic regions in relation to local and regional environmental correlates is crucial to estimate its reproductive potential as prerequisite for species survival (Ison et al. 2014). "
[Show abstract][Hide abstract] ABSTRACT: Background and aims – The main reproductive traits of the native African food tree species, Pentadesma
butyracea Sabine (Clusiaceae), which is threatened in Benin and Togo, were examined in Benin to gather
basic data necessary to develop conservation strategies in these countries.
Methodology – Data were collected on phenological pattern, floral morphology, pollinator assemblage,
seed production and germination conditions on 77 adult individuals from three natural populations
occurring in the Sudanian phytogeographical zone.
Key results – In Benin, Pentadesma butyracea flowers once a year during the dry season from September
to December. Flowering entry displayed less variation among populations than among individuals within
populations. However, a high synchrony of different floral stages between trees due to a long flowering
period (c. 2 months per tree), might still facilitate pollen exchange. Pollen-ovule ratio was 577 ± 213
suggesting facultative xenogamy. The apical position of inflorescences, the yellowish to white greenish
flowers and the high quantity of pollen and nectar per flower (1042 ± 117 μL) represent floral attractants
that predispose the species to animal-pollination. The main pollinators were two sunbirds (Cyanomitra
verticalis, Cinnyris coccinigastrus) and three Hymenoptera (Apis mellifera, Meliponula togoensis,
Hypotrigona sp.). Mean fruit set reached 49%, and absolute fruit production increased with tree size. Seeds
were desiccation-sensitive (i.e. recalcitrant) with a maximum duration of hydrated storage of three months.
Germination of seeds was most successful and rapid at 30°C (50% after nine days).
Conclusions – Our results indicate that the natural reproduction of P. butyracea is not limited by its ecology
so that we hypothesize anthropogenic activities to be the reason for the threatened status of P. butyracea
in Benin and Togo. However, due to its recalcitrant seeds, the conservation of its genetic resources is not
feasible through ex situ conservation of seed banks but in situ strategies and/or ex situ conservation in
orchards should be successful.
"Evolutionary theory predicts shifts in phenological activity to periods when competition for generalist pollinators and dispersers is relaxed and will be favored by natural selection if plants maximize fitness resulting from increased pollen deposition and seed removal (Lobo et al. 2003; Elzinga et al. 2007). "
[Show abstract][Hide abstract] ABSTRACT: Disentangling the relative importance of biotic and abiotic constraints in plant reproduction is a major challenge in reproductive ecology. Here, we tested the ‘resource limitation hypothesis’ that predicts a high-level ovule abortion under resource scarcity; the ‘flowering displacement hypothesis’ that predicts low levels of pollen limitation driven by relaxed competition for pollinators; and the ‘herbivory escape hypothesis’ that predicts low impact by natural enemies during unfavorable conditions. We followed reproductive phenology, measured the seasonal variation in resource abundance, and calculated initial ovule budgets to estimate the relative importance of each limiting factor on final reproductive output. Ovule fate was determined of ovules in different positions within the pods, and a germination experiment was conducted to identify bottlenecks at the germination stage. Despite marked decreases in resource availability during the dry season, reproduction consistently occurred during mid-to-late dry season. Destruction by natural enemies and abortion were the most likely ovule fates, with only 2.2 % of flower buds converted into ripe fruits. Ovule fates were not random along fruit positions, with higher likelihood of well-formed seeds in fruit tips and higher likelihood of ovule abortion and non-fertilized ovules near the fruit bases. The benefits derived from flowering displacement to the dry season include reduced competition for pollinators and synchronization of seedling establishment with the onset of the rainy season. However, we found no support for the herbivory escape hypothesis. We argue that a cost-benefit approach is a useful framework to understand the evolutionary ecology of phenological strategies in seasonal environments.
"Flowering patterns of plant species could not independently exist apart from the effects of intrinsic genetic characteristics, which could also be explained with the help of biotic interactions from phylogenies (Elzinga et al. 2007; Frankie et al. 1974; Galloway and Burgess 2012). A well accepted distribution pattern is proposed as the unimodality (i.e. one significant peak during the whole flowering season), which is characteristic of plant communities located in lower latitudes (e.g. "
[Show abstract][Hide abstract] ABSTRACT: Aims Exploring flowering patterns and detecting processes are essential when probing into the nature of reproductive traits during
the life history and the interactions among different evolutionary clades. Such patterns are believed to be influenced by
many factors, but quantifying these impacts at the community-level remains poorly understood.
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