Flowering Phenology and the Influence of Seasonality in Flower Conspicuousness for Bees

Abstract

Flowering patterns are crucial to understand the dynamics of plant reproduction and resource availability for pollinators. Seasonal climate constrains flower and leaf phenology, where leaf and flower colors likely differ between seasons. Color is the main floral trait attracting pollinators; however, seasonal changes in the leaf-background coloration affect the perception of flower color contrasts by pollinators. For a seasonally dry woody cerrado community (Brazilian savanna) mainly pollinated by bees, we verified whether seasonality affects flower color diversity over time and if flower color contrasts of bee-pollinated species differ between seasons due to changes in the leaf-background coloration. For 140 species, we classified flower colors based on human-color vision, and for 99 species, we classified flower colors based on bee-color vision (spectral measurements). We described the community’s flowering pattern according to the flower colors using a unique 11 years phenological database. For the 43 bee-pollinated species in which reflectance data were also available, we compared flower color diversity and contrasts against the background between seasons, considering the background coloration of each season. Flowering was markedly seasonal, peaking at the end of the dry season (September), when the highest diversity of flower colors was observed. Yellow flowers were observed all year round, whereas white flowers were seasonal, peaking during the dry season, and pink flowers predominated in the wet season, peaking in March. Bee-bluegreen flowers peaked between September and October. Flowers from the wet and dry seasons were similarly conspicuous against their corresponding background. Regardless of flowering season, the yellowish background of the dry season promoted higher flower color contrast for all flower species, whereas the greener background of the wet season promoted a higher green contrast. Temporal patterns of flower colors and color contrasts were related to the cerrado seasonality, but also to bee’s activity, visual system, and behavior. Background coloration affected flower contrasts, favoring flower conspicuousness to bees according to the season. Thus, our results provide new insights regarding the temporal patterns of plant–pollinator interactions.

Major Flower Pigments Originate Different Colour Signals to Pollinators

“…In general, the clustering patterns of loci observed in the colour space of bees, flies, butterflies and birds were similar. Loci of flowers with chlorophylls occupied central position in all models and showed low chromatic contrast, which suggest that these flowers are difficult to perceive by the four groups of pollinators (Chittka et al, 1994;Endler and Mielke, 2005;Hannah et al, 2019), at least in environments where dominant background is green foliage (Endler, 2012;Bukovac et al, 2017;Martins et al, 2021). This fact may explain the low frequency of green flowers in local floras (Weevers, 1952;Dyer, 1996;Warren and Mackenzie, 2001).…”

Floristic composition, pollination and seed-dispersal systems in a target cerrado conservation area

“…In terms of importance, even for a small patch of vegetation, our study has reported the occurrence of several endemic cerrado species, as: Our cerrado sensu stricto species were pollinated mainly by bees, with more than a half of species presenting bee-pollinated flowers (Figure 4), as expected for Cerrado and other tropical vegetation systems (Gottsberger & Silberbauer-Gottsberger 2006, Monteiro et al 2021, Genini et al 2021) and stressing the relevance of preserving Cerrado remnants for this key ecosystem service. For the same community, Martins et al (2021) found that plant species with different flower colors presented distinct flowering peaks over the year but maintained color diversity over time. For example, while white flowers peaked in the transition between dry and wet season, matching with the community flowering peak, yellow flowers were distributed all year long, being an important resource during the dry season, when a reduced number of species is flowering (Martins et al 2021).…”

“…For the same community, Martins et al (2021) found that plant species with different flower colors presented distinct flowering peaks over the year but maintained color diversity over time. For example, while white flowers peaked in the transition between dry and wet season, matching with the community flowering peak, yellow flowers were distributed all year long, being an important resource during the dry season, when a reduced number of species is flowering (Martins et al 2021). The observed flowering pattern provide functional diversity over time, contributing to the presence of different groups of pollinators such as bees, small insects, flies and hummingbirds, and nocturnal pollinators such as Sphingidae moths and bats (Gottsberger & Silberbauer-Gottsberger 2006, Amorim et al 2009.…”

“…Table 1. List of plant species recorded in the cerrado sensu stricto, Itirapina, São Paulo State, Southeastern Brazil, and their respective voucher number, life form, dispersion syndrome, pollinator system, typical Cerrado species according to Durigan et al (2004Durigan et al ( , 2012 The inference of pollinators was made based on an extensive bibliographic survey, searching by the pollinators of Cerrado species from our study site performed by Martins (2019) and Martins et al (2021).…”

Determining factors of flower coloration

“…A posterior study showed that, instead, the corolla color of spring flowers in temperate deciduous forests are lighter than non-spring flowers, but not necessarily white (Hensel & Sargent 2012). In the Brazilian Savanna, yellow flowers were abundant year around, but white flowers peaked in the dry season, and pink flowers in the wet season (Martins et al 2021). Indeed, in Itatiaia National Park (Brazil), community level fitness increased with synchronous flowering and color similarities, using visual systems of bees, flies and birds (Bergamo et al 2020).…”