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.
Highlights
In tropical ecosystems, seasonal changes in rainfall, temperature, and day length are the primary flowering constraints (Morellato et al, 2000; Abrahamczyk et al, 2011; Cortés-Flores et al, 2017)
Using a community-level approach and the cerrado as a model of a tropical seasonally dry vegetation, we investigated the seasonality of flowering phenology, the flower color diversity, and the respective flower color contrasts according to the visual system of bees
We evaluated the temporal patterns of flower color diversity in the cerrado community and related species flowering time to the respective flower color according to human- and bee-color categories, similar to Camargo et al (2013) in which fruiting patterns were analyzed according to fruit color in the same cerrado area
Summary
Seasonal changes in rainfall, temperature, and day length are the primary flowering constraints (Morellato et al, 2000; Abrahamczyk et al, 2011; Cortés-Flores et al, 2017). Seasonality shapes flowering patterns, which are strongly related to the dynamics of plant communities, defining temporal changes in plant reproduction, resource availability for flower visitors, maintenance of plant–pollinator diversity, and plant reproductive success (Gentry, 1974; Lieth, 1974; Ramírez, 2006; Morellato et al, 2016). Hymenoptera are active throughout the year, a higher activity, especially in bees, has been observed mainly between November and June in cerrado woodland (D’Avila and Marchini, 2008) Eusocial bees, such as Apis mellifera and Trigona spinipes, are less susceptible to temperature and humidity variation, being important pollinators during drier periods when less resources are available (D’Avila and Marchini, 2008)
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