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Bimodal activity of diurnal flower visitation at high elevation.

ABSTRACT: Successful pollination in animal-pollinated plants depends on the temporal overlap between flower presentation and pollinator foraging activity. Variation in the temporal dimension of plant-pollinator networks has been investigated intensely across flowering seasons. However, over the course of a day, the dynamics of plant-pollinator interactions may vary strongly due environmental fluctuations. It is usually assumed there is a unimodal, diurnal, activity pattern, while alternative multimodal types of activity patterns are often neglected and deserve greater investigation. Here, we quantified the daily activity pattern of flower visitors in two different habitats contrasting high elevation meadows versus forests in Southwest China to investigate the role of abiotic conditions in the temporal dynamics of plant-pollinator interactions. We examined diurnal activity patterns for the entire pollinator community. Pollinator groups may differ in their ability to adapt to habitats and abiotic conditions, which might be displayed in their patterns of activity. We hypothesized that (a) pollinator communities show multimodal activity patterns, (b) patterns differ between pollinator groups and habitat types, and (c) abiotic conditions explain observed activity patterns. In total, we collected 4,988 flower visitors belonging to six functional groups. There was a bimodal activity pattern when looking at the entire pollinator community and in five out of six flower visitor groups (exempting solitary bees) regardless of habitat types. Bumblebees, honeybees, dipterans, lepidopterans, and other insects showed activity peaks in the morning and afternoon, whereas solitary bees were most active at midday. Activity of all six pollinator groups increased as solar radiation increased and then decreased after reaching a certain threshold. Our findings suggest that in habitats at higher elevations, a bimodal activity pattern of flower visitation is commonly employed across most pollinator groups that are diurnal foragers. This pattern may be caused by insects avoiding overheating due to elevated temperatures when exposed to high solar radiation at midday.

SUBMITTER: Xu X

PROVIDER: S-EPMC8495799 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Hoverflies (Diptera: Syrphidae) are among the most important pollinators, although they attract less attention than bees. They are usually thought to be rather opportunistic flower visitors, although previous studied demonstrated that they show colour preferences and their nectar feeding is affected by morphological constraints related to flower morphology. Despite the growing appreciation of hoverflies and other non-bee insects as pollinators, there is a lack of community-wide studies of flower visitation by syrphids. The aim of this paper is to provide a detailed analysis of flower visitation patterns in a species rich community of syrphids in a Central European grassland and to evaluate how species traits shape the structure of the plant-hoverfly flower visitation network. We found that different species varied in the level of specialisation, and while some species visited a similar spectre of flowers, others partitioned resources more strongly. There was a consistent difference in both specialisation and flower preferences between three syrphid subfamilies. Eristalinae and Pipizinae were more specialised than Syrphinae. Trait-based analyses showed that relative flower visitation (i) increased with plant height, but most strongly in Eristalinae; (ii) increased with inflorescence size in small species from all three subfamilies, but was independent of inflorescence size in large species of Eristalinae and Syrphinae; and (iii) depended on flower colour, but in a subfamily-specific way. Eristalinae showed the strongest flower colour preferences for white flowers, Pipizinae visited mostly white and yellow flowers, while Syrphinae were less affected by flower colour. Exploration of the structure of the plant-hoverfly flower visitation network showed that the network was both modular and nested. We also found that there were almost no differences in specialisation and relative visitation frequency between males and females. Overall, we showed that flower visitation in syrphids was affected by phylogenetic relatedness, body size of syrphids and several plant traits.

Project description:Much ecological research has focused on trying to understand why species are generalized or specialized in their interactions and how networks develop in a certain environment. It is now well known that traits such as phenology and abundance of a species are important determinants of its generalization level (i.e., number of different interactions or links to other species). Less information is available, however, on whether generalized and specialized species differ in particular traits of their interacting partners. Such partners might differ, for instance, in abundance and/or in the diversity of functional groups they belong to. Moreover, species might exhibit shifts through time (e.g., flowering season) in their partners' traits, though we know close to nothing on whether these changes do indeed occur. Assessing how such network links in both types of species are established is important for a better understanding of how different types of disturbance can affect community dynamics. Using data from four quantitative flower-visitation networks and independent measures of flower availability obtained when recording interactions, we test for such differences between species which have been previously categorized according to two specialization indexes: (1) number of partners (links), also named linkage level; this is a qualitative index and (2) complementary specialization d', named here selectiveness level; this is a quantitative index. We found that: (1) species with low linkage levels mainly interact with common species in the community whereas generalized species interact with a greater heterogeneity of partner's abundances and functional richness, (2) both selective and opportunistic species (with high and low d', respectively) interact with a similarly high functional richness (number of functional groups or families) of partners, and (3) generalized species are the only ones showing shifts along the season in their partners' traits, driven by changes in community species composition. The risk of extinction in front of a disturbance is generally expected to be highest for specialized species (with few partners) and selective species (which visit non-abundant or scarce partners). However, our findings show that by linking to abundant and/or to functionally diverse partners, respectively, these species may be maintained in the community and be less vulnerable to disturbances.

Project description:Background and aimsStudies of the effects of pollination on floral scent and bee visitation remain rare, particularly in agricultural crops. To fill this gap, the hypothesis that bee visitation to flowers decreases after pollination through reduced floral volatile emissions in highbush blueberries, Vaccinium corymbosum, was tested. Other sources of variation in floral emissions and the role of floral volatiles in bee attraction were also examined.MethodsPollinator visitation to blueberry flowers was manipulated by bagging all flowers within a bush (pollinator excluded) or leaving them unbagged (open pollinated), and then the effect on floral volatile emissions and future bee visitation were measured. Floral volatiles were also measured from different blueberry cultivars, times of the day and flower parts, and a study was conducted to test the attraction of bees to floral volatiles.Key resultsOpen-pollinated blueberry flowers had 32 % lower volatile emissions than pollinator-excluded flowers. In particular, cinnamyl alcohol, a major component of the floral blend that is emitted exclusively from petals, was emitted in lower quantities from open-pollinated flowers. Although, no differences in cinnamyl alcohol emissions were detected among three blueberry cultivars or at different times of day, some components of the blueberry floral blend were emitted in higher amounts from certain cultivars and at mid-day. Field observations showed that more bees visited bushes with pollinator-excluded flowers. Also, more honey bees were caught in traps baited with a synthetic blueberry floral blend than in unbaited traps.ConclusionsGreater volatile emissions may help guide bees to unpollinated flowers, and thus increase plant fitness and bee energetic return when foraging in blueberries. Furthermore, the variation in volatile emissions from blueberry flowers depending on pollination status, plant cultivar and time of day suggests an adaptive role of floral signals in increasing pollination of flowers.

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Bimodal activity of diurnal flower visitation at high elevation.

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