Effects of small-scale clustering of flowers on pollinator foraging behaviour and flower visitation rate

Abstract

Plants often grow in clusters of various sizes and have a variable number of flowers per inflorescence. This small-scale spatial clustering affects insect foraging strategies and plant reproductive success. In our study, we aimed to determine how visitation rate and foraging behaviour of pollinators depend on the number of flowers per plant and on the size of clusters of multiple plants using Dracocephalum moldavica (Lamiaceae) as a target species. We measured flower visitation rate by observations of insects visiting single plants and clusters of plants with different numbers of flowers. Detailed data on foraging behaviour within clusters of different sizes were gathered for honeybees, Apis mellifera, the most abundant visitor of Dracocephalum in the experiments. We found that the total number of flower visitors increased with the increasing number of flowers on individual plants and in larger clusters, but less then proportionally. Although individual honeybees visited more flowers in larger clusters, they visited a smaller proportion of flowers, as has been previously observed. Consequently, visitation rate per flower and unit time peaked in clusters with an intermediate number of flowers. These patterns do not conform to expectations based on optimal foraging theory and the ideal free distribution model. We attribute this discrepancy to incomplete information about the distribution of resources. Detailed observations and video recordings of individual honeybees also showed that the number of flowers had no effect on handling time of flowers by honeybees. We evaluated the implications of these patterns for insect foraging biology and plant reproduction.

Do local conspecific density and floral display size influence fruit set via pollinator visitation in Orchis militaris?

“…Although a positive correlation is expected between the time spent on a flower and the distance between flowers (Inouye et al 2015), density had no effect on handling time per flower. Similar results were obtained for various insect groups (Conner and Rush 1996, Ghazoul 2005, Akter et al 2017. They seemingly visit individual flowers in a constant manner irrespective of the number of open flowers (Akter et al 2017).…”

“…Similar results were obtained for various insect groups (Conner and Rush 1996, Ghazoul 2005, Akter et al 2017. They seemingly visit individual flowers in a constant manner irrespective of the number of open flowers (Akter et al 2017). The time spent per flower was negatively influenced by its position in the visitation sequence.…”

Experimental loss of generalist plants reveals alterations in plant-pollinator interactions and a constrained flexibility of foraging

“…It is likely that they were underutilised in the original community because of their small floral display, so their visitation benefited from the overall reduction of flower abundance after the removals. Smaller inflorescences may also provide more resources per flower, and thus be more rewarding to flower visitors on a per-visit basis 38 . Taken together, our results imply that foraging can be flexible but also constrained within a specific plant-trait space 39 .…”

Floral plasticity: Herbivore‐species‐specific‐induced changes in flower traits with contrasting effects on pollinator visitation

“…Herbivore‐induced changes in pollinator visitation are mediated by plasticity in flower traits. Plants attract pollinators through various flower traits: flower abundance, size, morphology, colour, volatiles, and rewards (nectar and pollen; Akter, Biella, & Klecka, ; Junker & Parachnowitsch, ). Flower traits are highly plastic and change readily in response to environmental factors, such as herbivory (Lucas‐Barbosa, van Loon, & Dicke, ; Strauss, ).…”