Close Encounters

Greater floral overlap and pollinator generalization favoured in a buzz-pollinated plant

Simultaneous flowering and low pollinator specialization led to greater reproductive success.

Individual plants within a population will exhibit differences in how they allot resources and respond to their environment. This is true of phenology and plant-pollinator interactions as well. Variation in these characteristics may influence individual reproductive success. Flowering time varies both within and among plant populations, and is influenced by environment, resource availability, and the pollinators themselves.

A high overlap of individual flowering time within a population will increase flower abundance, making the location more attractive to pollinators, as well as increasing the availability of mates for the plants, thereby increasing pollination success. On the other hand, a low overlap within a population could maintain pollinator populations over a greater length of time as well as reducing intraspecific competition and facilitating outcrossing.

Trembleya laniflora after Costa Soares et al. 2020.

In a recent paper out in Annals of Botany, lead author Natalia Costa Soares and colleagues gauged the reproductive benefit of higher versus lower flowering overlap, as well as the benefit of pollinator specialization versus generalization by the plant. The researchers used the crepuscular bee-pollinated plant Trembleya laniflora, which they studied across three distinct populations in the grasslands of southeastern Brazil. The species has a fairly specialized pollination system, with as many as 13 functionally specialized, buzz-pollinating bee species potentially visiting its flowers.

A high overlap in flowering time – temporal generalization – among individuals within the populations studied appears to affect neither pollinator interactions nor overall reproductive success. Pollinator generalization at the level of individual plants, however, improved reproduction in centrally-located plants with higher pollinator species richness. These results point to generalization at the level of the individual being important to the maintenance of a population with a highly specialized pollination system.

“The fact that the observed levels of individual temporal specialization were lower than expected by chance suggests that the overlap in phenology among individuals is somehow favoured in this species,” write the authors. “We consider that the higher diversity of pollinators, enhancing the probability of an individual receiving conspecific pollen from different plants, is a key factor driving reproductive success of T. laniflora.”