Explaining Variation in the Effect of Floral Density on Pollinator Visitation

Abstract

Pollinator responses to floral density have important implications for plant biology. In particular, a decline in pollinator visitation at low density can cause an Allee effect (a positive relation of fitness to density) in the plant population, which heightens that population's vulnerability to extinction. Empiricists have reported a variety of relations between flower or plant density and pollinator visitation rates. Here I develop and test a model that provides explanations for this diversity. The model assumes that pollinators distribute themselves between a focal patch of flowers and the surrounding environment so as to maximize foraging success. The resulting relation of per-flower visitation rate to focal-patch floral density is nonlinear, with positive effects at low floral densities and weaker or negative effects at higher densities. The relation is influenced by floral density in the surrounding environment and traits of both the plants and their pollinators. In a field experiment, floral density of Holocarpha virgata ssp. virgata had a nonlinear effect on per-flower visitation that was largely consistent with the model's predictions. By producing testable hypotheses based on biologically reasonable assumptions, this model serves as a starting point for explaining an important facet of plant-pollinator mutualisms.

Elevational disease distribution in a natural plant–pathogen system: insights from changes across host populations and climate

“…This is partially consistent with previous studies of the incidence of M. violaceum on the related host species S. latifolia which found that mid‐sized populations were more likely to be diseased than very small or very large populations (Antonovics et al , ). Such a non‐linear pattern is potentially due to a balance between epidemiological processes: smaller populations attract fewer long‐distance pollinators carrying spores from other populations (Essenberg ) and are more prone to loss of disease due to stochastic effects, while transmission in very large (often dense) populations may decline due to low pollinator/host ratios (Antonovics et al ). We did not find a significant decline in the incidence of disease among the largest size class (> 300 individuals), though it is possible that our methods of population sampling in areas where there was continuous host presence artificially minimized the sizes of the largest populations.…”

Understanding Linkage Rules in Plant-Pollinator Networks by Using Hierarchical Models That Incorporate Pollinator Detectability and Plant Traits

“…abundance, density and spatial distribution of flowers) modulates these preferences [43,44]. Floral traits are known to determine pollinator preferences [23].…”

Florally rich habitats reduce insect pollination and the reproductive success of isolated plants

“…Plant-pollinator interactions vary with plant population size, density, and habitat context (Essenberg, 2012;Mayer, Van Rossum & Jacquemart 2012). Habitats supporting a high abundance and species richness of flowering plants may either enhance or disrupt the transference of pollen to plants (Blaauw & Isaacs, 2014;Vanbergen et al, 2014).…”