Unclusterable, underdispersed arrangement of insect‐pollinated plants in pollinator niche space

Abstract

Pollinators can mediate facilitative or competitive relationships between plant species, but the relative importance of these two conflicting phenomena in shaping community‐wide pollinator resource use remains unexplored. This article examines the idea that the arrangement of large samples of plant species in Hutchinsonian pollinator niche space (n‐dimensional hypervolume whose axes represent pollinator types) can help to evaluate the comparative importance of facilitation and competition as drivers of pollinator resource use at the community level. Pollinator composition data were gathered for insect‐pollinated plants from the Sierra de Cazorla mountains (southeastern Spain), comprising ~95% of widely distributed insect‐pollinated species. The following questions were addressed at regional (45 sites, 221 plant species) and local (1 site, 73 plant species) spatial scales: (1) Do plant species clusters occur in pollinator niche space? Four pollinator niche spaces differing in dimensionality were considered, the axes of which were defined by insect orders, families, genera, and species. (2) If all plant species form a single, indivisible cluster, are they overdispersed or underdispersed within the cluster relative to a random arrangement? “Clusterability” tests failed to reject the null hypothesis that there was only one pollinator‐defined plant species cluster in pollinator niche space, irrespective of spatial scale, pollinator niche space, or pollinator importance measurement (proportions of pollinator individuals or flowers visited by each pollinator type). Observed means of interspecific dissimilarity in pollinator composition were smaller than randomly simulated values in the order‐, family‐, and genus‐defined pollinator niche spaces. This finding revealed an underdispersed arrangement of plant species in each of these pollinator niche spaces. In the undisturbed montane habitats studied, arrangement of insect‐pollinated plant species in the various niche spaces defined by pollinator composition did not support a major role for interspecific competition as a force shaping community‐wide pollinator resource use by plants, but rather suggested a situation closer to the facilitation‐dominated extreme in a hypothetical competition‐facilitation gradient. Results also highlight the importance of investigations on complete or nearly complete insect‐pollinated plant communities for suggesting and testing novel hypotheses on the ecology and evolution of plant–pollinator systems.

Heterospecific pollen deposition is positively associated with reproductive success in a diverse hummingbird‐pollinated plant community

“…Second, pollinator sharing in this community may have resulted in reproductive benefits for plants (Bergamo et al 2020). By blooming together, plants may promote facilitation, which is a reproductive strategy that increases the number of visitors, even if they deposit heterospecific pollen (Tur et al 2016, Thomson et al 2019, Herrera 2021). Facilitation has been an important factor decreasing pollen limitation and determining functional patterns in other plant communities pollinated by hummingbirds (Wolowski et al 2017, Bergamo et al 2018), and our results suggest this relationship in the studied community.…”

Plant phylogeny as a major predictor of flower visitation by nitidulid beetles, a lineage of ancestral angiosperm pollinators

“…Although a rigorous demonstration of their pollinating effectiveness would have required controlled experiments, circumstantial evidence suggests that the Nitidulidae recorded in pollinator censuses in this study should be considered as true pollinators of most plant species where they occurred. Examination of ~300 close-up photographs of Nitidulidae taken as part of pollinator census work (Herrera 2020(Herrera , 2021 revealed that they often S1 for details). Plant clades marked by arcs match those in Figure 2.…”

“…On the other hand, and perhaps more importantly, this study has provided a case example for the application of an analytical procedure apt to dissect objectively the importance of phylogenetic legacies, gross floral traits and ecological scenarios as predictors of interspecific variation in pollinator composition. Applied to sufficiently large and phylogenetically diverse samples of animal-pollinated plants, the analytical tools used here can help to shed light, from a different angle, on extant controversial issues in pollination research beyond ad hoc interpretations usually applied to small species samples (e.g., the reality of so-called "pollination syndromes"; Herrera 2020Herrera , 2021Krakos & Austin 2020).…”

“…Pollinator composition data used in this paper were collected during February-December 1997-2020 in the Sierra de Cazorla (Jaén Province, southeastern Spain), a region characterized by well-preserved natural habitats. Data were obtained for 251 plant species in 167 genera and 46 families (Supplementary Material Table S1), using field methods described in detail by Herrera (2020Herrera ( , 2021. The elemental sampling unit was the "pollinator census", consisting of a 3-min watch of a flowering patch whose total number of open flowers was also counted.…”

Seasonality of pollinators in Mediterranean montane habitats: cool-blooded bees for early-blooming plants

“…Data on bee pollinator composition and air temperature at the foraging sites of different bee species were collected during January-December 1997-2022 in a relatively small area of the Sierra de Cazorla, Jaén Province, southeastern Spain (see Herrera 2021: Fig. 2, for map of sampling sites).…”