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Data from: Trait matching and phenological overlap increase the spatio-temporal stability and functionality of plant-pollinator interactions

Citation

Chacoff, Natacha P.; Vázquez, Diego P.; Lomáscolo, Silvia B. (2020), Data from: Trait matching and phenological overlap increase the spatio-temporal stability and functionality of plant-pollinator interactions, Dryad, Dataset, https://doi.org/10.5061/dryad.8cz8w9gm1

Abstract

Morphology and phenology influence plant-pollinator network structure, but whether they generate more stable pairwise interactions with higher pollination success is unknown. Here we evaluate the importance of morphological trait matching, phenological overlap and specialisation for the spatio-temporal stability (measured as variability) of plant-pollinator interactions  and for pollination success, while controlling for species abundance. To this end, we combined a six-year plant-pollinator interaction dataset, with information on species traits, phenologies, specialisation, abundance and pollination success, into structural equation models. Interactions among abundant plants and pollinators with well-matched traits and phenologies formed the stable and functional backbone of the pollination network, whereas poorly-matched interactions were variable in time and had lower pollination success. We conclude that phenological overlap could be more useful for predicting changes in species interactions than species abundances, and that non-random extinction of species with well-matched traits could decrease the stability of interactions within communities and reduce their functioning.

Methods

Pollinator visitation

The visitation data come from a previously published study describing a plant-pollinator network from pollinator visits to flowers in a dryland ecosystem (Chacoff et al., 2018, Ecology 99: 21-28, https://doi.org/10.1002/ecy.2063). Data collection was conducted in sites lying at the lowlands of Villavicencio Nature Reserve, Mendoza, Argentina. Visitation data were collected weekly during three months during the flowering season (Austral spring and early summer, September-December) between 2006 and 2011. Pollinator visits to flowers were recorded in two 1-ha sites separated by ca. 5 km, with two additional 1-ha sites sampled in only in 2006 (one of them also sampled in 2007 for one 5-min observation period). Data from these sites were combined into a single network to improve sampling completeness of species and interactions occurring in the region. Pollinator visits to flowers were recorded between 7:00 and 14:00 in 5-min observation periods, a representative portion of the daily activity period of pollinators in our study sites. The original data from Chacoff et al. (2018) include 59 plant species, 196 flower visiting insect species, and 28015 interaction events (flower visits) involving 1050 different pairs of interacting species, but in this dataset we include only the 45 plant species and 135 flower visiting species for which morphological data were available.

Floral abundance

Plant abundance was estimated based on the density of flowers of each plant species, as flowers are the relevant plant structure for this interaction type. Flower abundance was estimated during the flowering season of all study years using fixed quadradts/transects. Several rare plant species were absent from our fixed quadrats and transects but present elsewhere in our study site; for those species we assigned an abundance of one flower, the minimum we could have detected with our sampling method. To estimate the abundance of flowers in the sites where species interactions were sampled, we counted the number of flowers per plant species per site using transects and quadrats. In 2006 we sampled forty 2 × 2 m quadrats per site (640 m2 total area), in 2007 five 50 × 2 m transects (500 m2 total), and in 2008-2011 two 50 × 2 m transects and four 20 × 8 m quadrats (840 m2 total per year). We summed the abundance of each flower species across years to obtain an overall measure of flower abundance per plant species: number of flowers per species over the entire sampling period (i.e. 4500 m2 sampled over the 6 years).

Phenological overlap

We estimated phenological overlap between any pair of interacting plant and pollinator species as the number of weeks (across the entire six-year sampling period) when these species co-occur.

Floral traits

Data on flower traits were measured for 45 species included in the network. For shrubs, trees, and herbaceous plants for which individuals are readily identified, we selected haphazardly three individuals in which we selected three flowers to measure all traits. For herbaceous plants for which individuals are hard to identify we measured nine flowers per species. In each flower we measured the following traits: (1) corolla length: distance between the tip of the petals and the base of the corolla, where we assumed that the nectaries resided (for flowers with open corollas, this measure equalled zero); (2) corolla aperture: the diameter of the opening at the point where the flower starts to narrow for tubular or semi-tubular flowers (it was a measure of a potential restriction for insects to get to the nectaries, assumed to be at the bottom of the tubular part; if the flower was not tubular, the flower was considered completely open and the aperture was the same as flower diameter); (3) maximum height: the height of the highest flower (inflorescence for Asteraceae) in the plant; (4) minimum height: the height of the lowest flower (inflorescence for Asteraceae) in the plant; (5) mean height: average of maximum and minimum height.

Insect traits

Insect species were identified to species level or, if this was not possible, to family or genus level and then classified as morphotypes. Traits were measured in up to five individuals of all the species or morphospecies recorded interacting for which we had at least two individuals in our collection. All traits were measured with a graduated ocular. Measured traits include: (1) body length: distance from the tip of the head to the tip of the abdomen; (2) body width: maximum width of body or head (lateral body axis); (3) body thickness: maximum thickness of body or head (dorsoventral body axis); (4, 5) proboscis length and proboscis width: for Hymenoptera, the length was measured as the length of the prementum and glossa completely extended (Harder, 1982, 1983) and maximum width was normally measured at the end of the prementum; for Diptera, total extended proboscis length was measured after slightly pulling it out of the head and grasping the labella with fine forceps, to prevent retraction due to the contractile basal part (Gilbert, 1981); maximum width was measured, in most of the cases, as the labella width; for Lepidoptera, proboscis length was the total length of the unrolled proboscis; finally, for Coleoptera we used the length and the width of the mandibles as measures of proboscis length and width, respectively.

Pollination success

To estimate pollination success, we counted the number of pollen tubes growing below the tip of the pistil resulting from pollen deposited by each pollinator species on the stigma of each plant species in one visit, relative to the pollen deposited by all pollinator species. We used data on pollen deposition for four of the most abundant plant species, Larrea divaricata and L. nitida (Zygophyllaceae), Opuntia sulphurea (Cactaceae) and Zuccagnia punctata (Fabaceae), from a previous study (Vázquez et al. 2012, Ecology 93; 719-725, https://doi.org/10.1890/11-1356.1). Pollen deposition on these four plant species was sampled in 2008, at the same sites as plant-pollinator interactions were sampled. Two of these plant species had many flower visitor species (L. divaricata had 52 and Z. punctata 56 visitor species), whereas the others had fewer flower visitors (L. nitida had 24 and O. sulphurea 33). We measured pollen deposition by three to seven pollinator species for each plant species (10 pollinator species, 19 different interactions [i.e. links]).

Usage Notes

Plant-pollinator data from Villavicencio Nature Reserve, including yearly plant-pollinator interaction matrices for six consecutive years (2006-2011), flower abundance for the same six years, phenological overlap among plant and pollinator species, plant and pollinator traits, and pollination success.

Funding

Consejo Nacional de Investigaciones Científicas y Técnicas, Award: PIP 6564

Consejo Nacional de Investigaciones Científicas y Técnicas, Award: PIP 2781

Fondo para la Investigación Científica y Tecnológica, Award: PICT 20805

Fondo para la Investigación Científica y Tecnológica, Award: PICT 1471

Fondo para la Investigación Científica y Tecnológica, Award: PICT 2010‐2779

Fondo para la Investigación Científica y Tecnológica, Award: PICT 2014-3168