DOI: 10.5061/dryad.16v7n
title: Data from: Scale-dependent shifts in the species composition of flower visitors with changing floral density

description: Responses of flower-visiting animals to floral density can alter
 interactions between plants, influencing a variety of biological
 processes, including plant population dynamics and the evolution of
 flowering phenology. Many studies have found effects of floral or plant
 density on pollinator visitation rates at patch scales, but little is
 known about responses of flower visitors to floral densities at larger
 scales. Here, I present data from an observational field study in which I
 measured the effects of floral density on visitation to the annual
 composite Holocarpha virgata at both patch (4 m(2)) and site (12.6 ha)
 spatial scales. The species composition of flower visitors changed with
 floral density, and did so in different ways at the two scales. At the
 site scale, average floral density within patches of H. virgata or within
 patches of all summer-flowering species combined had a significant
 positive effect on per-flowerhead visitation by the long-horned bee
 Melissodes lupina and no significant effects on visitation by any other
 taxa. At the patch scale, per-flowerhead visitation by honeybees
 significantly increased whereas visitation by M. lupina often decreased
 with increasing floral density. For both species, responses to patch-scale
 floral density were strongest when site-scale floral density was high. The
 scale-dependence of flower visitor responses to floral density and the
 interactions between site- and patch-scale effects of floral density
 observed in this study underscore the importance of improving our
 understanding of pollinators' responses to floral density at
 population scales.
description: VisitationPer-flowerhead visitation rates to Holocarpha virgata ssp. virgata (Asteraceae) and densities of flower-visiting insects in 2 x 2 m plots spanning the available range of floral densities at a variety of sites and dates within the flowering seasonSiteDataLatitude and longitude of the center point of each site used in Visitation.csv and area occupied by summer-flowering plants within 200m of the center of each site. See ReadMe file associated with Visitation.csv for further information.ObsDataDates of each observation recorded in Visitation.csv along with average H. virgata floral densities within H. virgata patches and average densities of floral resources within patches of all summer-flowering species observed within 200m of the center of each site during each observation. See ReadMe file associated with Visitation.csv for further information.NectarTotal nectar sugar produced by H. virgata flowerheads in 1 x 1 m plots of varying floral densities at the sites and dates used in Visitation.csv. Flowerheads were bagged in the morning before insects became active and nectar measured in the late morning or early afternoon, after the conclusion of flower visitation observations. See ReadMe file associated with Visitation.csv for more information.NectarTimingTotal nectar sugar measured in 11 bagged flowerheads of H. virgata at multiple points throughout a single day, August 22, 2010. Flowerheads were bagged before pollinators became active in the morning. At each measurement point, the flowerhead was emptied of nectar. See ReadMe file associated with Visitation.csv for further information.PollenPollen produced by H. virgata flowerheads in the 1 x 1 m plots also used for nectar measurements. Flowerheads were collected in the morning before insects became active. See ReadMe file associated with Visitation.csv for further information.HandlingTimesFlower handling times recorded during the flower visitation observations described above (and reported in Visitation.csv). See ReadMe file associated with Visitation.csv for further information.SearchSpeedsSearch speeds calculated from flight times and estimated distances between flowerheads, in 2009 (the summer before the rest of the data in this dataset were collected), for the main visitors to H. virgata. See ReadMe file associated with Visitation.csv for further information.BodySizeIntertegular spans of each of the four most common flower visitors to H. virgata. See ReadMe file associated with Visitation.csv for further information.