Zachary M. Portman | Geology Reports

USGS2022

Variation in foraging patterns as reflected by floral resources used by male vs female bees of selected species at Badlands National Park, SD

Female and male bees forage for different reasons: females provision nests with pollen appropriate for larval development and consume nectar for energy while males need only fuel their own energetic requirements. The expectation, therefore, is that females should visit fewer floral resource species than males, due to females’ focus on host plant species and their tie to the nest location. We used pollen collected from bees’ bodies and the flowers they were collected on to infer floral resource use in 2010-2012 at Badlands National Park, SD, USA. We collected bees on 24 1-ha plots centered on particular plant species. We compared number of floral species and families (1) associated with individual female and male bees (via generalized linear mixed models) and (2) accumulated by each sex (using rarefaction); and (3) effect of variation between sexes in plant-bee interactions via modularity analyses. Analyses were restricted to bee species with > 5 individuals per sex. Contrary to expectation, female and male bees differed infrequently in the number of floral resources they had visited, both on single foraging bouts and collectively when accumulated across all males and females of a species. When males and females did differ, males visited fewer floral species than females. Generalist and specialist bee species did not differ markedly in floral resource use by females and males. When separated by sex, seven of eleven species occupied different modules than they did when analyzed as a species; most of the bee species were connectors, thus important for stability of the network during perturbations.

South Dakota↗

USGS2021

Coflowering invasive plants and a congener have neutral effects on fitness components of a rare endemic plant

Network analyses rarely include fitness components, such as germination, to tie invasive plants to population-level effects on the natives. We address this limitation in a previously studied network of flower visitors around a suite of native and invasive plants that includes an endemic plant at Badlands National Park, South Dakota, USA. Eriogonum visheri coflowers with two abundant invasive plants, Salsola tragus and Melilotus officinalis , as well as a common congener, E. pauciflorum . Network analyses had suggested strong linkages between E. visheri and S. tragus and E. pauciflorum , with a weaker link to M. officinalis . We measured visitation, pollen deposited on stigmas, achene weight and germination over three field seasons (two for germination) in four populations (two in the final season) of E. visheri and applied in situ pollen treatments to E. visheri , adding pollen from other flowers on the same plant; flowers on other E. visheri plants; S. tragus, M. officinalis , or E. pauciflorum ; open pollination; or excluding pollinators. Insect visitation to E. visheri was not affected by floral abundance of any of the focal species. Most visitors were halictid bees; one of these ( Lasioglossum packeri ) was the only identified species to visit E. visheri all three years. Ninety-seven percent of pollen on collected E. visheri stigmas was conspecific, but 22% of flowers had >1 grain of E. pauciflorum pollen on stigmas and 7% had >1 grain of S. tragus pollen; <1% of flowers had M. officinalis pollen on stigmas. None of the pollen treatments produced significant differences in weight or germination of E. visheri achenes. We conclude that, in contrast to the results of the network analysis, neither of the invasive species poses a threat, via heterospecific pollen deposition, to pollination of the endemic E. visheri , and that its congener provides alternative pollen resources to its pollinators.

South Dakota↗