Supporting Information
Appendix S1: Allometric equation used to determine aboveground biomass estimates
We sampled natural populations of S. altissima and S. gigantea from natural populations at
ORNL, recorded the height of the stems and major braches (>10 cm), and oven dried each
individual (24 hr at 70 °C). We weighed each sample (n=15 per species) and determined an
allometric equation which estimates biomass (Weight (g) = (-0.071 + 0.0346 * height (cm) ^ 2).
We found no significant differences between the allometric equations for S. altissima and S.
gigantea; therefore, we pooled the data and used only one equation. This equation explained 83
% of the variation in biomass (dry weight) and both the linear (p < 0.001) and quadratic terms (p
= 0.007) were statistically significant.
Appendix S2: Taxonomic groups for pollinator identification
Pollinators were grouped into taxa based on differences the surveyor (MAG) could consistently
identify, from a range that did not influence pollinators (3m from the pot). Atteva aurea and
Chaliognathus pennsylvanicus were very common, and distinct enough to be identified to the
species level. Apis spp. and Bombus spp. visitors were identified at the genus level. We also
identified the following Lepidoptera and Hymenoptera families Halictidae, Hesperiidae,
Papilionoidea, Spechidae, Syrphidae, Tiphiidae and superfamily Vespoidea that commonly
visited flowers in the treatment pots. Especially common pollinators and the taxa in which they
were grouped included Apis mellifera (Apis), Bombus impatiens (Bombus), Agapostemon sp.
(Halictidae), Junonia coenia (Papilionoidea), Toxomerus sp. (Syrphidae), Scolia dubia
(Vespoidea), Polistes metricus (Vespoidea), and Polistes fuscatus (Vespoidea). The most
common pollinator taxa on S. gigantea were halictid bees, especially Agapostemon species, and
the most common pollinator taxa on S. altissima were Apis species and Bombus species.
Following the visual survey, flowering panicles were shaken onto a sheet of white paper to
assess insect pollinators which were present but had not moved between plants during the survey
time; by far the most common pollinator recorded in this way was Chauliognathus
pennsylvanicus.
Appendix S3: Species Diversity Effects
As expected due to low diversity (i.e., only two genotypes per pot), we did not detect an effect of
species diversity (monocultures vs. interspecific genotype mixtures) on most traits (but see perflower visitation) (Coarse root biomass: p = 0.953; Rhizome biomass: p = 0.402; Aboveground
vegetative biomass: p = 0.609; Floral biomass: p = 0.536; Pollinator visitation: p = 0.189; Perflower visitation: p = 0.003).
Appendix S4: Supplementary Table 1. Genotype contrasts for each trait, grouped by
neighbor genotype.
The genotypic identity of a neighbor genotype can determine whether selection can act on
genetic variation in a focal species. The results of post-hoc tests comparing the performance
(i.e., five different plant and pollinator traits) of three focal genotypes in the presence of a given
interspecific neighbor genotype show that statistically significant effects of focal plant genotypic
variation are dependent on the presence of particular neighbor genotypes. Different letters
within each column (i.e. traits) indicate significant differences in genotype means (α=0.05,
corrected for multiple comparisons using reverse-Bonferroni corrections).
Neighbor Genotype = G1
Coarse Root
Biomass
Rhizome
Biomass
Aboveground
Biomass
Floral
Biomass
Pollinator
Visitation
Focal Genotype A1
A
A
A
A
A
Focal Genotype A2
A
A
A
A
A
Focal Genotype A3
A
A
A
A
A
_____________________________________________________________________________________
Neighbor Genotype = G2
Coarse Root
Biomass
Rhizome
Biomass
Aboveground
Biomass
Floral
Biomass
Pollinator
Visitation
Focal Genotype A1
A
A
A
A
A
Focal Genotype A2
A
A
A
A
A
Focal Genotype A3
A
A
A
A
A
_____________________________________________________________________________________
Neighbor Genotype = G3
Coarse Root
Biomass
Rhizome
Biomass
Aboveground
Biomass
Floral
Biomass
Pollinator
Visitation
Focal Genotype A1
A
A
A
AB
B
Focal Genotype A2
A
A
A
B
B
Focal Genotype A3
A
A
A
A
A
_____________________________________________________________________________________
Neighbor Genotype = A1
Coarse Root
Biomass
Rhizome
Biomass
Aboveground
Biomass
Floral
Biomass
Pollinator
Visitation
Focal Genotype G1
A
A
A
A
A
Focal Genotype G2
B
A
A
B
AB
Focal Genotype G3
AB
A
A
B
B
_____________________________________________________________________________________
Neighbor Genotype = A2
Focal Genotype G1
Focal Genotype G2
Focal Genotype G3
Coarse Root
Biomass
Rhizome
Biomass
Aboveground
Biomass
Floral
Biomass
Pollinator
Visitation
A
B
B
A
A
A
A
B
AB
A
B
B
A
B
B
_____________________________________________________________________________________
Neighbor Genotype = A3
Coarse Root
Biomass
Rhizome
Biomass
Aboveground
Biomass
Floral
Biomass
Pollinator
Visitation
Focal Genotype G1
A
A
A
A
A
Focal Genotype G2
A
A
A
B
B
Focal Genotype G3
A
A
A
B
B
_____________________________________________________________________________________