Nonrandom Composition of Flower Colors in a Plant Community: Mutually Different Co-Flowering Natives and Disturbance by Aliens

<div><p>When pollinators use flower color to locate food sources, a distinct color can serve as a reproductive barrier against co-flowering species. This anti-interference function of flower color may result in a community assembly of plant species displaying mutually different flower colors. However, such color dispersion is not ubiquitous, suggesting a variable selection across communities and existence of some opposing factors. We conducted a 30-week study in a plant community and measured the floral reflectances of 244 species. The reflectances were evaluated in insect color spaces (bees, swallowtails, and flies), and the dispersion was compared with random expectations. We found that co-existing colors were overdispersed for each analyzed pollinator type, and this overdispersion was statistically significant for bees. Furthermore, we showed that exclusion of 32 aliens from the analysis significantly increased the color dispersion of native flowers in every color space. This result indicated that aliens disturbed a native plant–pollinator network via similarly colored flowers. Our results demonstrate the masking effects of aliens in the detection of color dispersion of native flowers and that variations in pollinator vision yield different outcomes. Our results also support the hypothesis that co-flowering species are one of the drivers of color diversification and affect the community assembly.</p></div

Box-and-whisker plot of (a) the dissimilarity and (b) the flowering duration of natives (N) and aliens (A).

<p>The band in each box, the bottom and the top of the box, and the ends of the whiskers represent the median, the 25th and 75th percentiles, and 1st and 99th percentiles, respectively. Small circles are outliers. <i>n</i> = 212 and 32 for natives and aliens, respectively. Symbols show (<b>a</b>) the adjusted <i>P</i> values of randomization test 3 and (<b>b</b>) the <i>P</i> value of GLM (†, <i>P</i> < 0.10; *, <i>P</i> < 0.05; ****, <i>P</i> < 0.0001).</p

Histograms of the dissimilarity index <i>D</i> of flower colors evaluated in the insect color spaces of four pollinator types.

<p>The left column shows the results for both native and alien species (<i>n</i> = 244); the right column shows the results excluding aliens (<i>n</i> = 212). The number of species with negative <i>D</i> (left) and positive <i>D</i> (right) is shown in each panel. The number of native species is shown in brackets. The triangle below the <i>x</i>-axis indicates the mean <i>D</i>. The symbols show the adjusted <i>P</i> values of randomization tests for the mean <i>D</i> (†, <i>P</i> < 0.10; *, <i>P</i> < 0.05; ***, <i>P</i> < 0.001; ****, <i>P</i> < 0.0001).</p

Phylogenic tree of BD080526

Phylogenic tree of BD08052