Fig. 5: Functional diversity plotted against species diversity, for the land snail communities on the Galápagos Islands.
From: The evolution of trait variance creates a tension between species diversity and functional diversity
Species diversity is normalized by the number of host plant species in each sub-community, to get a better index of species diversity relative to the number of available ecological opportunities. Labels are island name abbreviations: Alcedo Volcano (AL), Cerro Azul Volcano (CA), Darwin Volcano (DA), Espanola (ES), Fernandina (FA), Floreana (FL), Pinzon (PI), Santiago (SA), Santa Cruz (SC), Santa Fe (SF), San Cristobal (SL), Sierra Negra Volcano (SN), and Wolf Volcano (WF). Colors represent communities in the arid (yellow) and humid (blue) zones of the islands, which form independent subcommunities (n = 20 independent samples). The data do not support a positive relationship between species- and functional diversity. (A linear regression has slope − 0.03 ± 0.04 with p = 0.53; however, since the data are heteroscedastic and the expected patterns from our model as shown in Fig. 3 are not linear, to begin with, any such statistic should be treated as just an illustration.) The lack of a positive trend is retained even if one does not normalize species diversity with the number of host plant species (Supplementary Figure 14). Furthermore, a negative slope is retained in >90% of cases after randomizing the number of sampled individuals (Supplementary Note 7.2). This means that the results are robust against measurement error in relative abundances. [Further statistical information on the regression: p value based on two-sided t test; no correction for multiple comparison].
