Fig. 3.

Reciprocal bottom-up and top-down effects of functional diversity on the assembly of plant–animal mutualistic networks. a Variation in mean annual temperature (MAT [°C], red) and mean annual precipitation (MAP [mm yr⁻¹], blue), as well as land use (LU; filled circles, near-natural habitats; open circles, anthropogenic habitats) along the elevational gradient of Mount Kilimanjaro, Tanzania. The Bayesian hierarchical structural equation models in b, c tested for direct and indirect ‘functional diversity’-mediated effects of mean annual temperature, mean annual precipitation and land use on (b) niche breadth (partner diversity, e^H) and (c) niche partitioning (complementary specialisation, d′) of plants and animals via functional diversity of plant and animal communities (functional dispersion, FD; subscripts p and a for plants and animals, respectively). The lines in a represent loess smooth functions (degree = 2, span = 0.5) fitted to the temperature and precipitation data across the elevational gradient. In b, c only paths that were supported by the Bayesian variable selection (2log_e(Bayes factor) > 2) are shown (see Supplementary Table 2). Path colours depict bottom-up-mediated effects (blue), top-down-mediated effects (red) and direct abiotic effects (grey) on network structure. Grey double-headed arrows depict covariance terms that account for correlated errors due to common unmeasured sources of variance and due to reciprocal effects of functional diversity on the other trophic level. Path widths are proportional to standardised effect sizes. The values near the endogenous variables depict the marginal (r²) variance explained by fixed factors only, as well as the conditional (r_c²) variance explained by fixed and random factors combined (see Methods for details)⁷⁰. Sample sizes are n_obs = 126 observations, n_site = 53 study sites and n_mutualism = 3 mutualisms