Effects of plant species richness on the structure of plant-bird interaction networks along a 3000-m elevational gradient in subtropical forests

Ecological community diversity and structure has implications for bird seed-dispersal networks that change with environmental conditions and plant species richness along elevational gradients. In this study, we examined how plant-bird interactions change with plant species richness at both the network and species level, along a 3000-m elevational gradient in a subtropical forest ecosystem. At the network level, Shannon diversity interactions (H2) decreased consistently with elevation, with a concomitant decrease in network specialization (H2 '), likely due to lower plant and bird species richness at higher elevations. At the species level, the number of effective partners for both plants and birds decreased with increasing elevation, while the degree of specialization of both plants and birds on their partners increased with elevation. Specifically, we found a unimodal pattern where the effective partners of both birds and plants initially increased and then decreased with plant species richness. Furthermore, we found an inverted unimodal relationship between the degree of specialization and plant species richness, where the degree of specialization between birds and plants initially decreased and then increased with plant species richness. This study provides the first empirical evidence that changes in plant species richness with elevation can affect plant-bird interaction networks in subtropical forests.