Geometric constraints and area effects shape geographical patterns of aquatic plant diversity in a highly arid region

Abstract

Understanding large-scale spatial patterns and determinants of biodiversity is a major challenge in macroecology and biogeography. Although some recent studies have focused on macrophyte richness patterns at local, regional and global extents, the majority of studied based on coarse resolution data, and few studies directly tested existing broad-scale hypotheses. Here, we conducted the extensive geobotanical surveys in the highly arid region of northwestern China, which covers 1/4 of the total area of China. Using collected species-level data, we examined macrophyte richness patterns along latitudinal and longitudinal gradients, and tested the mid-domain effect (MDE) and area effect (AE) hypotheses for the geographical patterns. Our study showed that the richness patterns of all macrophytes, emergent plants and submerged plants showed a hump-shaped pattern along latitudinal and longitudinal transects. Regression analyses showed that the MDE and AE can shape observed longitudinal and latitudinal richness patterns, and in comparison to the AE, the MDE has stronger effects. The summed explanations of MDE and AE for latitudinal and longitudinal richness patterns of all macrophytes, emergent and submerged plants were all over 93%, although the independent effects of the two tested hypotheses were weak (<22.8%). Our findings implied that the combined effects of MDE and AE structuring longitudinal and latitudinal patterns of macrophyte richness in this highly arid region may be due to extensive dispersal limitations such as desert and mountain ranges, highly isolated aquatic habitats, and abundant habitat types in the relatively larger regions.