Latitudinal beta-diversity gradient of riverine macroinvertebrate: Interplays of climatic and land use factors

Climate change and land use have major effects on macroinvertebrate biodiversity, but it is unclear how they shape spatial variations, particularly at large scales. This study explored the latitudinal patterns of beta diversity in riverine macroinvertebrate assemblages and examined how they are shaped by climate and land use. Location: China (18 ºN–48 ºN) from 2006 to 2021. The major taxa studied were riverine macroinvertebrates. This is a comprehensive dataset covering macroinvertebrate taxa from 42 watersheds across China was compiled to explore the latitudinal patterns of taxonomic, functional, and phylogenetic beta diversities, including turnover and nestedness components. Generalized additive models were used to assess the impacts of climatic and land-use variables, selected from 20 climatic and 10 land-use candidates, on latitudinal patterns of beta diversity. The study revealed that taxonomic and functional beta diversities shared a non-monotonic latitudinal pattern with a minimum in regions located between 24 ºN and 30 ºN, in contrast to the monotonic pattern observed in phylogenetic beta diversity. Climatic stability and land use were shown to significantly modulate the taxonomic beta diversity of macroinvertebrates, particularly by diminishing spatial turnover in high-latitude regions (24–48 ºN) and augmenting nestedness in low-latitude regions (18–30 ºN) with latitude decreasing. Land use was identified as a key factor altering the nestedness component of functional beta diversity, while climatic factors predominantly influenced phylogenetic beta diversity by reducing spatial turnover with latitude decreasing. This study uncovers three facets of macroinvertebrate beta diversity with different latitudinal patterns, highlighting the variable influences of climate and land use on these spatial differences and the distinct mediation by turnover and nestedness processes. These insights provide a foundation for latitude-specific conservation strategies that aim at preserving the intricate tapestry of macroinvertebrate diversity in rivers.

Methods
We compiled a dataset of macroinvertebrate taxa of 42 riverine catchments across China, covering a broad inland region from 48 ° and 18 ° north latitude. Using China’s climate zoning (https://www.resdc.cn/data.aspx?DATAID=243) as a reference, we characterized China into five latitude zones: Zone A (42-48 °N), Zone B (36-42 °N), Zone C (30-36 °N), Zone D (24-30 °N), and Zone E (18-24 °N). Taxonomic data were primarily obtained from peer-reviewed studies published between 2006 and 2021. Macroinvertebrate traits were quantified using a binary coding approach that consisted of assigning each taxon to specific trait categories based on its predominant characteristics. Taxonomic distances based on the path lengths in Linnean taxonomic trees were employed as a proxy for the actual phylogeny. For climatic variables, average elevation, long-term temperature, and long-term precipitation data for the 1970–2000 period at a resolution of 1 km were retrieved from the WorldClim database. For land use variables, the land use percentage within each watershed was calculated using a dataset from 2015 at a spatial resolution of 30 m, including nine land use types, i.e., cropland, forest, shrubland, grassland, water, snow/ice, barren land, impervious land, and wetland, compiled by Yang & Huang (2022).