Ecological processes of soil fauna community construction
Most ecological patterns and processes in nature are scale-dependent (Gao et al., 2014; Widenfalk et al., 2015; Gao et al., 2021), that is, their community patterns and construction mechanisms could be different under different spatial scale conditions (Chase & Leibold, 2002), and may be simultaneously controlled by processes from multiple scales (Levin, 1992, Guo er al., 2018). Locally, pure spatial variables were important in regulating species composition, whereas the spatially structured environmental factors contributed most at regional scale at the northeast China (Gao et al., 2021). Our results supported the hypothesis that the effect of environmental processes on order turnover of soil fauna in East Asia is more important than that of neutral processes. Our study area and the obtained species taxon were different with the study of Gao et al. (2021). Therefore, our results were not entirely consistent with those of Gao’s.
The mechanism causing patterns of soil animal communities in East Asia was driven by environmental processes, but the driving paths of herbivorous and predatory animal communities may be different (Roslin et al., 2017). This study showed that the effect of environmental processes was more important than neutral processes for phytophage and predacity faunas, and that the effects of the latitude difference for predacity were minimal. The active dispersal abilities of soil animals separated by a Tullgren along the soil matrix was generally very limited (Gao et al., 2018). This may weaken the influence of the neutral process. In contrast, soil animals were sensitive to environmental changes (Fu et al., 2009; Wu, 2011). Thus, soil animals were more affected by environmental processes.
These results contrasted with the findings obtained by Zhang (2016) and Gao (2018), who determined that neutral processes explained more variation for soil faunas. This discrepancy may result partly from the use of spatial extents and species variables in the two studies. Zhang (2016) and Gao (2018) focused only on northeast of China and the two soil animal groups of beetles and mites. By comparison, our study covered 14 research samples and three temperature belts in East Asia. In particular, our taxon included almost all soil animal groups. Thus, we concluded that on a large scale, environmental processes explained more variation for turnover of soil faunas.
The effects of climate as an environmental factor on phytophages was greater than that of soil, but the effects of climate and soil factors in predators was basically the same. Climate, mainly temperature, drive the species conversion of forest trees and shrubs in East Asia (Chen et al., 2016), led to changes in the food resources of phytophagous. Therefore, the influence of climate was observed to be greater than that of soil as environmental driving factors. For predatory animals, the biotic interaction (predation behavior) strength increases towards the equator may cause the expansion of the resources available to the predator, leading to the expansion of the niche (Roslin et al., 2017). The width of niche could be restricted by more environmental factors, such as climate and soil. Therefore, climate factors and soil factors were almost equally important in the construction of soil animal communities in East Asia.
Finally, our study used order-level identification to ensure the consistency of soil fauna taxon in all sites in East Asia. Ponge and Salmon’s (2013) study showed that environmental filtering or species sorting culminated at the family level, and were obscured by convergent evolution and co-adaptation at higher taxonomic levels. High family-level diversity was commonly associated with a high structural or trait diversity (Terlizzi et al., 2009; Zou et al., 2020). Order-level classification was adequate for the needs of our research, because this study only focused on the presence/absence of information on species instead of specific traits of species. However, biological interactions processes, such as nutritional level and food web structure, phylogeny, and functional traits are the important factors that are often ignored in community ecology studies. Therefore, future research should consider more and better biological factors and distinguish the effects of neutral and environmental processes on a community assembly.