Fig. 5. Linear regression of the relationship between species diversity and functional diversity. The shaded areas are the 95% confidence
Intervals (Only P < 0.5 in the figure)
Discussion
4.1 Seasonal changes in community structure of macroinvertebrates
Community structure and functional diversity of macroinvertebrates can be affected by various environmental factors, and subjected to significant temporal and spatial variations(Sterling et al., 2016). Meanwhile, the spatiotemporal distribution of the macroinvertebrate communities can be affected by both hydrological and sedimentary conditions(Dou et al., 2022). Macroinvertebrates mostly inhabit the sediments or layers of river water-soil interface(Tews et al., 2004). Besides, the physical, chemical, and biological environments of the sediment all shared the community distribution(Schmera et al., 2017).
The population dynamics of macroinvertebrates are influenced by many factors like environmental variables(Magni et al., 2015). In the present study, affected by the subtropical marine monsoon climate, the Jingui River suffers from continuous rainfall in wet season, which is the primary natural disturbance to the river, resulting in more incredible flow velocity and changes in wet width. The compositions of macroinvertebrate communities are frequently influenced by flow velocity and are suitable for the survival of species that require different velocities and temperatures(Zhong et al., 2020). The water temperature and transparency are beneficial for the growth and reproduction of aquatic organisms(Jiang et al., 2021). The water velocity in dry season is slow, which is conductive to accumulation of sediments. Therefore, it provides habitats to predators, such as Plecoptera and Trichoptera, which are adapted to the riparian habitats(Chen et al., 2020). In this case, the number of species and quantity of zooplankton and aquatic vegetation increase dramatically, and the material basis and suitable habitats are provided to the macroinvertebrates with various life habits(Yang et al., 2017). Abundant material bases and complex habitats maintain the abundance of macroinvertebrates and the stability of ecosystem(Allen et al., 2002).
The environmental factors greatly affect the reproduction, growth, and population succession of macroinvertebrates, thus influencing the community structure and function of the entire stream ecosystem(Li et al., 2020). The distribution of FFG can be effectively reflected by classification of river nutrition which can be classified based on structure of FFG(Kelly et al., 2002). Meanwhile, macroinvertebrates can adapt to different environmental conditions by changing their feeding modes(Li et al., 2022). The abundance of FC increased in dry season, which indicated that a stable water flow rate is advantageous for the survival of the FC which are sensitive to disturbance and velocity. GC exhibited the most abundance in wet season when the organic matter fragments were relatively high(Yang et al., 2017). The results confirmed that increased collectors in the Jingui River were induced by the relatively abundant food resources. The quantity of periphytons, the essential food sources for scrapers, would inevitably increase in wet season, which improved the light usage of the stream(Zhong et al., 2020). Therefore, the exact potential mechanisms leading to seasonal dynamics of macroinvertebrates are worth further study.
4.2 Relative importance of species diversity and functional diversity
Functional diversity performance analysis of biological response to environmental drivers has already been extensively applied to the macroinvertebrate ecosystems recent years(Baker et al., 2021). Compositions of the functional diversity are becoming more important, as revealed in many studies(Schmera et al., 2017; Zhang et al., 2019). In the meantime, studying the relationship between species diversity and functional diversity is essential to investigate the effects of biodiversity on ecosystems(Alric et al., 2022).
The low FRic value is attributed to not full utilization of the resources available in the community(Erasmus et al., 2021). Meanwhile, it means that the species utilizing the advantages of these circumstances disappear due to the environmental conditions, reducing the buffering of the environmental fluctuations and weakening the ability of the community to resist invasion(Mouton et al., 2020). Simulation data of Mouchet revealed that the FRic value rises with increase in number of species(Mouchet et al., 2010), while different conclusion was reached in this study. Because there are more macroinvertebrates with high FRic value in wet season and dry season. FEve shows an abundance distribution in the ecological niche space of the community to effectively utilize all resources(Zhang et al., 2019). A low FEve value suggests that the resource is underutilized or overutilized, which can reflect the productivity, stability, and intrusion resistance. Correlation analysis revealed that the FEve positively correlates with S , H’, anddM . Under the moderate to severe interference, the functional diversity and species diversity negatively correlate with the results above(Baker et al., 2021). FDis is the average distance between the centroid of all species and each species’ traits in the multidimensional trait space, and it is a more intuitive functional diversity index, which is closely associated with RaoQ(Mason et al., 2005). Meanwhile, relationship between the functional diversity and the species diversity varied with different ecosystems. For example, Devictor found that the functional diversity decreased with increased abundance of species(Devictor et al., 2010). The analysis results told that the functional diversity showed a poor fitness with species diversity (R2 < 0.366), indicating a more complex nonlinear relationship between them. Zhang believed that the nonlinear relationship between them is essential because “functional diversity can provide more special information different from species diversity”(Zhang et al., 2015).
Conclusion
In this study, it was found that the community composition of macroinvertebrates in the Jingui River strongly fluctuated from wet season to dry season. GC were highly abundant, while SH were only limitedly presented. In normal season, the special environment with high depth and velocity increased the FEve, FDis, and RaoQ values. In dry season, the high DO and NH4+-N upregulated the FRic value. The results in this study suggested that the seasonality and hydrologic conditions strongly influenced the FFG and functional diversity of macroinvertebrates in the Jingui River. They built a foundation for future research on resource conservation and ecological monitoring.