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.