4.5 Roles of abundant and rare taxa in mediating interspecific
interactions
Network analysis can improve our understanding on the potential roles of
abundant and rare taxa in the complex interaction webs of fluvial
sediments. Our results illustrated that the co-occurrence network had
non-randomly connected properties and closely related taxa tended to be
interconnected and clustered together within the network, suggesting
that taxonomic relatedness plays a key role in determining the network
modular structure. This non-random pattern may reflect the effects of
environmental filtering and niche differentiation among species in the
Yarlung Tsangpo River sediments (Hu et al., 2017; Ju and Zhang, 2015).
Our results revealed that rare taxa rarely coexisted with abundant taxa
within the fluvial sediment network (Fig. 5a). This result may be
explained by the fact that abundant and rare taxa occupy different
ecological niches and respond differently to environmental variables
(Jiao et al., 2017). The topological properties of the network can also
reflect interactions between species (Xue et al., 2018). Previous
research has revealed that abundant taxa, with higher degree and
betweenness centrality values, are more connected with each other and
more often located in central positions, than rare taxa within the
network (Jiao et al., 2017; Zhang et al., 2021a). Our results showed
that the values of degree and betweenness centrality for abundant taxa
were significantly higher compared with rare taxa, implying that abundant
taxa may play a more important role in maintaining the co-occurrence
network than rare taxa (Röttjers and Faust, 2018). However, rare species
might be keystone taxa. In our study, five rare OTUs were identified as
underlying keystone taxa in the co-occurrence network (Table S5 and Fig.
S6). Considering the importance of keystone taxa in mediating
interspecific interactions (Sun et al., 2021), our results thus indicated
the potential roles of those rare keystone bacteria in maintaining
ecosystem stability in sediments of the Yarlung Tsangpo River. Our
results also showed that intermediate taxa had the most interactions
with both abundant and rare taxa, and more than half of the module hubs
and connectors belonged to intermediate taxa, indicating that
intermediate taxa may act as bridges between rare and abundant taxa
within the co-occurrence network.