3.2 Spatial and temporal variations in fish assemblage
structure
Fish assemblage structure varied significantly at the spatial scale.
NMDS ordination plot showed that sampling sites at 3rd-order stream were
mainly gathered to the lower left of the graph, while those of
4th-order sites were clustered to
the right (Fig. 2).
ANOSIM
confirmed that the fish assemblages differed significantly among stream
orders (Global R = 0.156, p=0.034<0.05). According to the SIMPER
analysis, fish assemblages in the Ren River basin were highly dominated
by cold-water or rheophilic species, such as R. oxycephalus ,S. macrolepi , M. omeiensis and G. herzensteini ,
except for the 4th-order sites (Table 3). Specially, fish assemblages in
1st-order sites were typified byR. oxycephalus , contributing
95.7% of the similarity. Fish assemblages in 2nd-order were typified byR. oxycephalus and G. herzensteini , contributing 78.3%
and 7.1% of the similarity, respectively. Fish assemblages in 3rd-order
sites were typified by R. oxycephalus , M. omeiensis andS. macrolepi , contributing 55.4%, 28.1% and 9.3% of the
similarity, respectively. From 1st-order sites to 3th-order sites, the
abundance of R. oxycephalus decreased gradually, while the
abundance of M. omeiensis and S. macrolepi increased
continuously. By contrast, fish assemblages in 4th-order sites were
predominated mainly by warm-water and lentic or eurytopic species, such
as Squalidus argentatus ,Hemiculter leucisculus and Z. platypus .
However, there was no significantly seasonal change in fish assemblages.
NMDS ordination plot revealed substantial overlap between fish
assemblages in wet and dry season (Fig. 3). ANOSIM further confirmed
that the fish assemblages did not show significant changes across
seasons (Global R = -0.022, p= 0.745>0.05).