3 RESULTS
Overall, two amphibian species, eleven fish species, three plankton
orders, and 48 benthic macroinvertebrate families were recorded in the
three surveys. Assemblages of amphibians, fishes, macroinvertebrates,
and planktons, respectively, all varied with connectivity gradient and
season (Fig. 3, Table S2; two-way PERMANOVA, p <0.05).
Consequently, the overall aquatic assemblage including all faunal groups
was significantly influenced both by connectivity gradient and season,
and their interaction was marginally significant (Fig. 4, Table S3). In
spring, “No-flow” pond assemblages were significantly different from
“Late” ponds and “Flowing” sites. In summer, significant differences
between “No-flow” pond assemblages and “Late” ponds remained, and
“Flowing” site assemblages were significantly different from all other
pond sites. In autumn, differences between “No-flow” pond and “Late”
pond assemblages became insignificant, and only the difference between
“Early” pond and “Flowing” site assemblages were significant (Fig.
4). In autumn, mean square of variation was lower between categories and
their residuals were higher.
Variation partitioning with generalized dissimilarity modelling showed
the factors driving the β-diversity between sites change seasonally. The
explained deviance of aquatic assemblage was 38% in spring, 57% in
summer, and 53% in autumn (Fig. 5a). Within the explained variation,
the proportion explained by connectivity (pure connectivity or
combination with environment) was 46% in spring, 44% in summer, and
then declined to 20% in autumn (Fig. 5b). The importance of each
environmental variable changed seasonally (Table S4). In spring,
connectivity at the downstream end and area of ponds significantly
influenced the assemblage, explaining 23% and 22% of the total
deviance, respectively. In summer, dissolved oxygen, water temperature,
area of ponds, and connectivity at the downstream end significantly
influenced on the assemblage, explaining 11%, 9%, 8% and 3% of the
total deviance, respectively. In autumn, area of ponds, flow velocity,
DO, temperature, and grain size significantly influenced on the
assemblage, explaining 28%, 13%, 7%, 6% and 3% of the total
deviance, respectively. Supplementary, we conducted variation
partitioning with generalized dissimilarity modelling for benthic
macroinvertebrates, fish, and planktons in the same manner (we could not
apply the analysis to amphibian because of data limitations), and
confirmed that the contribution of connectivity to the whole variation
declined across seasons for all faunal groups (Fig. S1). CCA analysis of
the amphibious organisms (benthic macroinvertebrates and amphibians) in
autumn visually explained the effects of local environmental factors,
and the permutation test showed significant influence of the local
environmental factors on the assemblages
(F 9,12=1.56, P = 0.038) (Fig. 5c).
SIMPER analysis showed seasonal changes in the taxa contributing to the
assemblage difference along hydrological gradients (Table 1). Notably,
the simper analysis shows that the three taxa, Hynobius
retardatus , Rana pirica and Limnephilidae, which primarily
contributed to the variation between “No flow” and “Early” as well
as the variation between “Early” and “Late,” decreased by summer and
then autumn, potentially causing loss in variation between those
habitats in autumn. Furthermore, Leptophlebiidae and Nemouridae, which
were the two primarily important taxa creating the differences between
all ponds and flowing sites in summer, were both present in ponds and
flowing sites in spring but disappeared only in ponds by summer. This
led to the clear difference of the ponds and flowing site assemblages.