1.3 Stratified sampling
We systematically established 282 stratified sampling sites acording to
Yunnan’s hydrographic network. We were unable to sample from sites
located in inaccessible terrain, including deep valleys and high
mountains. Sites with strong human disturbance was also avoided. At last
228 randomly distributed sites (Ripley’s K, p = 0.2435) were
remained(Figure 2). To ensure the phenological consistency and clear
aquatic-terrestrial boundary of the sites, sampling was conducted from
the southernmost to the northernmost and between February 27th, 2014 and
June 8th, 2014. At each site, 5 sampling points were set paralleled with
the river both in the aquatic and terrestrial habitats with a distance
of 10 meters (Figure 1b). Totally 2,250 sampling points were set (Figure
1a), 30 sampling points were lost due to no soil there. Using the
five-point sampling method in 1m×1m squares (Figure 1b), samples
consisted of ~50 g of mixed soil (or sediment) and were
collected at a depth of 0~10 cm below the surface at
each sampling point. Totally we collected 2,250 specimens from 228
sites. Samples were then stored in a disposable self-sealing bag at room
temperature. We recorded habitat information, including location,
longitude, latitude, and altitude of each sampling site. Samples were
sent to the laboratory within 1 week of collection, immediately followed
by NTF identification processing.