3.4. The variation of Species_estimated, Singletons, Uniques, ACE, ICE,
and Chao2
Species_estimated (Figure 5): Transects A and
C approached a gentle level earlier than others. The estimated species
curve reaches zero prematurely indicating a homogeneous habitat among
the plots investigated. There were three species in transect A:Aleuritopteris squamosa , Selaginella stauntoniana , andS. pseudopaleifera ; while there were two species in transect C,Pteris Vittata and A. squamosa . Species increase in
transect A and C stopped at the plots 3 and 2 separately. There were no
new species discovered in the following plots. In contrast, species
accumulation curves in the other four transects keep going up from plot
1 to plot 10, showing a high possibility to find new species in the next
plot. This indicates a heterogeneity of habitat among the plots.
Singletons (Figure 5): It was zero in transects
A and C because no species grew as a single individual. In transect F,
the Singletons approached 1, and there was only one species
(Histiopteris incise) found in plot 4. Unlike transects A,
C, and F, Singletons increased quickly without a turnover in transect B,
D, and E. The maximum of Singletons happens in transect B bearing
approximately nine species, Pteris vittata, P. ensiformis ,P. excelsa , P. fauriei , Lygodium japonicum,
Selaginella delicatula , Adiantum philippense , Microlepia
speluncae, and Phymatosorus scolopendria . These species are
generally distributed worldwide in a broad niche. However, none of them
colonize the whole plot. Instead, other species take advantage. Extreme
water reliance takes charge of this. Water suspended in the air and
absorbed in the living substance is vital to the growing and
regeneration process.
Uniques (Figure 5): According to the curves,
transects A and C were in low Unique . Transect A was riverine;
plots in this transect had similar habitats. Transect C was a ravine
along a mountain slope, and it featured fragmented rocks and bare
surface soil from plot 1 at the bottom to plot 10 at the top. Plots in
this transect had similar habitats too. Therefore, there were very few
species found in these two transects, and these species were presented
in the plots from 1-10 evenly. In opposite to transects A and C,Unique increased in the plots of transects B, D, E, and F,
indicating that more species and habitats were expected in the next
plot. Transects D and F, for example, were riverine transects, the same
with transect A, but the growing substance and canopy coverage made the
habitat more suitable for fern and fern allies. When the investigated
plots increased continuously, new records were found occupying a single
plot or sharing a plot with other species, e.g .,Selaginella helferi , S. biformis , S. doederleinii ,Histiopteris incisa , and Equisetum hyemale .
ACE, ICE, and Chao2 (Figure 5):They verified each other by displaying similar curve shapes. Species
richness in transect B, D, and F were much higher than other transects.
The maximum richness was 22 species detected in transect B whereas only
two species were detected in transect C.
FIGURE 5 The variance of estimated species, rarity, and
abundance in plots 1-10 of each transect. (Red = transect A; blue =
transect B; black = transect C; green = transect D; orange = transect E;
purple = transect F)
3.5. Indicator species
Eight species are screened out to represent the Yuanjiang dry-hot valley
as shown in Table 4. All indicators perched at the altitudes 490
~ 690 m although some of them distributed down to 260 m.
All indicators require a humid environment although they grow in
different river segments (Figure 6).
Table 4. Indicator candidates in Yuanjiang dry-hot valley.