3.1 Ecology niche analysis in environmental
space
There were no novel components in the environment context comparison
between study sites as shown by MOP, MESS and ExDet (see Figure
S2.1-S2.2) indicated that the results of our subsequent niche analysis
were reasonably comparable under similar conditions.
It can be seen in Niche A that the observed niche of two new
distribution populations both overlapped with the native area, but some
of the new northern area exceeded the native edge (Fig.1a). Analyzing
the spatial relationships between niches (Fig.2a), we found only a small
minority of low latitudes in China were analogous with Myanmar’s
sedentary populations and India’s wintering populations in niche
occupation (Fig.2b), and most of the population had no reference data
because it was beyond the native niche (Fig.2d). In contrast, the niche
occupation of the Malay Peninsula’s populations completely overlapped
with Sri Lanka’s sedentary populations (Fig.2c).
The observed Malay Peninsula population niche was nearly totally within
the original native range (Stability=99.42%), while the new northern
population only partially overlapped with the native niche
(Stability=22.39%). The results of Schoener’s D quantification showed
that compared with the original native area, niche divergence of the new
northern population was significantly higher than expected (P
< 0.05), representing significant niche expansion. The niche
equivalence and conservatism of the new southern population were
significant (P < 0.05). In addition, the present population
niches were still similar to the native area, and the expansion of the
new northern population only accounted for 2.32% of the whole
population (Fig.3) (Table 1). Nevertheless, when the three observed
niches were compared with the original native niche, there was an
incomplete niche match in overlap D value (the maximum value was 0.59)
(Table 1), indicating that in recent dispersal years, the Asian openbill
niche changed or resulted in an unbalanced regional distribution,
especially for individuals in China.
A comparison of response range to occurrence within each environment
variable between native and new northern populations revealed that five
precipitation-related factors did not change, three of five temperature
factors showed that the new northern population had a lower temperature
tolerance than the native population, and the other two factors (Mean
Temperature of Wettest Quarter and Mean Temperature of Warmest Quarter)
were included in the native range. These results suggest that the
climate conditions of the population in southwest China were similar to
the native population during the high precipitation and temperature
season, while temperatures in China sites were colder than native
range’s in the dry winter season (Fig.4).