138 
Ganl. Bull. Singapore 70 (Suppl. 1) 2018 
Table 5. A summary of eigenvectors of each environmental variable, eigenvalues, percentage 
(%) of variance explained by the first four axes resulted from the PCA for odonates at Nee Soon 
freshwater swamp forest. 
Environmental variable 
Abbreviation 
PC 1 
PC 2 
PC 3 
PC 4 
Acidity 
PH 
-0.277 
-0.022 
0.050 
-0.173 
Dissolved oxygen (%) 
DO 
0.035 
0.399 
0.124 
0.066 
Stream velocity 
VEL 
-0.032 
0.373 
-0.038 
-0.159 
Stream width 
WID 
-0.153 
0.134 
0.261 
-0.235 
Stream depth 
DEP 
-0.288 
0.046 
0.226 
-0.024 
Macrophytes and Woody Debris 
MPW 
0.185 
0.052 
0.204 
0.417 
Leaf litter (%) 
LL 
0.177 
-0.275 
-0.010 
-0.069 
Sand (%) 
SA 
-0.198 
0.197 
-0.352 
0.158 
Silt (%) 
SI 
0.103 
-0.070 
0.341 
-0.402 
Bank shape 
BSH 
-0.276 
0.243 
0.077 
-0.080 
Bank with hanging root 
BRO 
0.157 
0.137 
-0.330 
0.209 
Bank covered with shrub and grass 
BSG 
0.154 
0.231 
0.174 
0.028 
Riparian vegetation heterogeneity 
RHE 
-0.138 
-0.001 
0.279 
0.506 
Riparian canopy cover 
RCA 
0.325 
0.211 
-0.186 
-0.040 
Stream order 
SO 
-0.192 
0.314 
0.181 
-0.027 
Distance from forest edge 
FE 
0.341 
0.076 
-0.027 
-0.018 
Distance from nearby open area 
OA 
0.290 
0.148 
-0.132 
-0.148 
Distance from nearby swampy area 
SW 
0.223 
-0.248 
0.141 
-0.214 
Oxidation-Reduction Potential 
ORP 
0.287 
0.163 
0.256 
0.148 
Total Dissolved Solids 
TDS 
0.008 
0.033 
0.091 
0.220 
Salinity 
SAL 
-0.217 
-0.174 
-0.131 
0.150 
Temperature 
TEM 
-0.092 
-0.352 
-0.016 
0.147 
Pool (%) 
POL 
0.160 
-0.118 
0.402 
0.171 
Eigenvalue 
6.056 
3.823 
2.613 
1.961 
% variance 
26.328 
16.621 
11.363 
8.525 
low pH value, stream with low angle smooth bank and stream surrounded by swampy 
area primarily explained the low diversity and richness of the odonate community in 
most of Nee Soon freshwater swamp forest. The presence of pool habitats, substrate 
with more silt, less sand, less overhanging root in stream bank, high heterogeneity of 
riparian vegetation and the wider channel will partially explain the high diversity level 
of odonates in the outskirts and open areas of the Nee Soon freshwater swamp forest. 
