3.1 Distribution pattern of microclimate and microhabitat
structure
We found high horizontal and vertical variation in microclimate (air
temperature: R2 = 0.92,F 7, 59 = 47.72, P < 0.01;
relative humidity: R2 = 0.91,F 7, 59 = 81.96, P < 0.01) and
microhabitat structure in our study site (Fig. 2). In general, air
temperature increased and relative humidity decreased with vertical
height based on linear regression model (Fig. 2). In addition, we found
significant effects of horizontal position on temperature and humidity
(Table S2). The estimated vertical change in air temperature was 0.13˚C
per 10 m, while estimated horizontal change was 0.36 ˚C per 10 m (Table
S2). The relative humidity was estimated to decrease 1.4% per 10 m
vertical increase, and the horizontal variation was also 1.4% per 10 m
horizontal distance. The photosynthetic photon flux density (PPFD)
increased with vertical height (as PPFD was normalized within each
vertical transect, we could not compare this across transects,R2 = 0.35, F 1, 62 =
32.84, P < 0.01; Table S2, Fig. 2). The total leaf area
generally decreased towards the upper canopy but did not show
significant horizontal variation (note that leaf area data was missing
for Transect 7; R2 = 0.22,F 6, 48 = 2.32, P = 0.05; Table S2, Fig.
2).
Distribution of ant assemblages along vertical and horizontal
gradients
In total, 35,710 individual ants from 138 species in 31 genera were
sampled. Both ant abundance (ln (X+1) tranformed,R2 = 0.67, F 7, 59 =
2.32, P < 0.01) and richness
(R2 = 0.66, F 7, 59 =
16.65, P < 0.01) significantly decreased with vertical
height, and varied across transects (horizontal positions) (Table S3,
Fig. 3). Both NMDS plots and adonis analysis showed clustering of ant
assemblages both vertically and horizontally (Fig. S2; adonis analysis
(abundance based), vertical stratification: F = 1.8,
R2 = 0.09, P = 0.01; across transects: F= 6.4, R2 = 0.39, P = 0.001).
Dissimilarity partitioning revealed that the pairwise assemblage
dissimilarity between sampling points was largely composed by assemblage
turnover, meaning the pairwise dissimilarity was mostly explained by
replacement of assemblage composition between sampling points. Using
either straight line distance or maximum surface travel distance
calculated, we detected a significant increase in
total (unpartitioned) pairwise
dissimilarity with increasing distance between sampling points (MRM
analyses; Table 1, Fig. 4). While no distance effects were detected in
turnover, there were positive effects of distance on the nestedness
component of pairwise dissimilarity. Both vertical and horizontal
distance showed significant positive effects on total pairwise
dissimilarity between sampling points. The effect size of vertical
distance on pairwise dissimilarity of ant assemblages was slightly
higher than that of horizontal distance, but the explanatory power of
both predictors was low (Table S4).
When pooling the data of sampling points within the same transect or
vertical stratum to examine distance-decay patterns between
transects/strata, we observed strong effects of vertical distance on
pairwise dissimilarity indexes between vertical strata. In contrast, we
found no effects of horizontal distance on pairwise assemblage
dissimilarity between transects (MRM analyses, Table 2, Fig. 5). When
comparing across the same distances vertically and horizontally,
pairwise dissimilarity was consistently higher horizontally than
vertically (Table 2, Fig. 5).
By comparing the effects of vertical distance on assemblage
dissimilarity within vertical transect and effects of horizontal
distance within vertical strata, we found greater small-scale pairwise
dissimilarity (higher intercepts) over horizontal distance within the
same vertical strata than over vertical distance within the same
vertical transect (linear regression: R2 =
0.60, F 1, 17 = 25.03, P <0.01,
Fig. 6C). However, the effects of vertical distance on pairwise
dissimilarity was more apparent and much stronger than that of
horizontal distance, presenting a distance-decay pattern within each
transect (linear regression: R2 = 0.73,F 1, 17 = 46.45, P <0.01, Fig.
6D). We did not find differing horizontal turnover of ant assemblages in
different vertical strata (Fig. 6A, Table 3). We also did not detect
significant interactive effects between horizontal distance and vertical
height on horizontal pairwise dissimilarity of ant assemblages within
each vertical stratum (linear regression: R2 =
0.005, F3 , 127 = 0.22, P<0.89; coefficient of horizontal distance: p = 0.77;
coefficient of vertical height: p = 0.95; horizontal distance *
vertical height: p = 0.73). Hence, change in horizontal
dissimilarity of assemblages did not depend on height, as would be
expected if ant mosaics were driving more rapid increase in disimilarity
at greater heights in the canopy.
3.3 Explanatory factors for ant assemblage distribution
patterns
Results from Canonical Correspondence Analysis (CCA) and backward model
selection suggested both air temperature and relative humidity
significantly associated with ant assemblage composition, while PPFD and
total leaf area did not show significant effects (Table 4, Figure S5).