Community trends from RLQ analysis
RLQ analysis illustrated how traits, species and habitat features varied
together. Two axes explained 90.3% of the total inertia in the three
tables, also accounting for most variability (> 72-79%)
along the first two axes of the environmental variables (R-table) and
species’ functional traits (Q-table) separately (Table S1). Traits and
environmental variables were particularly strongly related to the first
RLQ axis (Fig. 1(a) and (b)).
Both major RLQ axes were related strongly to elevation. The first axis
reflected a significant altitudinal trend towards narrower river
stretches with faster flows, well vegetated banks and channels with
boulders and pebbles while sandy banks, altered riparian cover, human
settlements and human activities declined (Fig. 1(a)).
Feeding traits correlated
significantly with this axis as species using more terrestrial prey from
the river margins increased towards higher elevations (e.g. Plumbeous
Water Redstart; White-capped Water Redstart (Phoenicurus
leucocephalus ) whereas species using a blend of terrestrial and aquatic
prey declined (e.g White-throated Kingfisher (Halcyon smyrnensis )
(Fig. 1(b)). Simultaneously, species using aquatic prey solely such as
the Brown Dipper (Cinclus pallasii) and Little Forktail(Enicurus scouleri) increased along this axis. Overall, the
contribution of ‘aquatic’ feeding was minimal and neutral as
aquatic-feeding species persisted at both ends of the axis.
The second axis of the RLQ mostly represented a significant decline in
riparian vegetation cover and boulder-strewn banks but an increase in
pebble banks and islands at higher elevation – typical of upland
braided reaches. Bird traits varying significantly on this axis included
an increase in clutch-size, but a decline in body size, tarsus size,
bill size and aquatic/terrestrial foraging as species such as River
Lapwing, Common Sandpiper (Actitis hypoleucos) , Blue
Whistling-thrush (Myophonus caeruleus) and Spotted Forktail(Enicurus maculatus) dropped out of the community (Fig. 1).
Strong, significant relationships among the trait, habitat and species
abundance data were corroborated by the global RLQ permutation test (p
<0.001 for model 2 of Dray et al. 2014). This held across all
regions suggesting a uniform pattern in the species–trait–environment
relationship at the community level. Model 2 was rejected (p=0.0005) and
Model 4 accepted (p=0.608) together suggesting that i) species
distributions were influenced by environmental conditions, dominantly
through changes related to elevation and ii) species composition
reflected significant variations in trait character that also tracked
elevation on both major axes.