Analysis of niche conservatism among the 57 species
In the present study, each of the 57 species showed differences in their
niches indicated by the δ 13C andδ 15N values. In overall, the stable isotope
values ranged from -36.707 to -18.129 for δ 13C,
represented by Cirrhinus mrigala and Misgurnus
anguillicaudatus ; and from 5.184 to 21.525 forδ 15N, represented by Paramisgurnus
dabryanus and Neosalanx brevirostris (Fig. 2).
Pairwise species niche
differences (EDBEC, Euclidean
distances between ellipse centroid) ranged from 0.063 to 15.256, with
the shortest distance occurring between two bitterling species
(Acheilognathus rhombeus and Rhodeus sinensis ), and the
most distant between a minnow and a loach, Pseudolaubuca
engraulis and Misgurnus anguillicaudatus (Fig. 3).
The plot of pairwise species trophic niche differences against genetic
distances showed a rough positive pattern, indicating possible niche
conservatism. Further analysis showed that, the positive relationships
were significant while genetic distances less than 0.24, but niche
differences may reach saturation and showed a stable trend while genetic
distances larger than 0.24. Besides, at the very far genetic distance
(Fig. 3, Fig. 4), some species pairs showed very little niche
differences, indicating niche
convergence. For instance,
trophic differences (EDBEC) between Silurus asotus andSiniperca scherzeri was only 0.35.
In addition, we also found that species niche differences were
distributed in skew, with most species pairs (87.22%) bearing not very
much differences (EDBEC less than 6), while only a few species pairs
(12.78%) had considerable differences in their trophic niches (EDBEC
more than 6) (Fig. 5).