Year and seasonal plant-frugivore network
During the observations throughout the year, we recorded 2235
interactions events between 14 bird species (2 Order 7 families) and 13
plant species (9 Order 10 families) connected by 110 links (Fig.2). Each
plant species interacted on an average with 7.08±1.01 (Mean±SD) birds,
and each bird species interacted on an average with 6.13±1.15 plant
species (Fig.2). We registered 9,106 fruit-eating individual birds, and
92.89% of them foraged fruits of more than five individual plants
(Fig.2). Passerine frugivores were relatively important in our study
system, involving 13 species that consumed fruits, representing 98.26%
of the total interaction number (Fig.2). The plant species most commonly
consumed by birds was Cayratia japonica with 724 interactions
(32.39%), while the bird species most frequently recorded wasPycnonotus xanthorrhous with 644 interactions (28.81%) (Fig.2).
Compared with the predicted
networks generated by the null model (N=1000), the observed
plant-frugivore network exhibited relatively a lower connectance
(C = 0.604), lower interaction
diversity(H2 =3.91), lower interaction evenness
(E2 =0.751), higher nestedness (nestedness=0.715),
and higher specialization (H´ =0.091) (Fig.3). These results
indicated that the observed network had fewer realized connections and a
more stable subset of interactions than that of the predicted network,
species exhibiting higher feeding dependence, and lower interaction
frequencies.
The contributions of the interaction connections, to the total
connections of the network, in different seasons were different (Fig.4).
Interaction connections contributed 13.38% and 14.68% to the annual
network in spring and summer, and 38.79% and 33.15% to the annual
network in autumn and winter, respectively.
The specialization
(H2´ ), and
interaction evenness
(E2 ) of the network were higher in spring and
summer than that in autumn and winter. However, connectance (C),
nestedness, and interaction diversity (H2 ) were
contrary to the specialization and interaction evenness (Table1). The
number of frugivore bird and fruit plant species was positively
correlated with the contributions of the interaction connections between
birds and fruit plants in different seasons
(Rb2=0.954, P=0.023;
Rp2=0.297, P=0.455).
Fig.4 The connections of different seasons contribution to the total
plant-frugivore network, the color bars with the gradient of pink to
yellow below the main figure indicate the proportion of interaction
connections to the total network in different seasons.
Table 1 Main quantitative description of seasonal variation of
interaction network