Results
Effects of artificial ecological islands on macroinvertebrates
In total, 12956 macroinvertebrate specimens were collected in the park;
85 taxa belonging to 13 orders and 6 classes were identified, most of
which were arthropods (62 species, accounting for 72.94%). Mollusks
were second with 15 species (17.65%). There were only 8 species
(9.41%) of annelids. SIMPER analysis showed that only 3 species were
the primary contributors at all sites, Parafossarulus striatulus(35.72%), Palaemon modestus (34.84%) and Radi plicatula(13.49%), with a cumulative contribution of approximately 84% and a
total similarity of 38.17 (the list was truncated when 80% was
reached).
The species and abundance of macroinvertebrate fauna in the park
increased continuously in 3 years. The abundance of Chironomuslarvae decreased, but those of Odonata and Rhynchobdellida Blanchard
increased continuously (Figure 3).
The species abundance and diversity were higher in the island
communities than in the open-water
area.
Regarding the two water levels on the islands, the richness in the
shallow-water-level area was higher but not as evenly distributed as
that in the deep-water-level area (Figure 4).
Two-way crossed ANOSIM showed that there were significant differences
among the open-water area and island two levels regarding the
macrobenthos community composition in 3 years (Table
1).
ANOVA showed that in the 12 orders used as classifiers, the mean
abundances of 8 orders in the open-water area and on the islands were
statistically different (Table 2). Additionally, there were three orders
of classifiers that were significantly different between the two island
levels (Table 2). The hierarchical cluster dendrogram of the 20
macrobenthos communities assessed with SPSS software was basically
consistent with the MDS. There were two groups: islands and open-water
area (Figures 5 & 6). Due to the large changes in substrate,
hydrophytes and depth in open-water area samples, the order was not
relatively uniform.
Effects of substrate and construction time of the artificial ecological
islands on macroinvertebrates
Following MDS, we placed island B into the SSI group, and the community
composition differed significantly between the two substrates (Table 3,
Figures 5 and 6). Seven taxa between the two were significantly
different (Table 2). The PSI groups had more species and were more
evenly distributed than the SSI. In the MDS results (Figure 7), the
island group was divided into two groups (dimension 2), and the division
was related to the different substrates. In the classification, PSI B
was classified as a SSI. The possible reason is that island B has a
large area, and a few stones were laid around the island. The outlying
part of the island is covered with a few pebbles; only the part near the
centre of the island is covered with more pebbles. It is also covered
with cattails, reeds and other vegetation, making it similar to the soil
islands. To explore the change trend in macroinvertebrate diversity with
the extension of island construction time, we also compared the
community compositions of the islands with two construction ages. The
results showed that there were significant differences (Table 3), and 3
of the 12 orders were significantly different (Table 2). The species and
diversity were higher on the islands that were built relatively later
(Figure 7). Compared with the vegetation biodiversity and abundance on
these islands, the PSIs were higher in plant species and biodiversity
than SSIs although plant abundance was lower. In addition, the
vegetation biodiversity on the PSI built first was higher than that on
the PSI built later, while the vegetation biodiversity on SSI built
first was lower than that on SSI built later. (Figure 8).
Effects of artificial ecological islands on waterfowl
In total, 5987 individuals were recorded, and 33 species identified in
the park belonged to 8 families and 7 orders. SIMPER analysis showed
that nine species contributed the most in three years: Fulica
atra (15.49%), Podiceps cristatus (10.28%), Chlidonias
hybrida (9.66%), Egretta alba (8.59%), Aythya ferina(8.47%),Anas
poecilorhyncha (7.63%), Podiceps ruficollis (7.61%)Chlidonias leucoptera (6.83%) and Anas platyrhynchos(4.85%), with a cumulative contribution of approximately 80% and a
total similarity of 65.42.
Changes in the species composition of waterfowl in the shallow water
areas that consisted of islands and deep water areas without islands are
shown in Figure 9. There were more wading bird species than swimming
birds in the park, but the wading birds were less abundant. Comparing
the distribution of waterfowl at the two water levels, the number and
abundance of species in the shallow water area were higher than those in
the deep water area, Charadriidae, Scolopacidae and Ardeidae, for
example. In contrast, the shallow water areas had more Podicipedidae and
Rallidae.
Pearson correlation analysis showed that there was a negative
correlation between the diversities (H’) of waterfowl and
macroinvertebrates (r = -0.997, P = 0.05). Therefore, the
waterfowl and macroinvertebrate data were compared. The
macroinvertebrate diversity index had an upward trend, but the waterfowl
diversity index decreased (Figure 10). The possible reason for the
effects on the composition of the waterfowl community is that summer is
the peak tourist season in the park, and the number of visitors
gradually increased during those years. The number of visitors was
negatively correlated with the diversity (\(r_{H^{\prime}}\) = -1.000) and
richness (\(r_{d}\) = -0.999) of waterbirds. Human activities interfere
with the foraging behaviours of birds and reduce their activity space.