The depth diversity gradient (DDG) patterns of macrophytes
The mean depth pattern of submerged macrophytes’ alpha and gamma
richness is hump-shaped, showing a peak between −1 and −2 m respectively
(Fig. 2a,c). The mean alpha richness at the hump’s peak is 4.5 species
(sd = 2.2), whereas the mean gamma richness peak is 11.4 species (sd =
5.1). In contrast, Beta richness shows a decreasing curve with its
highest richness being 7.0 species (sd = 4.0) between surface and −1 m
depth (Fig. 2b). However, all three richness components show high
standard deviations in the depth classes. They vary across depth classes
between 1.9 and 2.3 species for alpha richness, between 3.7 and 4.1 for
beta richness and from 5.1 till 5.6 for gamma richness (see individual
DDG curves for all lakes in Supporting information).
Comparing the richness components across depths revealed only
significant differences between mid and greater depths, but not for
shallower depth (Supporting information).
Plotting the DDG measures for all three richness components (Fig. 2d-f)
we find a hump-shaped pattern for alpha richness and a bi-modal pattern
for beta and gamma richness.
Looking at the DDG patterns of single field campaigns, for alpha
richness, hump-shaped curves with a peak between -2 and -4 m are most
frequent (52%) (Fig. 2g-i). For beta richness the majority are
decreasing curves (40%) while for gamma richness hump-shaped curves
with a peak between -1 and -2 m were slightly prevailing (39%)., All
depth pattern types are found for all three measures.
The three depth-dependent richness measures are significantly correlated
with one another (p < 0.05). The strongest correlation
shows beta and gamma richness (cor = 0.95), followed by alpha and gamma
richness (cor = 0.85) and alpha and beta richness (cor = 0.64). TheDmax and Rmax do not
correlate within the respective richness components
(p < 0.05). However, the Dmaxvalues across the three richness components correlates with each other.
Similarly, Rmax also correlates across the three
richness components (p < 0.05). For correlation
coefficients see Supporting information. However, a Chi-square test
shows, that pattern types and richness components are statistically
significantly associated (p = 0.0005).