Species richness components and depth diversity gradient
measures
As depth-independent component of species richness, we calculated gamma
richness as the total number of species per lake and year.
As depth-dependent component of species richness, we determined for
every lake and year an additive alpha richness as the number of species
per depth range averaged across of transects (Fig. 1b). The gamma
richness for every lake and year was defined as the total number of
species per depth range (Fig. 1c). We then calculated an additive beta
richness as gamma richness minus alpha richness (Tuomisto 2010) (Fig.
1d).
To further characterize the diversity depth gradient, we identified the
peak of the richness depth curve (Fig. 1c). For each transect we
filtered the depth with the maximal species number. Thereafter, we
averaged this valued across transects per lake and year, from now on
termed the depth with maximal alpha richness
(D(α,max) ). The corresponding maximal species
number averaged across transects is termed the maximal alpha richness
(R(α,max) ). Similarly, the depth with maximal
gamma richness (D(γ,max) ) is the depth of the
maximal gamma richness (R(γ,max) ) along depth, as
well as maximal beta depth (D(β,max) ) describes
maximal beta richness (R(β,max) ) along depth.