Table 2. Responses of total phytoplankton (chlorophyll-a) and cyanobacteria at different levels of taxonomic resolution (species, genus, class), to Daphnia grazing in each of the experiments performed in June, July and August.
Algal community | June experiment | July experiment | August experiment | |||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
R2 | F-value (1,4) | Equation | P-value | Response | R2 | F-value (1,4) | Equation | P-value | Response | R2 | F-value (1,4) | Equation | P-value | Response | ||
Species | Aph. gracile | 0.59 | 5.67 | NS | 0.076 | − | 0.87 | 27.65 | Y = -0.0002*X + 0.0989 | 0.006** | − | 0.78 | 13.93 | Y = -0.0002*X + 0.2580 | 0.020* | − |
Aph. klebahnii | 0.45 | 3.27 | NS | 0.145 | − | 0.19 | 0.95 | NS | 0.386 | + | 0.78 | 14.24 | Y = -0.0001*X−0.1113 | 0.020* | − | |
D. crassum | 0.25 | 1.3 | NS | 0.318 | − | 0.63 | 6.85 | Y = 0.0001*X−0.1936 | 0.059† | + | 0.43 | 3.07 | NS | 0.155 | − | |
D. flos-aquae | 0.68 | 8.58 | Y = -0.0004*X + 0.2339 | 0.044* | − | 0.34 | 2.04 | NS | 0.226 | + | 0.76 | 12.64 | Y = -0.0002*X + 0.0532 | 0.024* | − | |
D. lemmermanii | 0.58 | 5.63 | NS | 0.078 | − | 0.32 | 1.88 | NS | 0.242 | − | 0.89 | 32.45 | Y = -0.0003*X + 0.1005 | 0.006** | − | |
M. viridis | 0.35 | 2.2 | NS | 0.212 | − | 0.25 | 1.33 | NS | 0.314 | − | 0.28 | 1.56 | NS | 0.28 | − | |
M. wesenbergii | 0.37 | 2.31 | NS | 0.203 | − | 0.35 | 2.17 | NS | 0.215 | + | 0.11 | 0.51 | NS | 0.514 | − | |
M. botrys | 0.66 | 7.81 | Y = -0.0000*X + 0.2673 | 0.049* | − | 0.9 | 36.03 | Y = -0.0010*X + 0.3072 | 0.004** | − | 0.67 | 8.04 | Y = -0.0003*X + 0.2884 | 0.048* | − | |
P. agardhii | 0.04 | 0.17 | NS | 0.703 | + | 0.117 | 0.531 | NS | 0.506 | − | 0.82 | 18.43 | Y = −0.0001*X + 0.0147 | 0.012* | − | |
Genus | Aphanizomenon | 0.81 | 17.44 | Y = -0.0002*X + 0.0301 | 0.014* | − | 0.31 | 1.83 | NS | 0.247 | − | 0.78 | 14.49 | Y = -0.0001*X + 0.1709 | 0.020* | − |
Dolichospermum | 0.35 | 2.17 | NS | 0.215 | − | 0.56 | 5.03 | NS | 0.088 | + | 0.28 | 1.59 | NS | 0.276 | − | |
Microcystis | 0.74 | 11.39 | Y = -0.0001*X + 0.0795 | 0.028* | − | 0.49 | 3.85 | NS | 0.121 | − | 0.58 | 5.58 | Y = −0.0004*X−0.0068 | 0.078 | − | |
Planktothrix | 0.04 | 0.17 | NS | 0.703 | + | 0.117 | 0.531 | NS | 0.506 | − | 0.82 | 18.43 | Y = −0.0001*X + 0.0147 | 0.012* | − | |
Community | Total cyanobacteria (a) | 0.68 | 8.34 | Y = -0.0001*X−0.0796 | 0.044* | − | 0.1 | 0.454 | NS | 0.537 | − | 0.84 | 20.25 | Y = -0.0001*X + 0.1167 | 0.010* | − |
Total phytoplankton (chlorophyll-a) | 0.85 | 22.04 | Y = -0.0001*X−0.0931 | 0.008** | − | 0.49 | 3.84 | NS | 0.122 | − | 0.89 | 31.62 | Y = -0.0001*X + 0.1287 | 0.004** | − |
Probability levels of F-values of linear regression analyses (n = 6) are denoted in bold typing as follows:
* 0.05 < P ≥ 0.01
** P < 0.01
Equations are given for P < 0.05 (with exception of a marginally significant relationship for Dolichospermum crassum in the July experiment, P = 0.059†) and negative slopes indicate taxa that are suppressed by the grazers, and positive slopes indicate taxa that benefit from the grazer presence. For clarification we show the type of responses to grazing in a separated column based on the sign of the slopes from the linear regression analyses as: − (negative slopes) and + (positive slopes). Note that grazing effects were assessed on dominant cyanobacterial taxa present throughout the three experiments. Experimental data can be found in S1 File (Supporting Information). (a) Adapted from [35].