Table 2. Statistical analysis of the differences in the measured variables between individuals in the heterospecific group (the second and third columns show the measures for each species, and the fourth column shows the measures between species) based on linear mixed model analysis.
| Variable | Chinese bream | Qingbo | Chinese bream-Qingbo | Linear mixed model |
|---|---|---|---|---|
| Mean speed (cm s−1) | 4.34 ± 0.67 | 4.34 ± 0.63 | F1,23 = 0.278P = 0.603 | |
| Speed while moving (cm s−1) | 4.99 ± 0.57 | 5.00 ± 0.59 | F1,23 = 0.013P = 0.911 | |
| Synchronization of speed | 0.84 ± 0.01 | 0.83 ± 0.01 | 0.84 ± 0.00 | F2,38 = 0.970P = 0.388 |
| Inter-individual distance (cm) | 4.54 ± 0.21 | 5.06 ± 0.29 | 4.82 ± 0.23 | F2,38 = 0.579P = 0.565 |
| Percent time moving (%) | 57.70 ± 3.42 | 57.42 ± 0.03 | F1,23 = 0.025P = 0.876 | |
| Percent time swimming at the front (%) | 19.07 ± 3.34 | 30.94 ± 3.34 | t1,14 = − 2.516P = 0.025 | |
| Percent startle response (%) | 93.75 ± 6.25 | 81.25 ± 9.15 | F1,7 = 2.333P = 0.170 | |
| Startle response consistency (%) | 87.50 ± 12.50 | 62.50 ± 18.30 | 81.25 ± 9.15 | F2,38 = 1.371P = 0.266 |
Notes.
The mean swimming speed, speed while moving and percent time moving were measured individually with a total of 32 values for each variable. The linear mixed model included a fixed effect (species) and a random effect (group number) resulting in 1, 23 degrees of freedom. The percent startle response was measured at the whole group level for each species for a total of 16 values. The linear mixed model included a fixed effect (species) and a random effect (group number), resulting in 1, 7 degrees of freedom. The synchronization of speed, inter-individual distance and startle response consistency were variables describing and interaction between pairs of group members (i.e., between two Chinese bream, two qingbo and between Chinese bream and qingbo) for a total of 48 values for each variable, resulting in 2, 38 degrees of freedom. The percent time swimming at the front were measured at whole group level for a total of 16 values. However, the values did not meet the statistical assumptions for a linear mixed model. Therefore, the mean of each species was tested by an independent sample t-test, and the degrees of freedom were 1, 14.