Table 1

Minimum adequate regression models required to explain variation in cichlid coloration, color morph, and species diversity. Fourteen environmental variables were measured: habitat patch size, distance from the mainland, maximum water depth, mean size of rock boulders and its variation, mean steepness of shore slope and its variation, resource abundance (measured as cichlid fish abundance), predator abundance: Nile perch and piscivorous birds, water transparency, bandwidth of the transmission light spectrum, transmission of 400 nm light, and the ratio of transmission 580 nm by 400 nm. Of the last four, being different measures of the light environment, only one, which correlated highest with the dependent variable, was included in the regression model design procedure. Therefore, 11 environmental variables plus sampling effort were included. Cichlid diversity, resource abundance, and abundance of Nile perch and birds were determined over three 3-month periods spread over 3 years, water transparency and light transmission of the water were measured twice with an interval of 1 year. Fish coloration and light transmission were measured and quantified as described in (31) and Fig. 1. Regression models were calculated by a stepwise variable-selection procedure (32) with forward selection and a minimum F value of 4 for variables to enter the model. Significance levels: *P < 0.05, **P< 0.01, ***P < 0.001, ****P < 0.0001.

Dependent variableExplanatory variables (and the sign of correlation)r2FP-value modelr2model
Coloration
Redness ofH. nyererei Width of tranmission spectrum (+)0.89161.94*** * <0.00010.95
Bird density (+)0.0410.64*
Mean rock size (+)0.035.74
Blueness of VBL* Water transparency (+)0.6535.32*** 0.00010.86
Maximum depth(+)0.179.71*
Shore slope (−)0.044.01
Color morph diversity
VBL color morph T400 nm(+)0.8559.05*** <0.00010.99
number* Maximum depth (+)0.1042.09***
Distance to the mainland (+)0.0330.96***
Area size (+)0.00910.02*
Nile perch abundance (−)0.00610.70*
Shannon-Wiener indexT400 nm(+)0.7980.99*** * <0.00010.91
of VBL morph diversity* Variation in boulder size (+)0.1217.25**
Species diversity
Total species numberWidth of transmission spectrum (+)0.7036.04*** * 0.00030.77
Sampling effort (+)0.074.26
Neochromis spp. numberWater transparency (+)0.7989.69*** * <0.00010.95
Shore slope (−)0.0929.36***
Variation in shore slope (+)0.046.33*
Sampling effort (+)0.035.70*
Nyererei spp. number§Width of transmission spectrum (+)0.6019.14** 0.00110.60
Paralabidochromis T580 nm/T400 nm(−)0.5034.66*** 0.00020.83
spp. numberSampling effort (+)0.2823.24***
Nile perch abundance (−)0.054.27
Shannon-Wiener index− (No variable withF > 4)
of species diversity|
  • * VBL, Neochromis “velvet black”/“blue scraper”.

  • Maximum depth is the depth of the deepest point within 100 m around each station and a measure of the time for which the area around each station is flooded again after the desiccation of the lake.

  • T400 nm, transmission at 400 nm; T580 nm, transmission at 580 nm.

  • § Nyererei complex is an undescribed genus (7, 33).

  • | See (27).