Fig. 2.

Illustration of the two alternative stable states. a, b When the model starts with a low initial population density of cyanobacteria (CB), it develops towards an anoxic ecosystem with, a high abundances of phototrophic sulfur bacteria (PB) and sulfate-reducing bacteria (SB) and, b a high concentration of reduced sulfur (S _R) but low oxygen concentration (O). c, d When the model starts with a high initial population density of cyanobacteria, it develops towards an oxic ecosystem with, c high abundances of cyanobacteria and, d high concentrations of oxygen and oxidized sulfur (S _O). Parameter values are given in Supplementary Table 1, with P _b = 9.5 μM, α _O = 8 × 10⁻⁴ h⁻¹. Initial conditions: a, b N _PB = N _SB = 1 × 10⁷ cells L⁻¹, N _CB = 5 × 10¹ cells L⁻¹, S _O = 300 μM, S _R = 300 μM, O = 10 μM, P = 10 μM; c, d N _PB = N _SB = 1 × 10² cells L⁻¹, N _CB = 1 × 10⁸ cells L⁻¹, S _O = 500 μM, S _R = 50 μM, O = 300 μM, P = 4 μM