x1 = species_1 x2 = species_2 x3 = species_3 x4 = species_4 x5 = species_5 x6 = species_6 x7 = species_7 x8 = species_8 x9 = species_9 x10 = species_10 x11 = species_11 x12 = species_12 x13 = species_13