English: Relationships between phytoplankton species richness and temperature or latitude
(A) The natural logarithm of the annual mean of monthly phytoplankton richness is shown as a function of sea temperature (k, Boltzmann’s constant; T, temperature in kelvin). Filled and open circles indicate areas where the model results cover 12 or less than 12 months, respectively. Trend lines are shown separately for each hemisphere (regressions with local polynomial fitting). The solid black line represents the linear fit to richness, and the dashed black line indicates the slope expected from metabolic theory (−0.32). The map inset visualizes richness deviations from the linear fit. The relative area of three different thermal regimes (separated by thin vertical lines) is given at the bottom of the figure. Observed thermal (B) and latitudinal (C) ranges of individual species are displayed by gray horizontal bars (minimum to maximum, dots for median) and ordered from wide-ranging (bottom) to narrow-ranging (top). The x axis in (C) is reversed for comparison with (B). Red lines show the expected richness based on the overlapping ranges, and blue lines depict the species’ average range size (±1 SD, blue shading) at any particular x value. Lines are shown for areas with higher confidence.