This is needed when the logarithmic y-axis spans less than one order of magnitude, in which case the ggplot2 default produces no ticks. Thanks to Heather Turner at https://stackoverflow.com/questions/14255533/pretty-ticks-for-log-normal-scale-using-ggplot2-dynamic-not-manual
log_breaks(n = 6)Approximate number of ticks
A function that can be used as the break argument in calls to scale_y_continuous() or scale_x_continuous()