When building a diversity heat map and specifying the color gradient and then the mode, when you set it as Natural Breaks (Jenks) the values in the color classes are not equivalent to the number of species you checked in the taxa tab. What do jerks represent then? And is there a way to specify your classes based on number of species rather than this seemingly arbitrary number?
The figures relate to whatever attribute is selected in the column drop-down in the styles dialog. After specifying any of the modes to get QGIS to give you a ‘best guess’ for the breaks, you can disregard them and manually edit them youself, setting the breaks at whatever levels make sense for your data. Just double-click the values in the little table and then edit the upper and lower bounds. (Note that this is a QGIS question rather than a FSC plugin question - there might be a better forum for those questions elsewere.)
There’s a good overview of what Jenks are here:
The best place for general GIS Q&A is the Geographical Information Systems StackExchange. It has a particularly active QGIS tag. Absolutely fine to ask here if not sure, though.