Mapping threatened ecosystems in Australia

This is an interesting map, recently published as part of the Bioscience article 'The Spatial Distribution of Threats to Species in Australia', Evans et al., BioScience, 61(4):281-289. 2011.

Figure 3: The distribution of the predominant threats to biodiversity across Australia. The “predominant threat” is the threat affecting the greatest number of species in each subcatchment. Where two or more threats affect an equivalent number of species, we consider there to be no predominant threat occurring in these subcatchments, displayed here in shades of gray.
Darker colors indicate a larger overall number of threats occurring in the subcatchment. White indicates areas where no threatened species occur.

 This is quite a novel way to highlight the range of threats to Australian ecosystems, putting them in a spatial context.  The article argues that the use of such a spatial and visual analysis will aid mitigation efforts and help identify location-specific threats.

However, I think there is a danger with the above map that it could be mis-read, i.e. 'no predominant threat' could be read as 'no threat', whereas it actually signifies that there are threats but no particular class of threat dominates.  This mistake can be made more easily because the 'no threat' value is missing from the key - I presume this to be the white areas.   Also, where there are several threats from multiple sources this map masks out threats which don't dominate but which may be significant (though more detail is given in the paper and multiple maps - which are perhaps more useful).  Really, I'm not too sure how useful this combined map really is - it seems to have more potential to mis-lead than to inform.  As as geographer, I often find the lack of basic cartography in such maps (full legend, north arrow, scale?!) to be frustrating.