Abstract: To help draw the boundary between the Palaearctic and Oriental for ants (Formicidae) in China, distribution records were compiled. Of 67 Oriental genera in East Asia, 34 (51 %) reach no higher than 25° N, the median reach. Of 11 Palaearctic genera six (55 %) are known no further south than 31° N, the median reach for these taxa, and none south of 22° N. Richness of Oriental genera exceeded that of Palaearctic genera below about 37° N. Distribution data were organised by both 5° latitudinal band and by January mean minimum temperature band, and bands were compared using Simple Matching Coefficients of Similarity, non-metric Multidimensional Scaling, and cluster analysis. By all these approaches the greatest separation was around 25 to 26° N, but was disproportionately influenced by Oriental taxa. The proportion of East Asian Palaearctic genera exceeded the proportion of East Asian Oriental genera at around 28° N, where winter temperature is about 1 to 2° C. This approach, independent of genus richness of each component, suggests a Palaearctic-Oriental boundary close to the northern limit of the Mid-tropical Climatic Zone. By this boundary, some 10 % of East Asian genera are confined to the Palaearctic, 38 % to the Oriental, and 52 % common to both. Temperature tolerance is probably of prime importance in limiting the Oriental fauna, and altitude has a strong influence. Further work with altitude-referenced data is needed in the central China region.

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