Taxonomic differentiation in species richness gradients among European butterflies (Papilionoidea, Hesperioidea): contribution of macroevolutionary dynamics

We examine spatial differences in patterns of species richness among butterfly families in Europe and North Africa. When compared to global proportions for the whole region there is a surplus of Nymphalidae in northern Europe, of Pieridae in North Africa and the Mediterranean islands, of Lycaenidae in Iberia and Greece, of Hesperiidae in the Algarve, and a deficit of Satyridae outside the mountain areas. For the Lycaenidae and Satyridae the spatial bias in numbers of species corresponds with a bias for endemism in southern Europe, regions of refuge and persistence during Pleistocene polyglaciation. We argue that regional surpluses of species in at least these two families are governed more by net species production than by species maintenance. Differences in species richness between families are related to ecological amplitude and dispersal capacity which determine balances between migration, clade isolation, speciation and extinction. Taxa capable of migrating long distances (e.g. many Nymphalidae) are able to colonize distant locations but are less amenable to clade isolation, speciation or extinction; whereas, specialized taxa with limited capacity for migration (e.g. most Satyridae) cannot colonize distant habitats but more readily undergo clade furcation, speciation or extinction. Yet, only taxa initially able to disperse and extend their ranges can undergo clade furcation. Dispersal capacity divides into extrinsic and intrinsic parameters. Both are influenced by environmental changes, particularly resource geography, associated with Pleistocene glacial cycles. Changes in resource geography, by influencing extrinsic components of dispersal and in turn reinforcing intrinsic components of dispersal, result in a polarization in evolutionary dynamics; one extreme is extensive migration, gene flow and gene pool homogeneity, the other is isolation, speciation or extinction. At the isolation end of this scale, the balance between clade evolution and extinction depends on the nature of environmental change and landscape structure.