Structure of communities of ground-dwelling animals at the junction of two phytogeographic zones

Changes in the structure of tenebrionid beetle, lizard and rodent communities along the aridity gradient that determines the position of a phytogeographic province boundary were studied to test: (1) whether there are two different species assemblages on either side of the boundary (2) the extent of their differentiation and (3) if they are composed of different or the same faunal elements. Several ordination methods were tested for their capacity to reflect community structure, and discriminant function analysis was selected as the primary method of ordination. Each of the ordination axes reflected a complex environmental gradient. The latter was different for each taxon. The gradient of productivity cross-cuts ecological space for each animal group in an individual manner. Revealed spatial assemblages of species were related to the level of productivity. There was one assemblage of species at high productivity and one or two assemblages occurred at low productivity in each taxon. The alpha-diversity curve of rodents changed weakly along the productivity gradient, whereas those of lizard and beetle communities were distinctly unimodal and had maxima near the middle of the gradient. beta-diversity curves of rodents had a concave shape, but those of lizard and beetle communities increased from low productivity values to the middle of the gradient and after that weakly declined to the upper (productive) end of the gradient. Seven types of ranges or areographic groups of species were distinguished. Each species assemblage was composed of different faunal elements. Comparison of the results of ecological and areographic analyses demonstrated that two assemblages of rodents and lizards represent different guilds within the same community rather than different communities. The phytogeographic border for these taxa is an ecological rather than a geographical boundary. The difference between the two tenebrionid assemblages appears to be zoogeographical rather than ecological, and coincides with the phytogeographic boundary.