Variation in zoogeographical composition along an elevational gradient: the tenebrionid beetles of Latium (Central Italy)

The aim of this paper is to propose the use of chorotype analysis of species assemblages on an elevational gradient to detect the main historical and ecological factors responsible for current faunal settings. A comprehensive faunistic database was used to assess species abundance across 100 m belts in Latium (Central Italy). Species were assigned to chorotypes according to their ranges. Entropy and evenness indices were applied to both species abundances and chorotype frequencies recorded in each belt. Both species and chorotype entropy decreased with elevation, whereas species and chorotype evenness increased. Chorotypes centred on the Mediterranean basin decreased with increasing elevation, chorotypes centred in Europe and Asia had similar frequencies among belts and endemic species increased with elevation. A cluster analysis with species presence/absence data, revealed three main clusters grouping respectively: i) all belts above 1700 m; ii) belts between 901 and 1500 m; and iii) belts between 0 and 900 m. An analysis based on chorotype frequencies produced very similar results. We can conclude that: high elevation assemblages are less diversified, but more balanced than lowland assemblages, in terms of both species and chorological composition. Belts similar in species composition (presence/absence) are also similar in zoogeographical composition (frequency of chorotypes). This indicates that elevation is a factor that strongly selects species’ attributes and especially their geographical distribution. Variations in chorotype composition along an elevational gradient may be used to trace the history of biotas.