Elevational Patterns of Generic Diversity in the Tenebrionid Beetles (Coleoptera Tenebrionidae) of Latium (Central Italy)

Abstract

The concept of generic diversity expresses the ‘diversification’ of species into genera in a community. Since niche overlap is assumed to be higher in congeneric species, competition should increase generic diversity. On the other hand, generic diversity might be lower in highly selective environments, where only species with similar adaptations can survive. We used the distribution of tenebrionid beetles in Central Italy to investigate how generic diversity varies with elevation from sea level to 2400 m altitude. Generic diversity of geophilous tenebrionids decreased sharply with elevation, whereas the generic diversity of xylophilous tenebrionids showed similarly high values across the gradient. These results suggest that geophilous species are more sensitive to variation in environmental factors, and that the advantages of close relationships (similar adaptations to harsh conditions) are greater than the possible drawbacks (competition). This is consistent with the fact that geophilous tenebrionids are mostly generalist detritivores, and hence weakly affected by competition for resources. By contrast, xylophilous species are more protected from harsh/selective conditions, but more limited by competition for microhabitats and food. Our results support the environmental filtering hypothesis for the species composition of tenebrionid beetles along an elevational gradient.

Conservation Biogeography of Tenebrionid Beetles: Insights from Italian Reserves

“…Minimum elevation had a negative influence in all cases except for the xylophilous species. This is consistent with the thermophilic preferences shown by most tenebrionids, and their decline in species richness with elevation [31,33]. Mean elevation also had a negative influence on geophilous species.…”

“…I considered both species and subspecies, but the word "species" will be used for simplicity. I omitted from the analysis the genus Lagria and the subfamily Alleculinae (formerly considered as a separate family), because of their peculiar ecology (in contrast to other tenebrionids, they are flower-visiting insects) and paucity of distributional data [13,33]. Each species was classified according to the main lifestyle of the adults either as geophilous (i.e., adults that occur in the soil) or xylophilous (e.g., adults that occur in rotten wood or on living trees) using information reported in Aliquò et al [55] and personal observations.…”

“…This negative effect should be particularly apparent if maximum and/or minimum elevation are used as predictors of species richness. It is known that tenebrionid richness tends to decline with elevation, as the cold climatic conditions of high altitudes are not favourable for them [31,33]. Thus, we expect that, if most of the species are Mediterranean elements mainly associated with lowland areas, species richness should decrease rapidly with increasing minimum elevation.…”

“…Variation of species richness with elevation is a biogeographical diversity pattern that is known to follow various forms [31,32]. One of the most commonly observed rules is a monotonic decrease of species richness with increasing elevation; thus, within a certain elevational gradient, high-altitude areas tend to have fewer species than lowland areas of the same size [31][32][33]. This might imply that montane areas, where most of the territory is at high elevations, should host less species than areas which include sectors at lower elevation.…”

Beetle Species–Area Relationships and Extinction Rates in Protected Areas

“…This may be interpreted as a consequence of the fact that, in a mainland context, a large elevational gradient implies that most of the study area is at high altitudes. Since, in general, richness tends to decrease with elevation [94][95][96], the negative influence of elevational range may be a reflection of this general trend. Moreover, in the specific case of the Hydradephaga, the negative impact of the elevational range on species richness may be explained by the fact that, with increasing elevation, lentic waters became rare.…”