Environmental and geographical factors affecting the Iberian distribution of flightless Jekelius species (Coleoptera: Geotrupidae)

The degree of influence of environment, location and geography on the distribution of closely-related Jekelius nitidus and Jekelius hernandezi, coleopteran species endemic to the Iberian Peninsula, was examined. Niche envelope model predictions of probable absence points were based on available presence information. Presence-absence information for each of the two species was logistic-regressed against climate, altitude, lithology, spatial and river basin variables from each of 100 km(2) UTM Iberian Peninsula squares. Models predict that environmental conditions are suitable for both species in an area larger than that in which they have been found. The best-fitting environment model for J. nitidus, based on summer precipitation, area underlain by siliceous rocks, area with siliceous sediments and aridity index, explains more than 81% of total deviance. The final model, which includes spatial and river basin variables, accounts for nearly of 89% of total deviance. The best-fitting environment model for J. hernandezi, based on the area underlain by calcareous rocks, summer precipitation, aridity index, altitude and minimum annual temperature, explains 63% of total deviance. The final model based on both spatial and river basin variables accounts for nearly 70% of total deviance. Our results suggest that climate influences the distribution of both species similarly and that the acidic or basic nature of the substrate is the environment variable that most influences the occurrence of both species. The major degree of influence of river basin variables, together with lithologic variables, on the current distribution of both species may be due to the limited mobility of these flightless species.