Factors controlling the spatial species richness pattern of four groups of terrestrial vertebrates in an area between two different biogeographic regions in northern Spain

Aim To examine the influence of environmental variables on species richness patterns of amphibians, reptiles, mammals and birds and to assess the general usefulness of regional atlases of fauna. Location Navarra (10,421 km²) is located in the north of the Iberian Peninsula, in a territory shared by Mediterranean and Eurosiberian biogeographic regions. Important ecological patterns, climate, topography and land‐cover vary significantly from north to south. Methods Maps of vertebrate distribution and climatological and environmental data bases were used in a geographic information systems framework. Generalized additive models and partial regression analysis were used as statistical tools to differentiate (A) the purely spatial fraction, (B) the spatially structured environmental fraction and (C) the purely environmental fraction. In this way, we can evaluate the explanatory capacity of each variable, avoiding false correlations and assessing true causality. Final models were obtained through a stepwise procedure. Results Energy‐related features of climate, aridity and land‐cover variables show significant correlation with the species richness of reptiles, mammals and birds. Mammals and birds exhibit a spatial pattern correlated with variables such as aridity index and vegetation land‐cover. However, the high values of the spatially structured environmental fraction B and the low values of the purely environmental fraction A suggest that these predictor variables have a limited causal relationship with species richness for these vertebrate groups. An increment in land‐cover diversity is correlated with an increment of specific richness in reptiles, mammals and birds. No variables were found to be statistically correlated with amphibian species richness. Main conclusions Although aridity and land‐cover are the best predictor variables, their causal relationship with species richness must be considered with caution. Historical factors exhibiting a similar spatial pattern may be considered equally important in explaining the patterns of species richness. Also, land‐cover diversity appears as an important factor for maintaining biological diversity. Partial regression analysis has proved a useful technique in dealing with spatial autocorrelation. These results highlight the usefulness of coarsely sampled data and cartography at regional scales to predict and explain species richness patterns for mammals and birds. The accuracy of models appears to be related to the range perception of each group and the scale of the information.     

Mitochondria, reactive oxygen species and longevity: some lessons from the Barja group

To demonstrate that an uncoupling of respiration and phosphorylation, measured in vitro, reflects an in vivo situation, we badly need in vivo measurements of some uncoupling-linked parameters. The importance of this assertion is illustrated by studies of Barja and co-workers. A lower rate of H(2)O(2) production by mitochondria isolated from long-lived birds compared with short-lived mammals of the same body weight (see publications by Barja's and Sohal's groups) could be explained by (i) an in vivo difference or (ii) an in vitro artefact. In both cases, the reason for lower H(2)O(2) production may well be the same, i.e. a mild uncoupling of respiration in avian mitochondria showing lowered respiratory control. Again, this should be due to an in vivo operation of some bird-specific natural uncouplers (the first case) or stronger in vitro damage to the avian mitochondria during their isolation and incubation (the second). The latter possibility seemed more probable when Barja and co-workers revealed that the level of antioxidants in birds is lower than in mammals. However, further studies by the same group showed that the degree of unsaturation of fatty acids in birds is lower than in mammals, indicating a greater resistance of avian mitochondria to oxidative damage in vitro. Indeed, it was found that lipid peroxidation in isolated avian mitochondria occurs at a much lower rate than in mammals. More importantly, the in vivo level of peroxidation of lipids and proteins appears to be lower in birds than in mammals. Thus, it seems probable that longer lifespan of birds really does correlate with a slower rate of production of H2O2 by mitochondria in vivo.