Geographic and environmental effects on the distribution of Iberian forest bird richness

Abstract

The peninsular effect is a biogeographical rule according to which species richness decreases as a function from the distance to the mainland base of peninsulas. However, this pattern is frequently obscured by the effect of environmental variables. In this paper we study the relative effect of the geographic location and some environmental variables on the distribution of the richness of Iberian forest birds. Results suggest that both the geographic location and some environmental variables (temperature, precipitation, forest coverage…) affect the species richness. We have also explored if these results can change according to the particular features of the study areas. To approach this, we defined two corridors of a similar length. The Atlantic corridor was quite homogeneous in the study environmental variables while the Mediterranean showed a sharp gradient from moist northern to dry south. Results showed that in the Atlantic corridor, distance to continent and not environmental variables were the main correlates to species richness while in the Mediterranean corridor environmental variables were the best correlates to richness distributions. These results are used to discuss some methodological and biogeographical aspects of the forest bird distribution across the Iberian Peninsula.