The relationship between the terrain slope and biodiversity conservation: a perspective from the specialist avifauna of Mexico

The main threats to biodiversity are those associated with transforming natural ecosystems due to anthropogenic activities, such as increasing population density, raising the agricultural frontier, and urban expansion, which lead to a high demand for natural resources. The degradation of vegetation cover tends to appear mainly in flat areas due to ease of access, leading to changes in the dynamics and composition of biological communities. The transformation process entails gradual losses in the distribution and richness of species, particularly those associated with conserved vegetation (i.e., primary vegetation). In this work, we analyzed whether the potential richness distributions of conserved vegetation specialist bird species increase with the terrain slope in Mexico, considering it a proxy for landscape transformation. We recategorized the land-use Mexican coverages INEGI VII into transformed and conserved coverages and characterized the slope in each. Further, we estimated the spatial pattern of richness by creating species distribution models (SDMs) for 56 conserved land cover specialist birds. We analyzed this pattern using spatial autoregressive models (SAR) and described the species distribution in conserved coverages. We found a statistically significant and positive relationship between bird richness and terrain slope, suggesting that steep slopes in Mexico represent biodiversity refuges. On the other hand, we identified areas where transformation patterns have intensified in areas of slight and moderate slopes, leading to a loss of between 60 % and 75 % of the distribution of some species, evidencing an advance of anthropization toward areas of greater slope.