Effect of grassland mosaic structure and dynamism on the reproductive habitat suitability for Alectoris graeca in central Apennines

Abstract

Over the last several decades, the Mediterranean region has been subjected to mountain abandonment and farming cessation, leading to changes in vegetation and coenological features of grasslands, contextually to the strong decline of the rock partridge (Alectoris graeca). Our hypothesis was that the ongoing dynamic processes leading to the compositional changes of grasslands in central Apennines affect the habitat suitability for the singing male (territorial male defending its reproductive site). In 2015, we defined the presence/absence of spring territorial singing males in seven sites (1,250-2,400 m a.s.l.), by the census in 74 playback stations, distributed along 15 transects. We characterized the topography and the vegetation mosaic of such sites according to the collected topographic and vegetation cover data in 59 randomly selected plots (100 m × 100 m) along the transects. To understand the relations among the environmental variables and the effect of the composition and dynamism of the vegetation mosaics on the presence/absence of the singing male, we used principal components analysis and generalized linear mixed-effect modelling. Our results emphasized the marked overlap between the general environmental conditions, which proved to define the habitat suitability for A. graeca, and the characteristics of the site chosen by the singing male for starting the reproductive activities. Moreover, we found that the site suitability for the singing male decreases when the vegetation recovery processes are ongoing, because of the spread of coarse tall grasses-dominated communities and/or grassland types with dense turf. Tall grass-dominated communities and thick-turf grasslands exert their negative effect decreasing the habitat suitability for the singing male starting from low cover values. Therefore, it is conceivable that singing male’s suitable habitat will be dramatically restricted to the steepest south-facing slopes, where topographic and soil conditions do not allow the spread of grasslands with dense turf and of invasive/dominant tall grasses, increasing the threat to the species due to the effect of climate change on the vegetation features.