Reduced trophic niche breath is associated with higher productivity in a recovering apex predator population [Dataset]

Understanding trophic and demographic dynamics of apex predators is of paramount importance for ecosystems conservation. Apex predators are usually free from predation and, thus, main drivers of population dynamics are trophic resources availability affecting breeding performance. Albeit food habits have been described in many apex species, the effects of changes in the trophic niche on long-term demographic dynamics are poorly known. We describe the long- term (N = 25 years) changes in trophic niche breath of a recovering golden eagle population in a Mediterranean landscape (North Spain), and searched for potential correlates with their productivity (i.e., number of fledged eaglets per controlled pair) as a proxy of their breeding performance (N = 290 pairs*years). We identified a total of 3,475 prey items from 77 species; rabbits, hares and red-legged partridges were the most frequent prey consumed (overall 51%), followed by roe deer (10%), red-billed chough, red foxes and woodpigeons, all of them with >5%. Prey diversity in eagle’s diet decreased along the study period. Rabbits and roe deer consumption increased, hares and partridges decreased, while foxes, choughs and woodpigeons showed no significant trends. Prey diversity and red-legged partridge consumption were negatively correlated with productivity at territory level, while rabbits, corvids and pigeons showed strong positive relationship with productivity. The size of the territory showed the strongest positive relation with productivity, while roughness was negatively correlated. Rabbits and ungulates showed negative and positive correlation with roughness, respectively, while predators consumption has a negative relation with the size of the territory. Our findings give insights the potential trophic mechanisms driving the dynamics of recovering apex predator populations; a reduction in the trophic niche breath towards specific groups of prey, which could be due to a higher availability and individual specificity towards these prey species, might enhance productivity at territory level and, ultimately, influence population dynamics facilitating the recovery process. The remarkable increasing consumption of wild ungulates and predators, and even of other apex consumers, suggest that the current population recovery and reduced trophic niche breath may facilitate this eagle population to exhibit its apex role and contribute to ecosystem functionality.