We calculated wildlife and livestock diversity indices for each of the 10 × 10 km UTM grid cells within mainland Spain. To quantify diversity, we used species richness of terrestrial vertebrate groups—that is, mammals, birds, amphibians and reptiles—and richness of local livestock breeds, calculated by either summing the species or summing the breeds present in each UTM grid cell.

We calculated livestock breed richness using all local breeds of bovine, ovine, caprine, asinine, equine and porcine species managed by extensive traditional livestock systems. To identify local breeds, we consulted two sources of information. First, we used the Official Catalogue of Livestock Breeds of Spain, in order to determine currently recognized breeds, either increasing in number or under threat of extinction. Second, we reviewed the FAO DAD‐IS to identify breeds of mainland Spain that were not in the Official Spanish Catalogue but did appear in alternative breed catalogues. These breeds were considered extinct by the FAO as Spanish Ministry does not account for breed extinction. Extinct breeds have only recently undergone population declines, especially during the last decades of the 20th century. Thus, our data set encompasses all extant and recently extinct breeds, based on their historical distributions, prior to being exposed to the effects of agricultural intensification over the last decades.

We documented a total of 128 local breeds: 44 bovine, 38 ovine, 19 caprine, 9 porcine and 18 equine, including horses and donkeys. With these breeds, we computed the following three different indicators of livestock agrobiodiversity: total breed richness, bovine breed richness and ovine breed richness. The distribution of each breed, corresponds to its area of origin—that is, the region where the breed was first recorded—and was delimited and digitized after a comprehensive review, comparison and integration of the distributional descriptions in all catalogues of Spanish breeds. When a clear description of the area of origin was unavailable, we assigned the oldest area where the breed was distributed before the agrarian industrialization. 

Vertebrates species richness—that is, amphibians, reptiles, birds, mammals—was extracted from the Spanish Inventory of Terrestrial Vertebrate Species (MITECO, 2019b) and additional sources for completion (López & Martín, 2019; MITECO, 2019a). We grouped the vertebrate taxa according to the following criteria. First, as general metrics of wildlife diversity, we calculated each group total richness using native species and excluding exotic, littoral and marine species for all groups. We additionally excluded species from aquatic environments for mammals, birds and reptiles. Our vertebrate data set included a total of 76 mammal species, 177 nesting bird, 41 reptile species and 28 amphibians. Second, to deepen our understanding of wildlife–livestock relationship, we further subsetted each vertebrate group based on specific habitat preferences related to agricultural landscapes and livestock uses. For mammals, we considered lagomorphs, and artiodactyls as small and large herbivores, respectively. For birds, we used steppe birds, related to extensive agricultural landscapes and scavengers, feeds on livestock carcasses. Reptiles were divided into rocky habitats and shrubby habitats. Amphibians were separated into aquatic and land‐based, according to whether their adult phase is developed in water bodies.

To examine whether the relationships between wild and domesticated biodiversity are mediated by either environmental factors or human impacts, we calculated average values of a suite of variables for each grid cell. We extracted climate from the WorldClim database, used annual mean temperature (BIO1), annual precipitation (BIO12) and precipitation seasonality (BIO15) variables (Fick & Hijmans, 2017). To characterize human disturbance of natural systems, we used the terrestrial Human Footprint for 2009 (Venter et al., 2018).