The organization of ecological assemblages has important implications for ecosystem functioning, but little is known about how scavenger communities organize at the global scale. Here, we test four hypotheses on the factors affecting the network structure of terrestrial vertebrate scavenger assemblages and its implications on ecosystem functioning. We expect scavenger assemblages to be more nested (i.e. structured): 1) in species‐rich and productive regions, as nestedness has been linked to high competition for carrion resources, and 2) regions with low human impact, because the most efficient carrion consumers that promote nestedness are large vertebrate scavengers, which are especially sensitive to human persecution. 3) We also expect climatic conditions to affect assemblage structure, because some scavenger assemblages have been shown to be more nested in colder months. Finally, 4) we expect more organized assemblages to be more efficient in the consumption of the resource. We first analyzed the relationship between the nestedness of the scavenger assemblages and climatic variables (i.e. temperature, precipitation, temperature variability and precipitation variability), ecosystem productivity and biomass (i.e. NDVI) and degree of human impact (i.e. human footprint) using 53 study sites in 22 countries across five continents. Then, we related structure (i.e. nestedness) with its function (i.e. carrion consumption rate). We found a more nested structure for scavenger assemblages in regions with higher NDVI values and lower human footprint. Moreover, more organized assemblages were more efficient in the consumption of carrion. However, our results did not support the prediction that the structure of the scavenger assemblages is directly related to climate. Our findings suggest that the nested structure of vertebrate scavenger assemblages affects its functionality and is driven by anthropogenic disturbance and ecosystem productivity worldwide. Disarray of scavenger assemblage structure by anthropogenic disturbance may lead to decreases in functionality of the terrestrial ecosystems via loss of key species and trophic facilitation processes.

Species assemblages often have a non-random nested organization, which in vertebrate scavenger (carrion-consuming) assemblages is thought to be driven by facilitation in competitive environments. However, not all scavenger species play the same role in maintaining assemblage structure, as some species are obligate scavengers (i.e., vultures) and others are facultative, scavenging opportunistically. We used a database with 177 vertebrate scavenger species from 53 assemblages in 22 countries across five continents to identify which functional traits of scavenger species are key to maintaining the scavenging network structure. We used network analyses to relate ten traits hypothesized to affect assemblage structure with the "role" of each species in the scavenging assemblage in which it appeared. We characterized the role of a species in terms of both the proportion of monitored carcasses on which that species scavenged, or scavenging breadth (i.e., the species "normalized degree"), and the role of that species in the nested structure of the assemblage (i.e., the species "paired nested degree"), therefore identifying possible facilitative interactions among species. We found that species with high olfactory acuity, social foragers, and obligate scavengers had the widest scavenging breadth. We also found that social foragers had a large paired nested degree in scavenger assemblages, probably because their presence is easier to detect by other species to signal carcass occurrence. Our study highlights differences in the functional roles of scavenger species and can be used to identify key species for targeted conservation to maintain the ecological function of scavenger assemblages.

The assessment of temporal and spatial availability of food resources is an important prerequisite in developing improved management tools for effective conservation action. It is especially useful in the conservation of avian scavengers inhabiting regions where livestock move on a regular basis (transhumance). Important management decisions can be taken on the basis of theoretical analyses that need to be regularly checked. In this case study, we consider models of Griffon vulture Gyps fulvus, Egyptian vulture Neophron percnopterus and bearded vulture Gypaetus barbatus populations in a part of Spain with one of the highest densities of scavenging birds, and where traditional farming practices remain. We applied bioinspired Population Dynamic P System models (PDP) to assess these species' population trends against the distribution, quantity and availability of carrion for food. We show asymmetries in the availability of food resources, which are substantially higher in summer due to transhumant movements. In the study area, a lack of food resources in winter leads to a seasonal reduction in food supplies to levels unable to meet the energetic requirements of the most abundant vulture species, the Griffon vulture. Our results suggest that regardless of active management (e.g. supplementary feeding sites) and the birds' use of other potential food resources not included in the model, Griffon vultures are able to find important alternative food resources in more remote areas. We show the importance of variations at spatio-temporal scales in the objective forecasting of population trends, and in the correct application of management actions. Because of the importance of robust assessments for management applications, we discuss the advantages and limitations of ecological modelling for avian scavengers, highlighting the importance of transhumance processes and transboundary approaches.

Translocations are an increasing feature of threatened species conservation plans, but the impact of removal of individuals on the source population is seldom studied. Using computational Population Dynamics P System models and the Pyrenean Bearded Vulture population as a case study we looked at: the effect on the source population of alternative strategies for removal of individual birds for use in reintroduction projects; and the trade‐offs between the various management options. According to our models (over a 30 year prediction horizon) the removal of one clutch, juvenile or non‐territorial adult each year over an 11 year period, results in an annual loss of 1.57, 3.71 and 0.97 territories, respectively. We forecast the impact of a plausible removal scenario for the Pyrenees source population (the removal of five clutches and five non‐territorial adults each year over 11 years), leading to a predicted loss of 16 breeding territories. Nevertheless, changes in demographic parameters, mainly in productivity and adult survival, could substantially affect these predicted results. With the current demographic parameters, the removal scenarios that were estimated to not affect population size after 30 years (95% CI) are limited to: (1) the removal of five clutches and five non‐territorial adults during a single year; (2) the annual removal of five non‐territorial adults during a 6 year period; and (3) the annual removal of five clutches during a 6 year period. Our results suggest that removals from the Pyrenean Bearded Vulture source population should be performed with caution due to uncertainties arising from stochastic changes in survival and productivity.

Over millennia, human intervention has transformed European habitats mainly through extensive livestock grazing. “Dehesas/Montados” are an Iberian savannah-like ecosystem dominated by oak-trees, bushes and grass species that are subject to agricultural and extensive livestock uses. They are a good example of how large-scale, low intensive transformations can maintain high biodiversity levels as well as socio-economic and cultural values. However, the role that these human-modified habitats can play for individuals or species living beyond their borders is unknown. Here, using a dataset of 106 adult GPS-tagged Eurasian griffon vultures (Gyps fulvus) monitored over seven years, we show how individuals breeding in western European populations from Northern, Central, and Southern Spain, and Southern France made long-range forays (LRFs) of up to 800 km to converge in the threatened Iberian “dehesas” to forage. There, extensive livestock and wild ungulates provide large amounts of carcasses, which are available to scavengers from traditional exploitations and rewilding processes. Our results highlight that maintaining Iberian “dehesas” is critical not only for local biodiversity but also for long-term conservation and the ecosystem services provided by avian scavengers across the continent.