Aim Anthropogenic food subsidies are increasingly present in ecosystems, but their impacts remain poorly understood. Big game hunting is a growing activity that annually subsidizes ecosystems with tonnes of carrion world-wide. By feeding on carrion, scavengers support key ecosystem functions and services, becoming key vectors to transfer the impacts of human-mediated food subsidies across ecosystems. We characterize and compare the structure of vertebrate communities feeding on these subsidies, namely big game hunting remains, at a global scale.Location Global.Methods We collected data from a countrywide field study in Spain and broadened it up to nine regions in four continents by reviewing scientific literature. We analysed the structure of the scavenger communities considering species composition, richness and scavenging frequency.Results Seventy-nine vertebrate species, 19% globally threatened, scavenged food subsidies from big game hunting world-wide. Scavenger richness (2.0-11.0% of vertebrates/region) positively correlated with total vertebrate richness. Although scavenger communities at hunting remains varied among regions, we describe a general structural pattern. Birds and mammals dominate consumption, with birds scavenging twice more frequently than mammals -but more mammal species scavenge compared to birds. Generalists dominate scavenging globally, especially where the presence of obligate scavengers (vultures) and apex predators (e.g. wolves, hyenas, eagles) is low.Main conclusions Anthropogenic food from hunting subsidizes many vertebrate species from different trophic levels and conservation status and thus is expected to affect from populations to ecosystems. Obligate scavengers and apex predators seem to play a key role structuring the scavenger community through top-down mechanisms. The general structure of scavenger communities we describe here provides a benchmark for comparisons of subsidized and non-subsidized communities. More data on the spatio-temporal availability of anthropogenic food subsidies and their consumption by scavengers world-wide are needed to efficiently preserve biodiversity, and the associated ecological functions and services, in increasingly subsidized ecosystems.

No abstract

Summary 1.Illegal human behaviour such as those affecting natural resource use or resulting from humanwildlife conflicts threaten the sustainable management of ecosystems and the conservation of biodiversity worldwide. However, the frequently scarce and incomplete data owing to the sensitive nature of illegal activities pose a challenge to developing tools to properly understand and prevent those activities. 2. We used species distribution models to identify factors related to a prominent illegal activity, wildlife poisoning, and to produce detailed, spatially explicit maps of the risk of occurrence in NW Spain. We alleviated the constraints of imperfect information and occurrence of absences by using presence-only methods, that is, maximum entropy modelling (MaxEnt). To our knowledge, this is the first time that this method has been used in the context of illegal activities affecting wildlife. 3. A total of 112 poisoning events involving 228 individuals of 25 different species were reported in the study area from 2000 to 2010. Most of the reported deaths (90AE8%) were birds of prey (52AE6%) and mammalian carnivores (38AE2%), of which 95AE2% were scavengers. Illegal poisoning affected eleven species classified as endangered at national and ⁄ or global level. 4. Our models highlighted the perceived risk of livestock predation by wolves Canis lupus, although not by bears Ursus arctos, as a major motivation for poisoning. The existence of protected areas was positively correlated to this illegal practice, while socioeconomic factors had less influence on predicting its occurrence. Over 56% of the study area was predicted to be under risk of illegal poisoning. 5. Synthesis and applications. We demonstrate a new use for presence-only models, illustrated using MaxEnt, to assist conservation managers dealing with illegal activities. This approach allows the main causes of an illegal practice to be identified and generates spatially explicit risk maps. Managers can take advantage of this modelling approach to allocate the scarce resources available in conservation to key sectors and locations. In our study system, actions against illegal poisoning should aim to resolve the potential conflict existing between cattle-farming and wolves, especially in protected areas.

Aim Recent works on biodiversity–ecosystem functioning (BEF) relationships highlight abundance fluctuations of common species as more important for delivering ecosystem services than changes in species richness and composition in real‐world ecosystems. However, evidence on BEF relationships in natural ecosystems is still limited, especially for large vertebrates. Here, we aimed to disentangle the relative roles of species richness, composition and abundance of vertebrate scavenger communities in the ecological process of carcass elimination, a pivotal ecosystem service, in natural ecosystems. We evaluated the variability in the scavenging function across ecosystems, and examined the factors explaining it. Location Nine natural ecosystems, seven in Europe and two in Africa. Major taxa studied Vertebrates. Time period 2006–2013. Methods We obtained BEF relationships from vertebrate scavengers consuming ungulate carcasses monitored through motion‐triggered remote cameras. We used the Price equation to tease out the relative roles of species richness, composition and abundance in the scavenging efficiency of vertebrates. Results We recorded 46 vertebrate scavenging species, 30 in Spain and 16 in South Africa. Two main patterns drove BEF relationships. Species richness and composition drove carcass consumption in ecosystems where functionally dominant scavengers were rare, whilst context dependent effects (including species abundance) did so where functionally dominant species were common. Contrastingly to previous studies, abundance fluctuations in vertebrate scavengers were not exclusively related to common species but to the specialization of obligate scavengers (i.e., Gyps vultures) to rapidly gather at carcasses and to the top‐down control exerted by large predators. Main conclusions Rare and threatened species such as vultures and top predators become functionally key species in scavenging processes, highlighting that the delivery of ecosystem services still stands as a general argument for biodiversity conservation in vertebrate communities. Human persecution of vultures and top predators worldwide is expected to alter ecosystem functioning and services such as nutrient recycling or disease control.

Understanding the distribution of biodiversity across the Earth is one of the most challenging questions in biology. Much research has been directed at explaining the species latitudinal pattern showing that communities are richer in tropical areas; however, despite decades of research, a general consensus has not yet emerged. In addition, global biodiversity patterns are being rapidly altered by human activities. Here, we aim to describe large‐scale patterns of species richness and diversity in terrestrial vertebrate scavenger (carrion‐consuming) assemblages, which provide key ecosystem functions and services. We used a worldwide dataset comprising 43 sites, where vertebrate scavenger assemblages were identified using 2,485 carcasses monitored between 1991 and 2018. First, we evaluated how scavenger richness (number of species) and diversity (Shannon diversity index) varied among seasons (cold vs. warm, wet vs. dry). Then, we studied the potential effects of human impact and a set of macroecological variables related to climatic conditions on the scavenger assemblages. Vertebrate scavenger richness ranged from species‐poor to species rich assemblages (4–30 species). Both scavenger richness and diversity also showed some seasonal variation. However, in general, climatic variables did not drive latitudinal patterns, as scavenger richness and diversity were not affected by temperature or rainfall. Rainfall seasonality slightly increased the number of species in the community, but its effect was weak. Instead, the human impact index included in our study was the main predictor of scavenger richness. Scavenger assemblages in highly human‐impacted areas sustained the smallest number of scavenger species, suggesting human activity may be overriding other macroecological processes in shaping scavenger communities. Our results highlight the effect of human impact at a global scale. As species‐rich assemblages tend to be more functional, we warn about possible reductions in ecosystem functions and the services provided by scavengers in human‐dominated landscapes in the Anthropocene.

A socioecological approach to biodiversity conservation has recently been encouraged. We examined farmer perceptions of ecosystem services provided by scavenging vertebrates in Spain through face-to-face surveys with farmers in seven large extensive livestock systems. Scavenging services (i.e., carrion consumption) was the most perceived benefit whereas the role of some scavengers as predators was the most recognized damage. The most beneficial scavengers perceived were vultures. Overall, we detected a "Dr. Jekyll and Mr. Hyde" paradox as the same species and species within the same guild can be dually perceived as beneficial or harmful. Our findings provide evidence that traditional extensive farming linked to experience-based and local ecological knowledge drives positive perceptions of scavengers and their consideration as ecosystem services providers. Research on social perceptions can contribute to the conservation of scavengers by raising awareness about the ecosystem services provided by this functional group.

.Disentangling the processes that shape the organization of ecological assemblages and its implications for species coexistence is one of the foremost challenges of ecology. Although insightful advances have recently related community composition and structure with species coexistence in mutualistic and antagonistic networks, little is known regarding other species assemblages, such as those of scavengers exploiting carrion. Here we studied seven assemblages of scavengers feeding on ungulate carcasses in mainland Spain. We used dynamical models to investigate if community composition, species richness and structure (nestedness) affect species coexistence at carcasses. Scavenging networks showed a nested pattern in sites where highly effi cient, obligate scavengers (i.e., vultures) were present and a non-nested pattern everywhere else. Griffon Vulture ( Gyps fulvus ) and certain meso-facultative mammalian scavengers (i.e., red fox, Vulpes vulpes , and stone marten, Martes foina ) were the main species contributing to nestedness. Assemblages with vultures were also the richest ones in species. Nested species-rich assemblages with vulture presence were associated with high carcass consumption rates, indicating higher interspecifi c competition at the local scale. However, the proportion of species stopping the consumption of carrion (as derived from the competitive dynamic model) stabilized at high richness and nestedness levels. This suggests that high species richness and nestedness may characterize scavenging networks that are robust to high levels of interspecifi c competition for carrion. Some facilitative interactions driven by vultures and major facultative scavengers could be behind these observations. Our fi ndings are relevant for understanding species' coexistence in highly competitive systems.

BackgroundHierarchical partitioning (HP) is an analytical method of multiple regression that identifies the most likely causal factors while alleviating multicollinearity problems. Its use is increasing in ecology and conservation by its usefulness for complementing multiple regression analysis. A public-domain software “hier.part package” has been developed for running HP in R software. Its authors highlight a “minor rounding error” for hierarchies constructed from >9 variables, however potential bias by using this module has not yet been examined. Knowing this bias is pivotal because, for example, the ranking obtained in HP is being used as a criterion for establishing priorities of conservation.Methodology/Principal FindingsUsing numerical simulations and two real examples, we assessed the robustness of this HP module in relation to the order the variables have in the analysis. Results indicated a considerable effect of the variable order on the amount of independent variance explained by predictors for models with >9 explanatory variables. For these models the nominal ranking of importance of the predictors changed with variable order, i.e. predictors declared important by its contribution in explaining the response variable frequently changed to be either most or less important with other variable orders. The probability of changing position of a variable was best explained by the difference in independent explanatory power between that variable and the previous one in the nominal ranking of importance. The lesser is this difference, the more likely is the change of position.Conclusions/SignificanceHP should be applied with caution when more than 9 explanatory variables are used to know ranking of covariate importance. The explained variance is not a useful parameter to use in models with more than 9 independent variables. The inconsistency in the results obtained by HP should be considered in future studies as well as in those already published. Some recommendations to improve the analysis with this HP module are given.