The Millennium Ecosystem Assessment was the first world-wide interdisciplinary research programme aiming to define an integrative framework of the relationships between ecosystem processes and human needs and well-being (MEA 2005). Including ecosystem services in conservation assessment would improve the societal relevance of biodiversity conservation and should then better support their translation into effective conservation actions (Egoh et al. 2007). In this context, the role of the scientific community is to deliver the knowledge and tools necessary to assess the return of services on investments in nature (Daily & Matson 2008; Daily et al. 2009). Although the need to protect ecological processes is clearly illustrated by the ecosystem service framework, turning the conclusions from the MEA into conservation actions remains challenging (Kremen et al. 2008). Beyond the need for scientific research on ecological processes, interdisciplinary studies are required because the success or failure of conservation efforts mostly relies on societal choices.
‘Scavengers provide one of the most important yet underappreciated and little-studied ecosystem services of any avian group’ (Şekercioğlu 2006). Vultures are specialized in scavenging (Ruxton & Houston 2004), and they have been identified as providers of ecosystem services (Şekercioğlu, Daily & Ehrlich 2004; Şekercioğlu 2006; Markandya et al. 2008). Recycling carcasses from livestock and wildlife, scavengers maintain energy flows higher in food webs (DeVault, Rhodes & Shivik 2003; Wilson & Wolkovich 2011). Vultures lead other scavengers to dead animals (Houston 1979) and limit the spread of diseases and of undesirable mammalian scavengers (Prakash et al. 2003). However, several vulture species are threatened world-wide and their populations are decreasing (Şekercioğlu 2006; IUCN 2010). Although vultures provide multiple services through carcass disposal, human practices have reduced the quantity and the safety of their trophic resources. Reduction in livestock mortality through veterinary progress, changes in agro-pastoral practices (Thiollay 2006; Olea & Mateo-Tomás 2009) or legislation dealing with organic waste and imposing their systematic destruction (Tella 2001; Camiña 2004) all reduce the quantity of food available for vultures. Moreover, livestock sanitary treatments (Oaks et al. 2004; Blanco et al. 2009) or pesticides (Virani et al. 2011) can result in vulture poisoning.
Supplementary feeding through the artificial provisioning of sites has been identified as a useful tool for scavenger conservation (Friedman & Mundy 1984; Oro et al. 2008), and it can be considered relevant especially for urgent and middle-term management (Azmanis 2009). However, in farming areas, feeding stations directly managed by farmers, called light feeding stations, seem to be more relevant for long-term vulture conservation (Dupont et al. 2011). In France, the first experimental trials of light feeding stations agreed by sanitary authorities have been conducted in the Grands Causses region. Thanks to the success of this experimental design, French law has institutionalized light feeding stations in 1998. Although European directive 142/2011/CE authorized the creation of light feeding stations in 2011, not all countries enforced this regulation. Since the ‘mad cow’ crisis caused by bovine spongiform encephalopathy in cattle, carcass disposal has been undertaken by private companies in many European countries. However, using vultures represents an alternative, sustainable ecological service. The viability of vulture populations, sanitary considerations and air quality as well as monetary costs are all influenced by carcass disposal management and farmer choices. With regard to the ecological service, carcasses made available for vultures can be considered as the demand for this ecological service, and the ability of vultures to eliminate carcasses as the offer of the service. The correspondence between the offer and the demand will affect the consequences of carcass disposal management. From an interdisciplinary framework based on an example of this socio-ecological system in the Grands Causses region (southern France), we aimed to (i) identify the decision criteria that lead farmers to use either the ecological service or the industrial service through interviews and (ii) assess the consequences of various carcass disposal strategies resulting from farmer decision criteria through agent-based modelling.