Drivers of scavenging efficiency and stability at vertebrate scavenger assemblages in Nepal

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Aishwarya Bhattacharjee, Biology, Queens College, City University of New York, NY, Dikpal Karmacharya, Ornithological Research and Conservation, Global Primate Network, Kathmandu, Nepal, Rishi Baral, Annapurna Conservation Area Project, National Trust for Nature Conservation, Pokhara, Nepal, José Antonio Sánchez Zapata, Department of Applied Biology, Universidad Miguel Hernández, Elche, Spain and José D. Anadón, Instituto Pirenaico de Ecología, Zaragoza, Spain; Biology, Queens College, New York City, NY

Background/Question/Methods
Vertebrate scavengers support critical ecosystem functions and services through the consumption of decaying organic material in the environment (i.e. nutrient recycling). Biodiversity-ecosystem functioning (BEF) research offers a general consensus that increased biodiversity enhances or maintains ecosystem functions, which facilitates the delivery of ecosystem services that can benefit human well being. However, BEF research largely focuses on plant and invertebrate communities, and rarely considers the ecological processes and associated ecosystem stability driven by large terrestrial vertebrates. Across a north-south landscape in Central Nepal, we monitored 42 scavenging trials with motion-triggered remote cameras between 2018-2019 to collect data on vertebrate scavenger diversity and carcass consumption. We used Gower’s distance and principal coordinate analysis to calculate trait-based indices based on recorded species. We tested three hypotheses to consider the relative effects of taxonomic diversity, functional traits, and functional diversity on two different processes that drive scavenging efficiency: carrion detection time and carrion consumption rate. Additionally, we investigate whether a positive diversity-stability relationship applies in the case of scavenging as an ecosystem function, by comparing measures of scavenging efficiency between assemblages partitioned by measures of low, medium and high biodiversity.
Results/Conclusions
From our set of a priori hypotheses, we find that different combinations of species and trait-based indices explain two underlying processes of scavenging efficiency in this guild. Biomass and functional richness influence scavengers’ capacity for efficient carcass detection, whereas biomass and key dominant traits (i.e. proportion of carnivorous diets) drive consumption rate. We identify vultures as key species that account for the combination of biomass and proportion of carnivores in this system. We also present evidence of a positive diversity-stability relationship, with abundance and functional richness reducing variation in carcass consumption at assemblages. This preliminary investigation on diversity-stability relationships in a scavenging guild provides a unique insight towards the factors that may enhance the resilience of their ecosystem functions. As a first, our study documents scavenging function, and comparatively examines the related contributions of taxonomic and functional diversity, in a distinct landscape-gradient in South Asia. Overall, we shed light on an understudied functional guild in BEF research and contribute to a deeper understanding of the mechanisms that maintain function and stability for a critical functional guild of terrestrial vertebrates, including species of significant conservation concern.