Abstract

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.

Highlights

  • Community structure is a key determinant of ecosystem functioning (Hooper et al 2005, Bannar-Martin et al 2017), biodiversity conservation (Tylianakis et al 2010) and community stability (Landi et al 2018)

  • We used the 20 km scale for all our analyses. Both rWNODF and rNODF were related to the weight of the monitored carcasses, but none of the metrics were related to the spatial autocovariance or the presence of obligate scavengers (Fig. 3, Supplementary material Appendix 2 Table A2.2)

  • When we evaluated the effect of the covariates associated to network properties, both nestedness metrics were related to network connectance and matrix size

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Summary

Introduction

Community structure is a key determinant of ecosystem functioning (Hooper et al 2005, Bannar-Martin et al 2017), biodiversity conservation (Tylianakis et al 2010) and community stability (Landi et al 2018). Disentangling the factors affecting the organization of ecological communities is essential for understanding ecosystem functioning and prioritizing conservation efforts. Networks have been widely used to compare the structure of ecological communities at the global scale (Dalsgaard et al 2013, Schleuning et al 2014, Song et al 2017), and several studies have revealed that the structure of ecological networks may be affected by global-scale factors such as current and past climate (Martín-González et al 2015, Sebastián-González et al 2015, Song et al 2017, Albouy et al 2019, Mendoza and Araújo 2019), or human impact (Sebastián-González et al 2015, Mendoza and Araújo 2019). The effect of each factor is contingent upon the type of ecological assemblage under study (e.g. it is different for seed-dispersal and for pollination assemblages, Sebastián-González et al 2015, Song et al 2017). It is important to identify the processes driving these large-scale patterns for different types of assemblages

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