Abstract
Predicting the functional consequences of biodiversity loss in realistic, multitrophic communities remains a challenge. No existing biodiversity–ecosystem function study to date has simultaneously incorporated information on species traits, network topology, and extinction across multiple trophic levels, while all three factors are independently understood as critical drivers of post‐extinction network structure and function. We fill this gap by comparing the functional consequences of simulated species loss both within (monotrophic) and across (bitrophic) trophic levels, in an ecological interaction network estimated from spatially explicit field data on tropical fecal detritus producer and consumers (mammals and dung beetles). We simulated trait‐ordered beetle and mammal extinction separately (monotrophic extinction) and the coextinction of beetles following mammal loss (bitrophic extinction), according to network structure. We also compared the diversity effects of bitrophic extinction models using a standard monotrophic function (the daily production or consumption of fecal detritus) and a unique bitrophic functional metric (the proportion of daily detritus production that is consumed). We found similar mono‐ and bitrophic diversity effects, regardless of which species traits were used to drive extinctions, yet divergent predictions when different measures of function were used. The inclusion of information on network structure had little apparent effect on the qualitative relationship between diversity and function. These results contribute to our growing understanding of the functional consequences of biodiversity from real systems and underscore the importance of species traits and realistic functional metrics to assessments of the ecosystem impacts of network degradation through species loss.
Highlights
The ongoing biodiversity crisis has spurred over 20 years of investigation into the impacts of species loss on ecosystem functioning and societal well-being (Hooper et al 2012; Naeem et al 2012)
Of the 102 dung beetle species and nine mammal species originally sampled across the 100-ha grid, we estimated significant co-occurrence between a total of 15 beetle and seven mammal species, which were included in subsequent analyses (Fig. 1)
Values of body mass and abundance as well as occupancy were uncorrelated for mammals, while dung beetle abundance positively correlated with occupancy (b = 3.68, t13 = 4.77, P = 0.0004)
Summary
The ongoing biodiversity crisis has spurred over 20 years of investigation into the impacts of species loss on ecosystem functioning and societal well-being (Hooper et al 2012; Naeem et al 2012). A broad scientific consensus holds that a greater intratrophic-level diversity of genes, species, and functional traits is more efficient at capturing resources, contributes to greater biomass production (Cardinale et al 2011), nutrient cycling, and decomposition rates (Hooper et al 2012), and leads to the widely observed positive, saturating relationship between biodiversity and ecosystem functioning. The detection of clear and consistent associations between biodiversity loss and ecological function in complex natural systems remains elusive (Thebault and Loreau 2003), in part because diversity effects in real systems can be obscured by several factors.
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