Abstract
Biodiversity-ecosystem function (BEF) relationships have been a major topic since the 1990’s, increasing in importance due to sustainability and extinction crises. However, the shapes of BEF relationships are not easily correlated with habitat, taxa, or diversity. We propose and test two predictors for BEF relationship shapes: 1) individual species growth rates (as indicative of coexistence and competitive abilities) and functional performance, and 2) BEF shapes of specific functions underlying a broader function. Darlingtonia californica is a carnivorous plant with modified leaves housing bacteria that contribute toward insect prey degradation and nitrogen provision. We isolated 14 distinct bacterial strains from fluid obtained from D. californica‘s modified leaves. We grew the isolates in monoculture and mixed culture and evaluated each culture using degradation assays, and protein, ammonia, nitrate, chitinase, and protease quantification assays. We ask three specific questions related to our two proposed predictors of BEF shapes: 1) can we predict the function and assembly of a community based on individual species functions? 2) does a species function and growth rate correlate? 3) does degradation overall correlate with other functions in the metabolic processing of nitrogen? We found that increased degradative function was correlated with decreased species growth rates, highly functioning mixed cultures could result from both highly functioning isolates or moderately functioning isolates, and degradative function did not rely on nitrogen processing pathways. Our analysis suggests that BEF relationships present a metabolic trade-off between degradative function and bacterial division rates, but not with nitrogen processing. Additionally, while species with strong functional contributions can also be good competitors, they may also be poor competitors or play complex roles in community assembly.