Abundance and Functional Roles, Not Richness, Govern Wood-Fall Degenerative Ecosystem Function in the Deep Sea.

AbstractBiological diversity is widely recognized as a key driver of ecosystem function, yet the mechanisms underlying biodiversity-ecosystem function (BEF) relationships in natural systems, particularly for regenerative processes, remain poorly understood. We examined the BEF relationship in deep-sea xylophagous bivalve communities using 63 experimental wood falls deployed ∼2,000 m deep in the Gulf of Mexico. This system allowed us to combine natural community assembly with controlled wood-fall deployments to examine how trophic partitioning, species dominance, and community-level properties influence total wood consumption, our metric of ecosystem function. We identified 26,324 individuals from 12 xylophagous bivalve species, which occupied complementary trophic niches, although their contributions to wood consumption varied substantially. Wood consumption increased with total abundance and, to a lesser extent, species richness, but richness effects largely reflected underlying variation in abundance. Analyses using the Price equation and species randomization approaches revealed that ecosystem function was primarily driven by a core group of abundant species, with occasional nonrandom contributions from rare species. These results indicate that in naturally assembled deep-sea communities, total abundance and key species' functional capacity outweigh species richness or phylogenetic diversity as predictors of ecosystem function, emphasizing the importance of individual species roles in shaping BEF relationships.