Secondary production increases with species richness but decreases with species evenness of benthic invertebrates

Biodiversity is known to regulate ecosystem functioning under controlled
experimental conditions. However, the ‘real-world’ consequences of
biodiversity change remain uncertain, as biodiversity–ecosystem function
(BEF) relationships observed in nature may be influenced by other drivers.
Attempts to disentangle BEF relationships from the effects of confounding
factors have so far focused mainly on primary producers, leaving
relatively little known about the impact of changes in consumer diversity
despite ecosystems experiencing species extirpations and introductions
across trophic levels. Using data from 176 benthic invertebrate
assemblages distributed throughout the North Sea, we studied how a
fundamental ecological function – secondary production – varies in
relation to two components of biodiversity – consumer species richness and
evenness – while statistically controlling the effects of abiotic and
biotic covariates. Production was enhanced as richness increased or
evenness decreased. The relationship with evenness was attributable to its
negative covariance with the abundance of small organisms; however, the
relationship with richness could not be fully explained by other drivers.
Our study reaffirms experimental findings about the functional importance
of species richness and suggests that losing or gaining consumer species
will affect secondary production over a broad range of biodiversity (20 to
118 species) in natural ecosystems.