DOI: 10.5061/dryad.15dv41nz3
title: Diversity mediates the responses of invertebrate density to duration and frequency of rivers’ annual drying regime

description: Predicting the impacts of global change on highly dynamic ecosystems
 requires a better understanding of how communities respond to disturbance
 duration, frequency and timing. Intermittent rivers and ephemeral streams
 are dynamic ecosystems that are recognized as the most common fluvial
 ecosystem globally. The complexity of the drying process can give rise to
 different annual and antecedent hydrological conditions, but their effect
 on aquatic communities remains unclear. Here, using aquatic invertebrates
 from 33 streams across a flow-intermittence gradient, we assessed how
 annual (drying duration and frequency) and recent drying characteristics
 (duration of the last dry period and flowing duration since the last
 rewetting) affect the density and diversity metrics of communities and
 trophic groups while controlling for other key abiotic factors (dissolved
 oxygen and altitude). We characterized invertebrate communities using
 taxonomy and functional traits to capture biological features that
 increase vulnerability to drying. In addition, using structural equation
 modelling (SEM), we evaluated pathways by which drying characteristics
 directly impact invertebrate density and whether diversity indirectly
 mediates such relationships. We show that drying frequency drove
 reductions in diversity at the community level and within trophic groups,
 whereas both the drying duration and frequency had a negative influence on
 density metrics. Reductions in taxonomic richness were linked to increased
 annual drying duration, whereas functional diversity declined in response
 to annual drying frequency. Filterer, predator and shredder trophic groups
 exhibited the strongest negative responses to drying. Recent drying
 characteristics had a minor effect on density and diversity metrics. Our
 SEM results demonstrated that diversity mediates the negative impacts of
 annual drying duration and frequency on invertebrate density through
 reductions in their taxonomic richness and functional diversity. Our
 results underscore the importance of considering multiple drying
 characteristics together with the interdependence of density and diversity
 to better anticipate drying responses in freshwater ecosystems.
description: In this paper, using aquatic invertebrates from 33 streams across
 a flow-intermittence gradient, we assessed how annual (drying duration and
 frequency) and recent drying characteristics (duration of the last dry
 period and flowing duration since the last rewetting) affect the density
 and diversity metrics of communities and trophic groups while controlling
 for other key abiotic factors (dissolved oxygen and altitude). We
 characterized invertebrate communities using taxonomy and functional
 traits to capture biological features that increase vulnerability to
 drying. In addition, using structural equation modelling (SEM), we
 evaluated pathways by which drying characteristics directly impact
 invertebrate density and whether diversity indirectly mediates such
 relationships. This code re-creates analysis of the
 field dataset.