Search

The relationship between detritivore diversity and decomposition can provide information on how biogeochemical cycles are affected by ongoing rates of extinction, but such evidence has come mostly from local studies and microcosm experiments. We conducted a globally distributed experiment (38 streams across 23 countries in 6 continents) using standardised methods to test the hypothesis that detritivore diversity enhances litter decomposition in streams, to establish the role of other characteristics of detritivore assemblages (abundance, biomass and body size), and to determine how patterns vary across realms, biomes and climates. We observed a positive relationship between diversity and decomposition, strongest in tropical areas, and a key role of abundance and biomass at higher latitudes. Our results suggest that litter decomposition might be altered by detritivore extinctions, particularly in tropical areas, where detritivore diversity is already relatively low and some environmental stressors particularly prevalent.

Chlorpyrifos is one of the most widely used agricultural insecticides in the world, but to date there is limited empirical information about its potential to interact with other common agricultural stressors. We conducted a 15-d, community-level, microcosm experiment evaluating individual and combined effects of chlorpyrifos, nutrient enrichment, and sedimentation on stream invertebrate communities (abundance, biomass, richness, size structure, composition) and ecosystem processes (primary productivity and leaf decomposition). We found that sedimentation was the most detrimental stressor, with significant negative impacts on most invertebrate community and ecosystem function variables. Even though chlorpyrifos did not cause significant invertebrate mortality in the microcosms, it still altered ecosystem function by lowering leaf decomposition rates, probably through sublethal inhibition of invertebrate shredders. Furthermore, we observed a significant reversal interaction between chlorpyrifos and sediment for small-sized invertebrates collected in gravel (abundance in sediment × insecticide microcosms was 2.4 times lower than predicted by additivity), as well as an antagonistic interaction with nutrients on invertebrate richness in the same microhabitat (richness in nutrient × insecticide microcosms was 1.6 times higher than predicted by additivity). Our results suggest that chlorpyrifos has the potential to alter freshwater ecosystem function and interact non-additively with other common agricultural stressors. These findings are in keeping with a growing body of research highlighting that multiple stressor interactions and ecosystem processes should be considered when evaluating the impacts of organic toxicants on freshwater ecosystems., (© 2017 by the Ecological Society of America.)

Recent evidence shows that in lotic, physically‐dominated ecosystems like large rivers, zooplankton can develop spatially structured assemblages and fulfill functionally important roles. While refuting the long‐standing notion that riverine zooplankton communities are numerically depauperate and spatially homogeneous, this also shows that the importance of abiotic and biotic drivers and the consistency of ecological patterns are still poorly understood for these communities.We collected zooplankton along 300 km of the Illinois River for 5 years to test the influence of a suite of biotic and abiotic variables on zooplankton density, biomass, and diversity. We hypothesized abiotic variables such as temperature, turbidity, and velocity would be predominant predictors, with biotic variables like planktivory becoming important when physical factors do not constrain them.Results showed basin‐wide declines in zooplankton taxonomic richness as planktivory from the invading silver carp (Hypophthalmichthysmolitrix) increased. In contrast, density and biomass were explained by abiotic factors at the basin scale, with velocity, turbidity, and pH driving biomass and velocity driving density. We also found that both the driving factors and the plankton responses varied among the upper, middle, and lower sections of the Illinois River.We conclude that while zooplankton communities of the Illinois River are highly structured in space, the driving forces behind their distribution patterns are not simple. Instead, there is a complex spatio‐temporal template of biological, chemical, and hydraulic factors shaping these communities in the Illinois River. Along with emphasizing the importance of spatial heterogeneity in large river ecosystems, these results also support a growing view that invasive species interactions can supersede the well‐established role of abiotic factors in explaining global freshwater diversity losses. This also highlights the importance of including long‐term zooplankton sampling in ecological monitoring programs in diverse and productive large river systems like the Illinois. [ABSTRACT FROM AUTHOR]