Impacts of detritivore diversity loss on instream decomposition are greatest in the tropics.

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.

Latitude dictates plant diversity effects on instream decomposition.

Running waters contribute substantially to global carbon fluxes through decomposition of terrestrial plant litter by aquatic microorganisms and detritivores. Diversity of this litter may influence instream decomposition globally in ways that are not yet understood. We investigated latitudinal differences in decomposition of litter mixtures of low and high functional diversity in 40 streams on 6 continents and spanning 113° of latitude. Despite important variability in our dataset, we found latitudinal differences in the effect of litter functional diversity on decomposition, which we explained as evolutionary adaptations of litter-consuming detritivores to resource availability. Specifically, a balanced diet effect appears to operate at lower latitudes versus a resource concentration effect at higher latitudes. The latitudinal pattern indicates that loss of plant functional diversity will have different consequences on carbon fluxes across the globe, with greater repercussions likely at low latitudes.

Nutrients and sediment modify the impacts of a neonicotinoid insecticide on freshwater community structure and ecosystem functioning.

Pesticides are important contributors to the global freshwater biodiversity crisis. Among pesticides, neonicotinoids are the best-selling class of agricultural insecticides and are suspected to represent significant risks to freshwater and terrestrial ecosystems worldwide. Despite growing recognition that neonicotinoid impacts may be modified by the presence of additional stressors, there is limited information about their interactions with other agricultural stressors in freshwater ecosystems. We conducted an outdoor pond-mesocosm experiment to investigate the individual and interactive effects of nutrients, fine sediment, and imidacloprid (a neonicotinoid insecticide) inputs on freshwater community structure (density, diversity, and composition of zooplankton and benthic invertebrates) and ecosystem functioning (ecosystem metabolism, primary production, and organic matter decomposition). We hypothesized antagonistic nutrient-imidacloprid, and synergistic sediment-imidacloprid interactions, affecting aquatic invertebrate communities. The three stressors had significant individual and interactive effects on pond ecosystems. The insecticide neutralized the positive effects of nutrient additions on benthic invertebrate richness and mitigated the negative effects of sediment on zooplankton communities (antagonistic interactions). Moreover, we observed compensatory responses of tolerant benthic invertebrates, which resulted in reversal interactions between sediment and imidacloprid. Furthermore, our observations suggest that imidacloprid has the potential to increase net ecosystem production at environmentally relevant concentrations. Our findings support the hypothesis that the impacts of imidacloprid may be modified by other agricultural stressors. This has important implications on a global scale, given the widespread use of these pesticides in intensive agricultural landscapes and the growing body of literature suggesting that traditional pesticide assessment frameworks, based on laboratory toxicity tests alone, may be insufficient to adequately predict effects to complex freshwater ecosystems.

Chlorpyrifos interacts with other agricultural stressors to alter stream communities in laboratory microcosms.

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.

Global distribution of a key trophic guild contrasts with common latitudinal diversity patterns.

Most hypotheses explaining the general gradient of higher diversity toward the equator are implicit or explicit about greater species packing in the tropics. However, global patterns of diversity within guilds, including trophic guilds (i.e., groups of organisms that use similar food resources), are poorly known. We explored global diversity patterns of a key trophic guild in stream ecosystems, the detritivore shredders. This was motivated by the fundamental ecological role of shredders as decomposers of leaf litter and by some records pointing to low shredder diversity and abundance in the tropics, which contrasts with diversity patterns of most major taxa for which broad-scale latitudinal patterns haven been examined. Given this evidence, we hypothesized that shredders are more abundant and diverse in temperate than in tropical streams, and that this pattern is related to the higher temperatures and lower availability of high-quality leaf litter in the tropics. Our comprehensive global survey (129 stream sites from 14 regions on six continents) corroborated the expected latitudinal pattern and showed that shredder distribution (abundance, diversity and assemblage composition) was explained by a combination of factors, including water temperature (some taxa were restricted to cool waters) and biogeography (some taxa were more diverse in particular biogeographic realms). In contrast to our hypothesis, shredder diversity was unrelated to leaf toughness, but it was inversely related to litter diversity. Our findings markedly contrast with global trends of diversity for most taxa, and with the general rule of higher consumer diversity at higher levels of resource diversity. Moreover, they highlight the emerging role of temperature in understanding global patterns of diversity, which is of great relevance in the face of projected global warming.

Clasificación trófica de insectos acuáticos en ocho quebradas protegidas de la ecorregión cafetera colombiana / Trophic classification of aquatic insects in eight sheltered streams of the Colombian coffee ecoregion / Classificação trófica de insetos aquáticos em oito córregos protegidos da ecorregião cafetera colombiana

Objetivo. Determinar la estructura trófica del ensamblaje de insectos acuáticos asociados a ocho quebradas de la ecorregión cafetera colombiana. Materiales y métodos. Se colectaron insectos acuáticos en ocho quebradas protegidas por corredores de bosque en la cuenca del río La Vieja. Los taxa encontrados fueron asignados a grupos dietarios con base en una clasificación regional, generada a partir de la revisión del contenido estomacal de los insectos, en quebradas boscosas de la cuenca del río Otún. Resultados. En total se colectaron 2019 individuos distribuidos en 73 grupos taxonómicos, de los cuales 60 fueron clasificados en grupos dietarios. Los colectores fueron el grupo más abundante (55%), seguido por los fragmentadores (31%) y los depredadores (10%). Los raspadores sólo representaron el 0,05% de la muestra y el 3,95% restante no pudo ser clasificado por falta de información. Conclusiones. La dominancia de colectores y fragmentadores refleja la importancia de la materia orgánica particulada gruesa (hojarasca), como recurso alimentario para la entomofauna. La similitud de la estructura trófica entre esta comunidad y otras estudiadas en quebradas similares, sugiere la posibilidad de un patrón común para las quebradas andinas. Se evidenció la falta de información sobre ecología trófica de insectos acuáticos tropicales; 50% de los taxa colectados no presentaron reportes de este tipo en el trópico y para el 20% no existe información en el trópico ni en la zona templada.

Objective. To determine the trophic structure of the aquatic insect assembly associated to eight streams in the Colombian coffee-growing ecoregion. Materials and methods. Aquatic insects were collected in eight forested streams located in La Vieja river basin. The taxa collected were assigned to dietary groups according to a regional classification based on the gut content analysis of aquatic insects associated to forested streams of the Otún river basin. Results. 2019 individuals belonging to 73 taxa were collected and 60 were classified into dietary groups. The most abundant group was collectors (55%), followed by shredders (31%) and predators (10%). Scrapers represented only 0.05% of the sample and the remaining 3,95% could not be classified due to lack of information. Conclusions. The dominance of collectors and shredders reveals the importance of coarse particulate organic matter (leaf litter) as a food resource for the insect fauna. Similarities between the trophic structure of this community and other communities studied in similar streams, suggest the possibility of a common pattern for Andean streams. This study evidenced the lack of knowledge on trophic ecology of tropical aquatic insects; 50% of the taxa collected did not have this kind of information for the tropics and 20% had no information neither for the tropics nor temperate zones.

Objetivo. Determinar a estrutura trófica da assembléia de insetos aquáticos associados a oito córregos da ecorregião cafetera colombiana. Materiais e métodos. Foram coletados insetos aquáticos em oito córregos protegidos por corredores florestais na bacia do rio La Vieja. Os taxa encontrados foram designados a grupos de dieta baseados numa classificação regional, gerada a partir da análise do conteúdo estomacal dos insetos, em córregos da bacia do rio Otún. Resultados. Foram coletados 2.019 indivíduos pertencentes a 73 grupos taxonômicos, dos quais 60 foram classificados em grupos alimentares. Os coletores foram o grupo mais abundante (55%), seguido por fragmentadores (31%) e predadores (10%). Os raspadores representaram apenas 0,05% da amostra e os restantes 3,95% não puderam ser classificados devido à falta de informação. Conclusões. O predomínio de coletores e fragmentadores reflete a importância da matéria orgânica particulada grossa (serrapilheira), como recurso alimentar para a fauna de insetos. A semelhança entre a estrutura trófica desta comunidade e outras estudadas em córregos similares, sugerem a possibilidade de um padrão comum para córregos andinos. Este estudo revelou a falta de informação sobre a ecologia alimentar de insetos aquáticos tropicais, 50% dos taxa coletados não apresentaram nenhum registro deste tipo no trópico, e para o 20% não há informação nem nos trópicos nem na zona temperada.