Search

More freshwater ecosystems are drying in response to global change thereby posing serious threat to freshwater biota and functions. The production of desiccation-resistant forms is an important adaptation that helps maintain biodiversity in temporary freshwaters by buffering communities from drying, but its potential to mitigate the negative effects of drying in freshwater ecosystems could vary greatly across regions and ecosystem types. We explored this context dependency by quantifying the potential contribution of desiccation-resistance forms to invertebrate community recovery across levels of regional drying prevalence (defined as the occurrence of drying events in freshwaters in a given region) and ecosystem types (lentic, lotic) in temporary neotropical freshwaters. We first predicted that regional drying prevalence influences the selection of species with desiccation-resistant forms from the regional species pools and thus increases the ability of communities to recover from drying. Second, we predicted lentic freshwaters harbor higher proportions of species with desiccation-resistant forms compared to lotic, in response to contrasted hydrologic connectivity. To test these predictions, we used natural experiments to quantify the contribution of desiccation-resistant forms to benthic invertebrate community recovery in nine intermittent streams and six geographically isolated temporary wetlands from three Bolivian regions differing in drying prevalence. The contribution of desiccation-resistant forms to community recovery was highest where regional drying prevalence was high, suggesting the species pool was adapted to regional disturbance regimes. The contribution of desiccation-resistant forms to community recovery was lower in streams than in wetlands, emphasizing the importance of hydrologic connectivity and associated recolonization processes from in-stream refuges to recovery in lotic systems. In all regions, the majority of functional traits were present in desiccation-resistant taxa indicating this adaptation may help maintain ecosystem functions by buffering communities from the loss of functional traits. Accounting for regional context and hydrologic connectivity in community recovery processes following drying can help refine predictions of freshwater biodiversity response to global change. [ABSTRACT FROM AUTHOR]

Abstract: We developed and validated a single multimetric index based on predictive models that could evaluate anthropogenic disturbances in streams of three disparate ecoregions of Bolivia. To do so, we examined 45 candidate metrics reflecting different aspects of macroinvertebrate assemblage structure and function gleaned from available literature and for their potential to indicate degradation. More importantly, we integrated functional trait metrics to improve the sensitivity of our index. To quantify possible deviation from reference conditions, we first established and validated statistical models describing metric responses to natural environmental differences in the absence of any significant anthropogenic disturbance. We considered that the residual distributions of these models described the response range of each metric, independently of natural environmental influence. After testing the sensitivity of these residuals to a gradient of anthropogenic disturbance, we retained eight metrics that were used in the final assemblage index, four metrics based on richness and composition and four metrics based on biological traits. Our index performed well in discriminating between reference and disturbed sites, giving a significant negative linear response to a gradient of physical and chemical anthropogenic disturbances. After employing a probability survey design and sampling a relatively small number of sites throughout all major ecoregions of Bolivia, we believe our methodology can be used to develop a monitoring tool to evaluate status and trends in biological condition for streams of the entire country despite its complex and heterogeneous geology and climate. [ABSTRACT FROM AUTHOR]

We developed a preliminary macroinvertebrate-based multi-metric index to assess streams biotic condition in the Upper Isiboro-Sécure basin (Bolivia). To do so we used eight local habitat descriptors and twelve metrics describing the structure and function of macroinvertebrate assemblages from 38 reference and 29 disturbed sites. Stepwise multiple linear regression procedures were first applied using the reference data to elaborate models describing metrics response to natural environmental in the absence of any significant disturbance. In a second step we used residuals distribution of each of the twelve models to select the most effective metrics in discriminating between reference and disturbed sites. These metrics were: number of Ephemeroptera, Plecoptera and Trichoptera taxa (EPT), abundance of EPT, relative abundance of EPT, abundance of Chironomidae and relative abundance of Chironomidae. Finally, after converting residual values of these 5 remaining metrics into probabilities, we added values to obtain a final index score and interpreted this score as excellent, good, moderate, poor or very poor. Our final multi-metric index distinguished well between natural and human-induced variation in biological condition and showed a significant negative response to a gradient of disturbances. This type of approach could be used in the near future to develop a nation wide index by increasing regional-scale monitoring. [ABSTRACT FROM AUTHOR]