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Abstract

Several studies have revealed that beta-diversity patterns are tightly coupled to differences in habitat heterogeneity and the spatial distance among headwaters. However, addressing the relative role of these factors over time is yet to be done, particularly in those factors acting at the local scale. Here, we investigated the temporal responses of stream invertebrate communities to habitat simplification and flow variability in two stretches of a high-Andean stream: an undisturbed and a channelized stretch. Both stretches were sampled every month in two hydrologically different years: a “regular year” and a year under the influence of the La Niña phenomenon. Using four types of beta diversity (Jaccard, Percentage difference, Raup-Crick, and Gower), we tested two hypotheses: (H1) the temporal flow dynamics affect beta diversity, increasing its temporal variability. (H2) The effect of flow temporal dynamics would change because of the habitat simplification, being the temporal variability of beta diversity higher in the simplified (channelized) stretch. Contrarily to our expectations, we observed a significant mismatch between beta diversity metrics: while some indicated an increase, others indicated a decrease in the temporal variability. Nevertheless, taken together and interpreted in an ecological context, our results indicate that habitat simplification changes the temporal patterns of beta diversity. Specifically, our findings suggest that habitat simplification induces the functional homogenization of the community and diminishes the extent of change in community composition between sampling occasions. At the channelized stretch, we found that the community comprised species with adaptations to flow-related constraints primarily whose occurrence varied little among sampling occasions. These findings are relevant to Andean streams’ bioassessment, as certain programs rely on taking a ‘snapshot” to assess the ecosystem’s health or the effect of an anthropogenic stressor. Our study suggests that this snapshot may be biased if both the habitat heterogeneity and the history of high-flow events are not explicitly considered.

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