decline and functional in communities

Hydrological intermittency drives diversity decline and in Abstract: Over the last decades, the combined effects of global climate changes and severe land use modifications have been exacerbating river hydrological alterations and habitat fragmentation in many Mediterranean rivers. This trend is predicted to intensify, with expected significant impacts on taxonomic and functional diversity of benthic communities in the next future. The present research aims at investigating the long-term combined effects of flow intermittency, climate and land use changes on benthic diatom communities, by analysing data collected over 11 years in Mediterranean streams of the NW-Italy. We demonstrated that the ongoing global changes and local environmental pressures determined a significant decline in diatom species diversity at both local and regional scales. More in detail, flow intermittency affected both diatom diversity and life history traits, with communities of intermittent reaches taxonomically and functionally different and less heterogeneous than assemblages characterizing perennial ones. Communities inhabiting intermittent sections showed high percentages of small, mainly stalked and pioneer taxa belonging to the low profile guild, highlighting the strong environmental pressure exerted by the hydrological alterations. Conversely taxa colonizing permanent reaches were bigger, belonging to the high profile guild and able to produce colonies, denoting environmental stability. The results we obtained could be ascribed to the long-term effects of drying in Mediterranean streams and, as first in the literature, we highlight that diatoms are able to provide long-terms responses to environmental changes caused by water stress, when hydrological disturbance is persistent. She works on benthic diatoms in Mediterranean intermittent streams She works on diatoms with a focus on functional traits and intermittent streams ecological guilds life she on diatoms a focus on ecological guilds and life forms to the combined effects of the ongoing climate change and local environmental pressures. We highlighted a significant decline of diatom species at both local and regional scales due to the extinction of rare species and the increase of few dominant species in intermittent reaches. When considering community composition, we demonstrated a taxonomic change and a functional homogenization of the diatom communities inhabiting intermittent reaches, which were dominated by low profile, pioneer taxa, typical of disturbed conditions. Although flow intermittency is part of the natural hydrological cycle of Mediterranean rivers, its climate- and land use-driven exacerbation represents a threat to diatom benthic communities. These results are extremely alarming considering that Mediterranean rivers represent a biodiversity hotspot and provide fundamental ecosystem services worldwide. ABSTRACT Over the last decades, the combined effects of global climate changes and severe land use modifications have been 18 exacerbating river hydrological alterations and habitat fragmentation in many Mediterranean rivers. This trend is 19 predicted to intensify, with expected significant impacts on taxonomic and functional diversity of benthic communities 20 in the next future. 21 The present research aims at investigating the long-term combined effects of flow intermittency, climate and land use 22 changes on benthic diatom communities, by analysing data collected over 11 years in Mediterranean streams of the 23 NW-Italy. We demonstrated that the ongoing global changes and local environmental pressures determined a significant decline in 25 diatom species diversity at both local and regional scales. More in detail, flow intermittency affected both diatom 26 diversity and life history traits, with communities of intermittent reaches taxonomically and functionally different and 27 less heterogeneous than assemblages characterizing perennial ones. Communities inhabiting intermittent sections 28 showed high percentages of small, mainly stalked and pioneer taxa belonging to the low profile guild, highlighting the 29 strong environmental pressure exerted by the hydrological alterations. Conversely taxa colonizing permanent reaches 30 were bigger, belonging to the high profile guild and able to produce colonies, denoting environmental stability. 31 The results we obtained could be ascribed to the long-term effects of drying in Mediterranean streams and, as first in the literature, we highlight that diatoms are able to provide long-terms responses to environmental changes caused by water stress, when hydrological disturbance is persistent. homogeneous ( F 1,143 = 9.70, P = 0.002) those PER reaches. explained in light of three main factors: i) the intensity of the flow intermittency; ii) the diatom community composition; and iii) the combined effect of the land