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Plant dispersal traits determine hydrochorous species tolerance to connectivity loss at the landscape scale
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International audience. Aims: Landscape fragmentation has strong negative consequences on biodiversity. In networks of linear elements, connectivity loss results in a decreased length of connected elements and increased potential barriers, directly impacting the ability of plants to disperse. However, species vary in their tolerance to connectivity loss, likely due to differences in dispersal strategies. We investigated whether species tolerance to decreased ditch network connectivity is determined by seed traits. We selected, as a case study, water-dispersed plant species in a ditch network.Location: Ditch network in an intensive agricultural area in northern France.Methods: We selected 27 sites of 500 m 9 500 m, where we calculated connectivity indices based on the length of connected ditches, intersections and culvert number. For each parameter, we calculated plant tolerance levels by analysing species changes in occurrence in response to change in connectivity values. Concurrently, we measured in laboratory conditions five seed traits involved in plant movement and establishment in standing aquatic systems and analysed their explanatory power in plant tolerance to fragmentation.Results: All traits were significantly related to at least one component of ditch network connectivity. We interpreted the following two strategies in plant tolerance to connectivity loss from the results: (1) in networks where the connected network length was short, plants displayed short-distance dispersal with less efficient sexual reproduction, probably in favour of local vegetative multiplication; and (2) in networks with a high density of culverts or intersections, plants displayed seeds with reduced local retention, where seeds had the capacity to overcome long and frequent trapping events. In highly branched networks, plants also exhibited higher germination rates, promoting seed establishment when trapped along the banks. Seed capacity to be dispersed by wind at the water surface was only a marginal factor in plant tolerance to fragmentation.Conclusions: Connectivity loss acted as a filter on species seed traits. The results of our study offer an enhanced understanding of plant dispersal in fragmented standing aquatic networks and emphasize the importance of developing functional approaches in landscape studies.
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