Résumé
Global analyses of biodiversity consistently reveal recurrent patterns of
species distributions worldwide. However, unveiling the specific
mechanisms behind those patterns remains logistically challenging, yet
necessary for reliable biodiversity forecasts. Here, we combine theory and
experiments to investigate the processes underlying spatial biodiversity
patterns in dendritic, river-like landscapes, iconic examples of highly
threatened ecosystems. We used geometric scaling properties, common to all
rivers, to show that the distribution of biodiversity in these landscapes
fundamentally depends on how ecological selection is modulated across
space: while uniform ecological selection across the network leads to
higher diversity in downstream confluences, this pattern can be inverted
by disturbances when population turnover (i.e., local mortality) is higher
upstream than downstream. Higher turnover in small headwater patches can
slow down ecological selection, increasing local diversity in comparison
to large downstream confluences. Our results show that
disturbance-mediated slowing down of competitive exclusion can generate a
specific transient signature in terms of biodiversity distribution when
applied over a spatial gradient of disturbance, which is a common feature
of many river landscapes.