Is there really a drift paradox?

Abstract

1. Recent explanations for the persistence of freshwater invertebrates in the face of downstream drift (the so-called 'drift paradox') have centred largely on recolonization by upstream flight by preovipositing adults. 2. Such explanations do not cover the many important species often found in the drift that lack an aerial phase. Here we demonstrate conclusively that long-range aerial movements are not required to explain the drift paradox. 3. We show that small-scale movements along the streambed of the order of centimetres, combined with density dependence at some stage of the lifecycle, are sufficient to maintain populations over geological timescales. 4. Further, we demonstrate that the principal previous modelling study of the drift paradox was parameterized in a way that is more compatible with such small-scale movements than the long-range flight for which it was intended.