Dispersal in drift-prone macroinvertebrates: a case for density-independence

1. Studies of dispersal of macroinvertebrates in streams and rivers tend to be focused on drift, whilst benthic movements are usually considered to be less important.
2. Field-enclosure experiments with the mayfly Baetis rhodani indicate that net dispersal in this species is simply a proportional loss of individuals from the benthos.
3. Neither net upstream or downstream movements exhibited evidence of density-dependence in the form of curvilinear relationships between initial and final densities.
4. The net number of animals moving upstream did not differ significantly from the net number moving downstream.
5. The probable mechanisms behind density-independent dispersal are discussed, as are the implications for our understanding of population dynamics in relation to invertebrate drift.