Forum Identification of Relevant Time-scales in Non- Equilibrium Community Dynamics: Conclusions from Phytoplankton Surveys

New Zealand Journal of Ecology (1994) 18(2): 169-176 ©New Zealand Ecological Society 3) If disturbances are of intermediate frequency and/or intensity there will be repeated opportunities for the re-establishment of pioneer populations which would otherwise be outcompeted and the populations of the successful competitors could withstand the disturbance without completely taking over the community. Thus, a peak of diversity should be found at intermediate frequencies and intensities of disturbance. As a phytoplankton ecologist I cannot completely share Wilson’s interpretation of non-equilibrium explanations of the Paradox (briefly, ‘there is never time for competitive exclusion to operate’; Wilson, 1990), although I agree with his general conclusion: non-equilibrium dynamics, and non-equilibrium models (IDH and the Gradual Climate Change Model, GCC) are of particular importance. I do not deal with density dependence nor with equilibrium concepts. In pelagic environments biomass can be thousands to hundreds of thousands times more dilute than on land (Cohen, 1994). Therefore, many of the density dependent mechanisms or equilibrium concepts are difficult to interpret in hydrobiology, although there are instances where they can be of prime importance.