Resonance inflates carrying capacity in protist populations with periodic resource pulses

Resonance is an interaction between extrinsic environmental variability and intrinsic population processes that can raise population mean density or amplify environmental fluctuations in systems with periodic environmental fluctuations. This study empirically demonstrates significant effects on population dynamics from resonance and describes the conditions under which they occur. In a laboratory microcosm experiment with the ciliate protist Colpidium striatum, resources were periodically alternated between high and low concentrations at different frequencies., Resonance raised the mean population density of rapidly fluctuating treatments by 21% compared to a constant control run at the average nutrient concentration, and eventually approximated the mean density of the highest nutrient control. The resonant resource perturbations occurred on a time scale intermediate to the reproduction and starvation rates of the organisms. It is likely that metabolic nonlinearities in those reproductive and starvation responses interacted with the periodic resources fluctuations of intermediate frequency to produce the population boost through the cumulative Storage of resources in the cells of the protists. The populations also showed a frequency threshold effect in the translation of environmental variability into population variability. The patterns of population abundance and variability observed in this experiment indicate that resonance between intrinsic and extrinsic processes may be an important factor to consider in population dynamics.