Why do rotifer populations
present a typical sigmoid growth curve?
T. Yoshinaga, A. Hagiwara, K. Tsukamoto-2001
Hydrobiologia, 446/447: 99-105
Abstract:
To determine the underlying processes to population growth in the rotifer
Brachionus plicatilis, we conducted an experiment using 1.5 ml cultures for
70 days. All individuals were transferred daily to culture media containing
algae, and the number of individuals, clutch sizes and number of deaths were
counted. The population dynamics showed a typical sigmoid curve. The
population density increased exponentially from 10 to 682 individuals during
the first 7 days (exponential growth phase), and gradually up to about 1500
individuals during the next 30 days (post-exponential growth phase). The
population density then remained at a constant level with small fluctuations
during the rest of the experimental period (stationary phase). Mortalities
appeared from the post-exponential growth phase and were almost constant at
about 2% throughout the experimental period. The clutch size decreased from
5 to 1 during the first 5 days, and afterwards females laid only one egg
each. The proportion of non-reproductive females increased from 30%
(exponential growth phase) to 80% (post-exponential growth phase) to 90%
(stationary phase). These results suggest that the exponential growth phase
resulted from the imbalance between a high birth rate and a low death rate,
while the stationary phase was maintained by the compensation between low
birth and death rates.