LIFE-HISTORY RESPONSES TO VARIABLE ENVIRONMENTS - STARVATION AND REPRODUCTION IN PLANKTONIC ROTIFERS

Zooplankton live in environments where resource abundance and quality can vary drastically over time. Success in nonequilibrium environments depends in part on the ability to store energy and control its alloca tion during periods of extreme food limitation or outright starvation. Starvation resistance is one measure of the ability of a species to p ersist when energy intake is less than energy expenditure. The life-hi story responses of nine species of planktonic rotifers to food depriva tion were compared using cohort life-table experiments. Allometric pat terns of energy storage and respiration rate lead to the prediction th at larger species should have greater starvation resistance than small er species. Contrary to this prediction, when rotifers were acclimated to high resource levels and starved as young adults, body mass did no t predict starvation time, Rather, there was a trade-off between survi val and reproduction during starvation. Some species did not reproduce during starvation and had high starvation times (up to 5.0 d). Other species maintained or increased fecundity relative to fed controls and had low starvation times (as low as 0.4 d). Species with more rapid s enescence when fed tended to have shorter starvation times. However, t he interspecific trade-off between survival and reproduction remained after removing the effect of control survivorship. Differences in life -history responses to starvation may be critical in determining compet itive outcome and community structure in variable environments. When a cclimated to low food levels prior to food deprivation, simulating con ditions of declining resource abundance in nature, rotifer starvation time decreased. Juveniles had longer starvation times than adults, fur ther supporting the idea that allocating energy to reproduction decrea ses starvation resistance.