Instantaneous Population Growth Rate Research Articles

Effects of Nitrate and Phosphate Limitation on Cyclostat Growth of Two Freshwater Diatoms

The effects of N and P limitation on cell division and on cellular contents of limiting and non-limiting nutrients were examined in cyclostat cultures of the freshwater diatoms Asterionella formosa and Fragilaria crotonensis. Nutrient-limited cell cycles of both species were readily entrained by a 14 h/10 h light/dark cycle. In F. crotonensis, the maxima relative to the onset of the light phase of the photocycle occurred at approximately − 1 to +1 h for cell division, +11 to 13 h for cell N, and +21 to 23 h for cell P. In A. formosa the maxima occurred at approximately +3 to 10 h for cell division and +2 to 4 h for cell N and cell P. Changes in culture dilution rate (integrated growth) and in the type of nutrient limiting growth did not significantly alter these times for either species. The cell-number oscillations can be explained by a simple exponential function for the instantaneous population growth rate, which occurs after a single modal transition time τ, which is characteristic for each species. The consistency of phase relations between N and P limitations and culture dilution rates suggests that the temporal organization for events within the cell cycle of each organism is independent of the nutrient-limited status of the cell populations.

Jalysus spinosus: 1 Instantaneous Rate of Population Growth at Different Temperatures and Factors Influencing the Success of Storage2

The spined stilt bug, Jalysus spinosus (Say), an egg and aphid predator, had the highest instantaneous rate of population growth (r) (0.116) at 29.5° and 32.3°C, but the total number of eggs laid was less at the higher temperature. The period of nymphal development ranged from ca. 12 days at high temperatures to more than 50 days at 15.9°C. Fed stilt bugs survived better at cool temperatures than starved stilt bugs and could be successfully stored for up to 130 days. Stilt bugs in diapause tolerated starvation bettter than those not in diapause.

Effect of food type on the acute and chronic toxicity of copper to Daphnia magna

SUMMARY. Daphnia magna was maintained on two diets and exposed to acute and chronic copper stresses. Animals fed vitamin‐enriched algae were less sensitive to a chronic copper stress than animals fed a trout‐granule diet. This conclusion is based on the responses of cohorts as measured by survival, mean brood size and r, the instantaneous rate of population growth. Application factors were also significantly different for animals reared on the two foods (0.47 for algal‐fed animals, 0.12 for animals reared on trout‐granules). In contrast to chronic toxicity, 72 h LC50 values were not significantly different for animals maintained on the two foods. This suggests that the mechanism of toxic action is different for acute and chronic toxicity and that, if so, the ratio between chronic and acute toxicity would not be a constant under different environmental conditions.

An Analytic Model for Description of Temperature Dependent Rate Phenomena in Arthropods 1

A new description of temperature-dependent, rate phenomena was deduced to describe developmental time and ovipositional data for the McDaniel spider mite, Tetranychus mcdanieli McGregor. The derived equation accounted for asymmetry about optimum temperature and was of particular utility for description of systems operating at or above optimum temperatures. Ovipositional and developmental rate functions were used in a temperature-driven, discrete-time, simulation model describing McDaniel spider mite population dynamics. Temperature dependence of the instantaneous population growth rate was determined by fitting the derived rate-temperature function to data generated through simulation at various fixed temperatures. The functional relationship of important population parameters to temperature provided the mechanism for inclusion of phenological effects on mite populations in a synoptic apple pest management model. Two derived functions were fit to several published rate-temperature data sets. Adequacy of description (as indicated by R2 values) indicated general applicability of both functions for description of temperature-controlled, biological processes. Further, it was concluded that the singular perturbation method of matched asymptotes has potentially wide application in ecology, and an Appendix detailing the application of this method is included.

Acute and Chronic Toxicity of Copper to Four Species of Daphnia

The sensitivity of Daphnia magna, D. pulex, D. parvula, and D. ambigua to acute and chronic copper stresses was evaluated under laboratory conditions. Using 72-h LC50 values as the index, the two larger species were significantly less sensitive to an acute copper stress than were the two smaller species. All four species exhibited reductions in survival at Cu concentrations > 40 μg/liter. Daphnia magna exhibited a decrease in the instantaneous rate of population growth (r) at Cu concentrations > 60 μg/liter; r decreased in the other three species at concentrations > 40 μg/liter. Daphnia ambigua produced significantly smaller broods at Cu concentrations > 40 μg/liter, whereas mean bood sizes did not decrease in D. pulex and D. parvula until the Cu concentration exceeded 60 μg/liter. Daphnia magna did not exhibit any reduction in mean brood size related to copper concentration; reproduction in this latter species was inhibited only as a consequence of females dying before they reached reproductive maturity at concentrations > 80 μg/liter. Application factors, based on the highest concentration that did not reduce survival and 72-h LC50 values, ranged from 0.47 to 0.59 and were not significantly different for the four species. We concluded that the four species do not differ in their susceptibility to a chronic copper stress.