Life Table Response Research Articles

Variation in cadmium uptake, feeding rate, and life‐history effects in the gastropod Potamopyrgus antipodarum: Linking toxicant effects on individuals to the population level

A life-table response experiment was performed to investigate the effects of sediment-bound cadmium on individual life-history traits and feeding rates of four clones of Potamopyrgus antipodarum. Demographic effects were evaluated using a simple two-stage model to estimate population growth rate (lambda). Decomposition analysis was performed to investigate the contributions of each of the affected life-history traits to the effects observed on lambda, and elasticity analysis was applied to examine the relative sensitivity of lambda to changes in each of the life-history traits. Interclonal differences in tolerance to sediment-bound cadmium were statistically significant but were within an order of magnitude. There were no consistent patterns among clones in terms of which individual life-history trait was most or least sensitive to cadmium exposure. The relative performance of clones did not rank consistently across the cadmium gradient and was dependent on which trait was measured. Although lambda was most sensitive to changes in survival terms, the effects of cadmium on time to first reproduction and reproductive output were the major causes of reductions in lambda. Large percent reductions in some of the individual life-history traits were attenuated at the population level, but very small effects on population growth rate were statistically significant.

The Demographic Basis of Population Regulation in Columbian Ground Squirrels

Environmental factors influence the dynamics and regulation of biological populations through their influences on demographic variables, but demographic mechanisms of population regulation have received little attention. We investigated the demographic basis of regulation of Columbian ground squirrel (Spermophilus columbianus) populations under natural and experimentally food-supplemented conditions. Food supplementation caused substantial increases in population density, and population densities returned to pretreatment levels when the supplementation ended. Control (untreated) populations remained relatively stable throughout the study period (1981-1986). Because food resources regulated the size of the ground squirrel populations, we used life-table response experiment (LTRE) analyses to examine the demographic basis of changes in population growth rate and thus also demographic influences on population regulation. LTRE analyses of two food-manipulated populations revealed that changes in age at maturity and fertility rate of females generally made the largest contributions to observed changes in population growth rate. Thus, our results suggested that abundance of food resources regulated the size of our study populations through the effects of food resources on age at maturity and fertility rates. Our results also indicated that different demographic mechanisms can underlie population regulation under different environmental conditions, because lower juvenile survival substantially contributed to population decline, but in only one of the populations. Demographic analyses of experimental data, such as those presented here, offer a rigorous and unambiguous means to elucidate the demographic basis of population regulation and to help identify environmental factors that underlie dynamics and regulation of biological populations.

Life table responses and population dynamics of four cladoceran zooplankton during a reservoir flood

Life table responses and population dynamics of four cladoceran zooplankton during a reservoir flood

Immunogenicity of hepatitis B vaccine in oncology patients receiving chemotherapy.

We evaluated the immunogenicity and safety of three 40 micrograms doses of hepatitis B vaccine in oncology patients receiving chemotherapy. Of 76 patients screened for entry into the study, 13 (17%) already had been exposed to hepatitis B and were ineligible; 26 chose to join the study. The cumulative life-table response rate during the 12-month observation period was 70.8%; adequate immune response was linked to survival, 73% in survivors completing the study and 9% in nonsurvivors. Adverse effects were minor. We conclude that hepatitis B vaccine is safe and usually effective in inducing immunity in oncology patients younger than 60 years of age who are receiving chemotherapy.