title: Effect of interaction between density dependence and toxicant exposure on population growth rate of the potworm Enchytraeus doerjesi.
abstract: Laboratory cultures of the potworm Enchytreaus doerjesi were exposed to zinc-contaminated soil at nominal concentrations 0, 75, 150, 300, or 600 mg Zn/kg dry weight for four weeks (one generation) at five different initial densities (5, 10, 20, 40, or 80 individuals per 20 g soil). The final culture numbers and the instantaneous population growth rate, r(i) were used as measures of culture response to both factors. In all treatments, the number of individuals increased during the experiment; thus, all the cultures exhibited positive r(i) values. The population growth rates decreased significantly with increasing Zn concentration and were also affected by the initial density. However, the latter effect was nonlinear and the initial density of 20 individuals resulted in the highest r(i) values throughout the whole range of Zn concentrations tested, while the lowest population growth rates were recorded for the highest initial density. Significant interaction between zinc toxicity and population size was found for the two lowest initial densities, where synergistic effects were noted. No effect of density on zinc toxicity was found at initial densities of 20 to 80 individuals, most probably because the animals were fed ad libitum and thus were not food limited.
authors.affiliation: Department of Ecotoxicology, Institute of Environmental Sciences, Jagiellonian University, ul. Gronostajowa 7, 30-387 Kraków, Poland. uxkramar@cyf-kr.edu.pl
authors.forename: Paulina
authors.initials: P
authors.lastname: Kramarz
authors.forename: Malgorzata
authors.initials: M
authors.lastname: Zwolak
authors.forename: Ryszard
authors.initials: R
authors.lastname: Laskowski
mesh_terms: D000818:Animals; D009835:Oligochaeta / Q000187:drug effects* / Q000254:growth & development; D011156:Population Density; D011158:Population Growth; D012989:Soil Pollutants / Q000633:toxicity*; D015032:Zinc / Q000633:toxicity*
chemical_list: D012989:Soil Pollutants; D015032:Zinc