Joint effects of density dependence and toxicant exposure on Drosophila melanogaster populations.
Risk assessment of environmental contaminants is usually based on experiments on well-fed individuals held at low population densities. However, field populations are often subject to resource limitation. Individuals who are already stressed by crowding or food limitation may show greater susceptibility to toxicants. But density dependence could also reduce population-level impacts as toxicant-related mortalities may reduce competition for resources. This study examines the joint effects of toxicants and food availability on populations of Drosophila melanogaster. The interactions between the effects of food limitation and toxicant stress were dose dependent and strongly influenced by toxicity mechanisms. In food-limited conditions, a compensatory effect often occurred, with toxicant exposure having a lower proportional impact than at higher food levels. This provides further evidence that density-dependent population processes can produce an assimilative capacity for the effects of toxicants. But synergistic food-toxicant effects were also common and the interaction often switched between synergistic and compensatory at different toxicant concentrations and food supplies. There is no simple "less-than-additive", "additive" or "more-than-additive" relationship between density and toxicant effects, even for a single toxicant.
Centre for Ecology, Evolution and Conservation, University of East Anglia, Norwich NR4 7TJ, UK. guiyue2002@yahoo.com.cn
Yue
Y
Gui
Alastair
A
Grant
D000818:Animals; D002104:Cadmium / Q000633:toxicity*; D004132:Diflubenzuron / Q000633:toxicity*; D004331:Drosophila melanogaster / Q000187:drug effects* / Q000502:physiology; D004785:Environmental Pollutants / Q000633:toxicity*; D005260:Female; D005508:Food Deprivation; D007814:Larva / Q000187:drug effects / Q000502:physiology; D009538:Nicotine / Q000633:toxicity*; D048448:Phenylcarbamates / Q000633:toxicity*; D011156:Population Density
D004785:Environmental Pollutants; D048448:Phenylcarbamates; D002104:Cadmium; D009538:Nicotine; D004132:Diflubenzuron; C052034:fenoxycarb