Chapter 16 - Effects of Chemicals on Aquatic Populations

Abstract

Toxicant effects on individuals are ecologically meaningful only if the populations are also affected. Conclusions about effects of toxicants are complicated if immigration is possible, which can result in a lack of population-level changes even if the individuals are negatively affected by toxicants and their mortality increases. The simplest metrics that can be applied to the population effects of toxicants are the population size and growth rate. When considering the effects of contaminants on populations, the life history properties, such as time to sexual maturation, total offspring production, and average life length, must be taken into account whenever comparisons between species are made. A problem with translating results from laboratory experiments to predictions about the behavior of wild populations is that most laboratory experiments do not consider density-dependent phenomena that may be important for the responses of wild populations to toxicants. Genetic variability is an important component of populations, and often affected by contaminants. The first generation exposed to toxicants can tolerate them if their capacity to acclimate (phenotypic plasticity) is adequate. Further survival of the population is best if it is highly heterozygous. The development of toxicant tolerance is a good example of directional natural selection, and is fastest if the trait conferring tolerance is common even without the exposure.