ABSTRACT
The tolerance discussed in most chapters in this volume is a result of populations in contaminated environments being subjected to selection pressure and then becoming more tolerant to those contaminants. This evolutionary response may provide a measure of contaminant effects and can enable species to persist and perhaps even thrive, and thus contribute to the diversity of species. Discussed in Chapter 4 is pollution-induced community tolerance (PICT), wherein the community in the polluted environment becomes dominated by (1) species that have evolved greater tolerance and (2) species that are more tolerant to begin with. More tolerant species may be so because of reduced uptake of the toxicants, altered inducibility of cytochrome P-450 systems, differential binding to detoxifying molecules such as metallothioneins (see Chapter 6), or enhanced ability to store contaminants in intracellular structures that prevent damage to the cell. The inherent or induced tolerance of these species enables them to persist, and therefore contributes to increasing the overall diversity of the communities in which they live. However, tolerance comes with costs, and it has frequently been noted that populations adapted to one set of environmental stressors have increased susceptibility to other stressors.
