Abstract
Indirect effects in ecotoxicology are defined as chemical- or pollutant-induced alterations in the density or behavior of sensitive species that have cascading effects on tolerant species in natural systems. As a result, species interaction networks (e.g., interactions associated with predation or competition) may be altered in such a way as to bring about large changes in populations and/or communities that may further cascade to disrupt ecosystem function and services. Field studies and experimental outcomes as well as models indicate that indirect effects are most likely to occur in communities in which the strength of interactions and the sensitivity to contaminants differ markedly among species, and that indirect effects will vary over space and time as species composition, trophic structure, and environmental factors vary. However, knowledge of indirect effects is essential to improve understanding of the potential for chemical harm in natural systems. For example, indirect effects may confound laboratory-based ecological risk assessment by enhancing, masking, or spuriously indicating the direct effect of chemical contaminants. Progress to better anticipate and interpret the significance of indirect effects will be made as monitoring programs and long-term ecological research are conducted that facilitate critical experimental field and mesocosm investigations, and as chemical transport and fate models, individual-based direct effects models, and ecosystem/food web models continue to be improved and become better integrated.
Highlights
Introduction to Indirect EffectsMany synthetic chemicals and naturally occurring chemical pollutants impact living things by direct toxic action exerted on an organism’s physiology, behavior, reproduction, or survivorship
Progress to better anticipate and interpret the significance of indirect effects will be made as monitoring programs and long-term ecological research are conducted that facilitate critical experimental field and mesocosm investigations, and as chemical transport and fate models, individual-based direct effects models, and ecosystem/food web models continue to be improved and become better integrated
The purpose of this review is to address indirect effects that are a function of community ecology, and because changes in populations or communities may cascade to higher levels, indirect contaminant effects associated with ecosystem function and services will be discussed
Summary
Many synthetic chemicals and naturally occurring chemical pollutants (e.g., poly-nuclear aromatic hydrocarbons) impact living things by direct toxic action exerted on an organism’s physiology, behavior, reproduction, or survivorship. Perhaps the most well-known of these altered interactions, the community may change after exposure to a chemical contaminant or of and an indirect effect was observed in anincrease experimental whole-lake amendment of an endocrine aexample pollutant, relatively tolerant species may or decrease in abundance. An herbicide addition would have a direct effect most primary consumers) and pesticides (that are toxic to most primary and secondary consumers but not most primary producers) Indirect effects in this community would likely be pronounced and relatively predictable [11,12]. For pesticide exposure in a diverse community, the direct effect on relatively sensitive herbivore species density, and a positive indirect effect is exerted on primary producers as herbivory is reduced It is perhaps not surprising that indirect effects, those acting via altered behavior, have not yet been broadly studied and quantified; multiple organisms across the trophic spectrum must be studied simultaneously in real time using environmentally realistic mesocosms or field-based studies, and the system often must be studied for longer durations than are typical of toxicological exposures (i.e., months to years)
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