Skip to main content

Currently Skimming:

10 Ecologic Effects
Pages 274-295

The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.


From page 274...
... Evidence has been accumulating that environmental contaminants are affecting their populations (Colborn and Clement 1992~. Ecotoxicologic studies have been the primary field providing data on ecologic effects of hormonally active agents (HAAs)
From page 275...
... For wildlife species, the most common unit of concern and study is the population. The end points of concern are changes in population size or reproductive capacity.
From page 276...
... Population-level measures are perhaps the most useful for determining adverse effects because they are the most direct; the population is the level of organization at which effects are likely to occur first. The measures include population size, age structure, sex ratios, recruitment, and biomass (NRC 1981~.
From page 277...
... Understanding changes in population metrics as a function of contaminants might provide warning of potential population changes (NRC 1986a, 1995~. Several measurement end points can be used to determine the effect of any perturbation or chemical exposure on the structure and functioning of communities and ecosystems (NRC 1981, 1986a, 1993~.
From page 278...
... Related is the idea of the keystone species (Paine 1966) , which posits that removal of one predator can change the population sizes of several other species in a community.
From page 279...
... Temporal and Spatial Scales of Effects Temporal and spatial scales of exposure and effects are critical in evaluating evidence on the effects of environmental contaminants. Species sometimes are distributed evenly over the available and suitable habitat or they can occur in patches or discrete populations.
From page 280...
... It is important to establish plausible modes of action for a suspected agent. This, usually done through laboratory studies, is especially important if the presence or concentration of the suspected agent in the environment or organisms' exposure to it cannot be established easily, as might be the case if a suspected chemical can have an effect at extremely low concentrations.
From page 281...
... Next, changes in higher-level ecologic factors, such as community composition or primary productivity, must be plausibly related to established population-level effects or directly to the suspected agent. Whether the mode of action of the suspected agent is through a hormonal mechanism must be established.
From page 282...
... The failure of recruitment of the lake trout populations could be the result of several factors behavior, predation, genetics, changes in diet caused by changes in prey species composition, or inappropriate stocking practices but the evidence supports the hypothesis that toxic chemicals in eggs were, at least historically, responsible for some of the population decline (Walker and Peterson 1991; Walker et al.
From page 283...
... Many contaminants have been identified as hormonally active, but it is not known whether hormonal or other endocrine disrupting actions promote all of the observed health and population-level effects. However, the data indicate that environmental contaminants can affect fish, especially the reproductive capacity (see Chapter 5)
From page 284...
... It was postulated that, in the years when shrimp populations were depressed, the two fish that exhibited M-74 switched their diet to one of mostly herring without consuming any shrimp. However, although shrimp make up a significant proportion of the diet of Atlantic salmon in the Atlantic Ocean, they are not a significant proportion of the diet of salmonids in the Baltic Sea (P.
From page 285...
... birds, which are exposed to pollutants in contaminated fish. Two significant population effects have been changes in sex ratios in gull populations and population declines among gulls, cormorants, and terns.
From page 286...
... Population Declines Several species of fish-eating birds of the Great Lakes region have experienced population declines, which have been attributed to exposure to environmental contaminants (Keith 1966; Anderson and Hickey 1976; Fox et al.
From page 287...
... 1991~. Chicks with deformities often die soon after hatching, resulting in reduced fledgling success in the colony, and ultimately, in changes in age ratios and overall population size.
From page 288...
... 288 HORMONALLYACIIVE AGENTS IN THE ENVIRONMENT but it might not be detectable by simply enumerating the total population because immigration occurs from other colonies. The evidence that there continues to be toxicant-related embryonic death, deformities, and immune dysfunction in chicks strongly suggests that there are still population-level effects in the Caspian terns (More et al.
From page 289...
... Populations of some bird species have been monitored in the Great Lakes region for the past half century, and there is clear evidence for population decline, reproductive impairment, or both, in several fish-eating species. There is also convincing evidence for community-level effects: Many of the declines in bird populations seem to be caused by eating of contaminated fish.
From page 290...
... , and, beginn~ng in 1984, the viability of alligator eggs from this lake decreased significantly (Figure 10-2~. Recent data suggest that the juvenile population on Lake Apopka is increasing slowly, and egg viability has continued to vary, with most years exhibiting an average below that observed on other lakes (Rice et al.1996~.
From page 291...
... In addition to p,p'-DDE, alligator eggs (n = 23) collected in 1985 from Lake Apopka had detectable concentrations of p,p'-DDD (<1.8 ppm)
From page 292...
... It is likely that a reduced population size, coupled with the gonadal and sex-steroid abnormalities observed in juveniles, will affect the reproductive success of these alligators in the future and could pose significant long-term population and community threats. Mammals Data on the effects of mammalian exposure to environmental contaminants are limited and come mainly from work with ranch mink (Mustela visor)
From page 293...
... River Otter The river otter populations in Wales, England, and other regions in Europe declined in the 1950s, and home ranges were constricted (Mason and Macdonald 1986~. The changes have been attributed to contaminants in the food chain, because pollution was great during that time, and as the contaminant concentrations in these areas have declined, the otter populations have begun to increase (Mason and Macdonald 1993a)
From page 294...
... Moreover, such organochlorines have been associated with a variety dysfunctions, which might provide an explanation for population declines. Chapter 7 of this volume describes a correlation between feeding on PCBcontaminated fish and impaired immune response in seals and whales.
From page 295...
... and the declines of some seal populations in the North Sea are due in part to the hormonal activity of pollutants, although the evidence is not conclusive. The evidence that implicates HAAs in population declines of lake trout in the Great Lakes is less strong, but it still seems quite likely that HAAs have been among the several factors in those declines.


This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More information on Chapter Skim is available.