JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. The University of Notre Dame is collaborating with JSTOR to digitize, preserve and extend access to American Midland Naturalist.ABSTRACT: The impact of stress upon the dynamics of host and parasite populations is varied. It may be expressed physiologically or behaviorally in either the host or the parasite. The outcome of stress may be an increase or a decrease in natality and mortality which may then result in significant changes in the densities of the involved populations. At the ecosystem level, stress may be manifested either directly or indirectly on individuals or populations, but the outcome is change in natality or mortality and, hence, in the density of the affected species. The varied response to stressor input at the individual, population and ecosystem levels is dictated by the capacity for adaptability present at each level; the response may be modified, however, by the unique combination of environmental characteristics at the time of stressor input.

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. The American Society of Parasitologists is collaborating with JSTOR to digitize, preserve and extend access to The Journal of Parasitology. ABSTRACT:Nine species of enteric parasites were recovered from 357 Chrysemys scripta in a variety of habitats located on the Savannah River Plant near Aiken, South Carolina. Camallanus trispinosus was the most common nematode, present in more than 90% of the hosts; Spinoroura chelydrae was observed less frequently (73%). Mean infrapopulation densities of C. trispinosus were substantially higher than S. chelydrae (130.7 vs. 22.3). Two trematodes, Telorchis medius and Macravestibulum sp. were present in low densities and were relatively low in prevalence (27.1% and 10.3%, respectively). Four species of Neoechinorhynchus were recovered (N. pseudemydis, N. emyditoides, N. chrysemydis, and N. chelonus), with N. pseudemydis being most common (50%) and having the highest mean density (22.0/host). An unidentified species of acanthocephalan was also recovered from several turtles. Significant, but low, positive correlations were observed between mean densities of the two nematodes and plastron length, small intestine length and host weight. Mean infrapopulation densities of Neoechinorhynchus spp. were significantly correlated with plastron length, host weight, and small intestine length. Camallanus trispinosus was heavily recruited in September and October and lost in mid to late summer; S. chelydrae was lost during hibernation and rapidly recruited in early spring. Neoechinorhynchus spp. were recruited heavily at least twice each year, with greatest loss occurring just prior to, or simultaneously with, recruitment. There was substantial variability in abundance and distribution of all enteric helminths among the ecologically diverse habitats on the SRP. Some of the variability was attributed to substantive perturbation, i.e., thermal effluent, as well as immigration and emigration of infected and uninfected turtles.

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