Grantee Research Project Results
Final Report: Modeling the Individual and Interactive Risks to an Amphibian Population Resulting from Breeding Site Contamination and Terrestrial Habitat Loss
EPA Grant Number: R829087Title: Modeling the Individual and Interactive Risks to an Amphibian Population Resulting from Breeding Site Contamination and Terrestrial Habitat Loss
Investigators: Rowe, C. L. , Hopkins, William A.
Institution: University of Maryland Center for Environmental Science , University of Georgia
EPA Project Officer: Packard, Benjamin H
Project Period: January 1, 2002 through December 31, 2003 (Extended to December 17, 2004)
Project Amount: $280,059
RFA: Wildlife Risk Assessment (2001) RFA Text | Recipients Lists
Research Category: Biology/Life Sciences , Ecological Indicators/Assessment/Restoration , Aquatic Ecosystems
Objective:
Our overall objective in this research project was to examine population dynamics of eastern narrow-mouth toads (Gastrophryne carolinensis) in South Carolina in relation to stresses that vary temporally (directly influencing different life stages for different durations) and spatially (occurring in distinct habitat types). To accomplish this objective, we employed stage- and age-based matrix population models to integrate results from novel experiments and existing data, allowing us to examine the individual and interactive risks to the population associated with aquatic habitat contamination and per capita reduction in terrestrial habitat.
Summary/Accomplishments (Outputs/Outcomes):
This research project was designed to examine potential population-level effects of environmental stressors operating at distinct temporal and spatial scales on the eastern narrowmouth toad (Gastrophryne carolinensis). Variables of interest were contamination of aquatic breeding/nursery habitats and reduction in per capital terrestrial habitat availability. We examined the influences of contaminants on embryos and larvae during the temporally short aquatic life stages that are completed in spatially limited (bounded) breeding sites. Influences of mixed trace elements derived from coal combustion wastes on embryonic survival were determined experimentally, whereas larval survival was estimated from literature values. For terrestrial life stages, being much longer in duration and occupying a much greater spatial extent than aquatic stages, we used existing experimental data (based upon studies of effects of densities of terrestrial juveniles and adults) to examine potential population-level responses to per capita terrestrial habitat availability. Surveys also were conducted to quantify fecundity of females breeding in the vicinity of contaminated and reference breeding sites. We then used stage-based and age-based matrix population models to integrate and identify effects of characteristics of the habitats on estimates of population growth rates.
When embryos derived from females were hatched in the presence of water and sediments from their respective sites, embryonic survival was reduced in contaminated conditions (58%) compared to uncontaminated conditions (88%). Survival of embryos derived only from reference site females and hatched under contaminated or reference conditions, however, did not differ (95% survival for both treatments). Thus it appears that the maternal environment strongly influences susceptibility of offspring to contaminants. Average fecundity was 599 ± 39 and 716 ± 36 eggs/female in the contaminated and uncontaminated sites, respectively. Existing data on juvenile and adult traits resulting from experimental manipulation of per capita habitat availability demonstrated that reductions in habitat availability (increased density) results in reduction in survival and growth, and an increased time to the first reproductive event.
Results of the age-based models suggest that terrestrial habitat availability did not directly modify the importance of specific age classes on population growth rate. There was an interaction, however, between terrestrial habitat availability and conditions in the aquatic habitat. Under conditions of low terrestrial habitat availability and contamination of the aquatic habitat, population growth rate was influenced primarily by survival through the first year (embryos, larvae, terrestrial metamorphs), followed by survival through second year (terrestrial juveniles). Under conditions of high terrestrial habitat availability, population growth rate also was influenced by survival through the first year; however, survival through ensuing years was relatively unimportant. In examining the contribution of specific life stages to population growth rates, larval survival (aquatic) and juvenile/adult survival (terrestrial) had the greatest influences, followed by hatching success and fecundity. Stresses incurred only in the terrestrial environment (juveniles and adults) because of limited habitat availability brought about a 19 percent reduction in population growth rate compared to conditions of high habitat availability. Stresses incurred only in the contaminated habitat (embryos, larvae) brought about a 33 percent reduction in population growth rate compared to a reduction in terrestrial habitat. Thus, under the conditions of this study, influences of contaminants derived from coal combustion wastes on aquatic life stages of G. carolinensis proved more substantial than influences of per capita habitat availability for terrestrial life stages in regulating projected population growth rates. In a worst-case scenario in which aquatic life stages were exposed to contaminants following conditions in which terrestrial juveniles and adults experienced habitat limitations, population growth rate was reduced by 46 percent compared to uncontaminated conditions in which terrestrial habitat was more abundant.
Age-based models confirmed the importance of early life stages/ages to population growth rates. Demographic decomposition analysis revealed that, when exposed to contaminants, survival through the first year (comprised of all aquatic life stages and initial terrestrial juvenile period) was the primary driver of population growth rate regardless of terrestrial habitat availability. Under conditions of limited habitat availability and contaminant exposure, second year survival was also an important contributor to population growth rate. When terrestrial habitat was more abundant following contaminant exposure, second year survival had little effect on population growth rate, as fecundity during the first breeding season had much greater influence.
The overall results of this study suggest that anthropogenic modifications to temporally and spatially distinct factors may individually and interactively have significant influences on population growth rates of G. carolinensis. Reduction in per capita terrestrial habitat availability for juveniles and adults, as may occur by conversion or fragmentation of landscapes, can strongly influence population growth rates, yet the combined effects of contaminants on fecundity, hatching success, and larval survival may have a much greater influence. A combined effect of aquatic contamination and terrestrial habitat reduction can have exceptional influences on population growth rate, reducing it by nearly one-half compared to more benign conditions.
An unanticipated, yet extremely important finding of this research project, was the observation of parental contributions to offspring survival via maternal transfer of contaminants and/or elevated sensitivity of offspring to contaminants; such a mechanism has not previously been observed in amphibians. Embryos derived from females breeding in the contaminated habitat and hatched under contaminated conditions experienced much higher mortality than did embryos from females breeding elsewhere hatched under contaminated conditions. Thus it appears that contaminant effects may not be exerting effects solely through direct, environmental exposure, but also through a more indirect, parentally-mediate route.
Because of the complex life cycles characteristic of most extant amphibians, stressors operating at distinct spatial and temporal scales can influence specific life stages independently and interactively. In examining issues such as declining amphibian populations, it is essential that approaches that combine investigation of all portions of the life cycle be employed so that an overall assessment of population trends can be obtained.
We are currently preparing two manuscripts based upon this project. Both manuscripts will be submitted to peer-reviewed journals within 2 months of the date of this report. Copies of resulting publications will be forwarded upon release.
Journal Articles on this Report : 1 Displayed | Download in RIS Format
Other project views: | All 2 publications | 1 publications in selected types | All 1 journal articles |
---|
Type | Citation | ||
---|---|---|---|
|
Salice C, Rowe C, Pechmann J, Hopkins W. Multipel Stressors and Complex Life Cyccles:Insights From a Population-level Assessment of Breeding Site Comtamination and Terrestrial Habitat Loss in an Amphibian. ENVIRONMENTAL TOXICOLOGY AND CHEMISTRY 2011;30(12):2784-2882. |
R829087 (Final) |
Exit Exit |
Supplemental Keywords:
water, land, sediment, risk assessment, ecological effects, animal, amphibian, population, cumulative effects, metals, heavy metals, trace elements, coal ash, selenium, effluent, aquatic, terrestrial, scaling, biology, ecology, environmental science, ecotoxicology, land management, modeling, field surveys, experimental exposures, Southeast, South Carolina, SC, power utilities, coal,, RFA, Scientific Discipline, Waste, Geographic Area, Ecosystem Protection/Environmental Exposure & Risk, Aquatic Ecosystems & Estuarine Research, Ecosystem/Assessment/Indicators, exploratory research environmental biology, wildlife, State, Ecological Effects - Environmental Exposure & Risk, Monitoring/Modeling, Aquatic Ecosystem, Habitat, Southeast, Ecology and Ecosystems, Ecological Risk Assessment, Incineration/Combustion, coal combustion wastes, ecological exposure, anthropogenic stress, anthropogenic stresses, predicting risk, stressors, demographic data, contaminants, contaminated habitats, dose-response, endocrine disrupting chemical, amphibians, animal responses, endocrine disruptors, multiple stressors, modeling, amphibian, habitat loss, terrestrial, breeding site contamination, terrestrial habitat loss, anthropogenic, breeding site contamination, Savannah River Site, anthropogenic stressors, contaminant impact, South Carolina (SC), ecosystem stress, contaminant stressors , ecological response, amphibian populationProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.