2002 Progress Report: Modeling the Individual and Interactive Risks to an Amphibian Population Resulting from Breeding Site Contamination and Terrestrial Habitat LossEPA Grant Number: R829087
Title: 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 , University of Georgia
EPA Project Officer: Hahn, Intaek
Project Period: January 1, 2002 through December 31, 2003 (Extended to December 17, 2004)
Project Period Covered by this Report: January 1, 2002 through December 31, 2003
Project Amount: $280,059
RFA: Wildlife Risk Assessment (2001) RFA Text | Recipients Lists
Research Category: Biology/Life Sciences , Ecological Indicators/Assessment/Restoration , Ecosystems
The overall objective of this research project is to examine the individual and interactive risks associated with aquatic habitat contamination and per capita reduction in terrestrial habitat for a population of eastern narrow mouth toads (Gastrophryne carolinensis) in South Carolina. This objective is being met by incorporating existing data on post-metamorphic traits and data currently being gathered on embryonic and larval traits and incorporated into stage-based matrix population models. In a reference site, and in a site contaminated by coal combustion residues, we are conducting: (1) site-specific surveys of female fecundity; and (2) experimental exposures of embryos and larvae to conditions representative of those in the field sites. When all survey and experimental data are available, they will be incorporated into stage-based matrix population models to compare and contrast effects of contaminants in the aquatic embryonic/larval environment with per capita habitat reductions in the terrestrial, juvenile/adult environment.
The severe drought in the Southeastern United States in 2002 precluded breeding attempts by most individuals in our study populations, which rely on shallow, temporary pools for breeding. Most affected by the climate was the contaminated site, which produced only one gravid animal despite tremendous sampling efforts. In the reference area, where a drift fence was in place from previous studies, we obtained fecundity data for 22 females that entered the site in search of water. Reference females weighed (mean ± 1 SD) 2.4 ± 0.3 g, had snout-vent length of 29.5 ± 2.6 mm, and contained 797 ± 218 eggs. The single female from the contaminated site had corresponding values of 1.9 g, 29.0 mm, and 602 eggs. Using the egg masses produced by 16 of the reference females, we completed a hatching success experiment, in which 120 eggs from each female were held in water and sediment from the study sites (8 replicates per site). Hatching success did not differ between sites (reference 93 ± 11 percent hatch; contaminated 98 ± 2 percent hatch).
Data collected thus far provide values for fecundity (reference site) and hatching success (both populations). These data will be used in conjunction with data on fecundity, hatching success, and metamorphic success that will be gathered in summer 2003, to construct population models. Although the small number of animals captured during surveys limits the power of the existing data set, results of the embryonic exposures do support our hypothesis that effects of contaminants on embryos are unlikely to have large overall effects, primarily because of the short duration of exposure. Upcoming studies with larvae will determine whether chronic exposure throughout larval development influences recruitment of juveniles from the contaminated site.
Future activities of this research project (CY 2003) involve a renewed attempt at field collections to provide ample data for fecundity estimates and adequate animals for exposure studies. We have installed a drift fence in the contaminated site so that, if climatological conditions do not improve in 2003, we will be able to intercept breeding adults searching for breeding sites. We are confident that we will obtain sufficient data in the coming field season to support our proposed modeling efforts.
Because the field-based portion of this project was planned to have been completed in Year 1 of the project, but must extend into Year 2 because of the drought, we have applied for and been granted a 1 year no-cost extension on this project.