Geology topics

Tiffany S. Garcia

Publications and source records attributed to Tiffany S. Garcia.

5 recordsLinked to original sources

USGS2025

Mercury trophic transfer to a freshwater biosentinel: Quantifying controlled bioaccumulation in larval dragonflies

Mercury bioavailability and biomagnification in freshwater systems can be highly variable; thus, tissue data from biosentinel taxa can be useful to assess risk. Dragonfly larvae have emerged as biological indicators of mercury impairment, yet their mercury biodynamics over time and across exposure levels are not well understood. Evaluating these attributes using controlled experimental approaches is an important step to validate larval dragonflies as biosentinels for spatial and temporal trends in mercury risk. We conducted an experimental series quantifying methylmercury trophic transfer from dosed prey to predatory dragonfly larvae at environmentally relevant concentrations. Dragonfly total mercury concentrations increased proportionally by factors of 2.7 to 4.2 with each doubling of prey methylmercury concentration, responding to dietary treatments in 7–28 days and reaching equilibrium in as little as 40 days, supporting their utility to indicate changing mercury exposure regimes. Dosed dragonflies biomagnified methylmercury by factors of 1.0 ± 0.1 to 3.4 ± 0.2 relative to their prey, and biomagnification efficiency decreased by over 40% for each doubling of prey methylmercury concentration. Dragonfly development had dose-dependent effects on bioaccumulation: mercury concentrations increased with growth and decreased with age in higher exposure treatments, whereas they decreased with growth and increased with age in lower exposure treatments. Bioaccumulation also varied taxonomically; within treatments, mean mercury concentrations for each genus varied up to 10% from family-level means. Dragonfly sex, size, and body condition did not significantly affect mercury concentrations. These results help validate and expand the utility of dragonfly larvae as biosentinels to monitor mercury risk and better protect wildlife and human health.

Oregon↗

USGS2024

A meta-analysis of mercury biomagnification in freshwater predatory invertebrates: Community diversity and dietary exposure drive variability

Accurate estimates of methylmercury (MeHg) exposure are valuable to actionably assess risk and protect wildlife and human health. MeHg trophic transfer is a critical driver of risk: MeHg is generally biomagnified by a factor of 8.3 ± 7.5 from one trophic level to the next, averaged across freshwater communities (mean ± standard deviation). This variability can produce disparate risks even where basal MeHg concentrations are similar. Taxonomy may be one driver of this variability: physiologically diverse groups, like vertebrates and invertebrates, may assimilate MeHg differently. To determine whether taxonomy affects trophic transfer efficiency, we conducted a meta-analysis characterizing predatory invertebrate MeHg biomagnification. Our analyses estimated that freshwater predatory invertebrates biomagnify MeHg by factors of 2.1 ± 0.2 to 4.3 ± 0.3, with a 98.9 ± 0.4% posterior probability that factors are below 5 (mean ± standard error). When vertebrates or primary producers were included, a site’s trophic magnification factor was 18.6 ± 6.2 to 54.1 ± 7.7% higher than estimates for invertebrates alone. Biomagnification was inversely correlated to prey MeHg concentration and varied among systematic and functional groups. These data suggest that predatory invertebrates biomagnify MeHg less efficiently than vertebrates and that a community’s diversity and structure determine its biomagnification efficiency. Incorporating organismal variation in trophic transfer estimates may improve the assessment, communication, and management of MeHg risk.

Environmental Science & Technology↗

USGS2022

Treading water: Conservation of headwater-stream associated amphibians in northwestern North America

Headwater streams of the Pacific Northwest of North America are home to 52 amphibian species, spanning a diversity of taxa and life histories. Headwater stream-associated amphibians occur both within coldwater-stream channels and throughout adjacent riparian habitat, reflective of the important role of old-growth forests in providing cool, moist microclimates for these sensitive species. Forests of the Pacific Northwest have undergone substantial change over the last century, due to a legacy of resource extraction and ever-evolving forest management practices, as well as climate change. These and other stressors have challenged the adaptive capacity of headwater stream-associated amphibians, as more than half of these species are considered to be of conservation concern at the state, provincial, or federal level in the U.S. and Canada. Here, we overview the primary threats to the persistence of this unique and imperiled taxonomic group and emphasize the urgent need for more research and conservation action to mitigate future decline.

Alaska, British Columbia, Idaho, Oregon, Washingto↗

USGS2021

Taricha granulosa (Rough-skinned newt) predation

We found skeletal remains of fully digested Taricha granulosa in the stomach contents of 4 free-ranging, presumably healthy Strix varia (Barred Owl) collected from Roseburg, Oregon. This study recorded stomach contents from S. varia collected as part of a lethal removal experiment in localities near Cle Elum, Washington, Alsea, Oregon, and Roseburg, Oregon. In the stomach of one S. varia , we identified the remains of 14 individual T. granulosa .

Oregon, Wasington↗

USGS2015

Evaluating multi-level models to test occupancy state responses of Plethodontid salamanders

Plethodontid salamanders are diverse and widely distributed taxa and play critical roles in ecosystem processes. Due to salamander use of structurally complex habitats, and because only a portion of a population is available for sampling, evaluation of sampling designs and estimators is critical to provide strong inference about Plethodontid ecology and responses to conservation and management activities. We conducted a simulation study to evaluate the effectiveness of multi-scale and hierarchical single-scale occupancy models in the context of a Before-After Control-Impact (BACI) experimental design with multiple levels of sampling. Also, we fit the hierarchical single-scale model to empirical data collected for Oregon slender and Ensatina salamanders across two years on 66 forest stands in the Cascade Range, Oregon, USA. All models were fit within a Bayesian framework. Estimator precision in both models improved with increasing numbers of primary and secondary sampling units, underscoring the potential gains accrued when adding secondary sampling units. Both models showed evidence of estimator bias at low detection probabilities and low sample sizes; this problem was particularly acute for the multi-scale model. Our results suggested that sufficient sample sizes at both the primary and secondary sampling levels could ameliorate this issue. Empirical data indicated Oregon slender salamander occupancy was associated strongly with the amount of coarse woody debris (posterior mean = 0.74; SD = 0.24); Ensatina occupancy was not associated with amount of coarse woody debris (posterior mean = -0.01; SD = 0.29) . Our simulation results indicate that either model is suitable for use in an experimental study of Plethodontid salamanders provided that sample sizes are sufficiently large. However, hierarchical single-scale and multi-scale models describe different processes and estimate different parameters. As a result, we recommend careful consideration of study questions and objectives prior to sampling data and fitting models.

PLoS ONE↗