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Craig A. Stricker

Publications and source records attributed to Craig A. Stricker.

86 records · Page 5Linked to original sources
USGS2011

Benthic macroinvertebrate and fish communities in Lake Huron are linked to submerged groundwater vents

Groundwater can be an important source of nutrients and energy to aquatic ecosystems, but quantifying the inputs and biogeochemical importance remains challenging. A series of submerged groundwater vents in northern Lake Huron were examined to determine the linkage between groundwater nutrients and aquatic food webs. We collected samples of key food-web components from groundwater vent and reference habitats and analyzed them for 13 C, 15 N, and 34 S isotopes. Dissolved inorganic carbon (DIC) in the groundwater was depleted in 13 C, while aqueous sulfate was enriched in 34 S (mean differences between groundwater and reference sites were –3.9‰ and +12.0‰, respectively). Benthic primary producers, macroinvertebrates, and benthivorous fish had significantly lower δ 13 C values in groundwater environments, and benthivorous fish were somewhat depleted (–2.5‰) in δ 34 S at groundwater sites compared to reference sites. However, δ 15 N values were not different between groundwater and reference sites, and pelagic components of the ecosystems (plankton and planktivorous and piscivorous fish) were similar in both δ 13 C and δ 15 N. These data suggest benthic metazoan communities surrounding groundwater vents are partially linked to groundwater-derived benthic primary production, while planktivorous and piscivorous communities not directly associated with the benthos do not rely on groundwater nutrients.

Aquatic Biology↗
USGS2011

Effects of climate change on nutrition and genetics of White-tailed Ptarmigan

White-tailed Ptarmigan ( Lagopus leucura ) are well suited as a focal species for the study of climate change because they are adapted to cool, alpine environments that are expected to undergo unusually rapid climate change. We compared samples collected in the late 1930s, the late 1960s, and the late 2000s using molecular genetic and stable isotope methods in an effort to determine whether White-tailed Ptarmigan on Mt. Evans, Colorado, have experiences recent environmental changes resulting in shifts in genetic diversity, gene frequency, and nutritional ecology. We genotyped 115 individuals spanning the three time periods, using nine polymorphic microsatellite loci in our genetic analysis. These samples were also analyzed for stable carbon and nitrogen isotopic composition. We found a slight trend of lower heterozygosity through time, and allelic richness values were significantly lower in more recent times, but not significantly using an alpha of 0.05 ( P < 0.1). We found no changes in allele frequencies across time periods, suggesting that population sizes have not changed dramatically. Feather δ 13 C and δ 15 N values decreased significantly across time periods, whereas the range in isotope values increased consistently from the late 1930s to the late time periods. Inferred changes in the nutritional ecology of White-tailed Ptarmigan on Mt. Evans relate primarily to increased atmospheric deposition of nutrients that likely influenced foraging habits and tundra plant composition and nutritional quality. Future work seeks to integrate genetic and isotopic data with long-term demographics to develop a detailed understanding of the interaction among environmental stressors on the long-term viability of ptarmigan populations.

Studies in Avian Biology↗
USGS2010

Stable isotopes differentiate bottlenose dolphins off west-central Florida

Distinguishing discrete population units among continuously distributed coastal small cetaceans is challenging and crucial to conservation. We evaluated the utility of stable isotopes in assessing group membership in bottlenose dolphins ( Tursiops truncatus ) off west-central Florida by analyzing carbon, nitrogen, and sulfur isotope values (δ 13 C, δ 15 N, and δ 34 S) of tooth collagen from stranded dolphins. Individuals derived from three putative general population units: Sarasota Bay (SB), nearshore Gulf of Mexico (GULF), and offshore waters (OFF). Animals of known history (SB) served to ground truth the approach against animals of unknown history from the Gulf of Mexico (GULF, OFF). Dolphin groups differed significantly for each isotope. Average δ 13 C values from SB dolphins (−10.6‰) utilizing sea grass ecosystems differed from those of GULF (−11.9‰) and OFF (−11.9‰). Average δ 15 N values of GULF (12.7‰) and OFF (13.2‰) were higher than those of SB dolphins (11.9‰), consistent with differences in prey trophic levels. δ 34 S values showed definitive differences among SB (7.1‰), GULF (11.3‰), and OFF (16.5‰) dolphins. This is the first application of isotopes to population assignment of bottlenose dolphins in the Gulf of Mexico and results suggest that isotopes may provide a powerful tool in the conservation of small cetaceans.

Florida↗
USGS2010

Isotopic characterization of flight feathers in two pelagic seabirds: Sampling strategies for ecological studies

We wish to use stable-isotope analysis of flight feathers to understand the feeding behavior of pelagic seabirds, such as the Hawaiian Petrel ( Pterodroma sandwichensis ) and Newell&rsquo;s Shearwater ( Puffinus auricularis newelli ). Analysis of remiges is particularly informative because the sequence and timing of remex molt are often known. The initial step, reported here, is to obtain accurate isotope values from whole remiges by means of a minimally invasive protocol appropriate for live birds or museum specimens. The high variability observed in D 13 C and D 15 N values within a feather precludes the use of a small section of vane. We found the average range within 42 Hawaiian Petrel remiges to be 1.3&permil; for both D 13 C and D 15 N and that within 10 Newell&rsquo;s Shearwater remiges to be 1.3&permil; and 0.7&permil; for D 13 C and D 15 N, respectively. The D 13 C of all 52 feathers increased from tip to base, and the majority of Hawaiian Petrel feathers showed an analogous trend in D 15 N. Although the average range of DD in 21 Hawaiian Petrel remiges was 11&permil;, we found no longitudinal trend. We discuss influences of trophic level, foraging location, metabolism, and pigmentation on isotope values and compare three methods of obtaining isotope averages of whole feathers. Our novel barb-sampling protocol requires only 1.0 mg of feather and minimal preparation time. Because it leaves the feather nearly intact, this protocol will likely facilitate obtaining isotope values from remiges of live birds and museum specimens. As a consequence, it will help expand the understanding of historical trends in foraging behavior

Hawaii↗
USGS2010

Are inland wolf-ungulate systems influenced by marine subsidies of Pacific salmon?

Wolves ( Canis lupus ) in North America are considered obligate predators of ungulates with other food resources playing little role in wolf population dynamics or wolf–prey relations. However, spawning Pacific salmon (Oncorhyncus spp.) are common throughout wolf range in northwestern North America and may provide a marine subsidy affecting inland wolf–ungulate food webs far from the coast. We conducted stable‐isotope analyses for nitrogen and carbon to evaluate the contribution of salmon to diets of wolves in Denali National Park and Preserve, 1200 river‐km from tidewater in interior Alaska, USA. We analyzed bone collagen from 73 wolves equipped with radio collars during 1986–2002 and evaluated estimates of salmon in their diets relative to the availability of salmon and ungulates within their home ranges. We compared wolf densities and ungulate : wolf ratios among regions with differing salmon and ungulate availability to assess subsidizing effects of salmon on these wolf–ungulate systems. Wolves in the northwestern flats of the study area had access to spawning salmon but low ungulate availability and consumed more salmon (17% ± 7% [mean ± SD]) than in upland regions, where ungulates were sixfold more abundant and wolves did or did not have salmon spawning areas within their home ranges (8% ± 6% and 3% ± 3%, respectively). Wolves were only 17% less abundant on the northwestern flats compared to the remainder of the study area, even though ungulate densities were 78% lower. We estimated that biomass from fall runs of chum (O. keta) and coho (O. kisutch) salmon on the northwestern flats was comparable to the ungulate biomass there, and the contribution of salmon to wolf diets was similar to estimates reported for coastal wolves in southeast Alaska. Given the ubiquitous consumption of salmon by wolves on the northwestern flats and the abundance of salmon there, we conclude that wolf numbers in this region were enhanced by the allochthonous subsidy provided by salmon and discuss implications for wolf–ungulate relations.

Ecological Applications↗
USGS2010

Evolution of Ore Deposits and Technology Transfer Project: Isotope and Chemical Methods in Support of the U.S. Geological Survey Science Strategy, 2003-2008

Principal functions of the U.S. Geological Survey (USGS) Mineral Resources Program are providing assessments of the location, quantity, and quality of undiscovered mineral deposits, and predicting the environmental impacts of exploration and mine development. The mineral and environmental assessments of domestic deposits are used by planners and decisionmakers to improve the stewardship of public lands and public resources. Assessments of undiscovered mineral deposits on a global scale reveal the potential availability of minerals to the United States and other countries that manufacture goods imported to the United States. These resources are of fundamental relevance to national and international economic and security policy in our globalized world economy. Performing mineral and environmental assessments requires that predictions be made of the likelihood of undiscovered deposits. The predictions are based on geologic and geoenvironmental models that are constructed for the diverse types of mineral deposits from detailed descriptions of actual deposits and detailed understanding of the processes that formed them. Over the past three decades the understanding of ore-forming processes has benefited greatly from the integration of laboratory-based geochemical tools with field observations and other data sources. Under the aegis of the Evolution of Ore Deposits and Technology Transfer Project (referred to hereinafter as the Project), a 5-year effort that terminated in 2008, the Mineral Resources Program provided state-of-the-art analytical capabilities to support applications of several related geochemical tools to ore-deposit-related studies. The analytical capabilities and scientific approaches developed within the Project have wide applicability within Earth-system science. For this reason the Project Laboratories represent a valuable catalyst for interdisciplinary collaborations of the type that should be formed in the coming years for the United States to meet its natural-resources and natural-science needs. This circular presents an overview of the Project. Descriptions of the Project laboratories are given first including descriptions of the types of chemical or isotopic analyses that are made and the utility of the measurements. This is followed by summaries of select measurements that were carried out by the Project scientists. The studies are grouped by science direction. Virtually all of them were collaborations with USGS colleagues or with scientists from other governmental agencies, academia, or the private sector.

Circular↗
USGS2009

Does a lack of design and repeatability compromise scientific criticism? A Response to Smith et al. (2009)

In a recent paper published in The Auk , Smith et al. (2009) raised serious concerns over an apparent lack of reproducibility in their study of stable hydrogen isotope values (&delta;D f ) in raptor feathers. The authors based their concerns on results obtained from different laboratories to which they submitted original and blind &ldquo;repeats&rdquo; over a multiyear period. A regression of the original sample &delta;D versus &ldquo;repeat&rdquo; measurements showed an increase in the magnitude of residuals with increasing &delta;D f , especially for values greater than about &minus;80&permil; (Smith et al. 2009: fig. 2). Because of this, the authors &ldquo;caution against the continued use of &delta;D f for predicting geographic origin, and for addressing important conservation questions&rdquo; (p. 41) and conclude that &ldquo;it is counterproductive to move forward [with hydrogen isotopes in avian studies] without first establishing full confidence in the technique that underlies such insights and conservation recommendations&rdquo; (p. 45). We disagree with these sentiments.

The Auk↗
USGS2008

Stable isotope and trace element studies of black bear hair, Big Bend ecosystem, Texas and Mexico

Hair from black bears (Ursus americanus), collected from four areas in the Big Bend ecosystem, has been analyzed for stable isotopes of carbon, nitrogen, and sulfur to determine major food sources and for trace metals to infer possible effects of environmental contaminants. Results indicate that black bears are largely vegetarian, feeding on desert plants, nuts, and berries. Mercury concentrations in bear hair are below safe level standards (

Report↗