Understanding species habitat requirements is incomplete without insight into nutrition, including various aspects of foraging ecology. Traditional diet studies can be challenging because of logistics, issues related to resource availability, and observations are often short-term in nature based on gut contents or scat. Additionally, perturbations such as species introductions, habitat degradation, pollution, and climate change can drastically alter the availability and quality of dietary resources. Stable isotope techniques offer a useful tool for gaining longer-term insight into the dietary habits for a variety of wildlife species.
In collaboration with other USGS scientists, Federal and State agencies, and university researchers, Trust Species and Habitats scientists are using stable isotopes to:
- understand the foraging habits of polar bears, providing context from which future changes because of habitat loss can be inferred;
- investigate nutritional stress as the cause of population decline in Stellar sea lions;
- assess the effects of a gillnet ban on bottlenose dolphin;
- reconstruct aquatic food web pathways before and after exotic species invasions;
- determine the arrival time on arctic breeding grounds of a long-distance migratory shorebird based on a shift in diet; and
- clarify the role of marine-derived nutrients to juvenile salmon. Findings from this work are providing valuable insight into the foraging ecology of species of management or conservation concern.
The Stable Isotope Laboratory maintained by the Crustal Geophysics and Geochemistry (CGG) and Fort Collins Science Center (FORT) is a state-of-the-art facility with modern instrumentation capable of analyzing the isotopic composition of nearly any conceivable sample matrix. Laboratory staff and principal investigators have significant expertise in isotope systematics of the geosphere, biosphere, and hydrosphere. The Laboratory has demonstrated innovative approaches to challenging questions and as such, has significant latitude to address emerging issues in ecosystem science such as this.
Below are publications associated with this project.
Age-specific vibrissae growth rates: a tool for determining the timing of ecologically important events in Steller sea lions
Steller sea lions (SSL; Eumetopias jubatus) grow their vibrissae continually, providing a multiyear record suitable for ecological and physiological studies based on stable isotopes. An accurate age-specific vibrissae growth rate is essential for registering a chronology along the length of the record, and for interpreting the timing of ecologically important events. We utilized four methods to es
Authors
L.D. Rea, A.M. Christ, A.B. Hayden, V.K. Stegall, S.D. Farley, Craig A. Stricker, J.E. Mellish, John M. Maniscalco, J.N. Waite, V.N. Burkanov, K.W. Pitcher
Individual specialization in the foraging habits of female bottlenose dolphins living in a trophically diverse and habitat rich estuary
We examine individual specialization in foraging habits (foraging habitat and trophic level) of female bottlenose dolphins (Tursiops truncatus) resident in Sarasota Bay, Florida, USA, by analyzing time series of stable isotope (δ15N and δ13C) values in sequential growth layer groups within teeth. The isotope data provide a chronology of foraging habits over the lifetime of the individual and allow
Authors
Sam Rossman, Peggy H. Ostrom, Megan Stolen, Nélio B. Barros, Hasand Gandhi, Craig A. Stricker, Randall S. Wells
Stable isotope values in pup vibrissae reveal geographic variation in diets of gestating Steller sea lions Eumetopias jubatus
Multiple factors, including limitation in food resources, have been proposed as possible causes for the lack of recovery of the endangered western segment of the Steller sea lion population in the United States. Because maternal body condition has important consequences on fetal development and neonatal survival, the diets of pregnant females may be particularly important in regulating population
Authors
Rick D. Scherer, Andrew C. Doll, Lorrie D. Rea, Aaron M. Christ, Craig A. Stricker, Briana Witteveen, Thomas C. Kline, Carolyn M. Kurle, Michael B. Wunder
Stable carbon and nitrogen isotope trophic enrichment factors for Steller sea lion vibrissae relative to milk and fish/invertebrate diets
Nutritional constraints have been proposed as a contributor to population declines in the endangered Steller sea lion Eumetopias jubatus in some regions of the North Pacific. Isotopic analysis of vibrissae (whiskers) is a potentially useful approach to resolving the nutritional ecology of this species because long-term (up to 8 yr) dietary information is sequentially recorded and metabolically ine
Authors
Craig A. Stricker, Aaron M. Christ, Michael B. Wunder, Andrew C. Doll, Sean D. Farley, Lorrie D. Rea, David A. S. Rosen, R. D. Scherer, Dominic J. Tollit
Improved arrival-date estimates of Arctic-breeding Dunlin (Calidris alpina arcticola)
The use of stable isotopes in animal ecology depends on accurate descriptions of isotope dynamics within individuals. The prevailing assumption that laboratory-derived isotopic parameters apply to free-living animals is largely untested. We used stable carbon isotopes (δ13C) in whole blood from migratory Dunlin (Calidris alpina arcticola) to estimate an in situ turnover rate and individual diet-sw
Authors
Andrew C. Doll, Richard B. Lanctot, Craig A. Stricker, Stephen M. Yezerinac, Michael B. Wunder
Unexpected hydrogen isotope variation in oceanic pelagic seabirds
Hydrogen isotopes have significantly enhanced our understanding of the biogeography of migratory animals. The basis for this methodology lies in predictable, continental patterns of precipitation δD values that are often reflected in an organism’s tissues. δD variation is not expected for oceanic pelagic organisms whose dietary hydrogen (water and organic hydrogen in prey) is transferred up the fo
Authors
Peggy H. Ostrom, Anne E. Wiley, Sam Rossman, Craig A. Stricker, Helen F. James
Seasonal persistence of marine-derived nutrients in south-central Alaskan salmon streams
Spawning salmon deliver annual pulses of marine-derived nutrients (MDN) to riverine ecosystems around the Pacific Rim, leading to increased growth and condition in aquatic and riparian biota. The influence of pulsed resources may last for extended periods of time when recipient food webs have effective storage mechanisms, yet few studies have tracked the seasonal persistence of MDN. With this as o
Authors
Daniel J. Rinella, Mark S. Wipfi, Coowe M. Walker, Craig A. Stricker, Ron A. Heintz
Retrospective analysis of bottlenose dolphin foraging: a legacy of anthropogenic ecosystem disturbance
We used stable isotope analysis to investigate the foraging ecology of coastal bottlenose dolphins (Tursiops truncatus) in relation to a series of anthropogenic disturbances. We first demonstrated that stable isotopes are a faithful indicator of habitat use by comparing muscle isotope values to behavioral foraging data from the same individuals. δ13C values increased, while δ34S and δ15N values de
Authors
Sam Rossman, Nélio B. Barros, Peggy H. Ostrom, Craig A. Stricker, Aleta A. Hohn, Hasand Gandhi, Randall S. Wells
Effects of trophic level and metamorphosis on discrimination of hydrogen isotopes in a plant-herbivore system
The use of stable isotopes in ecological studies requires that we know the magnitude of discrimination factors between consumer and element sources. The causes of variation in discrimination factors for carbon and nitrogen have been relatively well studied. In contrast, the discrimination factors for hydrogen have rarely been measured. We grew cabbage looper caterpillars (Trichoplusia ni) on cabba
Authors
Jacob M. Peters, Nathan Wolf, Craig A. Stricker, Timothy R. Collier, Carlos Martinez del Rio
Isotope and Chemical Methods in Support of the U.S. Geological Survey Science Strategy, 2003-2008
Principal functions of the Mineral Resources Program are providing information to decision-makers related to mineral deposits on federal lands and predicting the environmental consequences of the mining or natural weathering of those deposits. Performing these functions requires that predictions be made of the likelihood of undiscovered deposits. The predictions are based on geologic and geoenviro
Authors
R. O. Rye, C.A. Johnson, G.P. Landis, A. H. Hofstra, P. Emsbo, C. A. Stricker, A.G. Hunt, B.G. Rusk
Discrimination of carbon and nitrogen isotopes from milk to serum and vibrissae in Alaska Steller sea lions (Eumetopias jubatus)
Knowledge of diet-tissue stable isotope discrimination is required to properly interpret stable isotope values and to identify possible diet shifts, such as might be expected from nursing through weaning. This study compared ??13C and ??15N of paired serum and vibrissal roots with those of ingested milk (n = 52) from free-ranging Steller sea lion (Eumetopias jubatus (Schreber, 1776)) pups (1-11 mo
Authors
V.K. Stegall, Sean D. Farley, Lorrie D. Rea, K.W. Pitcher, R. O. Rye, C.L. Kester, C. A. Stricker, C.R. Bern
- Overview
Understanding species habitat requirements is incomplete without insight into nutrition, including various aspects of foraging ecology. Traditional diet studies can be challenging because of logistics, issues related to resource availability, and observations are often short-term in nature based on gut contents or scat. Additionally, perturbations such as species introductions, habitat degradation, pollution, and climate change can drastically alter the availability and quality of dietary resources. Stable isotope techniques offer a useful tool for gaining longer-term insight into the dietary habits for a variety of wildlife species.
In collaboration with other USGS scientists, Federal and State agencies, and university researchers, Trust Species and Habitats scientists are using stable isotopes to:
- understand the foraging habits of polar bears, providing context from which future changes because of habitat loss can be inferred;
- investigate nutritional stress as the cause of population decline in Stellar sea lions;
- assess the effects of a gillnet ban on bottlenose dolphin;
- reconstruct aquatic food web pathways before and after exotic species invasions;
- determine the arrival time on arctic breeding grounds of a long-distance migratory shorebird based on a shift in diet; and
- clarify the role of marine-derived nutrients to juvenile salmon. Findings from this work are providing valuable insight into the foraging ecology of species of management or conservation concern.
The Stable Isotope Laboratory maintained by the Crustal Geophysics and Geochemistry (CGG) and Fort Collins Science Center (FORT) is a state-of-the-art facility with modern instrumentation capable of analyzing the isotopic composition of nearly any conceivable sample matrix. Laboratory staff and principal investigators have significant expertise in isotope systematics of the geosphere, biosphere, and hydrosphere. The Laboratory has demonstrated innovative approaches to challenging questions and as such, has significant latitude to address emerging issues in ecosystem science such as this.
- Publications
Below are publications associated with this project.
Age-specific vibrissae growth rates: a tool for determining the timing of ecologically important events in Steller sea lions
Steller sea lions (SSL; Eumetopias jubatus) grow their vibrissae continually, providing a multiyear record suitable for ecological and physiological studies based on stable isotopes. An accurate age-specific vibrissae growth rate is essential for registering a chronology along the length of the record, and for interpreting the timing of ecologically important events. We utilized four methods to esAuthorsL.D. Rea, A.M. Christ, A.B. Hayden, V.K. Stegall, S.D. Farley, Craig A. Stricker, J.E. Mellish, John M. Maniscalco, J.N. Waite, V.N. Burkanov, K.W. PitcherIndividual specialization in the foraging habits of female bottlenose dolphins living in a trophically diverse and habitat rich estuary
We examine individual specialization in foraging habits (foraging habitat and trophic level) of female bottlenose dolphins (Tursiops truncatus) resident in Sarasota Bay, Florida, USA, by analyzing time series of stable isotope (δ15N and δ13C) values in sequential growth layer groups within teeth. The isotope data provide a chronology of foraging habits over the lifetime of the individual and allowAuthorsSam Rossman, Peggy H. Ostrom, Megan Stolen, Nélio B. Barros, Hasand Gandhi, Craig A. Stricker, Randall S. WellsStable isotope values in pup vibrissae reveal geographic variation in diets of gestating Steller sea lions Eumetopias jubatus
Multiple factors, including limitation in food resources, have been proposed as possible causes for the lack of recovery of the endangered western segment of the Steller sea lion population in the United States. Because maternal body condition has important consequences on fetal development and neonatal survival, the diets of pregnant females may be particularly important in regulating populationAuthorsRick D. Scherer, Andrew C. Doll, Lorrie D. Rea, Aaron M. Christ, Craig A. Stricker, Briana Witteveen, Thomas C. Kline, Carolyn M. Kurle, Michael B. WunderStable carbon and nitrogen isotope trophic enrichment factors for Steller sea lion vibrissae relative to milk and fish/invertebrate diets
Nutritional constraints have been proposed as a contributor to population declines in the endangered Steller sea lion Eumetopias jubatus in some regions of the North Pacific. Isotopic analysis of vibrissae (whiskers) is a potentially useful approach to resolving the nutritional ecology of this species because long-term (up to 8 yr) dietary information is sequentially recorded and metabolically ineAuthorsCraig A. Stricker, Aaron M. Christ, Michael B. Wunder, Andrew C. Doll, Sean D. Farley, Lorrie D. Rea, David A. S. Rosen, R. D. Scherer, Dominic J. TollitImproved arrival-date estimates of Arctic-breeding Dunlin (Calidris alpina arcticola)
The use of stable isotopes in animal ecology depends on accurate descriptions of isotope dynamics within individuals. The prevailing assumption that laboratory-derived isotopic parameters apply to free-living animals is largely untested. We used stable carbon isotopes (δ13C) in whole blood from migratory Dunlin (Calidris alpina arcticola) to estimate an in situ turnover rate and individual diet-swAuthorsAndrew C. Doll, Richard B. Lanctot, Craig A. Stricker, Stephen M. Yezerinac, Michael B. WunderUnexpected hydrogen isotope variation in oceanic pelagic seabirds
Hydrogen isotopes have significantly enhanced our understanding of the biogeography of migratory animals. The basis for this methodology lies in predictable, continental patterns of precipitation δD values that are often reflected in an organism’s tissues. δD variation is not expected for oceanic pelagic organisms whose dietary hydrogen (water and organic hydrogen in prey) is transferred up the foAuthorsPeggy H. Ostrom, Anne E. Wiley, Sam Rossman, Craig A. Stricker, Helen F. JamesSeasonal persistence of marine-derived nutrients in south-central Alaskan salmon streams
Spawning salmon deliver annual pulses of marine-derived nutrients (MDN) to riverine ecosystems around the Pacific Rim, leading to increased growth and condition in aquatic and riparian biota. The influence of pulsed resources may last for extended periods of time when recipient food webs have effective storage mechanisms, yet few studies have tracked the seasonal persistence of MDN. With this as oAuthorsDaniel J. Rinella, Mark S. Wipfi, Coowe M. Walker, Craig A. Stricker, Ron A. HeintzRetrospective analysis of bottlenose dolphin foraging: a legacy of anthropogenic ecosystem disturbance
We used stable isotope analysis to investigate the foraging ecology of coastal bottlenose dolphins (Tursiops truncatus) in relation to a series of anthropogenic disturbances. We first demonstrated that stable isotopes are a faithful indicator of habitat use by comparing muscle isotope values to behavioral foraging data from the same individuals. δ13C values increased, while δ34S and δ15N values deAuthorsSam Rossman, Nélio B. Barros, Peggy H. Ostrom, Craig A. Stricker, Aleta A. Hohn, Hasand Gandhi, Randall S. WellsEffects of trophic level and metamorphosis on discrimination of hydrogen isotopes in a plant-herbivore system
The use of stable isotopes in ecological studies requires that we know the magnitude of discrimination factors between consumer and element sources. The causes of variation in discrimination factors for carbon and nitrogen have been relatively well studied. In contrast, the discrimination factors for hydrogen have rarely been measured. We grew cabbage looper caterpillars (Trichoplusia ni) on cabbaAuthorsJacob M. Peters, Nathan Wolf, Craig A. Stricker, Timothy R. Collier, Carlos Martinez del RioIsotope and Chemical Methods in Support of the U.S. Geological Survey Science Strategy, 2003-2008
Principal functions of the Mineral Resources Program are providing information to decision-makers related to mineral deposits on federal lands and predicting the environmental consequences of the mining or natural weathering of those deposits. Performing these functions requires that predictions be made of the likelihood of undiscovered deposits. The predictions are based on geologic and geoenviroAuthorsR. O. Rye, C.A. Johnson, G.P. Landis, A. H. Hofstra, P. Emsbo, C. A. Stricker, A.G. Hunt, B.G. RuskDiscrimination of carbon and nitrogen isotopes from milk to serum and vibrissae in Alaska Steller sea lions (Eumetopias jubatus)
Knowledge of diet-tissue stable isotope discrimination is required to properly interpret stable isotope values and to identify possible diet shifts, such as might be expected from nursing through weaning. This study compared ??13C and ??15N of paired serum and vibrissal roots with those of ingested milk (n = 52) from free-ranging Steller sea lion (Eumetopias jubatus (Schreber, 1776)) pups (1-11 moAuthorsV.K. Stegall, Sean D. Farley, Lorrie D. Rea, K.W. Pitcher, R. O. Rye, C.L. Kester, C. A. Stricker, C.R. Bern