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Glassic HC, Guy CS, Tronstad LM, Lujan DR, Briggs MA, Albertson LK, Koel TM. Invasive predator diet plasticity has implications for native fish conservation and invasive species suppression. PLoS One 2023; 18:e0279099. [PMID: 36827303 PMCID: PMC9956068 DOI: 10.1371/journal.pone.0279099] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2022] [Accepted: 11/29/2022] [Indexed: 02/25/2023] Open
Abstract
Diet plasticity is a common behavior exhibited by piscivores to sustain predator biomass when preferred prey biomass is reduced. Invasive piscivore diet plasticity could complicate suppression success; thus, understanding invasive predator consumption is insightful to meeting conservation targets. Here, we determine if diet plasticity exists in an invasive apex piscivore and whether plasticity could influence native species recovery benchmarks and invasive species suppression goals. We compared diet and stable isotope signatures of invasive lake trout and native Yellowstone cutthroat trout (cutthroat trout) from Yellowstone Lake, Wyoming, U.S.A. as a function of no, low-, moderate-, and high-lake trout density states. Lake trout exhibited plasticity in relation to their density; consumption of cutthroat trout decreased 5-fold (diet proportion from 0.89 to 0.18) from low- to high-density state. During the high-density state, lake trout switched to amphipods, which were also consumed by cutthroat trout, resulting in high diet overlap (Schoener's index value, D = 0.68) between the species. As suppression reduced lake trout densities (moderate-density state), more cutthroat trout were consumed (proportion of cutthroat trout = 0.42), and diet overlap was released between the species (D = 0.30). A shift in lake trout δ13C signatures from the high- to the moderate-density state also corroborated increased consumption of cutthroat trout and lake trout diet plasticity. Observed declines in lake trout are not commensurate with expected cutthroat trout recovery due to lake trout diet plasticity. The abundance of the native species in need of conservation may take longer to recover due to the diet plasticity of the invasive species. The changes observed in diet, diet overlap, and isotopes associated with predator suppression provides more insight into conservation and suppression dynamics than using predator and prey biomass alone. By understanding these dynamics, we can better prepare conservation programs for potential feedbacks caused by invasive species suppression.
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Affiliation(s)
- Hayley C. Glassic
- Montana Cooperative Fishery Research Unit, Department of Ecology, Montana State University, Bozeman, Montana, United States of America,* E-mail:
| | - Christopher S. Guy
- Department of Ecology, U.S. Geological Survey, Montana Cooperative Fishery Research Unit, Montana State University, Bozeman, Montana, United States of America
| | - Lusha M. Tronstad
- Wyoming Natural Diversity Database, University of Wyoming, Laramie, Wyoming, United States of America
| | - Dominique R. Lujan
- Department of Zoology and Physiology, University of Wyoming, Laramie, Wyoming, United States of America
| | - Michelle A. Briggs
- Montana Cooperative Fishery Research Unit, Department of Ecology, Montana State University, Bozeman, Montana, United States of America,Department of Ecology, Montana State University, Bozeman, Montana, United States of America
| | - Lindsey K. Albertson
- Department of Ecology, Montana State University, Bozeman, Montana, United States of America
| | - Todd M. Koel
- U.S. National Park Service, Yellowstone Center for Resources, Native Fish Conservation Program, Yellowstone National Park, Wyoming, United States of America
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Christianson D, Coleman TH, Doan Q, Haroldson MA. Physiological consequences of consuming low-energy foods: herbivory coincides with a stress response in Yellowstone bears. CONSERVATION PHYSIOLOGY 2021; 9:coab029. [PMID: 34345432 PMCID: PMC8325456 DOI: 10.1093/conphys/coab029] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/13/2021] [Revised: 03/25/2021] [Accepted: 04/08/2021] [Indexed: 06/13/2023]
Abstract
Meat, fruit, seeds and other high-energy bear foods are often highly localized and briefly available and understanding which factors influence bear consumption of these foods is a common focus of bear conservation and ecology. However, the most common bear foods, graminoids and forbs, are more widespread but of lower quality. We poorly understand how herbage consumption impacts bear physiology, such as endocrine system function that regulates homeostasis and stress responses. Here, we described bear diets with a novel approach, measuring the concentration of chlorophyll in bear scats (faecal chlorophyll) to index the proportion of the recent diet that was composed of leaves from graminoids and forbs. We measured faecal chlorophyll and faecal cortisol in 351 grizzly (Ursus arctos, n = 255) and black bear (Ursus americanus, n = 96) scats from Yellowstone National Park in 2008-2009. We compared models of faecal chlorophyll and faecal cortisol concentrations considering the effects of spatial, dietary, scat and bear-specific factors including species. Faecal chlorophyll levels were the strongest predictor of faecal cortisol in a manner that suggested an endocrine response to a low-energy diet. Both compounds were highest during the spring and early summer months, overlapping the breeding season when higher energy foods were less available. Effects of scat composition, scat weathering, bear age, bear sex, species and other factors that have previously been shown to influence faecal cortisol in bears were not important unless faecal chlorophyll was excluded from models. The top models of faecal chlorophyll suggested grazing was primarily influenced by spatial attributes, with greater grazing closer to recreational trails, implying that elevated cortisol with grazing could be a response to anthropogenic activity. Our results confirm that higher stress hormone concentrations correspond with lower quality diets in bears, particularly grazing, and that faecal chlorophyll shows promise as a metric for studying grazing behaviour and its consequences.
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Affiliation(s)
- David Christianson
- Department of Ecosystem Science and Management, University of Wyoming, Laramie, WY 82071, USA
| | - Tyler H Coleman
- Sequoia-Kings Canyon National Park, National Park Service, 47050 Generals Highway, Three Rivers, CA 93271, USA
| | - Quint Doan
- School of Forestry and Environmental Studies, Yale University, 370 Prospect Street, New Haven CT 06511, USA
| | - Mark A Haroldson
- U.S. Geological Survey, Northern Rocky Mountain Science Center, Interagency Grizzly Bear Study Team, 2327 University Way, Suite 2, Bozeman, MT 59717, USA
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Abstract
Invasive predatory lake trout Salvelinus namaycush were discovered in Yellowstone Lake in 1994 and caused a precipitous decrease in abundance of native Yellowstone cutthroat trout Oncorhynchus clarkii bouvieri. Suppression efforts (primarily gillnetting) initiated in 1995 did not curtail lake trout population growth or lakewide expansion. An adaptive management strategy was developed in 2010 that specified desired conditions indicative of ecosystem recovery. Population modeling was used to estimate effects of suppression efforts on the lake trout and establish effort benchmarks to achieve negative population growth (λ < 1). Partnerships enhanced funding support, and a scientific review panel provided guidance to increase suppression gillnetting effort to >46,800 100-m net nights; this effort level was achieved in 2012 and led to a reduction in lake trout biomass. Total lake trout biomass declined from 432,017 kg in 2012 to 196,675 kg in 2019, primarily because of a 79% reduction in adults. Total abundance declined from 925,208 in 2012 to 673,983 in 2019 but was highly variable because of recruitment of age-2 fish. Overall, 3.35 million lake trout were killed by suppression efforts from 1995 to 2019. Cutthroat trout abundance remained below target levels, but relative condition increased, large individuals (> 400 mm) became more abundant, and individual weights doubled, probably because of reduced density. Continued actions to suppress lake trout will facilitate further recovery of the cutthroat trout population and integrity of the Yellowstone Lake ecosystem.
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Koel TM, Tronstad LM, Arnold JL, Gunther KA, Smith DW, Syslo JM, White PJ. Predatory fish invasion induces within and across ecosystem effects in Yellowstone National Park. SCIENCE ADVANCES 2019; 5:eaav1139. [PMID: 30906863 PMCID: PMC6426464 DOI: 10.1126/sciadv.aav1139] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/15/2018] [Accepted: 01/31/2019] [Indexed: 05/30/2023]
Abstract
Predatory fish introduction can cause cascading changes within recipient freshwater ecosystems. Linkages to avian and terrestrial food webs may occur, but effects are thought to attenuate across ecosystem boundaries. Using data spanning more than four decades (1972-2017), we demonstrate that lake trout invasion of Yellowstone Lake added a novel, piscivorous trophic level resulting in a precipitous decline of prey fish, including Yellowstone cutthroat trout. Plankton assemblages within the lake were altered, and nutrient transport to tributary streams was reduced. Effects across the aquatic-terrestrial ecosystem boundary remained strong (log response ratio ≤ 1.07) as grizzly bears and black bears necessarily sought alternative foods. Nest density and success of ospreys greatly declined. Bald eagles shifted their diet to compensate for the cutthroat trout loss. These interactions across multiple trophic levels both within and outside of the invaded lake highlight the potential substantial influence of an introduced predatory fish on otherwise pristine ecosystems.
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Affiliation(s)
- Todd M. Koel
- Yellowstone Center for Resources, Mammoth Hot Springs, Yellowstone National Park, WY 82190, USA
| | - Lusha M. Tronstad
- Wyoming Natural Diversity Database, University of Wyoming, Laramie, WY 82071, USA
| | - Jeffrey L. Arnold
- Yellowstone Center for Resources, Mammoth Hot Springs, Yellowstone National Park, WY 82190, USA
| | - Kerry A. Gunther
- Yellowstone Center for Resources, Mammoth Hot Springs, Yellowstone National Park, WY 82190, USA
| | - Douglas W. Smith
- Yellowstone Center for Resources, Mammoth Hot Springs, Yellowstone National Park, WY 82190, USA
| | - John M. Syslo
- Montana Cooperative Fishery Research Unit, Montana State University, Bozeman, MT 59717, USA
| | - Patrick J. White
- Yellowstone Center for Resources, Mammoth Hot Springs, Yellowstone National Park, WY 82190, USA
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Carroll EL, Bruford MW, DeWoody JA, Leroy G, Strand A, Waits L, Wang J. Genetic and genomic monitoring with minimally invasive sampling methods. Evol Appl 2018; 11:1094-1119. [PMID: 30026800 PMCID: PMC6050181 DOI: 10.1111/eva.12600] [Citation(s) in RCA: 88] [Impact Index Per Article: 14.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2017] [Accepted: 01/02/2018] [Indexed: 12/12/2022] Open
Abstract
The decreasing cost and increasing scope and power of emerging genomic technologies are reshaping the field of molecular ecology. However, many modern genomic approaches (e.g., RAD-seq) require large amounts of high-quality template DNA. This poses a problem for an active branch of conservation biology: genetic monitoring using minimally invasive sampling (MIS) methods. Without handling or even observing an animal, MIS methods (e.g., collection of hair, skin, faeces) can provide genetic information on individuals or populations. Such samples typically yield low-quality and/or quantities of DNA, restricting the type of molecular methods that can be used. Despite this limitation, genetic monitoring using MIS is an effective tool for estimating population demographic parameters and monitoring genetic diversity in natural populations. Genetic monitoring is likely to become more important in the future as many natural populations are undergoing anthropogenically driven declines, which are unlikely to abate without intensive adaptive management efforts that often include MIS approaches. Here, we profile the expanding suite of genomic methods and platforms compatible with producing genotypes from MIS, considering factors such as development costs and error rates. We evaluate how powerful new approaches will enhance our ability to investigate questions typically answered using genetic monitoring, such as estimating abundance, genetic structure and relatedness. As the field is in a period of unusually rapid transition, we also highlight the importance of legacy data sets and recommend how to address the challenges of moving between traditional and next-generation genetic monitoring platforms. Finally, we consider how genetic monitoring could move beyond genotypes in the future. For example, assessing microbiomes or epigenetic markers could provide a greater understanding of the relationship between individuals and their environment.
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Affiliation(s)
- Emma L. Carroll
- Scottish Oceans Institute and Sea Mammal Research UnitUniversity of St AndrewsSt AndrewsUK
| | - Mike W. Bruford
- Cardiff School of Biosciences and Sustainable Places Research InstituteCardiff UniversityCardiff, WalesUK
| | - J. Andrew DeWoody
- Department of Forestry and Natural Resources and Department of Biological SciencesPurdue UniversityWest LafayetteINUSA
| | - Gregoire Leroy
- Animal Production and Health DivisionFood and Agriculture Organization of the United NationsRomeItaly
| | - Alan Strand
- Grice Marine LaboratoryDepartment of BiologyCollege of CharlestonCharlestonSCUSA
| | - Lisette Waits
- Department of Fish and Wildlife SciencesUniversity of IdahoMoscowIDUSA
| | - Jinliang Wang
- Institute of ZoologyZoological Society of LondonLondonUK
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Keay JA, Robbins CT, Farley SD. Characteristics of a naturally regulated grizzly bear population. J Wildl Manage 2018. [DOI: 10.1002/jwmg.21425] [Citation(s) in RCA: 38] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Affiliation(s)
- Jeffrey A. Keay
- U.S. Geological SurveyAlaska Science CenterP.O. Box 9Denali National ParkAK99755USA
| | - Charles T. Robbins
- School of the Environment and School of Biological SciencesWashington State UniversityPullmanWA99164‐4236USA
| | - Sean D. Farley
- Alaska Department of Fish and Game333 Raspberry RoadAnchorageAK99518USA
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Selecting the best stable isotope mixing model to estimate grizzly bear diets in the Greater Yellowstone Ecosystem. PLoS One 2017; 12:e0174903. [PMID: 28493929 PMCID: PMC5426898 DOI: 10.1371/journal.pone.0174903] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2016] [Accepted: 03/17/2017] [Indexed: 11/19/2022] Open
Abstract
Past research indicates that whitebark pine seeds are a critical food source for Threatened grizzly bears (Ursus arctos) in the Greater Yellowstone Ecosystem (GYE). In recent decades, whitebark pine forests have declined markedly due to pine beetle infestation, invasive blister rust, and landscape-level fires. To date, no study has reliably estimated the contribution of whitebark pine seeds to the diets of grizzlies through time. We used stable isotope ratios (expressed as δ13C, δ15N, and δ34S values) measured in grizzly bear hair and their major food sources to estimate the diets of grizzlies sampled in Cooke City Basin, Montana. We found that stable isotope mixing models that included different combinations of stable isotope values for bears and their foods generated similar proportional dietary contributions. Estimates generated by our top model suggest that whitebark pine seeds (35±10%) and other plant foods (56±10%) were more important than meat (9±8%) to grizzly bears sampled in the study area. Stable isotope values measured in bear hair collected elsewhere in the GYE and North America support our conclusions about plant-based foraging. We recommend that researchers consider model selection when estimating the diets of animals using stable isotope mixing models. We also urge researchers to use the new statistical framework described here to estimate the dietary responses of grizzlies to declines in whitebark pine seeds and other important food sources through time in the GYE (e.g., cutthroat trout), as such information could be useful in predicting how the population will adapt to future environmental change.
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Tronstad LM, Hall RO, Koel TM. Introduced lake trout alter nitrogen cycling beyond Yellowstone Lake. Ecosphere 2015. [DOI: 10.1890/es14-00544.1] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
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van Manen FT, Haroldson MA, Bjornlie DD, Ebinger MR, Thompson DJ, Costello CM, White GC. Density dependence, whitebark pine, and vital rates of grizzly bears. J Wildl Manage 2015. [DOI: 10.1002/jwmg.1005] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Frank T. van Manen
- U.S. Geological SurveyNorthern Rocky Mountain Science Center, Interagency Grizzly Bear Study Team2327 University Way, Suite 2BozemanMT59715USA
| | - Mark A. Haroldson
- U.S. Geological SurveyNorthern Rocky Mountain Science Center, Interagency Grizzly Bear Study Team2327 University Way, Suite 2BozemanMT59715USA
| | | | - Michael R. Ebinger
- College of Forestry and ConservationUniversity MontanaUniversity Hall, Room 309MissoulaMT59812USA
| | | | - Cecily M. Costello
- College of Forestry and ConservationUniversity MontanaUniversity Hall, Room 309MissoulaMT59812USA
| | - Gary C. White
- Department of Fish, Wildlife, and Conservation BiologyColorado State UniversityFort CollinsCO80523USA
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López-Alfaro C, Coogan SCP, Robbins CT, Fortin JK, Nielsen SE. Assessing Nutritional Parameters of Brown Bear Diets among Ecosystems Gives Insight into Differences among Populations. PLoS One 2015; 10:e0128088. [PMID: 26083536 PMCID: PMC4470632 DOI: 10.1371/journal.pone.0128088] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2014] [Accepted: 04/22/2015] [Indexed: 11/19/2022] Open
Abstract
Food habit studies are among the first steps used to understand wildlife-habitat relationships. However, these studies are in themselves insufficient to understand differences in population productivity and life histories, because they do not provide a direct measure of the energetic value or nutritional composition of the complete diet. Here, we developed a dynamic model integrating food habits and nutritional information to assess nutritional parameters of brown bear (Ursus arctos) diets among three interior ecosystems of North America. Specifically, we estimate the average amount of digestible energy and protein (per kilogram fresh diet) content in the diet and across the active season by bears living in western Alberta, the Flathead River (FR) drainage of southeast British Columbia, and the Greater Yellowstone Ecosystem (GYE). As well, we estimate the proportion of energy and protein in the diet contributed by different food items, thereby highlighting important food resources in each ecosystem. Bear diets in Alberta had the lowest levels of digestible protein and energy through all seasons, which might help explain the low reproductive rates of this population. The FR diet had protein levels similar to the recent male diet in the GYE during spring, but energy levels were lower during late summer and fall. Historic and recent diets in GYE had the most energy and protein, which is consistent with their larger body sizes and higher population productivity. However, a recent decrease in consumption of trout (Oncorhynchus clarki), whitebark pine nuts (Pinus albicaulis), and ungulates, particularly elk (Cervus elaphus), in GYE bears has decreased the energy and protein content of their diet. The patterns observed suggest that bear body size and population densities are influenced by seasonal availability of protein an energy, likely due in part to nutritional influences on mass gain and reproductive success.
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Affiliation(s)
- Claudia López-Alfaro
- Department of Renewable Resources, University of Alberta, 751 GSB, Edmonton, T6G 2H1, AB, Canada
- Departamento de Ciencias Ambientales y Recursos Naturales Renovables, Universidad de Chile, Av. Santa Rosa, 11315, Casilla 9206, Santiago Chile
- * E-mail:
| | - Sean C. P. Coogan
- Department of Renewable Resources, University of Alberta, 751 GSB, Edmonton, T6G 2H1, AB, Canada
- School of Biological Sciences and the Charles Perkins Centre, University of Sydney, Sydney, NSW 2006, Australia
| | - Charles T. Robbins
- School of the Environment and School of Biological Sciences, Washington State University, Pullman, WA, United States of America
| | - Jennifer K. Fortin
- School of Biological Sciences, Washington State University, Pullman, WA, United States of America
| | - Scott E. Nielsen
- Department of Renewable Resources, University of Alberta, 751 GSB, Edmonton, T6G 2H1, AB, Canada
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