Theses and Dissertations at Montana State University (MSU)
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Item Non-target effects of a novel invasive species management strategy: benthic invertebrate responses to lake trout embryo suppression in Yellowstone Lake, Wyoming(Montana State University - Bozeman, College of Letters & Science, 2020) Briggs, Michelle Anne; Chairperson, Graduate Committee: Lindsey Albertson; Lindsey K. Albertson, Dominique R. Lujan, Lusha M. Tronstad, Hayley C. Glassic, Christopher S. Guy and Todd M. Koel were co-authors of the article, 'Carcassd deposition to suppress invasive lake trout causes differential mortality of two common benthic invertebrates in Yellowstone Lake, Wyoming' in the journal 'Fundamental and applied limnology' which is contained within this thesis.; Lindsey K. Albertson, Dominique R. Lujan, Lusha M. Tronstad, Hayley C. Glassic, Christopher S. Guy and Todd M. Koel were co-authors of the article, 'Non-target effects of a novel suppression technique for invasive fishes: responses of benthic invertebrate communities' submitted to the journal 'Ecological applications' which is contained within this thesis.Invasive species threaten native biodiversity and ecosystem function, and suppression is often required to reduce these effects. However, invasive species management actions can cause harmful, unintended consequences for non-target taxa. In Yellowstone Lake, Wyoming, invasive lake trout (Salvelinus namaycush) have reduced abundance of the native Yellowstone cutthroat trout (Oncorhynchus clarkii bouvieri), decreasing availability of an important food source for aquatic and terrestrial predators. Gillnets are used to suppress adult lake trout, and the lake trout carcasses are then deposited onto spawning sites in the littoral zone to cause embryo mortality by reducing dissolved oxygen concentrations as they decay. However, this management action may have non-target effects on organisms in the lake, including benthic invertebrates, which comprise a large portion of native trout diets. Some taxa of invertebrates may benefit from the addition of nutrients to the littoral zone, while other taxa may experience mortality in response to low dissolved oxygen conditions caused by carcass decay. We conducted two field experiments to understand how carcass treatment affects benthic invertebrates in Yellowstone Lake. First, we conducted an in situ experiment with individual invertebrates housed in small chambers covered by carcasses to determine if carcass treatment causes mortality of hypoxia-tolerant amphipods and hypoxia-sensitive caddisflies. We found that carcass treatment caused increased mortality in caddisflies but not amphipods. Second, we conducted a field experiment to investigate how carcass treatment affects invertebrate communities when applied at entire spawning sites. We also compared invertebrate communities at cobble-dominated lake trout spawning sites to macrophyte-dominated sites to determine if carcass treatment could alter food web dynamics at a lake-wide scale. We found that carcass treatment causes non-target effects on benthic invertebrates, specifically reducing immobile taxa, hypoxia-sensitive taxa, and Chironomidae, and altering community structure. Areas dominated by macrophytes had more abundant and larger invertebrates than spawning sites. Due to the small spatial extent of spawning sites and the higher abundance of invertebrates at other habitats in the lake, we conclude carcass treatment can have localized non-target effects at a local scale but is unlikely to alter food-web dynamics at a lake-wide scale.Item Carcass monitoring and grizzly bear scavenging across two management jurisdictions of the northern Yellowstone winter range (1997-2012)(Montana State University - Bozeman, College of Agriculture, 2016) Regan, Brooke Sierra; Chairperson, Graduate Committee: Bok SowellSpring ungulate carcasses are an important food source for grizzly bears (Ursus arctos) on the Northern Yellowstone Winter Range (NYWR). The objectives of this study were to: 1) provide a 1997 - 2012 update on spring carcass monitoring surveys across the NYWR, 2) compare grizzly bear use of carcasses in the spring between the Gallatin National Forest (GNF) and Yellowstone National Park (YNP), and 3) compare detection rates for two carcass survey techniques implemented on the GNF in 2006, 2008, and 2009. Carcasses occurred on the NYWR at low quantities (x= 31 carcasses per year), with the exception of 'pulse' events in 1997, 2006, 2008, and 2011 (x = 152 carcasses per year). On average, 76% of the carcasses on the NYWR were elk, and 57% were classified as adults. Wilcoxon rank sum tests indicated that both the proportion of carcasses used by grizzly bears and the number of carcasses used per kilometer of transect was less (P = 0.010 and P = 0.018, respectively) on the GNF than YNP in 'pulse years' and did not differ (P = 0.470 and P = 0.550) in years characterized by low carcass counts. Direct evidence of human activity was documented at 80% of all mature elk carcass sites on the GNF, and was estimated by YNP management to not exceed 1% of all carcass sites in YNP, although no data was collected. Density of roads was higher (P < 0.001) on the GNF than in YNP. I used a multiple logistic regression framework to assess the correlates of grizzly bear carcass use and found that the only significant parameter of ecological interest to predict grizzly bear use of carcasses was road density. The odds that grizzly bears scavenged on a given survey area in a given year decreased 83% for every 1 km/6.15 km 2 increase in road density. A Wilcoxon rank sum test of carcass detection rates for strategically and systematically placed transects revealed no differences or higher detection rate ranks for the less resource intensive strategic method. Managers of multi-use ungulate winter ranges may consider spring road closures that limit human activity, in order to enhance foraging opportunities for grizzly bears.