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Impacts of forest mortality on streamflow in whitebark pine forests within the greater Yellowstone ecosystem
(Montana State University - Bozeman, College of Letters & Science, 2024) Rautu, Teodora Stefana; Co-chairs, Graduate Committee: Brian V. Smithers and Danielle E. M. Ulrich
Increasing forest mortality across the western U.S. raises concerns about its impact on streamflow. The hydrologic role of whitebark pine (Pinus albicaulis Engelm.) is of particular interest given its ongoing decline and prevalence at the upper treeline where precipitation is highest. Understanding the link between disturbed whitebark pine forests and streamflow is essential for better informing water resource management. In Chapter One, I investigated streamflow changes in two Wyoming whitebark pine watersheds: Upper Wind River (53% area affected by beetle outbreak) and Buffalo Fork (53% area affected by beetle outbreak and fire). Streamflow significantly increased post-beetle for Upper Wind River but did not significantly change post-disturbance for Buffalo Fork, attributed to the fire's limited spatial extent and post- beetle effects potentially occurring in the pre-disturbance period. In Chapter Two, I integrated Leaf Area Index into a hydrologic model to reflect changing canopy conditions and assessed water balance variables that drove the observed changes in streamflow in Chapter One. I found that an increase in annual precipitation primarily led to the increase in observed streamflow more so than forest mortality, and snowpack and snowmelt were consistent predictors of streamflow metrics. My findings suggest monitoring snow dynamics for accurate real-time and future streamflow forecasting. In Chapter Three, I used streamflow field data and the same hydrologic model to assess the impact of increasing tree mortality on streamflow within a whitebark pine- dominated watershed in Big Sky, Montana. After simulating mortality levels ranging from 0-90% for one year, tree mortality did not substantially impact streamflow until the 90% mortality level where annual flow and late summer flow substantially increased. Considering that mortality levels between 25-50% are more representative of whitebark pine mortality in one year, the lack of substantial impacts on snowpack and streamflow at the 25-50% mortality levels challenges the traditional assumption that whitebark pine mortality would lead to reduced snowpack and reduced late summer flow in open watersheds with 30% forest cover. Future studies should assess the multi-decade impacts of whitebark pine mortality on hydrologic processes and consider species differences in evapotranspiration as other subalpine species replace whitebark pine.
Irrigation ditches as novel intermittent stream networks that provide energetic subsidies to terrestrial ecosystems via aquatic insect emergence
(Montana State University - Bozeman, College of Letters & Science, 2024) Heili, Nathaniel Maxwell; Chairperson, Graduate Committee: Wyatt F. Cross
Non-perennial streams dominate fluvial networks, comprising over half of lotic ecosystems globally. Although little attention has been paid to these systems relative to those that are perennial, perhaps even less is known about the ecology of artificial intermittent streams. In irrigated river valleys, ditches comprise a substantial proportion of surface water networks, but little is known about their relative contributions to lotic habitat, freshwater biodiversity, and ecosystem processes. Because ditches are abundant and permeate arid floodplains, they create new opportunities for cross-ecosystem subsidies through emergence of adult aquatic insects. Here, we mapped the extent of an irrigation ditch network relative to natural surface waters in the Gallatin River Valley, Montana, USA. We also quantified the magnitude, composition, and phenology of aquatic insect emergence in ditches throughout a full irrigation season and compare emergence to nearby natural streams in the valley. We found that non-perennial streams, both natural and artificial, dominated the surface-water network, representing over 70% of total length. Irrigation ditches also constituted 37% and 23% of total length and surface area of all waterbodies in the valley, respectively. Insect emergence production from ditches averaged 32.0 mg m -2 d -1 and exceeded fluxes from nearby natural streams, which contained more classically sensitive taxa (i.e., Ephemeroptera, Trichoptera, and Plecoptera). Ditches varied in water temperature, substrate size, and flow permanence, leading to distinct emergence timing, species composition, and magnitudes of biomass flux. One of the study ditches dried early because of more 'junior' water rights, but this ditch provided the largest emergence subsidy, including a pulse of dipteran emergence at the onset of flow cessation. Annual production from intermittent ditches was ~6 g m -2 y -1 and was comparable to estimates from natural perennial streams. Although our study focused on one river valley of the western US, results suggest that these ecosystems contribute broadly to lotic habitat, heterogeneity, and cross-ecosystem subsidies via aquatic insect emergence. Given increasing demand for water and changes to flow regimes and water management driven by climate change, additional study is needed on these novel and underappreciated artificial ecosystems.
Pollinator conservation and restoration in semi-natural ecosystems
(Montana State University - Bozeman, College of Letters & Science, 2022) Glenny, William Robb; Chairperson, Graduate Committee: Laura Burkle; This is a manuscript style paper that includes co-authored chapters.
Semi-natural ecosystems are areas with biological and physical characteristics that resemble natural ecosystems but are also affected by anthropogenic disturbances. Semi-natural ecosystems are also areas with high insect pollinator diversity. Land management actions within semi-natural ecosystems may therefore be important to counteract future declines of insect pollinators. However, current restoration strategies for insect pollinator communities are based on evidence from agricultural ecosystems, which have frequent human interventions to ensure plant success, neglect the importance of nesting materials, and primarily benefit generalist species. To inform management actions for the conservation and restoration of insect pollinators in semi- natural ecosystems, I (1) synthesized the current understanding of the effects of common land management actions on insect pollinators on public lands in the US, (2) identified habitat characteristics which structure the taxonomic and functional diversity of bee communities, (3) evaluated the strength of influence of mechanisms associated with diet breadth across groups of bee species and (4) designed a conceptual model which can be used to select flowering plant species to provide food resources for bee communities in semi-natural ecosystems. Management actions that increase the abundance of floral and nesting resources to support bee species from different functional groups are required to conserve and restore insect pollinator communities in semi-natural ecosystems. I found that (1) management actions have positive, neutral, and negative effects on insect pollinators, but research trends vary depending on the taxon and habitat type, (2) the taxonomic and functional diversity of bee communities are structured by the abundance of both floral and nesting resources, (3) patterns of abundance across space and time have a more positive effect on the diet breadth of bumble bee species compared to non- bumble bee species, and (4) wildflower species that receive a high visitation rate and richness, occupy functionally important positions within bee-flower interaction networks, and are spatially and temporally widespread are important to provide bee communities with food resources in semi-natural ecosystems. These wildflower species may be particularly important to include within seed mixes to revegetate semi-natural ecosystems and provide food resources for insect pollinators.
Comparing juvenile physiology and morphology of two high-elevation pines, Pinus albicaulis and Pinus balfouriana
(Montana State University - Bozeman, College of Letters & Science, 2023) Sparks, Katherine Elizabeth; Chairperson, Graduate Committee: Danielle Ulrich
Whitebark pine (Pinus albicaulis, PIAL) and foxtail pine (P. balfouriana, PIBA) are slow-growing, high-elevation, five needled ("high five") white pines and are foundation and keystone species in alpine and subalpine environments, providing essential resources and habitat for many species including the Clark's nutcracker and grizzly bears. In recent years, PIAL has experienced significant decline due to an amalgamation of climate change, white pine blister rust, and mountain pine beetle. As a result, PIAL is listed as endangered under the Canadian Species at Risk Act and threatened under the United States Endangered Species Act. Conversely, PIBA has experienced minimal decline. PIBA also exists in two disjunct populations, one in southern California (PIBAS) and one in northern California (PIBA N), resulting in the species being split into two sub-species (P. balfouriana subsp. austrina and balfouriana). Our study compared the physiology and morphology of the two species (PIAL and PIBA) and the two foxtail populations (PIBA N and PIBAS) to better understand how they interact with and respond to abiotic and biotic stressors in their high-elevation environments. We grew four-year-old PIAL and PIBA juveniles in a common greenhouse environment. In total, we measured 159 traits describing their morphology, biomass, stomata, xylem, budburst phenology, physiology, whole plant Volatile Organic Compounds (wpVOCs), phloem volatile resin (PVR) compounds, and Non-Structural Carbohydrates (NSCs). We found that PIAL and PIBA displayed different suites of traits that enable them to persist in their high elevation habitats, characterized by similar abiotic stressors (cold temperatures, high winds, summer drought) and biotic stressors (white pine blister rust, bark beetle). The two foxtail populations were similar for most traits except for wpVOC concentration and composition where PIBAS had significantly higher wpVOC concentration than PIBA N. For most traits, PIAL was most similar to PIBA N and differed the most with PIBAS while PIBA N was the intermediate being more similar to both groups, especially in wpVOC composition and concentration.
Climate change at the air-water interface affects giant salmonfly (Pteronarcys californica) emergence timing and adult lifespan
(Montana State University - Bozeman, College of Letters & Science, 2023) Roche, Alzada Lois; Chairperson, Graduate Committee: Lindsey K. Albertson
Aquatic invertebrates experience complex temperature regimes throughout their life history, especially during the vulnerable life stage transition from aquatic to terrestrial habitats. When climate warming interacts with snowmelt in high elevation systems, it creates a novel set of conditions in which spring water temperatures remain within a narrow range from year-to-year while summer water and air temperatures rise. Giant salmonflies (Pteronarcys californica) depend on spring water temperature cues to time their large, synchronous emergence in early summer, but it is unknown how variable temperatures after this springtime cue affect life-history traits. We experimentally tested how changes in temperature in the 6 weeks before and after emergence affect emergence timing, emergence success, and adult lifespans. We found that the timing of emergence was 2.8 days earlier with each degree of warming during the weeks preceding emergence. However, there was no evidence that emergence success was affected by higher water temperature within our test temperature range (13-23°C). In the terrestrial adult stage, adult lifespans were shortened by increased air temperatures, especially when water temperatures during the aquatic juvenile stage had also been increased. The predicted lifespan was almost five times longer at the coldest air and water temperature combination than at the warmest (28 vs. 6 days). The shortest lifespans observed (3 days) are not likely to prevent successful reproduction, given that salmonflies can mate and oviposit within days of emergence. Still, because salmonflies can oviposit repeatedly for up to 80% of their lifespan, shortened lifespans may reduce total egg production and thus fitness. Our results indicate that rising water and air temperatures will impact not only the life history of the insects, but also the organisms in the riparian zone that rely on salmonfly emergence by altering the timing, magnitude, and duration of the nutrients provided by these large-bodied aquatic insects.
Effects of de-snaring on the demography and population dynamics of African lions
(Montana State University - Bozeman, College of Letters & Science, 2023) Banda, Kambwiri; Chairperson, Graduate Committee: Scott Creel
Lions and other African large carnivores are in decline, due in part to effects of illegal hunting with snares, which can reduce prey availability and directly kill or injure carnivores. It is difficult to effectively remove snares from large ecosystems by patrolling, but an additional approach to reduce effects on large carnivores is to monitor the population closely and de-snare individuals who are found in a snare or have broken free but still carry the wire (often with serious injury). The effectiveness of de-snaring programs to reduce impacts on large carnivores has not been directly tested. Here, we used long-term demographic data from 386 individually identified lions in the Luangwa Valley Ecosystem to test the effects on population growth (lambda) and population size (N) of a program to remove snares from injured lions and treat their wounds. Stochastic Leslie matrix projections for a period of five years showed that the population grew with the benefits of de-snaring but was expected to decline without de-snaring. Mean annual growth (lambda) was 1.037 (growth in 70% of years), closely matching observed changes in population size. Mean annual growth was 0.99 (with growth in 47% of years) for a model that assumed snared animals would have died if not treated, and 0.95 (with growth in 37% of years) for models that also accounted for super-additive effects via the death of dependent cubs and increased infanticide with increased male mortality. De-snaring requires intensive effort, but it can appreciably reduce the effect of snaring on lion population dynamics.
Bee and butterfly communities in roadside habitats: identifying patterns, protecting monarchs, and informing management
(Montana State University - Bozeman, College of Letters & Science, 2023) Meinzen, Thomas Claasen; Chairperson, Graduate Committee: Diane M. Debinski
Insect pollinators play a critical role in our natural and agricultural ecosystems. With global pollinator declines and habitat loss, attention has turned to roadside right-of-way lands (ROWs) as potential areas for supporting pollinator populations. Although many roadsides host flowering plants, understanding whether--and under what circumstances--roadsides actually benefit pollinator populations is critical for good conservation decision-making. Through a literature review, we found that pollinator population data (e.g., birth and death rates) are lacking to assess whether roadsides are a source or sink for pollinator populations. However, conscientious management practices, including reduced, well-timed mowing, selective, targeted spraying, and well-placed native plantings can improve roadsides' potential to support robust pollinator populations. Identifying roadside habitat for diverse pollinator communities and imperiled species is essential to prioritize pollinator-focused management practices across ROW systems. To support efforts to conserve monarch butterflies (Danaus plexippus), we surveyed 1,465 km (910 miles) of southern Idaho highways, mapping 1,363 patches of showy milkweed (Asclepias speciosa), the monarch's host plant. Roadside milkweed often bordered irrigated fields and crops; water availability may best explain its distribution. Existing statewide milkweed models (Svancara et al., 2019) did not effectively predict milkweed distribution in ROWs, suggesting the importance of roadside-specific factors, such as ROW management and disturbance history. To identify patterns of pollinator richness and abundance in Idaho ROWs, we surveyed butterflies and sampled bees at a randomized set of 63 100-meter (328-foot) roadside transects in southeastern Idaho, stratified by highway class and NDVI (greenness) category. Lower NDVI (less green) sites, those with more flowering plant species, and sites along smaller, less-trafficked highways supported significantly more species of bees, while ROWs with more abundant flowers were associated with more species of butterflies. Low NDVI sites were often characterized by native sagebrush plant communities, while sites of high NDVI were associated with high proportions of non-native plants, suggesting that NDVI might be useful both in predicting bee richness and abundance (low values) and locating developing noxious weed patches (high values). These results, together with our management recommendations, can help prioritize ROWs for pollinator protection and increase their capacity to support diverse pollinator communities.
Environmental drivers of bee community diversity in Yellowstone National Park
(Montana State University - Bozeman, College of Letters & Science, 2022) Switzer, Kristen Ann; Chairperson, Graduate Committee: Laura Burkle
Pollinators are essential to their ecosystems and facing large declines. Studies on environmental drivers of bee community composition are currently lacking in North America, particularly in national parks. Understanding how bee diversity and plant-bee interactions change across environmental gradients gives us insight into the resilience of bee communities in the future. We collected data at seven sites across an elevational gradient in Yellowstone National Park. Pan traps were used to collect bee diversity data from in 2010, 2011, 2012, and 2020, and hand-netting was used to collect plant-bee interaction data from June to August 2020. We hypothesized that elevation would be a major driver of bee abundance, species richness, and community composition and that bee diversity would decrease as elevation increased. We predicted bee diversity would peak in the middle of the growing season in response to floral diversity peaking at that time. Finally, we predicted plant-bee interactions would be more generalized at higher elevations and flower species richness would be a major driver of network specialization (H2'). Our results revealed that seasonality and elevation were major drivers of bee abundance and species richness, indicating that both spatial and temporal factors are important in driving bee community patterns. Bee species richness was highest in 2010 and declined over years, which may signal that changing environmental conditions are stressing bee communities. Bee abundance and species richness declined as each growing season progressed, which aligns with broader literature on various taxa and mirrors seasonal flower diversity patterns. Despite close alignment between bee and floral diversity patterns, flower species richness was only a significant driver of bee community composition, indicating that other environmental gradients were bigger drivers of bee abundance and species richness patterns. Bee species richness was a significant driver of plant-bee network specialization and elevation, slope, and flower species richness were marginally significant, suggesting that plant- bee interactions are influenced more by spatial than temporal variables. Additional studies focusing on bee diversity across growing seasons and years could provide insights into how changing environmental conditions in the future may influence bee diversity and community resilience in Yellowstone National Park.
Yellowstone Cutthroat Trout Recovery in Yellowstone Lake: Complex Interactions Among Invasive Species Suppression, Disease, and Climate Change
(Wiley, 2023-10) Glassic, Hayley C.; Chagaris, David D.; Guy, Christopher S.; Tronstad, Lusha M.; Lujan, Dominque R.; Briggs, Michelle A.; Albertson, Lindsey K.; Brenden, Travis O.; Walsworth, Timothy E.; Koel, Todd M.
n Yellowstone Lake, Wyoming, the largest inland population of nonhybridized Yellowstone Cutthroat Trout Oncorhynchus clarkii bouvieri, hereafter Cutthroat Trout, declined throughout the 2000s because of predation from invasive Lake Trout Salvelinus namaycush, drought, and whirling disease Myxobolus cerebralis. To maintain ecosystem function and conserve Cutthroat Trout, a Lake Trout gill netting suppression program was established in 1995, decreasing Lake Trout abundance and biomass. Yet, the response of Cutthroat Trout to varying Lake Trout suppression levels, collectively with the influence of disease and climate, is unknown. We developed an ecosystem model (calibrated to historical data) to forecast (2020–2050) whether Cutthroat Trout would achieve recovery benchmarks given disease, varying suppression effort, and climate change. Lake Trout suppression influenced Cutthroat Trout recovery; current suppression effort levels resulted in Cutthroat Trout recovering from historical lows in the early 2000s. However, Cutthroat Trout did not achieve conservation benchmarks when incorporating the influence of disease and climate. Therefore, the National Park Service intends to incorporate age‐specific abundance, spawner biomass, or both in conservation benchmarks to provide better indication of how management actions and environmental conditions influence Cutthroat Trout. Our results illustrate how complex interactions within an ecosystem must be simultaneously considered to establish and achieve realistic benchmarks for species of conservation concern.
Investigating the ability of arbuscular mycorrhizal fungi to mitigate the negative effects of warming and drought on native perennial forbs
(Montana State University - Bozeman, College of Letters & Science, 2022) Eggers, Jessica Avery; Chairperson, Graduate Committee: Laura Burkle; This is a manuscript style paper that includes co-authored chapters.
The ability of arbuscular mycorrhizal fungi (AMF) to mitigate the negative effects of warming and drought on plant hosts is known for crop species but is poorly understood for native, perennial forbs. Examining the indirect influence of AMF on forbs' responses to these stressors will provide a more complete understanding of how native forbs will be affected by climate change. In an experimental greenhouse study, we inoculated two native forb species (Achillea millefolium and Linum lewisii) with three separate AMF species (Rhizophagus clarus, Claroideoglomus etunicatum, and Gigaspora rosea), then exposed plants, including an uninoculated control treatment, to varying degrees of drought and heat stress in a factorial design. We tested the effects of warming or drought treatments on plants' physical, floral, phenological, and physiological traits, including biomass, height, floral abundance, flower size, first date of flowering, floral scent, and photosynthetic performance. For both forbs, AMF ameliorated the negative effects of drought and warming on plant survival and vegetative growth, but the magnitude of effect was specific to the forb species, climate treatment, and AMF inoculant. AMF also produced changes in forb phenology, floral scent (volatile organic compounds), and flowering success and duration, which have broad implications for plant-pollinator interactions and the links between belowground and aboveground symbioses. Together, these results indicate that AMF can assist native forbs in surviving, growing, and reproducing in a warmer and drier climate.

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