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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.
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.
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.
Physiological traits and stress tolerances of three high-elevation pine species
(Montana State University - Bozeman, College of Letters & Science, 2023) Wasteneys, Chloe Elizabeth; Chairperson, Graduate Committee: Danielle Ulrich
The increasing frequency and intensity of drought and heat events are increasing forest mortality rates worldwide. To improve restoration and management effort effectiveness for at- risk tree species and to accurately predict how these species will respond to future climates, the physiological mechanisms of seedling establishment and survival need to be fully understood. Using a greenhouse common garden approach, we compared the physiological traits and stress tolerances of three high-elevation five-needle pine species, Pinus albicaulis (PIAL), P. flexilis (PIFL), and P. longaeva (PILO). We measured a suite of physiological response curves to determine photosynthetic capacity, high-light tolerance, drought tolerance, and heat tolerance traits. We compared these traits among the three species (Q1), among three different ages of PIAL seedlings (2-, 3-, and 5-years-old; Q2), and among seven families of 2-year-old PIAL originating from different locations (Q3). Among species (Q1), only one heat tolerance trait (Tcrit, the temperature at which minimal fluorescence begins to increase) significantly differed and increased from PILO to PIFL to PIAL, suggesting that PIAL had greater heat tolerance than PIFL and PILO. Among PIAL ages (Q2), two drought tolerance traits, saturated water content (SWC) and leaf mass per area (LMA), and two heat tolerance traits, Tcrit and T50_EL (temperature that results in a 50% increase in electrolyte leakage), significantly differed among ages. SWC decreased, LMA and Tcrit increased, and T50_EL partially increased with increasing age, suggesting that older PIAL seedlings may be more drought and heat tolerant than younger PIAL seedlings. Among PIAL families (Q3), no traits significantly differed. However, we observed four significant correlations between our measured traits and growing season mean temperature and vapor pressure deficit of the seven PIAL families. Families from relatively cooler, wetter locations tended to have greater high-light tolerance and greater heat tolerance (based on T50_EL) while families from relatively warmer, drier locations tended to have greater heat tolerances (based on Tcrit and T50 measured with chlorophyll fluorescence). Together, these findings improve our understanding of physiological mechanisms underlying seedling establishment and our ability to predict how these species may be affected by future climates.
Wetland biodiversity in Grand Teton National Park
(Montana State University - Bozeman, College of Letters & Science, 2022) Levandowski, Mary Lynn; Chairperson, Graduate Committee: Andrea Litt; Andrea R. Litt was a co-author of the article, 'Spatial and temporal isolation and size of wetlands influence richness and functional composition of aquatic macroinvertebrates' which is contained within this thesis.; Andrea R. Litt, Megan F. McKenna, Shan Burson and Kristin L. Legg were co-authors of the article, 'Multi-method biodiversity assessments from wetlands in Grand Teton National Park' in the journal 'Ecological indicators' which is contained within this thesis.
Freshwater wetlands support high biodiversity, yet many wetlands are subject to shifts in precipitation and temperature under projected climate patterns. These changes can alter wetland hydrological regimes, potentially leading to longer or more frequent dry periods, with effects that differ among taxa. In this thesis we aim to build on the understanding about biodiversity in wetlands and how these species may be affected by climate change, in hopes of providing information for land management. To accomplish these goals, we first focused on macroinvertebrates, a group that employs diverse strategies for surviving wetland drying. We explored the roles of wetland size, spatial isolation, and temporal isolation on macroinvertebrate richness and community composition. In summer 2018, we collected macroinvertebrates from 18 wetlands in Grand Teton National Park. We found macroinvertebrate family richness increased with wetland depth and slower rates of drying. We also found the interaction between spatial and temporal isolation explained the most variation in community composition for all the life history strategies we examined. Second, we explored the utility of different automated tools to monitor biodiversity in wetlands. In 2017, we placed wildlife cameras, as well as acoustic (audible and ultrasonic) recorders at 4 permanent wetlands in Grand Teton National Park for a week in June and August; we also completed a visual survey during each of these time intervals. We compared the number and type of species detected by each method over the summer to evaluate the effectiveness of each method for monitoring. Using wildlife cameras, in addition to visual surveys, increased the observation time at surveyed wetlands, captured complementary species, and recorded dynamics in the water level during the summer. These two chapters provide insights about how changes resulting from increased drying may affect one of the most biodiverse taxa and offer methods that allow monitoring of many taxa simultaneously.
Climate-fire-vegetation dynamics in the Greater Yellowstone Ecosystem: recent trends and future projections in a changing climate
(Montana State University - Bozeman, College of Letters & Science, 2020) Emmett, Kristen Dawn; Co-chairs, Graduate Committee: Benjamin Poulter and David Roberts; Katherine M. Renwick and Benjamin Poulter were co-authors of the article, 'Disdentangling climate and disturbance effects on regional vegetation greening trends' in the journal 'Ecosystems' which is contained within this dissertation.; Katherine M. Renwick and Benjamin Poulter were co-authors of the article, 'Adapting a dynamic vegetation model for regional biomass, plant biogeography, and fire modeling in the western U.S.: evaluating LPJ-GUESSLMFIRECF' submitted to the journal 'Ecological modelling' which is contained within this dissertation.; Benjamin Poulter was a co-author of the article, 'Processed-based modeling approaches for climate-vegetation-fire feedbacks in the Greater Yellowstone Ecosystem' which is contained within this dissertation.
Climate change threatens to change forested ecosystems and wildfire characteristics across the globe. For the Greater Yellowstone Ecosystem (GYE), under future warming temperatures, wildfire activity is expected to increase and the suitable habitat for many dominant tree species is expected to shrink. Previous studies predict large high severity fires to occur more frequently, potentially so frequent that forests are unable to grow old enough to produce seeds and self-regenerate. Studies of suitable climate spaces show that previously habitable areas may become too warm or dry to support common GYE trees. The first goal of this dissertation was to use vegetation images from satellites to detect recent changes in forest productivity in the GYE, and then determine the relative importance of recent climate and disturbance observations in explaining these changes. We found that areas with detected increases in plant growth, or 'greening' trends, were associated with forested areas regenerating after wildfire. Detected decreases in plant growth, or 'browning' trends, were associated with areas that had recently burned. Historically dry areas with recent increases in precipitation were associated with greening trends. Warming of 0-2 °C was associated with greening trends, while greater increases in temperature (>2 °C) were correlated with browning trends. The key take-away is although forests in the GYE are usually considered temperature limited, changes in precipitation may be more important than previously thought. The second goal of this dissertation was to adapt a global vegetation computer model for regional applications to simulate forests and wildfire dynamics, ultimately to run simulations under future climate conditions to predict how forest extent and composition may change. Life history characteristics and climate limitations were aquired for the dominant GYE plant types to dictate their establishment, growth, competition, and mortality in the new model. Before running future simulations, it is required to evaluate how well the model represents current conditions. Adding new equations that calculate the initiation, spread, and effects of crown fires was required to reproduce recent vegetation abundance, distribution of plant types, and fire activity in the GYE. Methods, expected results, and implications of running future simulations are described in Chapter 4.
Linking plant and soil nutrient dynamics in temperate and tropical montane forests
(Montana State University - Bozeman, College of Letters & Science, 2018) Qubain, Claire Anne; Chairperson, Graduate Committee: David Roberts; Jia Hu (co-chair); Yuriko Yano and Jia Hu were co-authors of the article, 'Linking nitrogen allocation in douglas-fir to soil nitrogen availability in a western montane conifer forest' submitted to the journal 'Oecologia' which is contained within this thesis.; Diego Riveros-Iregui and Jia Hu were co-authors of the article, 'Climate and invasion drive soil nutrient dynamics in tropical montane forests of the Galapagos archipelago' submitted to the journal 'Ecology' which is contained within this thesis.
I built on our fundamental understanding of ecosystem function by examining how climate variability influences feedbacks between plant processes and soil nutrient dynamics. At Lubrecht Experimental Forest, I examined how variability in snow depth, precipitation, and soil moisture influenced seasonal nitrogen allocation in Douglas-fir. I then examined if N cycling within Douglas-fir synchronized with patterns of N availability in the soil. In this case, N availability in the soil influenced plant nutrient dynamics. On the other hand, on San Cristobal Island in the Galapagos Archipelago, plants fed back and influenced soil nutrient dynamics. Changes in precipitation, soil moisture, and temperature strongly controlled nutrient concentrations in the soil, and to a lesser degree, plant community type determined nutrient concentrations, especially N concentrations, in the soil.
The effects of climate-warming on solitary bees and their interactions with plants
(Montana State University - Bozeman, College of Letters & Science, 2019) Slominski, Anthony Hayden; Chairperson, Graduate Committee: Laura Burkle and Jia Hu (co-chair)
The ecological consequences of anthropogenic climate-warming remain poorly understood for pollinators. In order to better understand these consequences, and thus the consequences of climate-warming for pollination services, we must determine how pollinator life histories mediate responses to climate-warming. To help address these research needs, we conducted three studies. First, we used field-collected solitary bee species (i.e., Osmia spp. and Megachile spp.) to investigate how overwintering life stage (i.e., adult versus prepupae), body size, and sex influenced solitary bee survival, weight loss prior to emerging, and timing of emergence in response to manipulated seasonal temperature and the durations of seasons. Second, we manipulated the amount of asynchrony (days) between female solitary bee emergence and flowering periods. We used a mesocosm-based experimental design to investigate the effects of phenological asynchrony on the female lifespan, female interaction rates with flowers, and reproductive success. In a third study, we manipulated the amount of phenological difference between conspecific male and female solitary bees (i.e., the degree of protandry; males emerging prior to females), and investigated the influence of sex-specific phenological responses to temperature on male-female interactions and reproductive success. Our main findings and subsequent conclusions were that i) compared to bees that overwinter as prepupae, patterns in weight loss prior to emergence, adult longevity, and timing of emergence suggested that post-emergence fitness in adult-wintering bees may decrease under climate-warming as a result of increased energy depletion at the time of emergence, increasing asynchrony with flowering periods, and sex-specific phenological responses, ii) asynchrony between a spring-active female solitary bee species (i.e., Osmia cornifrons) and flowering periods caused reductions in offspring body size and reduced interaction rates between females and flowers, which could have consequences for both bee and plant reproductive success, and iii) when the degree of protandry was either reduced or increased from an intermediate level, the probability of female offspring production tended to decrease. This suggests that changes in the degree of protandry may influence the fitness tradeoffs associated with protandry, resulting in consequences for current and future solitary bee reproductive success.
Understanding the effects of wildfire on the functional traits of plants and bees
(Montana State University - Bozeman, College of Letters & Science, 2018) Durney, Janice Simone; Chairperson, Graduate Committee: Laura Burkle
Diversity, often assessed by species richness, fosters ecosystem success, promoting ecosystem services, stability, and adaptation. Evaluations of functional trait composition are a better indicator of ecological process dynamics. Functional trait variation of species within a community (i.e., inter-specific variation) and of individuals within a species (i.e., intra-specific variation) may reflect adaptations and phenotypic variation contributing to the functional diversity of a community in the face of change. Wildfires have shifted from mixed-severity to frequent high-severity fires, due to fire suppression and climate change, modifying ecosystem function, trait selection pressure, and species sorting. Traits involved in plant-pollinator interactions can be used to understand the mechanisms underlying shifting interactions across communities and how post-wildfire environmental conditions affect community assembly, structure, and stability. We tested how productivity, time-since-burn, and wildfire severity influenced mean functional trait values and inter- and intra-specific functional trait variation of plants and bees known to interact in southwestern Montana, USA. Fieldwork was conducted from 2013-2017 in two locations that differed in productivity with similar fire histories of recent-mixed-severity, recent-high-severity, older-high-severity burns, and unburned areas. Functional traits involved in plant-bee interactions were selected and measured among plant and bee species observed across these various productivity, time-since-burn, and fire severity levels. We found that as productivity and time-since-burn increased, the mean functional trait values and inter- and intra-specific functional trait variation of plants and bees increased. In addition, productivity, time-since-burn, and fire severity affected the functional trait values and variation of plant species more than bee species. These results suggest that as productivity and time-since-burn increases so does trait diversity - promoting ecosystem function and stability. The increased effect of productivity and time-since-burn on plant functional traits compared to bee traits suggests the dispersal abilities of bees allow them to cope with the effects of fire, while plant species are more prone to productivity and time-since-burn habitat filtering and species sorting, potentially due to limited mobility. Our results support previous findings that shifting wildfire regimes from mixed to high-severity burns increases species sorting and limits trait variation after wildfire regardless of productivity but trait variation increases as time-since-burn and productivity increases.
Understanding the present and past climate-fire-vegetation dynamics of southern South America (40 - 45°S)
(Montana State University - Bozeman, College of Letters & Science, 2020) Ogunkoya, Ayodele Gilbert; Chairperson, Graduate Committee: Benjamin Poulter; David Roberts (co-chair); Jed O. Kaplan, Cathy Whitlock, William Nanavati, Benjamin Poulter and David Roberts were co-authors of the article, 'Drivers of modeled forest cover change in southern South America are linked to climate and CO^2' which is contained within this thesis.; Jed O. Kaplan, Cathy Whitlock, William Nanavati, Benjamin Poulter, David Roberts and Steve Hostetler were co-authors of the article, 'Climate drivers of late-glacial to postgalacial forest cover along the eastern Andes of Northern Patagonia (lat. 40 - 45°S)' which is contained within this thesis.
The forest-steppe boundary that runs north-to-south along the eastern Andes is particularly dynamic over millennial time scales. Yet the relative role of long-term climate change and fire is poorly understood. In this study, I analyze the potential in using a process-based model in predicting species distribution, and the role fire and climate played in shaping the vegetation and treeline dynamics of Northern Patagonia (lat. 40 - 45 ° S). Paleoecological data, e.g., pollen, has been extensively used to study the relationship between climate and vegetation but has a low spatial resolution to distinguished between climate-fire-vegetation dynamics. Process-based model thus offers a transparent and robust method of incorporating a varying degree of complexity to understand fire behavior and fire-vegetation dynamics. Recently, LPJ-GUESS was parameterized to simulate major regional plant functional type (PFTs) and tree species distributions in this region. The model is able to predict regional species distribution across spatial scales by coupling establishment, growth, and mortality processes. Predicting spatial and temporal scale species distribution cannot be achieved without having the right climate and soil data, the climate data used was downscaled from 50 km to 1 km resolution using Worldclim climate data ( ~ 1 km) as the reference data. LPJ-GUESS model produced regional species distribution with fair to very good agreement with observation. The optimization of bioclimatic parameters and drought tolerance that is related to root depth, adaptability of plant to seasonal drought, and movement of nutrients consistently improved the accuracy of regional prediction of the species range. The model predicted that the vegetation distribution of present-day is mainly determined by climate and CO 2 rather than fire., while forest productivity responds strongly to elevated CO 2. However, based on the employed statistical methods of Canonical Correspondence Analysis (CCA) and Random Forest machine learning, combined with simulation results using paleoclimate. Results show that an increase in winter temperature drives the postglacial species distribution while changes in precipitation control radial growth and seedling establishment in the upper and lower treeline. These findings emphasize the importance of combining paleoecological methods with modeling to disentangle coarse-scale climate drivers from local influences.

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