bluuebunny/crossref_metadata_2025_split huggingface dataset:
Scale‐dependent responses of understory vegetation to the physical structure of undisturbed tundra shrub patches
Authors: Wallace Cory A. , Baltzer Jennifer L. 
Published: September 2022

AbstractMuch of the Arctic is experiencing rapid change in the productivity and recruitment of tall, deciduous shrubs. It is well established that shrub expansion can alter tundra ecosystem composition and function; however, less is known about the degree to which variability in the physical structure of shrub patches might mediate these changes. There is also limited information as to how different physical attributes of shrub patches may covary and how they differ with topography. Here, we address these knowledge gaps by measuring the physical structure, abiotic conditions, and understory plant community composition at sampling plots within undisturbed green alder patches at a taiga–tundra ecotone site in the Northwest Territories, Canada. We found surprisingly few associations between most structural variables and abiotic conditions at the plot scale, with the notable exceptions of canopy complexity and snow depth. Importantly, neither patch structure nor abiotic conditions were associated with the vegetation community at the plot scale when among‐patch variation was accounted for. However, among‐patch variation in plant community composition was significant and represented a gradient in the richness of tundra specialists and Sphagnum moss abundance. This gradient was strongly associated with mean patch snow depth, which was likely controlled at least in part by mean patch canopy complexity. Overall, natural variability in green alder patch structure had less of an association with abiotic conditions than expected, suggesting future changes in physical structure at undisturbed sites may have limited environmental impact at the plot scale. However, at the patch scale, increases in snow depth, likely related to canopy complexity, were negatively associated with tundra specialist richness, potentially due to phenological limitations associated with shortened growing seasons. In summary, our data suggest emergent properties exist at the patch scale that are not apparent at the plot scale such that plot‐scale measurements do not represent variation in understory community composition across the landscape. The results presented here will inform future work addressing spatial variability in shrub impacts on ecosystem function and increase our understanding of understory community variation within alder patch habitats at the taiga–tundra ecotone.
Predation probabilities and functional responses: How piscivorous waterbirds respond to pulses in fish abundance
Authors: Hostetter Nathan J. , Payton Quinn , Roby Daniel D. , Collis Ken , Evans Allen F. 
Published: September 2022

AbstractHow predators respond to changes in prey abundance (i.e., functional responses) is foundational to consumer–resource interactions, predator–prey dynamics, and the stability of predator–prey systems. Predation by piscivorous waterbirds on out‐migrating juvenile steelhead trout (Oncorhynchus mykiss) is considered a factor affecting the recovery of multiple Endangered Species Act‐listed steelhead populations in the Columbia River basin. Waterbird functional responses, however, may vary by predator species and location, with important implications to predator management strategies. We used a 13‐year dataset on waterbird abundance across seven breeding colonies (three Caspian tern [Hydroprogne caspia], two double‐crested cormorant [Nannopterum auritum], and two California and ring‐billed gull [Larus californicus and Larus delawarensis] colonies) and steelhead tag‐recovery data (>645,000 tagged and >32,000 recovered steelhead) to quantify weekly predation probabilities and functional responses across waterbird species, colonies, and years. Weekly predation probabilities were highly variable, ranging from 0.01 to 0.30 at tern colonies, 0.01 to 0.20 at cormorant colonies, and 0.03 to 0.13 at gull colonies. Per capita predation probabilities were an order of magnitude higher at inland tern and cormorant colonies relative to estuary colonies of the same species. Terns displayed Type II functional responses across colonies and years, where predation probabilities peaked at low steelhead abundances and declined as steelhead abundance increased (i.e., predator swamping). Cormorants nesting at the large estuary colony (several thousand birds) displayed a Type III functional response, but cormorants nesting at the smaller inland colony (several hundred birds) displayed a Type II response. Consumption probabilities of steelhead by gulls remained consistent across a large range of steelhead availability, suggesting a Type I or a Type III functional response, but a lack of colony abundance data prevented quantifying functional responses. The level of tern predation combined with Type II functional responses indicate possible population‐level impacts that could destabilize small or declining prey populations. Conversely, the apparent Type III functional responses of gulls and estuary nesting cormorants are indicative of prey switching behaviors targeted at periods of high steelhead abundance. Our results illustrate the complexity of predator–prey interactions and the importance of quantifying predator‐ and location‐specific functional responses when predicting the efficacy of management strategies to enhance prey populations.
Effects of urbanization on specialist insect communities of milkweed are mediated by spatial and temporal variation
Authors: Miles Lindsay S. , Murray‐Stoker David , Nhan Vanessa J. , Johnson Marc T. J. 
Published: September 2022

AbstractUrbanization drastically alters landscapes in ways that can threaten local biodiversity. Although species loss has been well documented in urban habitats, why some species persist and not others, and how species interactions change remain poorly understood, especially for species with specialized niche requirements. Here, we test the hypothesis that urbanization disrupts specialized plant–herbivore interactions, and these effects vary according to the characteristics of both cities and the features of the organisms themselves. To test this hypothesis, we surveyed milkweed specialist herbivore communities in the early and late growing season of the common milkweed (Asclepias syriaca) across six cities that varied in size by two orders of magnitude. Four results are most important to answering our research questions: (1) the abundance of herbivore species was higher in urban than in rural habitats, whereas leaf herbivory was higher in rural than in urban habitats, and these effects varied between seasons and among cities; (2) the higher species diversity and abundance are likely due to a few species being more associated with rural habitats and other species more common in urban habitats, and thus, urbanization alters insect community composition; (3) the species with the lowest dispersal abilities, Rhyssomatus lineaticollis and Liriomyza asclepiadis, were those that were most strongly affected by urbanization, with R. lineaticollis less abundant and L. asclepiadis more abundant in urban areas; and (4) urbanization influenced plant–herbivore interactions by reducing herbivory, but it did not alter species interactions among herbivorous insects. Biodiversity loss, particularly declines of habitat and host specialists, in urban areas remains a critical concern for conservation. Our results indicate that at least some specialist herbivores are more abundant in urban areas than in rural areas and that species interactions remain intact.
Localized carry‐over effects of pond drying on survival, growth, and pathogen defenses in amphibians
Authors: Le Sage Emily H. , Ohmer Michel E. B. , LaBumbard Brandon C. , Altman Karie A. , Reinert Laura K. , Bednark Jeffery G. , Bletz Molly C. , Inman Brady , Lindauer Alexa , McDonnell Nina B. , Parker Sadie K. , Skerlec Samantha M. , Wantman Trina , Rollins‐Smith Louise A. , Woodhams Douglas C. , Voyles Jamie , Richards‐Zawacki Corinne L. 
Published: September 2022

AbstractClimate change is increasing variability in precipitation patterns in many parts of the globe. Unpredictable changes in water availability can be particularly challenging for organisms that rely on precipitation‐fed water sources for completing their life cycle, such as many amphibian species. Although developmental plasticity can mitigate the impacts of changing environments for some species, this strategy can come at a cost to other fitness‐linked traits, such as immune function. We investigated localized variation in the capacity to respond to pond drying and evaluated whether developmental responses induced carry‐over effects in disease susceptibility in three leopard frog species (Rana [Lithobates] pipiens and Rana sphenocephala; two populations each, and one population of Rana chiricahuensis). Using mesocosms located near the site of collection (<15 km away) in five regions spanning a latitudinal gradient, we raised tadpoles under simulated fast drying, slow drying, or constant water levels. After metamorphosis, we characterized several aspects of the skin microbiome, immune function, and response to exposure to the fungal pathogen Batrachochytrium dendrobatidis (Bd). Note that for R. chiricahuensis, the only carry‐over effect measured was response to Bd exposure, for which we observed no effects of pond drying. We found that developmental plasticity in response to drying was rare, except in the southernmost population of R. sphenocephala. In this location, tadpoles responded by accelerating development, and frogs with shorter larval periods developed more severe infections following Bd exposure post‐metamorphosis, suggesting a trade‐off between surviving pond drying and pathogen defense investment. In the three other locations, a lack of accelerated metamorphosis in drying treatments was accompanied by increased mortality, decreased anti‐Bd function of the microbiome, and/or greater Bd infection after exposure. Overall, results suggest that faster drying conditions will likely have negative impacts on amphibians with long larval periods, both directly and indirectly via carry‐over effects. Because effects of drying exposure were not uniform within a species, our findings suggest that local responses may not be generalizable to other regions of the range. These multifaceted effects of climate change on pathogen defenses are increasingly relevant as emerging infectious diseases threaten global biodiversity.
Ungulate herbivores as drivers of aspen recruitment and understory composition throughout arid montane landscapes
Authors: Reikowski Elizabeth S. , Refsland Tyler , Cushman J. Hall 
Published: September 2022

AbstractHerbivory by wild and domestic ungulates can influence tree recruitment and understory forest communities throughout the world. Herbivore‐driven declines in tree recruitment have been observed for quaking aspen (Populus tremuloides), a foundation species whose health and management is recognized as a critical priority throughout much of its range. Livestock fencing is commonly used to promote aspen regeneration, but its effectiveness is rarely assessed, especially across large spatial scales. Using a livestock‐reduction experiment, we evaluated the effects of ungulate herbivory on aspen in the Great Basin and southern Cascades, an expansive and environmentally heterogeneous region where aspen faces the interacting threats of climate change, conifer encroachment, and herbivory. We found that livestock fencing only reduced the intensity of herbivore browsing on aspen when wild ungulate abundance was low and did not increase stem densities of aspen recruits. Contrary to expectations, wild ungulate abundance was a strong driver of browsing intensity on juvenile aspen within fenced, but not unfenced, aspen stands, and when the abundance of these herbivores was high, browsing intensity in fenced stands exceeded that in unfenced stands. The density of aspen recruits decreased with browsing intensity on juvenile aspen and with the density of both adult aspen and conifers, suggesting that both herbivory and intra‐ and interspecific competition are important drivers of recruitment. Fire history was also an important driver of recruitment, with stands that burned 10–20 years ago having the greatest density of aspen recruits. Finally, in the stand understory, we found that livestock fencing decreased forb cover, increased shrub species richness, and increased the cover of exotic annual grasses, a group dominated by Bromus tectorum. This latter finding suggests that livestock fencing may not be appropriate in areas where controlling the spread of this invader is a priority. In sum, our findings indicate that aspen recruitment is limited by browsing by both wild and domestic ungulates, is mediated by competition with neighboring trees and fire history, and will require management actions beyond livestock fencing, as this approach does not control browsing by wild ungulates.
Trends in soil microclimate and modeled impacts on germination timing in the sagebrush steppe
Authors: Terry Tyson J. , Hardegree Stuart P. , Madsen Matthew D. , Roundy Bruce A. , St. Clair Samuel B. 
Published: September 2022

AbstractPast and projected changes in climate affect soil microclimate, impacting seeds that use soil moisture and soil temperature as cues for germination. Seed germination and plant establishment are among the most important processes regulating plant community assembly in response to climate change. Changes in germination timing expose seedlings to new abiotic and biotic risk factors that can affect recruitment success. Species with seed dormancy strategies to avoid harsh winter conditions could experience more mortality if changes in germination timing cause early germination and subsequent exposure to freezing conditions. We analyzed soil microclimate trends in the sagebrush steppe from 1979 to 2017 using a soil physics model (SHAW) and calculated the germination timing of native species used in restoration efforts with wet‐thermal response curves from lab trials. We applied the germination curves to modeled soil microclimate at 10 sites in the sagebrush steppe. Our results indicate that warmer and wetter fall seasons have become more prevalent and will likely lead to accelerated germination of several native restoration species in the sagebrush steppe. Changes to spring soil conditions favor slightly more germination in early spring, but strong trends of earlier onset of spring soil conditions were not evident. Trends in climate have created drier and warmer summer seedbed conditions, likely to increase stress on seedlings. Historic cycles of alternating slow or fast germination appeared less frequently during the last 12 years of the study (2004–2016). Seedbed microclimate trends will likely impact seedling establishment by altering germination timing and exposing seeds to more harsh abiotic conditions, likely resulting in decreased recruitment of native species and increased abundance of invasive annual grasses.
Invertebrate herbivory accelerates shift towards forbs caused by warming in a sedge‐dominated alpine meadow
Authors: Cao Rui , Lu Guihua , Zhang Tong , Li Zhengpeng , Wu Xinwei , Sun Shucun 
Published: September 2022

AbstractInvertebrate herbivory is suggested to modulate community shifts caused by climate warming in grasslands. However, experimental evidence is lacking, especially in high elevation areas. We examined the interactive effect of experimental warming and the grassland caterpillar Gynaephora alpherakjj, a typical invertebrate herbivorous insect with sedge preference, on the structure of plant community in a sedge‐dominated alpine meadow in the Tibetan Plateau. We manipulated both herbivore and temperature in a full factorial field experiment using passive warming chambers over one plant‐growing season. Results show that simulated warming significantly increased the aboveground plant biomass (APB) of forbs and total APB, while the presence of caterpillars significantly decreased sedge APB and total APB. The increase in consumption of sedges by caterpillars under warmed conditions can largely be ascribed to the increase in feeding time of caterpillars. Importantly, the presence of caterpillars significantly decreased the APB ratio of sedges to forbs in the warmed but not in the unwarmed chambers. These results suggest that with a warming climate, invertebrate herbivory could accelerate community shifts from sedge dominance to forb dominance in only one plant‐growing season in the Tibetan alpine meadow. This shift would reduce the biomass of high‐quality forage and further threaten animal husbandry in this area. Considering the harm of G. alpherakjj to grasslands, its population should be controlled more strictly under the global warming scenario.
Spatial drivers of wetland bird occupancy within an urbanized matrix in the Upper Midwestern United States
Authors: Rahlin Anastasia A. , Saunders Sarah P. , Beilke Stephanie 
Published: September 2022

AbstractWetland birds are undergoing severe population declines in North America, with habitat degradation and wetland loss considered two of the primary causes. Due to the cryptic nature of many wetland bird species, the ecological conditions (e.g., matrix composition) that influence bird occupancy, and the relevant spatial scales at which to measure bird responses, remain unclear but may affect inference about wetland use and suitability. We conducted wetland bird surveys at 477 points across northeastern Illinois and northwestern Indiana within the highly urbanized landscape surrounding Chicago. Using remotely sensed land cover data, we built occupancy models for 10 wetland bird species (American Coot Fulica americana, Black‐crowned Night‐Heron Nycticorax nycticorax, Blue‐winged Teal Anas discors, Common Gallinule Gallinula galeata, Least Bittern Ixobrychus exilis, Marsh Wren Cistothorus palustris, Pied‐billed Grebe Podilymbus podiceps, Sora Porzana carolina, Swamp Sparrow Melospiza georgiana, and Virginia Rail Rallus limicola) to quantify their responses to wetland cover types (emergent wetland, forested wetland, riverine wetland, and freshwater pond) and urbanization at four spatial scales (200‐, 400‐, 800‐, and 2000‐m radial distances). We also included the distance to Lake Michigan as a covariate in occupancy models to account for ecological differences between coastal and inland wetlands. We found that relationships between land cover types and occupancy differed by species, as did the spatial scale of support. Generally, the presence of emergent wetlands or ponds at immediate (200 m) and local (400 m) spatial scales within the surrounding matrix was positively associated with wetland bird occupancy. Contrary to expectations, we did not find support for a negative relationship between urbanization and occupancy for most focal species, indicating that birds are using available wetland habitats despite surrounding development. While future research should evaluate management strategies at the watershed scale, our findings suggest that wetland conservation planning at immediate and local scales is likely to promote bird habitat use within highly modified landscapes of the Upper Midwestern United States.
Loss of riparian forests from wildfire led to increased stream temperatures in summer, yet salmonid fish persisted
Authors: Warren Dana R. , Roon David A. , Swartz Allison G. , Bladon Kevin D. 
Published: September 2022

AbstractNative salmonid fishes—cutthroat trout (Oncorhynchus clarkii) and steelhead/rainbow trout (Oncorhynchus mykiss)—are ecologically, culturally, and economically important species distributed across western North America. These fish are generally considered “cold‐water” adapted species. As such, recent studies have speculated about the potential effects of climate change on these native salmonids if stream temperature thresholds exceed 16–20°C during the summer. However, the magnitude of stream thermal responses to the slow but steady increases in regional temperatures associated with climate change remains uncertain and hard to predict. Comparatively, abrupt disturbances, such as wildfire, may produce almost instantaneous and substantial increases in stream temperatures that may persist for multiple years until near‐stream vegetation becomes re‐established. In the first summer following a severe wildfire in western Oregon, we observed the initial persistence of populations of O. clarkii clarkii (coastal cutthroat trout) and O. mykiss (rainbow/steelhead trout). The fire burned the entire catchment, including the riparian area (~76% of the watershed area burned at moderate or high severity), resulting in stream temperature that regularly exceeded 20°C and represented increases of 6–7°C relative to prefire conditions. However, the mechanisms enabling the persistence of cold‐water fishes despite the dramatic increases in stream temperature remain unclear and require further investigation. Nevertheless, wildfires represent acute natural disturbances that can substantially alter stream thermal regimes and provide unique insights that allow us to better understand how native fishes in natural systems cope with projected increases in stream temperatures.
Edge effects on decomposition in Sphagnum bogs: Implications for carbon storage
Authors: Nordström Emil , Eckstein Rolf Lutz , Lind Lovisa 
Published: September 2022

AbstractPeatlands provide multiple ecosystem services, including extensive carbon sequestration and storage, yet many peatlands have been degraded or destroyed. Peatlands' carbon storage capacity is connected to inherently low decomposition rates, causing the buildup of organic matter. This pattern could be explained by waterlogged conditions that reduce the amount of available oxygen for the decomposer community, a low pH that inhibits bacterial decomposition, or colder temperatures lowering metabolic rates. This study focused on edge effects on decomposition in the transition zone (lagg) between Sphagnum bogs and the surrounding forest, with the expectation that decomposition is lowest in the bog and highest in the forest but with a mix of factors causing intermediate decomposition rates near the bog edge. Transitional decomposition rates were measured across six bogs in central Sweden during the summer of 2021, following the Tea Bag Index. Three 20‐m transects, each containing seven pairs of tea bags, were buried across the margins of each bog, centered at the edge of the Sphagnum moss. Soil moisture content, pH, and plant composition were also recorded at each burial site, and temperature loggers placed evenly among four of the bogs. Our results confirmed our hypothesis regarding edge effects, with soil moisture levels showing a strong negative interaction with decomposition rate. The interaction between pH and decomposition rate was significant, but with an unexpected negative relation, most likely due to low pH in the surrounding forest. Temperature displayed no significance, and plants indicative of low decomposition rates included Vaccinium oxycoccos, Drosera rotundifolia, and Sphagnum species. In contrast to other studies, we did not find an increase in decomposition with increased species richness among the studied bog ecosystems. In conclusion, there is an edge effect on decomposition, and maintaining, or restoring, the hydrology of a peatland is the most important factor for continued carbon storage, with a rough estimation of an area decomposition rate possible to be estimated based on its vegetation.