William Bowman

• Professor
• University of Colorado Boulder

One of the most reliable features of natural systems is that they change through time. Theory predicts that temporally fluctuating conditions shape community composition, species distribution patterns, and life history variation, yet features of temporal variability are rarely incorporated into studies of species–environment associations. In this s...

Climate change is altering interactions among plants and pollinators. In alpine ecosystems, where snowmelt timing is a key driver of phenology, earlier snowmelt may generate shifts in plant and pollinator phenology that vary across the landscape, potentially disrupting interactions. Here we ask how experimental advancement of snowmelt timing in a t...

Climate change is altering interactions among species, including plants and pollinators. In alpine ecosystems, where snowmelt timing is a key driver of phenology, earlier snowmelt may generate shifts in plant and pollinator phenology that vary across the landscape, potentially disrupting interactions. Here we ask how experimentally induced changes...

Purpose Plants and soil microbes both influence how ecosystems respond to environmental change. Yet, we lack the ability to generalize how plants and soil microbes influence each other in the same or varying soil conditions. This limitation thwarts ecologists’ ability to understand and predict effects of environmental changes such as elevated anthr...

Key Concepts CONCEPT 25.1 Elements move among geologic, atmospheric, oceanic, and biological pools at a global scale. CONCEPT 25.2 Earth is warming because of anthropogenic emissions of greenhouse gases. CONCEPT 25.3 Anthropogenic emissions of sulfur and nitrogen cause acid deposition, alter soil chemistry, and...

Key Concepts CONCEPT 4.1 Each species has a range of environmental tolerances that determines its potential geographic distribution. CONCEPT 4.2 The temperature of an organism is determined by exchanges of energy with the external environment. CONCEPT 4.3 The water balance of an organism is...

Key Concepts CONCEPT 9.1 Populations are groups of individuals of the same species that vary in size over space and time. CONCEPT 9.2 Species vary in their distribution and abundance across their geographic range. CONCEPT 9.3 Species are limited in their distribution and abundance...

Key Concepts CONCEPT 17.1 Agents of change act on communities across all temporal and spatial scales. CONCEPT 17.2 Succession is the process of change in species composition over time as a result of abiotic and biotic agents of change. CONCEPT 17.3 Experimental work on...

Key Concepts CONCEPT 22.1 Nutrients enter ecosystems through the chemical breakdown of minerals in rocks or through fixation of atmospheric gases. CONCEPT 22.2 Chemical and biological transformations in ecosystems alter the chemical form and supply of nutrients. CONCEPT 22.3 Nutrients cycle repeatedly through the...

Key Concepts CONCEPT 12.1 Most carnivores have broad diets, whereas a majority of herbivores have relatively narrow diets. CONCEPT 12.2 Predation results in a wide range of capture and avoidance mechanisms. CONCEPT 12.3 Predator populations can cycle with their prey populations. CONCEPT 12.4 Predation...

Key Concepts CONCEPT 7.1 Life history patterns vary within and among species. CONCEPT 7.2 There are trade-offs between life history traits. CONCEPT 7.3 Organisms face different selection pressures at different life cycle stages. CONCEPT 7.4 Life history patterns can be classified along several continua....

Key Concepts CONCEPT 11.1 Populations can grow exponentially when conditions are favorable, but exponential growth cannot continue indefinitely. CONCEPT 11.2 Population size is determined by a combination of density-dependent and density-independent factors. CONCEPT 11.3 The logistic equation incorporates limits to growth and shows how...

Key Concepts CONCEPT 18.1 Patterns of species diversity and distribution vary at global, regional, and local spatial scales. CONCEPT 18.2 Global patterns of species diversity and composition are influenced by geographic area and isolation, evolutionary history, and global climate. CONCEPT 18.3 Regional differences in...

Key Concepts CONCEPT 21.1 Trophic levels describe the feeding positions of groups of organisms in ecosystems. CONCEPT 21.2 The amount of energy transferred from one trophic level to the next depends on food quality and on consumer abundance and physiology. CONCEPT 21.3 Changes in...

Key Concepts CONCEPT 8.1 Evolution is the basis for adaptive behavior. CONCEPT 8.2 Animals make behavioral choices that enhance their energy gain and reduce their risk of becoming prey. CONCEPT 8.3 Mating behaviors reflect the costs and benefits of parental investment and mate defense.... CONCEPT...

Key Concepts CONCEPT 15.1 In positive interactions, no species is harmed, and the benefits are greater than the costs for at least one species. CONCEPT 15.2 Each partner in a mutualistic interaction acts in ways that serve its own ecological and evolutionary interests. CONCEPT 15.3...

Key Concepts CONCEPT 24.1 Landscape ecology examines spatial patterns and their relationship to ecological processes. CONCEPT 24.2 Habitat loss and fragmentation decrease habitat area, isolate populations, and alter conditions at habitat edges. CONCEPT 24.3 Biodiversity can best be sustained by large reserves connected across...

Key Concepts CONCEPT 16.1 Communities are groups of interacting species that occur together at the same place and time. CONCEPT 16.2 Species diversity and species composition are important descriptors of community structure. CONCEPT 16.3 Communities can be characterized by complex networks of direct and...

Key Concepts CONCEPT 5.1 Organisms obtain energy from sunlight, from inorganic chemical compounds, or through the consumption of organic compounds. CONCEPT 5.2 Radiant and chemical energy captured by autotrophs is converted into stored energy in carbon–carbon bonds. CONCEPT 5.3 Environmental constraints have resulted in...

Key Concepts CONCEPT 13.1 Parasites typically feed on only one or a few host species, but host species have multiple parasite species. CONCEPT 13.2 Hosts have mechanisms for defending themselves against parasites, and parasites have mechanisms for overcoming host defenses. CONCEPT 13.3 Host and...

Key Concepts CONCEPT 19.1 Species diversity differs among communities as a consequence of regional species pools, abiotic conditions, and species interactions. CONCEPT 19.2 Resource partitioning is theorized to reduce competition and increase species diversity. CONCEPT 19.3 Processes such as disturbance, stress, predation, and positive...

Key Concepts CONCEPT 6.1 Evolution can be viewed as genetic change over time or as a process of descent with modification. CONCEPT 6.2 Natural selection, genetic drift, and gene flow can cause allele frequencies in a population to change over time. CONCEPT 6.3 Natural...

Key Concepts CONCEPT 10.1 Populations are dynamic entities that vary in size over time. CONCEPT 10.2 The risk of extinction increases in populations that fluctuate in size and/or are small.

Key Concepts CONCEPT 23.1 Conservation biology is an integrative discipline that applies the principles of ecology to the protection of biodiversity. CONCEPT 23.2 Biodiversity is declining globally. CONCEPT 23.3 Primary threats to diversity include habitat loss, invasive species, overexploitation, pollution, disease, and climate change.... CONCEPT....

Key Concepts CONCEPT 14.1 Competition can be direct or indirect, vary in its intensity, and occur between similar or dissimilar species. CONCEPT 14.2 Competing species are more likely to coexist when they use resources in different ways. CONCEPT 14.3 Competitive interactions can be modeled...

Key Concepts CONCEPT 1.1 Events in the natural world are interconnected. CONCEPT 1.2 Ecology is the scientific study of interactions between organisms and their environment. CONCEPT 1.3 Ecologists evaluate competing hypotheses about natural systems with observations, experiments, and models.

Key Concepts CONCEPT 2.1 Climate is the most fundamental component of the physical environment. CONCEPT 2.2 Winds and ocean currents result from differences in solar radiation across Earth’s surface. CONCEPT 2.3 Large-scale atmospheric and oceanic circulation patterns establish global patterns of temperature and precipitation.... CONCEPT...

Key Concepts CONCEPT 20.1 Energy in ecosystems originates with primary production by autotrophs. CONCEPT 20.2 Net primary production is constrained by both physical and biotic environmental factors. CONCEPT 20.3 Global patterns of net primary production reflect climate constraints and biome types. CONCEPT 20.4 Secondary...

Key Concepts CONCEPT 3.1 Terrestrial biomes are characterized by the growth forms of the dominant vegetation. CONCEPT 3.2 Biological zones in freshwater ecosystems are associated with the velocity, depth, temperature, clarity, and chemistry of the water. CONCEPT 3.3 Marine biological zones are determined by...

Plants are subject to trade‐offs among growth strategies such that adaptations for optimal growth in one condition can preclude optimal growth in another. Thus, we predicted that a plant species that responds positively to one global change treatment would be less likely than average to respond positively to another treatment, particularly for pair...

Purpose: Plants and soil microbes both influence how ecosystems respond to environmental change. Yet, we lack the ability to generalize how plants and soil microbes influence each other in the same or varying soil conditions. This limitation thwarts ecologists' ability to understand and predict effects of environmental changes such and elevated ant...

Understanding how global change drivers (GCDs) affect aboveground net primary production (ANPP) through time is essential to predicting the reliability and maintenance of ecosystem function and services in the future. While GCDs, such as drought, warming and elevated nutrients, are known to affect mean ANPP, less is known about how they affect inte...

Alpine areas will likely experience an increase in non-native plant species invasions. Increased human activity and environmental changes are expected to lower the environmental constraints for their establishment and spread. To understand and prepare for high elevation plant invasions it is necessary to evaluate the changes in environmental factor...

Significance Accurate prediction of community responses to global change drivers (GCDs) is critical given the effects of biodiversity on ecosystem services. There is consensus that human activities are driving species extinctions at the global scale, but debate remains over whether GCDs are systematically altering local communities worldwide. Acros...

A common response of plant communities to increased nitrogen (N) deposition is a shift in species’ abundances. Multiple factors have been proposed to explain the changes in abundance, notably competition and soil acidification. We hypothesized that a plant species that decreased in abundance with elevated N would have lower ectomycorrhizal fungi, a...

Atmospheric nitrogen and sulfur pollution increased over much of the United States during the twentieth century from fossil fuel combustion and industrial agriculture. Despite recent declines, nitrogen and sulfur deposition continue to affect many plant communities in the United States, although which species are at risk remains uncertain. We used...

The responses of species to environmental changes will determine future community composition and ecosystem function. Many syntheses of global change experiments examine the magnitude of treatment effect sizes, but we lack an understanding of how plant responses to treatments compare to ongoing changes in the unmanipulated (ambient or background) s...

The realization that anthropogenic nitrogen (N) deposition is causing significant environmental change in many ecosystems has led to lower emissions of reactive N and deposition rates in many regions. However, the impacts of N deposition on terrestrial ecosystems can be long lasting, with significant inertia in the return of the biota and biogeoche...

Recent bark beetle outbreaks in western North American subalpine forests have prompted managers to salvage log some beetle-affected stands. We examined the short-term (i.e., two to three years post-treatment) consequences of such salvage logging on vascular understory plant (i.e., graminoid, forb, and shrub) communities. At 24 lodgepole pine (Pinus...

Temporal stability of ecosystem functioning increases the predictability and reliability of ecosystem services, and understanding the drivers of stability across spatial scales is important for land management and policy decisions. We used species-level abundance data from 62 plant communities across five continents to assess mechanisms of temporal...

Questions Plant community composition can be influenced by multiple biotic, abiotic, and stochastic factors acting on the local species pool to determine their establishment success and abundance and subsequently the diversity of the community. We asked if the influences of biotic interactions on the composition of plant species in communities, as...

Significance Human activities have elevated nitrogen (N) deposition and there is evidence that deposition impacts species diversity, but spatially extensive and context-specific estimates of N loads at which species losses begin remain elusive. Across a wide range of climates, soil conditions, and vegetation types in the United States, we found tha...

An increasing number of network observatories have been established globally to collect long-term biogeochemical data at multiple spatial and temporal scales. Although many outstanding questions in biogeochemistry would benefit from network science, the ability of the earth- and environmental-sciences community to conduct synthesis studies within a...

Background: There is a paucity of information for mountain catchments, and in particular a lack of long-term data collection in alpine areas.Aims: The focus of this special issue is to synthesize alpine research undertaken in the last 20 years at high altitude research sites that comprise the Niwot Ridge Long Term Ecological Research (NWT LTER) pro...

Human activity in the last century has increased nitrogen (N) deposition to a level that has caused or is likely to cause alterations to the structure and function of many ecosystems across the United States. We synthesized current research relating atmospheric N deposition to effects on terrestrial and freshwater ecosystems in the United States, a...

Largely due to its varied topography, Colorado is home to many distinct ecosystems. Differences in elevation offer a wide range of precipitation and temperature patterns, from the snowy high mountains of the Western and Central parts of the state to the drier Great Plains and canyon country. These climate gradients, in turn, affect the major specie...

Here we review the numerous studies of plant-microbe interactions conducted at the Niwot Ridge LTER site in Colorado, USA. By synthesising work at scales ranging from the rhizosphere to the landscape, we offer a mechanistic view of how these interactions are essential to understanding the spatial and temporal structuring of plant and microbial comm...

Background: Nitrogen (N) deposition in the Front Range of the southern Rocky Mountains has been increasing for several decades, and has exceeded the critical load for several ecological metrics.Aims: Our objective was to predict potential future ecological changes in alpine zones in response to anthropogenic N deposition based on a review of resear...

Extensive tree mortality from insect epidemics has raised concern over possible effects on soil biogeochemical processes. Yet despite the importance of microbes in biogeochemical processes, how soil bacterial communities respond to insect-induced tree mortality is largely unknown. We examined soil bacterial community structure (via 16S rRNA pyroseq...

Background/Question/Methods Human alteration of the nitrogen (N) cycle has resulted in a drastic change in availability of biologically active N. Alpine ecosystems are particularly susceptible to increased inputs of N, as higher elevations receive disproportionately more precipitation and therefore high rates of N input. Previous alpine research,...

Ecosystem impacts from nitrogen (N) deposition are related to (1) the degree to which plant growth responds to increases in N supply and (2) soil buffering capacity. Herbaceous communities dominated by plants adapted to low nutrient supply typically have low capacity to take up inputs of N. As a result they are more highly susceptible to loss of ba...

This chapter reports the findings of a Working Group on how atmospheric nitrogen (N) deposition affects both terrestrial and freshwater biodiversity. Regional and global scale impacts on biodiversity are addressed, together with potential indicators. Key conclusions are that: the rates of loss in biodiversity are greatest at the lowest and initial...

To evaluate potential long-term effects of climate change and atmospheric nitrogen (N) deposition on subalpine ecosystems, the coupled biogeochemical and vegetation community competition model ForSAFE-Veg was applied to a site at the Loch Vale watershed of Rocky Mountain National Park, Colorado. Changes in climate and N deposition since 1900 result...

Nitrogen deposition, along with habitat loss and climate change, constitute a major threat to Earth’s biodiversity. Fossil fuel combustion and modern agriculture add more nitrogen to terrestrial and aquatic ecosystems than all natural processes combined. Because nitrogen often limits productivity, this enrichment it likely to have major ecological...

One significant unanswered question about biotic responses to climate change is how plant communities within topographically complex landscapes will respond to climate change. Alpine plant communities are strongly influenced by topographic microclimates which can either buffer or compound the effects of more regional climatic changes. Here, we anal...

Biodiversity has been described as the diversity of life on earth within species, among species, and among ecosystems. The rate of biodiversity loss due to human activity in the last 50 years has been more rapid than at any other time in human history, and many of the drivers of biodiversity loss are increasing, including habitat loss, overexploita...

Background/Question/Methods Subalpine forests throughout the western United States are experiencing an unprecedented irruption of mountain pine beetle (Dendroctonus ponderosae) resulting in widespread death of lodgepole pine (Pinus contorta). Managers aim to enhance lodgepole regeneration through dead tree removal and soil disturbance, but little...

Knowledge of import, export, and transport of nitrogen (N) in headwater catchments is essential for understanding ecosystem function and water quality in mountain ecosystems, especially as these ecosystems experience increased anthropogenic N deposition. In this study, we link spatially explicit soil and stream data at the landscape scale to invest...

We evaluated the ecological thresholds associated with vegetation and soil responses to nitrogen (N) deposition, by adding NH(4)NO(3) in solution at rates of 5, 10 and 30 kg N ha(-1) yr(-1) to plots in a species rich dry meadow alpine community in Rocky Mountain National Park receiving ambient N deposition of 4 kg N ha(-1) yr(-1). To determine the...

Human activity in the last century has led to a significant increase in nitrogen (N) emissions and atmospheric deposition. This N deposition has reached a level that has caused or is likely to cause alterations to the structure and function of many ecosystems across the United States. One approach for quantifying the deposition of pollution that wo...

Biodiversity has been described as the diversity of life on earth within species, between species and in ecosystems. Biodiversity contributes to regulating ecosystem services like climate, flood, disease, and water quality regulation. Biodiversity also supports and sustains ecosystem services that provide material goods like food, fiber, fuel, timb...

http://deepblue.lib.umich.edu/bitstream/2027.42/117159/1/eap20112183049.pdf

Deposition of anthropogenic N can potentially alter biogeochemistry of ecosystems, acidifying soils and surface waters, lowering availability of some nutrient cations, and increasing concentrations of toxic metals. Remote regions in western North America are exhibiting symptoms of ecological change due to N deposition. We used an existing N additio...

Background/Question/Methods The increasing prevalence of invasive plant species threatens the function of ecosystems and the organisms that rely on those functions and resources. Hence, it is important for us to improve our understanding of the factors that influence invasibility. Recent development in invasion theory indicates that environmental...

Inorganic nitrogen (N) availability hot spots have been documented in many ecosystems, but major uncertainties remain about their prevalence, timing, and causes. Using a novel mathematical definition of hot spots, spatially explicit measurements of KCl-extractable inorganic N, 2-week soil incubations in the field, ion-exchange resins deployed for 1...

The ForSAFE-VEG model was used to estimate atmospheric nitrogen deposition and climate effects on soil chemistry and ground vegetation in alpine and subalpine zones of the northern and central Rocky Mountains region in the USA from 1750 to 2500. Model simulations for a generalized site illustrated how the critical load of atmospheric nitrogen depos...

Niche complementarity, in which coexisting species use different forms of a resource, has been widely invoked to explain some of the most debated patterns in ecology, including maintenance of diversity and relationships between diversity and ecosystem function. However, classical models assume resource specialization in the form of distinct niches,...

Diverse plant litter mixtures frequently decompose differently than expected compared to the average of the component species decomposing alone, and it remains unclear why decomposition may respond non-additively to diversity. Here, we hypothesized that litter chemical composition and chemical diversity would be important determinants of the streng...

Background/Question/Methods The deposition of reactive nitrogen (N) has increased substantially due to agricultural and industrial activity. Anthropogenic N deposition has been implicated in a host of ecological changes, including both increases and decreases in NPP, loss of diversity and increased mortality of plants, and acidification of soils...

Nitrogen (N) availability in soils is influenced by many microbially catalyzed reactions such as N fixation, denitrification, and N mineralization from soil organic matter (SOM). Reaction rates for these processes are heterogeneous across landscapes, often forming hot spots that have disproportionately high N cycling activity. N cycling hot spots h...

Interactions between climate and ecosystems with complex topographic gradients generate unique source and sink habitats for water and nutrients as a result of precipitation, energy, and chemical redistribution. We examined these phenomena for a high-elevation site in the Colorado Front Range. Current changes in climate and atmospheric deposition of...

1. Plant carbon (C) and nitrogen (N) inputs to soil interact with microbes and abiotic factors like climate and pH to influence soil fertility and plant productivity. Although root exudates and root litter are important factors affecting the cycling of nutrients critical to plant growth, many studies remain focused on effects of above-ground litter...

Background/Question/Methods Biodiversity can strongly influence below-ground ecosystem function, and diverse plant litter mixtures frequently decompose substantially differently than expected, based on the average of individual component species. These strong “non-additive” effects constitute an important and poorly understood way in which diversit...

Alpine tundra of the Rocky Mountains is subject to relatively little direct anthropogenic environmental change, and provides a good ecosystem for the detection of human effects associated with climate change and atmospheric pollution. The majority of the plants have patterns of vegetative development which limit the degree to which they can respond...

This article was submitted without an abstract, please refer to the full-text PDF file.

This article was submitted without an abstract, please refer to the full-text PDF file.

Decomposition is a critical source of plant nutrients, and drives the largest flux of terrestrial C to the atmosphere. Decomposing soil organic matter typically contains litter from multiple plant species, yet we lack a mechanistic understanding of how species diversity influences decomposition processes. Here, we show that soil C and N cycling dur...

Anthropogenic nitrogen deposition over the past half century has had a detrimental impact on temperate ecosystems in Europe and North America, resulting in soil acidification and a reduction in plant biodiversity(1,2). During the acidification process, soils release base cations, such as calcium and magnesium, neutralizing the increase in acidity....

Many studies have shown that changes in nitrogen (N) availability affect primary productivity in a variety of terrestrial systems, but less is known about the effects of the changing N cycle on soil organic matter (SOM) decomposition. We used a variety of techniques to examine the effects of chronic N amendments on SOM chemistry and microbial commu...

Phenolics can reduce soil nutrient availability, either indirectly by stimulating microbial nitrogen (N) immobilization or directly by enhancing physical protection within soil. Phenolic-rich plants may therefore negatively affect neighboring plant growth by restricting the N supply. We used a slow-growing, phenolic-rich alpine forb, Acomastylis ro...

To understand the role biota play in resilience or vulnerability to environmental change, we investigated soil, plant, and microbial responses to a widespread environmental change, increased nitrogen (N). Our aim was to test the plant–soil threshold hypothesis: that changed biotic structure influences resilience to accumulated changes in N. For six...

Plant resource partitioning of chemical forms of nitrogen (N) may be an important factor promoting species coexistence in N-limited ecosystems. Since the microbial community regulates N-form transformations, plant partitioning of N may be related to plant-soil feedbacks. We conducted a (15)N tracer addition experiment to study the ability of two al...

This synthetic data set contains plant species relative abundance measures from 35 nitrogen (N) fertilization experiments conducted at 10 sites across North America. The data set encompasses the fertilization responses of 575 taxa from 1159 experimental plots. The methodology varied among experiments, in particular with regard to the type and amoun...

Phenotypic plasticity is predicted to be highly advantageous to alpine plants because of the extreme spatial and temporal heterogeneity of the alpine environment. Alpine plants are constrained in their vegetative plasticity by developmental preformation, however, they have the potential for reproductive plasticity via abortion of reproductive struc...

Phenolics are an important, biologically reactive component of the carbon (C) pool that moves from plants to soil. Once in soil, phenolics can regulate plant–soil feedbacks because of their influence on soil nitrogen biogeochemistry. Roots are a largely overlooked potential source of below‐ground phenolic C. We examined phenolic fluxes from plants...

The importance of interspecific competition as a cause of resource partitioning among species has been widely assumed but rarely tested. Using neighbor removals in combination with 15N tracer additions in the field, we examined variation among three alpine species in the uptake of 15N-NH4+, 15N-NO3-, and 15N-13C-[2]-glycine in intact neighborhoods,...

Repercussions of species loss on ecosystem processes depend on the effects of the lost species as well as the compensatory responses of the remaining species in the community. We experimentally removed two co-dominant plant species and added a 15N tracer in alpine tundra to compare how species' functional differences influence community structure a...

Increases in the deposition of anthropogenic nitrogen (N) have been linked to several terrestrial ecological changes, including soil biogeochemistry, plant stress susceptibility, and community diversity. Recognizing the need to identify sensitive indicators of biotic response to N deposition, we empirically estimated the N critical load for changes...

Abstract Increasing atmospheric CO2 may result in alleviation of salinity stress in salt-sensitive plants. In order to assess the effect of enriched CO2 on salinity stress in Andropogon glomeratus, a C4 non-halophyte found in the higher regions of salt marshes, plants were grown at 350, 500, and 650 cm3 m−3 CO2 with 0 or 100 mol m−3 NaCl watering t...

Ecologists are becoming increasingly aware of the role of aboveground-belowground relationships in controlling ecosystem processes and properties. Here, we review recent studies that show that relationships between aboveground and belowground communities operate over a hierarchy of temporal scales, ranging from days to seasons, to millennia, with d...

Although soils are often the largest sink for N in terrestrial ecosystems, litter can immobilize N during the first year of decay and could affect N retention in seasonally snow-covered ecosystems that have high N losses during snowmelt, a time when soil N retention and plant uptake can be low, and litter N retention could be high. In alpine ecosys...