Rick Wallen

12 Assessing the Effects of Climate Change and Wolf Restoration on Grassland Processes

Manipulating the system: How large herbivores control bottom-up regulation of grasslands

Journal of Ecology, Nov 9, 2017

1. Decades of grazing studies have identified a number of key plant and soil processes affected b... more 1. Decades of grazing studies have identified a number of key plant and soil processes affected by large herbivores and how those grazer effects vary among different grassland types. However, there remains little mechanistic understanding about how the effects of grazers on plants and soils may be biogeochemically linked in regulating grassland processes. 2. Here we measured monthly plant and soil variables, including soil moisture, soil nitrogen (N) availability, plant biomass, shoot N concentration and plant production, in grazed and ungrazed (fenced) grasslands during the 2012-2014 growing seasons. Measurements were used to assess direct and indirect biogeochemical pathways by which grazers influenced net above-ground plant production (NAP) in dry and mesic grasslands in Yellowstone National Park (YNP). 3. Herbivores only had direct effects on plant variables at the dry grassland compared to direct and indirect effects on both plant and soil variables at the mesic grassland. By enhancing leaf N content at both grasslands, grazers shifted the resource controlling NAP from N in ungrazed grassland to moisture, and potentially phosphorus and/or other soil nutrients, in grazed grassland. These results indicate the mechanistic linkage between top-down (herbivore) and bottom-up (soil resource) control of grassland production. Changing the resources that limit net above-ground plant production (NAP) likely has a profound impact on how grazed vs. ungrazed Yellowstone National Park (YNP) grasslands respond to environmental (e.g., climate, atmospheric N deposition) variability. Because grazing enhances leaf N among many types of grasslands, increasing the sensitivity of plant production to the availability of moisture and nutrients other than N may be a general response of grasslands to grazing.

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Chapter 14 Demography of Central Yellowstone Bison: Effects of Climate, Density, and Disease

Elsevier eBooks, 2008

ABSTRACT Over a century of concerted conservation recovered the bison population in Yellowstone N... more ABSTRACT Over a century of concerted conservation recovered the bison population in Yellowstone National Park from 23 animals in 1901 to 5000 by 2005. This conservation success led to societal conflicts and disagreements among various management entities regarding classic issues of overabundance (Garrott et al. 1993), combined with concerns over the risk of brucellosis transmission to domestic livestock when bison migrate out of the park (Cheville et al. 1998). As a result, more than 6700 bison have been culled since 1983 as they attempted to leave the park (Gates et al. 2005). These large‐scale removals are aimed at brucellosis risk management, but likely influence bison demographics and vital rates. The development of rigorously estimated vital rates that incorporate the effects of brucellosis and associated management actions is essential for formulating appropriate management strategies (e.g., vaccination, culling) for long‐term bison conservation. These estimates will also contribute to the growing scientific understanding of how climate, disease, and density affect managed ungulate populations. Fuller et al. (2007b) found high and consistent adult female survival and lower birth rates in brucellosis seropositive Yellowstone bison during 1995–2001. We focused on the central herd and incorporated additional information collected during 2002–2006 to extend those analyses by investigating density, climate, and brucellosis seroprevalence effects on age‐specific survival and fecundity.

Estimating probabilities of active brucellosis infection in Yellowstone bison through quantitative serology and tissue culture

Journal of Applied Ecology, Sep 20, 2011

1. Disease management along the boundaries of wildlife reserves is a growing conservation problem... more 1. Disease management along the boundaries of wildlife reserves is a growing conservation problem worldwide, as infected wildlife can migrate outside protected areas and pose a threat to livestock and human health. The bison Bison bison population in Yellowstone National Park has long been infected with Brucella abortus, but culling of Yellowstone bison to prevent transmission to cattle has been ineffective at reducing brucellosis infection. This management strategy is negatively affecting long-term bison conservation because of difficulties in diagnosing actively infected animals. 2. We integrated age-specific serology and B. abortus culture results from slaughtered Yellowstone bison to estimate probabilities of active brucellosis infection using a Bayesian framework. Infection probabilities were associated with age in young bison (0-5 years old) and with elevated antibody levels in older bison (>5 years old). Our results indicate that Yellowstone bison acquire B. abortus infection early in life but typically recover as they grow older. 3. A tool was developed to allow bison management to better reflect the probability that particular animals are infective, with the aim of conserving Yellowstone bison while reducing the risk of brucellosis transmission to cattle. Combining selective removal of infectious bison with additional management practices, such as vaccination, has the potential to advance an effective brucellosis reduction programme. 4. Synthesis and applications. We conclude that active B. abortus infection in Yellowstone bison is age dependent, which allows true infection probabilities to be estimated based on age and quantitative diagnostic tests. These findings have important application to disease management worldwide where accurate diagnostic tests for wildlife are unavailable. Estimation of true infection probabilities can replace culling practices that conflict with wildlife conservation. The ability to identify infective individuals can improve management practices that support conservation, particularly when human health is at risk or endangered wildlife species are involved.

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Yellowstone Bison—Should We Preserve Artificial Population Substructure or Rely on Ecological Processes?

Journal of Heredity, 2012

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Grand Canyon bison nativity, genetics, and ecology: Looking forward

The series also provides a forum for presenting more lengthy results that may not be accepted by ... more The series also provides a forum for presenting more lengthy results that may not be accepted by publications with page limitations. All manuscripts in the series receive the appropriate level of peer review to ensure that the information is scientifically credible, technically accurate, appropriately written for the intended audience, and designed and published in a professional manner. This report received formal, high-level peer review based on the importance of its content, or its potentially controversial or precedent-setting nature. Peer review was conducted by highly qualified individuals with subject area technical expertise and was overseen by a peer review manager.

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Predator foraging response to a resurgent dangerous prey

Functional Ecology, 2017

1. Prey switching occurs when a generalist predator kills disproportionately more of an abundant ... more 1. Prey switching occurs when a generalist predator kills disproportionately more of an abundant prey species and correspondingly spares a rarer species. Although this behavior is a classic stabilizing mechanism in food web models, little is known about its operation in free-living systems which often include dangerous prey species that resist predation. 2. We used long-term data from a large mammal system in northern Yellowstone National Park, USA, to understand how prey preference of a wild, generalist predator (Canis lupus) responds to a shift in prey species evenness involving rising numbers of dangerous prey (Bison bison) and dropping numbers of relatively safer prey (Cervus elaphus). 3. Contrary to the prey switching hypothesis, wolves attacked and killed disproportionately more of the rarer, but safer, species. Wolves maintained a strong preference against bison even when this species was more than twice as abundant as elk. There was also evidence that wolves were increasingly averse to hunting bison as relative bison abundance increased. 4. Wolves seldom hunted bison because capture success was limited to a narrow set of conditions: larger packs (>11 wolves) chasing smaller herds (10-20 bison) with calves. Wolves scavenged bison carrion instead and did so more frequently as bison abundance increased. 5. Our study demonstrates the overarching importance of prey vulnerability to understanding the prey preferences of generalist predators in ecological communities with dangerous prey. The formidable defenses of such prey diminish the potential for switching and its stabilizing influence on population dynamics. In these communities, shifts from hunting to scavenging are perhaps more likely than shifts in prey preference. The assumption of switching may, therefore, overestimate the stability of multi-prey systems that include dangerous prey species.

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Brucellosis Transmission between Wildlife and Livestock in the Greater Yellowstone Ecosystem: Inferences from DNA Genotyping

Journal of wildlife diseases, Apr 24, 2017

The wildlife of the Greater Yellowstone Ecosystem carries brucellosis, which was first introduced... more The wildlife of the Greater Yellowstone Ecosystem carries brucellosis, which was first introduced to the area by cattle in the 19th Century. Brucellosis transmission between wildlife and livestock has been difficult to study due to challenges in culturing the causative agent, Brucella abortus . We examined B. abortus transmission between American bison ( Bison bison ), Rocky Mountain elk ( Cervus elaphus nelsoni), and cattle ( Bos taurus ) using variable number tandem repeat (VNTR) markers on DNA from 98 B. abortus isolates recovered from populations in Idaho, Montana, and Wyoming, USA. Our analyses reveal interspecies transmission. Two outbreaks (2007, 2008) in Montana cattle had B. abortus genotypes similar to isolates from bison and elk. Nevertheless, similarity in elk and cattle isolates from the 2008 outbreak suggest that elk are the likely source of brucellosis transmission to cattle in Montana and Wyoming. Brucella abortus isolates from sampling in Montana appear to be divide...

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Genomics reveals historic and contemporary transmission dynamics of a bacterial disease among wildlife and livestock

Nature communications, May 11, 2016

Whole-genome sequencing has provided fundamental insights into infectious disease epidemiology, b... more Whole-genome sequencing has provided fundamental insights into infectious disease epidemiology, but has rarely been used for examining transmission dynamics of a bacterial pathogen in wildlife. In the Greater Yellowstone Ecosystem (GYE), outbreaks of brucellosis have increased in cattle along with rising seroprevalence in elk. Here we use a genomic approach to examine Brucella abortus evolution, cross-species transmission and spatial spread in the GYE. We find that brucellosis was introduced into wildlife in this region at least five times. The diffusion rate varies among Brucella lineages (∼3 to 8 km per year) and over time. We also estimate 12 host transitions from bison to elk, and 5 from elk to bison. Our results support the notion that free-ranging elk are currently a self-sustaining brucellosis reservoir and the source of livestock infections, and that control measures in bison are unlikely to affect the dynamics of unrelated strains circulating in nearby elk populations.

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10 Migration and Dispersal Key Processes for Conserving National Parks

Yellowstone's Wildlife in Transition

Chapter 14 Demography of Central Yellowstone Bison: Effects of Climate, Density, and Disease

Terrestrial Ecology, 2008

ABSTRACT Over a century of concerted conservation recovered the bison population in Yellowstone N... more ABSTRACT Over a century of concerted conservation recovered the bison population in Yellowstone National Park from 23 animals in 1901 to 5000 by 2005. This conservation success led to societal conflicts and disagreements among various management entities regarding classic issues of overabundance (Garrott et al. 1993), combined with concerns over the risk of brucellosis transmission to domestic livestock when bison migrate out of the park (Cheville et al. 1998). As a result, more than 6700 bison have been culled since 1983 as they attempted to leave the park (Gates et al. 2005). These large‐scale removals are aimed at brucellosis risk management, but likely influence bison demographics and vital rates. The development of rigorously estimated vital rates that incorporate the effects of brucellosis and associated management actions is essential for formulating appropriate management strategies (e.g., vaccination, culling) for long‐term bison conservation. These estimates will also contribute to the growing scientific understanding of how climate, disease, and density affect managed ungulate populations. Fuller et al. (2007b) found high and consistent adult female survival and lower birth rates in brucellosis seropositive Yellowstone bison during 1995–2001. We focused on the central herd and incorporated additional information collected during 2002–2006 to extend those analyses by investigating density, climate, and brucellosis seroprevalence effects on age‐specific survival and fecundity.

14 Balancing Bison Conservation and Risk Management of the Non- Native Disease Brucellosis

Yellowstone's Wildlife in Transition

Vaccination strategies for managing brucellosis in Yellowstone bison

Vaccine, 2010

Concerns over migratory bison (Bison bison) at Yellowstone National Park transmitting brucellosis... more Concerns over migratory bison (Bison bison) at Yellowstone National Park transmitting brucellosis (Brucella abortus) to cattle herds on adjacent lands led to proposals for bison vaccination. We developed an individual-based model to evaluate how brucellosis infection might respond under alternate vaccination strategies, including: (1) vaccination of female calves and yearlings captured at the park boundary when bison move outside the primary conservation area; (2) combining boundary vaccination with the remote delivery of vaccine to female calves and yearlings distributed throughout the park; and (3) vaccinating all female bison (including adults) during boundary capture and throughout the park using remote delivery of vaccine. Simulations suggested Alternative 3 would be most effective, with brucellosis seroprevalence decreasing by 66% (from 0.47 to 0.16) over a 30-year period resulting from 29% of the population receiving protection through vaccination. Under this alternative, bison would receive multiple vaccinations that extend the duration of vaccine protection and defend against recurring infection in latently infected animals. The initial decrease in population seroprevalence will likely be slow due to high initial seroprevalence (40-60%), long-lived antibodies, and the culling of some vaccinated bison that were subsequently exposed to field strain Brucella and reacted positively on serologic tests. Vaccination is unlikely to eradicate B. abortus from Yellowstone bison, but could be an effective tool for reducing the level of infection. Our approach and findings have applicability world-wide for managers dealing with intractable wildlife diseases that cross wildlife-livestock and wildlife-human interfaces and affect public health or economic well-being.

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Predicting Bison Migration out of Yellowstone National Park Using Bayesian Models

PLoS ONE, 2011

Long distance migrations by ungulate species often surpass the boundaries of preservation areas w... more Long distance migrations by ungulate species often surpass the boundaries of preservation areas where conflicts with various publics lead to management actions that can threaten populations. We chose the partially migratory bison (Bison bison) population in Yellowstone National Park as an example of integrating science into management policies to better conserve migratory ungulates. Approximately 60% of these bison have been exposed to bovine brucellosis and thousands of migrants exiting the park boundary have been culled during the past two decades to reduce the risk of disease transmission to cattle. Data were assimilated using models representing competing hypotheses of bison migration during 1990-2009 in a hierarchal Bayesian framework. Migration differed at the scale of herds, but a single unifying logistic model was useful for predicting migrations by both herds. Migration beyond the northern park boundary was affected by herd size, accumulated snow water equivalent, and aboveground dried biomass. Migration beyond the western park boundary was less influenced by these predictors and process model performance suggested an important control on recent migrations was excluded. Simulations of migrations over the next decade suggest that allowing increased numbers of bison beyond park boundaries during severe climate conditions may be the only means of avoiding episodic, large-scale reductions to the Yellowstone bison population in the foreseeable future. This research is an example of how long distance migration dynamics can be incorporated into improved management policies.

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Yellowstone Bison—Should We Preserve Artificial Population Substructure or Rely on Ecological Processes?

Journal of Heredity, 2012

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Estimating probabilities of active brucellosis infection in Yellowstone bison through quantitative serology and tissue culture

Journal of Applied Ecology, 2011

1. Disease management along the boundaries of wildlife reserves is a growing conservation problem... more 1. Disease management along the boundaries of wildlife reserves is a growing conservation problem worldwide, as infected wildlife can migrate outside protected areas and pose a threat to livestock and human health. The bison Bison bison population in Yellowstone National Park has long been infected with Brucella abortus, but culling of Yellowstone bison to prevent transmission to cattle has been ineffective at reducing brucellosis infection. This management strategy is negatively affecting long-term bison conservation because of difficulties in diagnosing actively infected animals. 2. We integrated age-specific serology and B. abortus culture results from slaughtered Yellowstone bison to estimate probabilities of active brucellosis infection using a Bayesian framework. Infection probabilities were associated with age in young bison (0-5 years old) and with elevated antibody levels in older bison (>5 years old). Our results indicate that Yellowstone bison acquire B. abortus infection early in life but typically recover as they grow older. 3. A tool was developed to allow bison management to better reflect the probability that particular animals are infective, with the aim of conserving Yellowstone bison while reducing the risk of brucellosis transmission to cattle. Combining selective removal of infectious bison with additional management practices, such as vaccination, has the potential to advance an effective brucellosis reduction programme. 4. Synthesis and applications. We conclude that active B. abortus infection in Yellowstone bison is age dependent, which allows true infection probabilities to be estimated based on age and quantitative diagnostic tests. These findings have important application to disease management worldwide where accurate diagnostic tests for wildlife are unavailable. Estimation of true infection probabilities can replace culling practices that conflict with wildlife conservation. The ability to identify infective individuals can improve management practices that support conservation, particularly when human health is at risk or endangered wildlife species are involved.

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Population forecasting: Assimilating models and data to understand dynamics of brucellosis in the Yellowstone bison population

ABSTRACT Background/Question/Methods Conserving the Yellowstone bison represents one of the great... more ABSTRACT Background/Question/Methods Conserving the Yellowstone bison represents one of the greatest success stories in the history of wildlife management in North America. However, success has not come without challenges. The most significant problem confronting those who manage the population today is conflict created by the risk of spread of brucellosis from bison to cattle. Modern, adaptive management aimed at minimizing this risk requires a model capable of forecasting the population’s dynamics and its disease status. We used a discrete time, stage structured model assimilated with time series of monitoring data and results of detailed process studies to forecast changes in abundance and diseases status of the Yellowstone bison population. A Bayesian, hierarchical approach allowed use of data from multiple sources, supported estimation of process variance and observation error, and provided true forecasts, that is, predictions with confidence envelopes. Results/Conclusions Model forecasts suggested changes in policy could enhance conservation of bison while reducing risks of transmission of brucellosis from bison to livestock. Episodic, large removals to regulate the size of the population could be replaced by culling a much smaller number of animals annually, thereby mimicking chronic, natural mortality. Targeting sero-negative animals for culling rather than sero-positive ones could reduce the probability of disease transmission. A forecasting model can enhance management and policy by allowing evaluation of alternative actions. These evaluations are made honest by comprehensive assessments of uncertainty.

Timing of parturition events in Yellowstone bison Bison bison: implications for bison conservation and brucellosis transmission risk to cattle

Wildlife Biology, 2010

Yellowstone bison Bison bison are chronically infected with brucellosis (caused by the bacterium ... more Yellowstone bison Bison bison are chronically infected with brucellosis (caused by the bacterium Brucella abortus), which raises concerns about possible transmission to cattle when they migrate to winter ranges outside the Yellowstone National Park. We monitored bison from April to mid‐June during 2004‐2007 to estimate the timing and location of parturition events that may shed tissues infected by B. abortus. Observed abortions (N = 29) occurred from January through 19 May, while peak calving (80% of births) occurred from 25 April to 26 May, and calving was finished by 5 June. Observed parturition events (N = 115) occurred in the Park and on the Horse Butte peninsula in Montana, USA, where cattle were not present at any time of the year. Allowing bison to occupy public lands outside the Park where cattle are never present (e.g. Horse Butte peninsula) until most bison calving is completed (late May or early June) is not expected to significantly increase the risk of brucellosis trans...

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Mitochondrial Genome Analysis Reveals Historical Lineages in Yellowstone Bison

PLOS ONE, Nov 23, 2016

Yellowstone National Park is home to one of the only plains bison populations that have continuou... more Yellowstone National Park is home to one of the only plains bison populations that have continuously existed on their present landscape since prehistoric times without evidence of domestic cattle introgression. Previous studies characterized the relatively high levels of nuclear genetic diversity in these bison, but little is known about their mitochondrial haplotype diversity. This study assessed mitochondrial genomes from 25 randomly selected Yellowstone bison and found 10 different mitochondrial haplotypes with a haplotype diversity of 0.78 (± 0.06). Spatial analysis of these mitochondrial DNA (mtDNA) haplotypes did not detect geographic population subdivision (F ST = -0.06, p = 0.76). However, we identified two independent and historically important lineages in Yellowstone bison by combining data from 65 bison (defined by 120 polymorphic sites) from across North America representing a total of 30 different mitochondrial DNA haplotypes. Mitochondrial DNA haplotypes from one of the Yellowstone lineages represent descendants of the 22 indigenous bison remaining in central Yellowstone in 1902. The other mitochondrial DNA lineage represents descendants of the 18 females introduced from northern Montana in 1902 to supplement the indigenous bison population and develop a new breeding herd in the northern region of the park. Comparing modern and historical mitochondrial DNA diversity in Yellowstone bison helps uncover a historical context of park restoration efforts during the early 1900s, provides evidence against a hypothesized mitochondrial disease in bison, and reveals the signature of recent hybridization between American plains bison (Bison bison bison) and Canadian wood bison (B. b. athabascae). Our study demonstrates how mitochondrial DNA can be applied to delineate the history of wildlife species and inform future conservation actions.

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Ungulate control of grassland production: grazing intensity and ungulate species composition in Yellowstone Park

Ecosphere, Nov 1, 2016

Knowledge of the envelope of grazing conditions within which grassland plant and soil processes a... more Knowledge of the envelope of grazing conditions within which grassland plant and soil processes are sustainable is important for the ecologically sound management of grazed grassland. Here we examined how a recent shift from elk to bison dominance of the northern ungulate community in Yellowstone National Park (YNP), and an associated increase in the duration that grassland was grazed, affected grazing intensity and aboveground net primary production (ANPP). Mean grazing intensity (GI, percentage ANPP removed) and stimulation (grazed ANPP minus ungrazed [exclosed] ANPP) were compared among three studies, two when elk (1988)(1989)(1999)(2000)(2001) and one when bison (2012-2014) dominated the northern YNP ungulate community. We also manipulated GI with small exclosures established for different lengths of time after the start of the growing season to directly determine the effect of the combination of grazing duration (GD) and GI on stimulation at a dry grassland and a mesic grassland. GI was greater under a bison-dominant grazing regime (49%) compared with that measured during the two earlier periods when elk were the dominant ungulate species (31%, 13%). Plotting stimulation on GI for sites sampled across all three studies revealed a unimodal relationship, with peak stimulation of 34% occurring at a GI of 40%. Manipulating GI indicated that the greater GI and longer GD of grazing under a bisondominant regime reduced stimulation at a mesic grassland and negated it completely at a dry grassland. These findings revealed that a shift in the grazing ungulate community composition and an associated change in the migratory behavior of the dominant species impacted YNP grassland processes. Results also showed that grassland ANPP was resilient to the relatively high rates of prolonged grazing by the bison-dominant community and did not reduce ANPP below paired, ungrazed conditions. However, YNP grassland should be continued to be monitored if such high rates of herbivory continue.

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