Browsing by Subject "Competition"

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Bobcat (Lynx rufus) spatial ecology and harvest in Minnesota.
(2012-05) Kapfer, Paul Michael
The bobcat (Lynx rufus) is the most widely distributed and abundant felid in North America, whose status is primarily monitored via harvest and associated data. I used a combination of harvest and field data to investigate factors affecting spatiotemporal dynamics of bobcat harvest and spatial ecology in Minnesota. In chapter one, I investigate the socioeconomic and ecological factors that affected the number of bobcats harvested in Minnesota. Management of game animals requires understanding of factors that affect harvest levels. Although influenced by international law, bobcat management is the responsibility of state or provincial agencies, and jurisdictional environmental, ecological, and regulatory differences may alter which variables influence harvest. Consequently, our understanding of the factors driving bobcat harvest should be at a scale similar to that at which they are managed. I associated 32 years of bobcat harvest data from Minnesota with socioeconomic (e.g., pelt prices, license sales) and ecological variables (e.g., prey abundance, bobcat-specific index of winter severity) to determine what variables most strongly influenced annual bobcat harvest. I constructed candidate negative binomial generalized linear models based on an information-theoretic approach and used quasi-likelihood Akaike's Information Criterion adjusted for small sample size to assess the relative performance of each model. My best model suggested that annual bobcat harvest in Minnesota was positively related to the proportion of scent stations visited by bobcats and season length, and negatively related to the proportion of days when the maximum temperature remained below the bobcat's lower critical temperature. My results differ from those of other studies examining factors influencing furbearer harvest that have suggested furbearer harvest is driven primarily by pelt price, and suggest that managers can influence the annual harvest of bobcats by changing season length. In chapter 2, I examine the factors affecting the spatial distribution of bobcat harvest in northeastern Minnesota. Understanding which factors limit species distributions is fundamental to predicting their response to and impact under environmental change. For species that are difficult to monitor, the spatial distribution of their harvest represents a common tool used for monitoring populations and can, with caution, be used to infer ecological relationships. Despite a nearly three-fold increase in abundance over the last 15 years and coincident increase in harvest, the spatial distribution of bobcat harvest in Minnesota has remained relatively static. Of particular interest is the near total absence of bobcat harvest in the northeastern portion of the state because it represents one of five regions designated critical habitat for the federally-threatened Canada lynx (Lynx canadensis), and anecdotal accounts suggest bobcats may threaten the persistence of Canada lynx populations. To explore potential explanations for the lack of bobcat harvest in this region I developed candidate binomial generalized linear models comparing townships where male and female bobcats were and were not harvested to determine whether hunter access and effort, climate, competition, prey abundance, or some combination thereof, accounted for the absence of bobcat harvest in this region. As judged by Akaike's Information Criterion corrected for small samples sizes, top-ranked models for males and females suggest that the distribution of bobcat harvest in northeastern Minnesota is primarily determined by bobcat ecology rather than hunter effort and access. The probability that a male or female bobcat was harvested in a township increased with white-tailed deer (Odocoileus virginianus), density and decreased with coyote (Canis latrans) density; harvest of females was also positively related to the proportion of a township composed of regenerating forest, an index of snowshoe hare (Lepus americanus) abundance. My results correspond with those of previous studies suggesting that bobcat populations can be suppressed by coyotes, that females are more reliant on snowshoe hare than males, and that white-tailed deer form an important component of the diet of bobcats at northern latitudes. Furthermore, my results suggest that reductions in winter-related mortality of white-tailed deer as predicted by climate change and consequent increases in deer density may remove one of the barriers to further colonization of the Arrowhead by bobcats, potentially increasing Canada lynx exposure to competition and genetic introgression. In chapter 3 I use data from two GPS radio-collared sibling adult female bobcats and compare estimated home range and core area size to previously published studies of bobcat space use in Minnesota and Wisconsin and provide the first published estimate of space use overlap among sibling adult females. Social organization influences carnivore demography, space use, density and abundance. In bobcats, social organization is thought to be affected by multiple interacting factors including relatedness, sex, and prey and conspecific density. To provide baseline data on the effect of relatedness on bobcat social organization, I examined space use and overlap among two sibling, adult female bobcats in east-central Minnesota, and compared these results to previously published research. Estimated bobcat home range size was similar to that of previous studies, suggesting stability in home range size across several decades and reliability in our estimates. Home range and core area overlap was within the range of previous studies. Importantly, the use of two different methods for estimating core area suggested that the subjective use of the 50% utilization distribution would have underestimated core area size and overlap. In the 4th and final chapter, I estimate how environmental features affect the suitability of habitat for bobcat reproduction and kitten survival and estimate the extent and distribution of bobcat breeding habitat in Minnesota. Distribution models have seen widespread adoption for a diversity of conservation applications because they require minimal data yet have proven highly predictive of the environmental features tolerated by animals. However, there has been limited integration of demography and distribution modeling despite empirical evidence suggesting that the environmental conditions supportive of reproduction are a subset of those supporting survival. I developed a maximum entropy distribution model of habitat suitable for bobcat reproduction and kitten survival using locations where kittens were harvested. My distribution model had good predictive ability and results suggest that the distribution of riparian forest is the preeminent environmental feature explaining the distribution of bobcat reproduction in Minnesota. Coyote abundance, row-crop agriculture and prairie were negatively associated with habitat suitability, mirroring the results of previous studies. Percentage of the study area providing suitable habitat for bobcat reproduction ranged from 23-76%, depending on the threshold used to discriminate between suitable and unsuitable habitat. Notably, I used data that agencies charged with managing bobcat populations largely already gather to develop a highly predictive model of the suitability of habitat for bobcat reproduction. Conservationists without access to harvest data can gather similar data from incidental observations of reproduction to provide better insight into the relative importance of environmental features for conservation planning and prioritization.
Capital structure and product market competition: evidence from the EU life insurance industry.
(2012-07) Osipov, Daniil Vladimirovich
Climate and competition affect growth and survival of transplanted sugar maple seedlings along a 1700‐km gradient
(Wiley, 2017) Putnam, Rachel C
Plant species distributions, broadly shaped by climate, may also be constrained by other species. The degree to which biotic factors affect range limits is unclear, however, and few experimental studies have investigated both biotic and abiotic factors across and beyond a species’ range. We examined seedling survival and net growth for three years in contrasting canopy type (closed canopy vs. gap) and neighbor density (clipped vs. unclipped) environments for northern, central, and southern populations of sugar maple (Acer saccharum) representing a climate- of- origin gradient, experimentally planted from Arkansas, USA to Ontario, Canada at ten forested sites along a 1700- km transect spanning beyond the species’ range. We hypoth-esized that each population’s highest survival and growth would occur in its region of origin, with poorer performance in cooler or warmer areas. Refuting this hypothesis, seedlings of all three populations had greater growth and survival in sites increasingly warmer than their point of origin, although they did show poorer growth and survival at increasingly colder sites. We also hypothesized that maple survival and net growth near and beyond range margins are con-strained primarily by cold temperature limitation in the north, where we expected neighbors to facilitate survival, and by competition in the south, where we expected to enhance survival and growth by reducing neighbor density. Results partially supported the hypothesis concerning biotic interactions: in canopy gaps, understory neighbors enhanced maple growth at the cool-est sites but did not suppress growth as expected at the warmest sites. As the northern popula-tion grew and survived reasonably well beyond the northern range limit, and as all populations performed best at warmer sites, including beyond the southern range limit, there was tepid, if any, support for the hypothesis that climate regulated the northern limit and absolutely no support for the hypothesis that competition regulated the southern limit. Together, these three- year ﬁndings with juvenile trees suggest that sugar maple range limits may instead be con-strained by factors besides climate and competition, by those factors at another life stage, and/or by climate events such as heat waves, droughts, and cold snaps that occur at longer return intervals.
Community assembly, invasion, and management of aquatic plant communities
(2022-12) Verhoeven, Michael
Determining what mechanisms drive native species declines and what governs their recovery is foundational to understanding community change, and successfully applying this knowledge to limit further losses or restore degraded ecosystems. Efforts to reduce invasive plant populations are often considered critical for halting degradation of native plant communities and fostering their subsequent recovery or restoration. To assess whether management of two invasive plants—Eurasian watermilfoil (Myriophyllum spicatum) and curlyleaf pondweed (Potamogeton crispus)—is likely to foster recovery of native aquatic plant communities, I integrate experimental and observational methods to study community assembly processes in aquatic plants. Chapter 1 builds the foundation for subsequent studies by constructing an observational monitoring database, compiled from more than 500,000 plant observations collected by disparate sources over a 19-year period. In Chapter 2, I use niche models to unpack how patterns of dominance seen in P. crispus and M. spicatum have likely arisen through different mechanisms, predicting direct competition with native species is less likely for P. crispus than M. spicatum. The aquatic plants database is used in Chapter 3 to assess invader control for boosting native plant communities in real-world management projects, with a focus on comparing the two invaders to test predictions from niche models. I show that limitations of monitoring data constrain estimation of causal effects of management. This limits the generalizability of the findings, highlighting the need for more strategic allocation of aquatic plant monitoring efforts and improved tracking of management interventions. In Chapter 4 I synthesize results of a 4-year, in-lake field experiment and the 19-year, statewide observational data, using community assembly theory to ascribe changes in plant communities to three major mechanisms (invader competition, environmental conditions, and regional species pools) and assess the scales at which these mechanisms shape aquatic plant communities. The results highlight complexity and interactivity of community assembly in this system, with mixed evidence for each mechanism and strong differences across scales. This research demonstrates that contrary to common dogma in aquatic plant management, invaders’ relationships with recipient communities are nuanced, and that invader control alone is insufficient to achieve restoration.
Cooperation, Competition, and Killing: Reproductive strategies of chimpanzees (Pan troglodytes)
(2023-08) Massaro, Anthony
Group-living commonly involves tensions between conflict and cooperation. Group members need one another to survive, but also compete for access to key resources such as food and mates. To better understand reproductive strategies in group-territorial species with sex-biased dispersal, I used decades of data from Gombe National Park, Tanzania to test hypotheses regarding how and why chimpanzees (Pan troglodytes) cooperate, compete, and fight. First, I found that male chimpanzees exhibit a consistently high degree of participation in boundary patrols (mean=75%) and that the best predictors of participation in patrols were sighting frequency and participation in hunting bouts, indicating a mutualistic payoff structure for male territorial effort. Second, I found that female chimpanzees produced copulation calls more frequently when they were nulliparous, and in the early days of their swelling. Thus, these calls likely function as an anti-infanticide strategy, inducing otherwise uninterested males to mate and maximizing the pool of potential sires. Females also called less frequently in the presence of higher-ranking females, indicating that intrasexual competition plays a role in call production. Third, I found that males killed by other chimpanzees suffered a higher-than-expected rate of genital wounding, but during non-fatal fighting, only in one of four communities (Kasekela) did males experience a higher-than-expected rate of genital wounds. Females in all four study communities experienced a higher-than-expected rate of genital wounds, indicating that genital wounding is an unlikely alternative to lethal aggression. Finally, I found that lethal aggression was more common in Mitumba than Kasekela. As a smaller community, Mitumba has fewer females and thus less overlap between reproductively active females and a greater opportunity to monopolize mating opportunities. Overall, this work emphasizes the importance of within-group reproductive competition.
Cutthroat or cartel? an analysis of price competition in farmers markets.
(2012-05) Horwich, Jeffrey Lloyd
While the civic and nutritional implications of farmers markets have captured researchers' attention, few have focused on how the "markets" in farmers markets actually work. This paper opens a crucial but largely unexplored field of economic inquiry: how are the prices consumers pay at the farmers market determined? An original dataset of farmers market prices, gathered across five cities over a full calendar year, allows a quantitative look at two specific questions: first, how do prices move as more vendors enter and compete to sell a product? Second, what relation do farmers market prices have to prices in conventional grocery outlets? Using a set of simple regressions and a novel meta-analysis technique, I find meaningful and statistically significant relationships between vendor numbers and price for some products, but not for others. More perishable products seem to display the effect much more powerfully, a result which agrees with theory on search costs and product differentiation. Another important finding is that even where median prices do not decline with vendor count, minimum prices often do, suggesting the diligent consumer can benefit. I also find evidence of price collusion in some markets and products. Finally, I find no discernible, consistent relationship between farmers market prices and supermarket prices. In addition to better informing consumers, these results suggest that policy-makers who wish to expand farmers markets as an option for the general public - and especially lower-income shoppers - have some options for fostering a more competitive environment. But even at the farmers market there is no free lunch, as there are likely trade-offs between consumer welfare and economic rents we may value for local agriculture.
Ecology and ecosystem impacts of common buckthorn (Rhamnus cathartica): a review
(2007) Knight, Kathleen S; Kurylo, Jessica S; Endress, Anton G; Stewart, J. Ryan; Reich, Peter B
In this review, we synthesize the current knowledge of the ecology and impacts of Rhamnus cathartica L., a shrub from Europe and Asia that is a successful invader in North America. Physiological studies have uncovered traits including shade tolerance, rapid growth, high photosynthetic rates, a wide tolerance of moisture and drought, and an unusual phenology that may give R. cathartica an advantage in the environments it invades. Its high fecundity, bird-dispersed fruit, high germination rates, seedling success in disturbed conditions, and secondary metabolite production may also contribute to its ability to rapidly increase in abundance and impact ecosystems. R. cathartica impacts ecosystems through changes in soil N, elimination of the leaf litter layer, possible facilitation of earthworm invasions, unsubstantiated effects on native plants through allelopathy or competition, and effects on animals that may or may not be able to use it for food or habitat.
Effects of competition on governance choice and project performance: evidence from clinical trials in the biotechnology industry.
(2010-02) Islam, Mazhar
In this dissertation, I incorporate the external competitive environment into the analysis of governance choice of technology projects and performance implications of such governance choice. From the perspective of R&D firms, I develop a theoretical framework that categorizes competitors in a technology domain into two groups R&D firms and vertically integrated firms. Furthermore, I identify the underlying mechanisms that drive the relationship between the presence of heterogeneous competitors and a R&D firm's choice of three alternative governance modes: internal organization, equity alliance and non-equity alliance. I test the framework on a unique data set that contains history of clinical trials in 24 therapeutic areas in the US biotechnology industry between 1996 to 2008.
Essays on Competition in Health Insurance
(2021-06) Ryan, Conor
This dissertation consists of three chapters. In the first chapter, with coauthors Roger Feldman and Stephen Parente, I use a novel data set from a private online marketplace to estimate the demand for individual health insurance among a set comprising many high-income consumers across 18 states. We find that consumers earning more than 4 times the federal poverty level are willing to pay $30 to $135 per month to increase the actuarial value of their insurance by 10 percentage points, much less than low-income consumers. In the second chapter, I show that regulations to address adverse selection and competition policy should be considered complements. To see the relationship, consider the incentive for a firm to offer a product that appeals to low-risk consumers and leads high-risk consumers to purchase insurance elsewhere. This incentive problem, which leads to inefficient consumer sorting, is worst in highly competitive markets and absent in a monopoly. I estimate a model of the individual insurance market by combining the data from chapter one with a risk prediction model to relate preferences to marginal cost. I find that the largest welfare cost in the non-group market comes from high markups. Distortions coming from extensive margin selection and inefficient sorting are significantly addressed by current policies targeting adverse selection which are successful in improving total welfare. However, in the most concentrated markets, insurance firms recapture most of the added surplus through higher markups. In the final chapter, I study the effect of competition on medical consumption through the cost-sharing terms---e.g. copays and coinsurance rates--- of the insurance products. These terms determine the out-of-pocket price of medical care, which affect a patient's medical decisions and thus the patient's health outcomes. Using medical claims data linked to insurance products, I estimate a model of imperfect competition that incorporates adverse selection, moral hazard, and selection on moral hazard. First, I show that, on average, less competition leads to higher levels of cost-sharing but multi-product firms respond by increasing the cost-sharing levels of some products and decreasing others. Second, I find that medical consumption and health respond to cost-sharing terms. A $10 increase in the primary care copay leads to a 5.4% decrease in medical consumption and a 0.1 percentage point increase in inpatient mortality. Putting these results together, I find that a reduction in competition via a merger leads to up to a 4% increase in the primary care copay, an average reduction in medical spending of $17 per person, and an additional six inpatient deaths per year. At estimates of the statistical value of a life, the reduction in spending is more than outweighed by the cost of additional deaths.
Institutional Accountability and competition for resources in undergraduate education among U.S. public four-year institutions.
(2012-01) Akey, Lynn D.
With a growing concern that society’s needs are not being met, there are heightened expectations for accountability for public purposes. At the same time higher education institutions are experiencing increasing competition, as well as decreasing state support for public higher education. The concern is that competition for resources is overtaking accountability for public purposes. Using an observational correlational research design, this study explored the relationships between institutional competition for resources and accountability for public purposes at the undergraduate level among 428 U. S. public four-year institutions. The study examined institutional competition organized around the four key markets that generate institutional revenues (student enrollment, research funding, public fiscal support, and private giving) and institutional accountability for public purposes defined by accountability measures most frequently included in state-level performance accountability systems (access, affordability, and completion). The relationship between institutional competition for resources and accountability for public purposes was also examined considering institutional fiscal health and market segment. The accountability triangle, resource dependency theory, and postsecondary market taxonomy provided a conceptual framework for the study. The results of the study indicate a statistically significant relationship between institutional competition for resources and institutional accountability for public purposes. In particular, a negative relationship was observed between institutional competition and accountability for access (R2 = .16) and affordability (R2 = .05), and a positive relationship was observed between institutional competition and accountability for completion (R2 = .09). Institutional fiscal health was a statistically significant factor in only the relationship between institutional competition and accountability for access producing an increase in the predictive power of the model (R2 = .16 to R2 = .18). In addition, no differences were found in the nature of the relationship between institutional competition and institutional accountability for public purposes across the market segments of higher education. Most importantly, this study provides empirical evidence of a relationship between the complicated constructs of institutional competition for resources and institutional accountability for public purposes at the undergraduate level within U.S. public four-year institutions. With the force of institutional competition likely to increase and the necessity for higher education to serve public purposes critical, additional research further exploring the relationships between institutional competition and institutional accountability at the undergraduate level is crucial.
Life, Death, And Coexistence: Exploring And Manipulating The Respiratory Lifestyle Of Shewanella Oneidensis
(2019-08) Kees, Eric
In their natural environment, microbes often exist in stressful, suboptimal, ever-changing conditions and have evolved innumerable and varied successful strategies for managing stresses and thriving in flux. Microbial ecosystems are defined not only by specialized members occupying defined narrow niches, but also members that move between niches and exist in a mode of constant opportunism. One such opportunistic group of organisms are those belonging to the genus Shewanella which are largely defined by their respiratory versatility. A particularly well-studied member of this genus, S. oneidensis, is the most versatile respiratory organism described to date, and is a model organism for extracellular electron transfer. This thesis explores the respiratory lifestyle of S. oniedensis primarily through the lens of cell physiology and competitive fitness under optimal growth conditions and those that yield catastrophic death. The second chapter of this thesis is a study in cofactor acquisition by a key respiratory enzyme in S. oneidensis MR-1. The periplasmic protein FccA is both a fumarate reductase and an electron carrier protein for extracellular electron transfer, that requires a flavin cofactor for its function. Through genetic manipulation, growth experiments, and biochemical experiments, we found that for S. oneidensis, self-secretion of flavins comes at minimal metabolic cost and is required for periplasmic flavoprotein cofactor acquisition. The third chapter is a probing of natural and engineered factors that enable survival under respiratory stress. Shewanella is considered an obligate respiring organism, and when placed under conditions in which respiration cannot normally function, it experiences massive loss in viability accompanied by cell lysis. Despite, 99-99.99% of cells undergoing death in this condition, many persist. This study leveraged synthetic proton motive force supplementation, which affords enhanced survival of S. oneidensis, to profile the innate strategies used to survive under respiratory stress. The key finding of this study is that the sodium motive force plays a key role in survival of S. oneidensis under respiratory stress, even when survival is enhanced by proton motive force supplementation. The fourth chapter of this thesis is a series of competition experiments reframing a central paradigm of the competitive exclusion principle: that two organisms occupying the same niche cannot coexist. This principle states that in this scenario any organism with a reproductive advantage will ultimately overtake a population. This study demonstrated that two engineered strains of S. oneidensis utilizing the same medium with the same food and nutrient sources, but growing a vastly different rates, can remain at stable frequencies when grown attached to an electrode as the sole sink of electrons in respiration. The primary reason for this stability is that the original parent population remains actively growing on a surface to which daughtered cells are constantly removed. While the scenario we have engineered to “break” the competitive exclusion principle could be considered a form of niche differentiation, it demonstrates an effective strategy to combat strain degeneration and contamination in industrial fermentation, by allowing a selected population of less competitively fit individuals to act indefinitely as a progenitor population. The work in this thesis brings special attention to the adaptation towards an obligate respiratory lifestyle in S. oneidenisis. The systems it has evolved to secrete flavins as both respiratory cofactors and intermediates and the marked death it experiences under respiratory stress together emphasize adaptations in Shewanella to thrive in redox stratified environments, supported by the wide variety of respiratory nodes it can utilize. Finally, this work highlights the utility of S. oneidensis as a test platform for ideas, with potential benefits for biotechnological and industrial applications.
Measuring warfare in wood: linking competition among wood-degrading fungi of northern forests to its ecological consequences
(2014-08) Song, Zewei
Competition between distinctive groups of fungi determines the pattern of wood decomposition in forests, but the outcome of these battles may shift in a changing climate. With more than 70% of Earth's biotic carbon stored in woody tissues, understanding the processes that unlock this carbon and release the greenhouse gas CO₂ is critical. For my thesis research, I am addressing several key questions about how fungi colonize and dominate wood on the forest floor. Quantitative PCR was developed to measure biomass of specific fungi from a community in Chapter one. This technique was coupled with ergosterol, dilute alkali solubility, pH and carbon component analysis to measure biotic and abiotic dynamic during wood decomposition. With these comprehensive tools, factors that may influence fungal competition and decomposition outcomes were studied in the following chapters. In Chapter two, wood type was shown not to influence the competition between a brown rot fungus and a white rot fungus. It is contrary to the observations on wood preferences in nature, but reflected different foraging strategies by fungi. This led to the study of Chapter three on priority effect. By increasing the inoculum potential either inside or outside wood substrate, I have shown evidence that a weak competitor fungus can outcompete its more aggressive opponents, thus achieving co-existence. Another two factors, temperature and endophytes, along with priority effect were studied in Chapter four. Endophytes showed a much larger effect in influencing wood decomposition than temperature, mostly through antagonisms against soil fungi. Studies on these factors reveals potential for a more comprehensive model for wood decomposition. Emphasis on the role of microbial components, especially the often neglected endophytic communities, is possible to explain the variability in wood decomposition that can not be explained by abiotic factors, alone.
Online Video Content's Impact on the Supportive Relationship Between Sport Organization and Sports Journalist: A Case Study of the Minnesota Twins Baseball Club and the Local Television Sports Journalists Who Cover Them
(2016-07) Nettleton, Christopher
Widespread acceptance of the Internet has created an opportunity for sport organizations to become their own online video content creator and publisher. This avenue allows sport organizations to utilize the two-way symmetrical model of public relations (Grunig & Hunt, 1984, p. 15) to participate in a “true” back-and-forth dialogue with their fans that informs current and future content production. However, this new opportunity circumvents the traditional mass media pathways, which may also have the consequence of creating competition between sport organizations and sports journalists. To explore this under-represented research area, this study employed a multimethod design to gain better understanding and answer this study’s lone research question: What impact has the increase in online self-published video content had on the supportive working relationship between sport organizations and the local television sports journalists who cover them on a regular basis? Using the case study of the Minnesota Twins Baseball Club and television sports journalists from the Minneapolis/St. Paul media market, this study identified competition between sport organization and sports journalists, and that competition’s apparent impact on the working relationship between the two parties. This study also finds that local television sports journalists’ denial of competition is a form of boundary-work (Gieryn, 1983) in response to this evolving working relationship.
Skilled Nursing Facility Use Under Hospital Controlled Bundled Payments
(2019-11) Weissblum, Lianna
Hospitals increasingly bear financial risk for health care spending after hospital discharge through payment reforms such as bundled payments and accountable care organizations. Under Model 2 of Medicare’s Bundled Payments for Care Improvement (BPCI) initiative, hospitals took on financial responsibility for health care use during an episode of care beginning at hospital admission and lasting up to 90 days after discharge. The financial success of Model 2 participants hinged on managing post-acute care use, including skilled nursing facility (SNFs) care. During BPCI, the primary drivers of SNF Medicare spending were length of stay and therapy intensity, which determined daily payment rates. SNF therapy intensity increased considerably in recent years, despite no significant changes in SNF patient frailty or outcomes. Reducing unnecessary overuse of SNF therapy would have lowered Medicare spending without decreasing quality of care. The objective of this study is to assess changes in SNF treatment intensity (length of stay, therapy intensity, payments) under BPCI Model 2, as well as changes in SNF referral patterns and the impact of SNF market power. I focus on lower extremity joint replacement (LEJR) episodes and compare the impact of Model 2 in a cohort of hospital participants that took on risk before it was mandatory (early adopters) to a cohort of hospitals that took on risk when it was mandatory (late adopters). I find that Model 2 hospital participation was associated with differential reductions in SNF use. During both early adopter and late adopter episodes, I found differential reductions in SNF days and Medicare payments. SNF therapy intensity declined for early adopter episodes only. Within SNF changes drove reductions in SNF length of stay and Medicare payments. However, SNF therapy intensity reductions in the early adopter population were driven by changes in SNF referral patterns. I find limited evidence for large changes in referral concentration or historical SNF quality and efficiency under BPCI Model 2 across both early and late adopter hospitals. In terms of the impact of SNF market power, I find that SNF treatment intensity reductions were greatest in SNF markets with the greatest excess capacity and competition when using counties to define markets across both the early and late adopter cohorts. However, differences were not typically significant due to low statistical power. Based on the results of a power analysis, more hospital participants, may be required to detect statistically significant differences, particularly when stratifying participants into groups. Alternative results using health service areas (HSAs) to define SNF markets were less conclusive.
Studies of the round goby (Neogobius melanostomus) population of the St. Louis River Estuary
(2013-12) Leino, Jared
This thesis consists of multiple chapters/studies including a review chapter (chapter 1), and two additional studies of which have abstracts that are embedded in the thesis.
Tree regeneration dynamics and drivers across the temperate-boreal transition zone.
(2012-03) Fisichelli, Nicholas Anthony
The upper Great Lakes region in central North America contains a forest transition zone where temperate and boreal tree species reach their northern and southern range limits, respectively. It is only within this narrow latitudinal band (~3 degrees), that relatively warm-adapted temperate and cold-adapted boreal tree species are found growing together in upland mesic sites. If climate is a main driver of forest dynamics within this region, recent and predicted climate change should result in major forest shifts, including the expansion of temperate species and range contraction of boreal species. Such changes should first be manifest in growth and abundance trends of tree species in the understory regeneration layers. In addition to climate, numerous other factors such as overstory composition, understory abiotic environment, competition with shrub and herbaceous layers, and browse pressure drive tree regeneration trends. Interrelationships and interactions among these drivers will ultimately determine the direction and rate of forest change. We explored these research topics through field studies of naturally established seedlings and saplings at 124 upland mesic forest sites across a three state (Minnesota, Wisconsin, and Michigan U.S.A) 170,000 km2 area of the temperate-boreal transition zone. Chapter 1 examined relative abundance shifts of temperate and boreal tree regeneration at two spatial scales: local ecotonal boundaries between temperate and boreal dominated stands and across the regional temperate-boreal transition zone. Because we compared understory performance across locally changing overstory composition, we calculated species regeneration success as the difference in relative abundance between the understory and overstory layers. At the local scale, both shade-tolerant temperate and boreal species exhibited positive tree regeneration success across ecotonal boundaries. However, across the region, regeneration performance varied with mean summer temperature and to a lesser extent mean annual precipitation. Changes in regeneration success were generally greatest at the warm end of the transition zone, with temperate broadleaf Acer saccharum, Fraxinus nigra, and Ostrya virginiana responding positively and boreal Abies balsamea showing significantly reduced performance. For the most frequent temperate species, Acer rubrum, regeneration success was greatest in boreal neighborhoods and at cool and dry sites. Other species did not exhibit detectable shifts in regeneration success, potentially due to traits such as shade-tolerance, palatability, and mode of reproduction. Overall we found that numerous tree species growing across the temperate-boreal transition zone are likely sensitive to climate at early stages of development, with observed shifts in regeneration success concomitant with the direction predicted in response to climate change. Chapter 2 assessed the relative importance of and interrelationships among explanatory variable sets in explaining the composition of the tree regeneration layer. We used redundancy analysis (RDA) and variation partitioning to quantify the unique, shared, and total explanatory power of four sets of drivers: climate, understory abiotic environment, overstory composition, and understory biota. The results showed that all four driver sets individually explained a significant portion of tree regeneration compositional variation and additionally that there were strong relationships among explanatory variables. Overstory composition, which directly influences seed availability and also was found to be closely associated with understory environmental conditions and biota, had approximately twice the explanatory power of any of the other three driver sets. Some of the strongest individual drivers were overstory Acer saccharum and Populus tremuloides, soil pH, mean summer temperature, and mean annual precipitation. Suites of associated drivers included cool, moist, sandy, and acidic conditions; overstory boreal broadleaf species, light availability, shrub abundance, and forb cover; and warm temperatures and graminoid cover. Due to the strong interrelationships among drivers, the direction and rate of forest change will likely depend on how the importance of drivers shifts with climate and, for the biotic drivers, on the rate and magnitude of their own responses to climate change. Chapter 3 investigated sapling height and radial growth rates of five temperate and boreal species. This study included over 1700 stems of naturally established, competing saplings growing at 14 sites across the temperate-boreal transition zone. Top performing linear mixed-effects models typically included two-way interactions among mean summer temperature, browse pressure, understory light levels, and initial sapling size. As hypothesized, temperate sapling growth increased and boreal growth decreased with increasing temperatures. However, the relative performance of competing species shifted depending on the level of browse pressure. Positive temperate growth responses to temperature were eliminated by heavy browse pressure, tilting growth rates in favor of less palatable boreal conifers at all but the warmest sites. Spatial variations in browse pressure levels across the region suggest that temperate expansion may proceed most rapidly in areas where browsing is least intense. Growth responses to temperature also varied with sapling size and, for the least shade-tolerant species in the study, Quercus rubra, light availability. Enhanced growth by temperate species in response to warmer temperatures was most detectable under favorable conditions including low browse pressure and high understory light availability, suggesting that any efforts to facilitate forest compositional changes will need to take into account these trends.

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