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1.  Evolutionary rescue can maintain an oscillating community undergoing environmental change 
Interface Focus  2013;3(6):20130036.
The persistence of ecological communities is challenged by widespread and rapid environmental change. In many cases, persistence may not be assured via physiological acclimation or migration and so species must adapt rapidly in situ. This process of evolutionary rescue (ER) occurs when genetic adaptation allows a population to recover from decline initiated by environmental change that would otherwise cause extirpation. Community evolutionary rescue (CER) occurs when one or more species undergo a rapid evolutionary response to environmental change, resulting in the recovery of the ancestral community. Here, we study the dynamics of CER within a three-species community coexisting by virtue of resource oscillations brought about by nonlinear interactions between two species competing for a live resource. We allowed gradual environmental change to affect the traits that determine the strength and symmetry of the interaction among species. By allowing the component species to evolve rapidly, we found that: (i) trait evolution can allow CER and ensure the community persists by preventing competitive exclusion during environmental change, (ii) CER brings about a change in the character of the oscillations (period, amplitude) governing coexistence before and after environmental change, and (iii) CER may depend on evolutionary change that occurs simultaneously with or subsequently to environmental change. We were able to show that a change in the character of community oscillations may be a signature that a community is undergoing ER. Our study extends the theory on ER to a world of nonlinear community dynamics where—despite high-frequency changes of population abundances—adaptive evolutionary trait change can be gradual and directional, and therefore contribute to community rescue. ER may happen in real, complex communities that fluctuate owing to a mix of external and internal forces. Experiments testing this theory are now required to validate our predictions.
PMCID: PMC3915851  PMID: 24516721
eco-evolutionary dynamics; community evolutionary rescue; competitive exclusion; intrinsic population cycles
2.  Hospital Safety Scores 
JAMA surgery  2014;149(5):413-414.
PMCID: PMC4254910  PMID: 24647884
3.  Stochastic environmental fluctuations drive epidemiology in experimental host–parasite metapopulations 
Environmental fluctuations are important for parasite spread and persistence. However, the effects of the spatial and temporal structure of environmental fluctuations on host–parasite dynamics are not well understood. Temporal fluctuations can be random but positively autocorrelated, such that the environment is similar to the recent past (red noise), or random and uncorrelated with the past (white noise). We imposed red or white temporal temperature fluctuations on experimental metapopulations of Paramecium caudatum, experiencing an epidemic of the bacterial parasite Holospora undulata. Metapopulations (two subpopulations linked by migration) experienced fluctuations between stressful (5°C) and permissive (23°C) conditions following red or white temporal sequences. Spatial variation in temperature fluctuations was implemented by exposing subpopulations to the same (synchronous temperatures) or different (asynchronous temperatures) temporal sequences. Red noise, compared with white noise, enhanced parasite persistence. Despite this, red noise coupled with asynchronous temperatures allowed infected host populations to maintain sizes equivalent to uninfected populations. It is likely that this occurs because subpopulations in permissive conditions rescue declining subpopulations in stressful conditions. We show how patterns of temporal and spatial environmental fluctuations can impact parasite spread and host population abundance. We conclude that accurate prediction of parasite epidemics may require realistic models of environmental noise.
PMCID: PMC3768316  PMID: 23966645
host–parasite; epidemiology; variation; red noise; spatial synchrony
4.  Climate change and habitat fragmentation drive the occurrence of Borrelia burgdorferi, the agent of Lyme disease, at the northeastern limit of its distribution 
Evolutionary Applications  2014;7(7):750-764.
Lyme borreliosis is rapidly emerging in Canada, and climate change is likely a key driver of the northern spread of the disease in North America. We used field and modeling approaches to predict the risk of occurrence of Borrelia burgdorferi, the bacteria causing Lyme disease in North America. We combined climatic and landscape variables to model the current and future (2050) potential distribution of the black-legged tick and the white-footed mouse at the northeastern range limit of Lyme disease and estimated a risk index for B. burgdorferi from these distributions. The risk index was mostly constrained by the distribution of the white-footed mouse, driven by winter climatic conditions. The next factor contributing to the risk index was the distribution of the black-legged tick, estimated from the temperature. Landscape variables such as forest habitat and connectivity contributed little to the risk index. We predict a further northern expansion of B. burgdorferi of approximately 250–500 km by 2050 – a rate of 3.5–11 km per year – and identify areas of rapid rise in the risk of occurrence of B. burgdorferi. Our results will improve understanding of the spread of Lyme disease and inform management strategies at the most northern limit of its distribution.
PMCID: PMC4227856  PMID: 25469157
climate change; emergence; habitat fragmentation; Lyme disease; range shift; white-footed mouse
5.  The Potential Connectivity of Waterhole Networks and the Effectiveness of a Protected Area under Various Drought Scenarios 
PLoS ONE  2014;9(5):e95049.
Landscape connectivity is considered a priority for ecosystem conservation because it may mitigate the synergistic effects of climate change and habitat loss. Climate change predictions suggest changes in precipitation regimes, which will affect the availability of water resources, with potential consequences for landscape connectivity. The Greater Calakmul Region of the Yucatan Peninsula (Mexico) has experienced a 16% decrease in precipitation over the last 50 years, which we hypothesise has affected water resource connectivity. We used a network model of connectivity, for three large endangered species (Baird’s tapir, white-lipped peccary and jaguar), to assess the effect of drought on waterhole availability and connectivity in a forested landscape inside and adjacent to the Calakmul Biosphere Reserve. We used reported travel distances and home ranges for our species to establish movement distances in our model. Specifically, we compared the effects of 10 drought scenarios on the number of waterholes (nodes) and the subsequent changes in network structure and node importance. Our analysis revealed that drought dramatically influenced spatial structure and potential connectivity of the network. Our results show that waterhole connectivity and suitable habitat (area surrounding waterholes) is lost faster inside than outside the reserve for all three study species, an outcome that may drive them outside the reserve boundaries. These results emphasize the need to assess how the variability in the availability of seasonal water resource may affect the viability of animal populations under current climate change inside and outside protected areas.
PMCID: PMC4022619  PMID: 24830392
6.  “Understanding the Volume-Outcome Effect in Cardiovascular Surgery: the Role of Failure to Rescue” 
JAMA surgery  2014;149(2):119-123.
To effectively guide interventions aimed at reducing mortality in low-volume hospitals, the underlying mechanisms of the volume-outcome relationship must be further explored. Reducing mortality after major post-operative complications may represent one point along the continuum of patient care that could significantly impact overall hospital mortality.
To determine whether increased mortality at low-volume hospitals performing cardiovascular surgery is a function of higher post-operative complication rates or of less successful rescue from complications.
We utilized patient-level data on Medicare beneficiaries undergoing coronary artery bypass grafting, aortic valve repair, or abdominal aortic aneurysm repair. For each operation, we first divided hospitals into quintiles of procedural volume. We then assessed hospital risk-adjusted rates of mortality, major complications, and “failure to rescue” (i.e., case fatality among patients with complications) within each volume quintile.
Medicare fee-for-service beneficiaries age 65 to 99.
A total of 119,434 Medicare beneficiaries undergoing one of three major cardiovascular operations between 2005 and 2006.
Hospital procedural volume.
Main Outcome Measure
Hospital rates of risk-adjusted mortality, major complications, and failure to rescue.
For each operation, hospital volume was more strongly related to failure to rescue rates than to complication rates. For example, patients undergoing aortic valve replacement at very low-volume hospitals (lowest quintile) were 12% more likely to have a major complication than those at very high-volume hospitals (highest quintile), but 57% more likely to die if a complication occurs.
Conclusion and Relevance
High-volume and low-volume hospitals performing cardiovascular surgery have similar complication rates but disparate failure to rescue rates. While preventing complications is important, hospitals should also consider interventions aimed at quickly recognizing and managing complications once they occur.
PMCID: PMC4016988  PMID: 24336902
7.  Evolutionary rescue and adaptation to abrupt environmental change depends upon the history of stress 
Whether evolution will be rapid enough to rescue declining populations will depend upon population size, the supply of genetic variation, the degree of maladaptation and the historical direction of selection. We examined whether the level of environmental stress experienced by a population prior to abrupt environmental change affects the probability of evolutionary rescue (ER). Hundreds of populations of two species of yeast, Saccharomyces cerevisiae and Saccharomyces paradoxus were exposed to a range of sublethal concentrations of salt for approximately a hundred generations before transfer to a concentration of salt lethal to the ancestor (150 g l–1 NaCl). The fitness of surviving populations of both species was a quadratic function of yield: fitness was greatest for large populations that had been selected on low salt concentrations (less than 20 g l−1 NaCl) and small populations that had adapted to high salt (more than 80 g l−1 NaCl). However, differences occurred between species in the probability of ER. The frequency of ER was positively correlated with salt concentration for S. cerevisiae, but negatively correlated with salt concentration in S. paradoxus. These results not only demonstrate that past environmental conditions can determine the probability of ER after abrupt environmental change, but also suggest that there may even be differences between closely related species that are worth further exploration.
PMCID: PMC3538446  PMID: 23209161
adaptation; rapid evolution; Saccharomyces cerevisiae; Saccharomyces paradoxus; population; environmental change
8.  Evolutionary rescue: an emerging focus at the intersection between ecology and evolution 
There is concern that the rate of environmental change is now exceeding the capacity of many populations to adapt. Mitigation of biodiversity loss requires science that integrates both ecological and evolutionary responses of populations and communities to rapid environmental change, and can identify the conditions that allow the recovery of declining populations. This special issue focuses on evolutionary rescue (ER), the idea that evolution might occur sufficiently fast to arrest population decline and allow population recovery before extinction ensues. ER emphasizes a shift to a perspective on evolutionary dynamics that focuses on short time-scales, genetic variants of large effects and absolute rather than relative fitness. The contributions in this issue reflect the state of field; the articles address the latest conceptual developments, and report novel theoretical and experimental results. The examples in this issue demonstrate that this burgeoning area of research can inform problems of direct practical concern, such as the conservation of biodiversity, adaptation to climate change and the emergence of infectious disease. The continued development of research on ER will be necessary if we are to understand the extent to which anthropogenic global change will reduce the Earth's biodiversity.
PMCID: PMC3538460  PMID: 23209175
extinction; rapid evolution; population; environmental change; genetics; experimental evolution
9.  In-Training Practice Patterns of Combined Emergency Medicine/Internal Medicine Residents, 2003–2007 
This study seeks to evaluate the practice patterns of current combined emergency medicine/internal medicine (EM/IM) residents during their training and compare them to the typical practice patterns of EM/IM graduates. We further seek to characterize how these current residents perceive the EM/IM physician's niche.
This is a multi-institution, cross-sectional, survey-based cohort study. Between June 2008 and July 2008, all 112 residents of the 11 EM/IM programs listed by the Accreditation Council for Graduate Medical Education were contacted and asked to complete a survey concerning plans for certification, fellowship, and practice setting.
The adjusted response rate was 71%. All respondents anticipated certifying in both specialties, with 47% intending to pursue fellowships. Most residents (97%) allotted time to both EM and IM, with a median time of 70% and 30%, respectively. Concerning academic medicine, 81% indicated intent to practice academic medicine, and 96% planned to allocate at least 10% of their future time to a university/academic setting. In evaluating satisfaction, 94% were (1) satisfied with their residency choice, (2) believed that a combined residency will advance their career, and (3) would repeat a combined residency if given the opportunity.
Current EM/IM residents were very content with their training and the overwhelming majority of residents plan to devote time to the practice of academic medicine. Relative to the practice patterns previously observed in EM/IM graduates, the current residents are more inclined toward pursuing fellowships and practicing both specialties.
PMCID: PMC3236164  PMID: 22224155
10.  Extinction Debt in Source-Sink Metacommunities 
PLoS ONE  2011;6(3):e17567.
In an increasingly modified world, understanding and predicting the consequences of landscape alteration on biodiversity is a challenge for ecologists. To this end, metacommunity theory has developed to better understand the complexity of local and regional interactions that occur across larger landscapes. While metacommunity ecology has now provided several alternative models of species coexistence at different spatial scales, predictions regarding the consequences of landscape alteration have been done exclusively for the competition-colonization trade off model (CC). In this paper we investigate the effects of landscape perturbation on source-sink metacommunities. We show that habitat destruction perturbs the equilibria among species competitive effects within the metacommunity, driving both direct extinctions and an indirect extinction debt. As in CC models, we found a time lag for extinction following habitat destruction that varied in length depending upon the relative importance of direct and indirect effects. However, in contrast to CC models, we found that the less competitive species are more affected by habitat destruction. The best competitors can sometimes even be positively affected by habitat destruction, which corresponds well with the results of field studies. Our results are complementary to those results found in CC models of metacommunity dynamics. From a conservation perspective, our results illustrate that landscape alteration jeopardizes species coexistence in patchy landscapes through complex indirect effects and delayed extinctions patterns.
PMCID: PMC3050922  PMID: 21408133
11.  Source–sink dynamics shape the evolution of antibiotic resistance and its pleiotropic fitness cost 
Understanding the conditions that favour the evolution and maintenance of antibiotic resistance is the central goal of epidemiology. A crucial feature explaining the adaptation to harsh, or ‘sink’, environments is the supply of beneficial mutations via migration from a ‘source’ population. Given that antibiotic resistance is frequently associated with antagonistic pleiotropic fitness costs, increased migration rate is predicted not only to increase the rate of resistance evolution but also to increase the probability of fixation of resistance mutations with minimal fitness costs. Here we report in vitro experiments using the nosocomial pathogenic bacterium Pseudomonas aeruginosa that support these predictions: increasing rate of migration into environments containing antibiotics increased the rate of resistance evolution and decreased the associated costs of resistance. Consistent with previous theoretical work, we found that resistance evolution arose more rapidly in the presence of a single antibiotic than two. Evolution of resistance was also more rapid when bacteria were subjected to sequential exposure with two antibiotics (cycling therapy) compared with simultaneous exposure (bi-therapy). Furthermore, pleiotropic fitness costs of resistance to two antibiotics were higher than for one antibiotic, and were also higher under bi-therapy than cycling therapy, although the cost of resistance depended on the order of the antibiotics through time. These results may be relevant to the clinical setting where immigration is known to be important between chemotherapeutically treated patients, and demonstrate the importance of ecological and evolutionary dynamics in the control of antibiotic resistance.
PMCID: PMC2288555  PMID: 17650474
evolutionary ecology; microbiology; infectious disease; antimicrobial resistance
12.  Economic Inequality Predicts Biodiversity Loss 
PLoS ONE  2007;2(5):e444.
Human activity is causing high rates of biodiversity loss. Yet, surprisingly little is known about the extent to which socioeconomic factors exacerbate or ameliorate our impacts on biological diversity. One such factor, economic inequality, has been shown to affect public health, and has been linked to environmental problems in general. We tested how strongly economic inequality is related to biodiversity loss in particular. We found that among countries, and among US states, the number of species that are threatened or declining increases substantially with the Gini ratio of income inequality. At both levels of analysis, the connection between income inequality and biodiversity loss persists after controlling for biophysical conditions, human population size, and per capita GDP or income. Future research should explore potential mechanisms behind this equality-biodiversity relationship. Our results suggest that economic reforms would go hand in hand with, if not serving as a prerequisite for, effective conservation.
PMCID: PMC1864998  PMID: 17505535

Results 1-12 (12)