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Sexually reproducing organisms require males and females to find each other. Increased difficulty of females finding mates as male density declines is the most frequently reported mechanism of Allee effects in animals. Evolving more effective mate search may alleviate Allee effects, but may depend on density regimes a population experiences. In particular, high-density populations may evolve mechanisms that induce Allee effects which become detrimental when populations are reduced and maintained at a low density. We develop an individual-based, eco-genetic model to study how mating systems and fitness trade-offs interact with changes in population density to drive evolution of the rate at which males or females search for mates. Finite mate search rate triggers Allee effects in our model and we explore how these Allee effects respond to such evolution. We allow a population to adapt to several population density regimes and examine whether high-density populations are likely to reverse adaptations attained at low densities. We find density-dependent selection in most of scenarios, leading to search rates that result in lower Allee thresholds in populations kept at lower densities. This mainly occurs when fecundity costs are imposed on mate search, and provides an explanation for why Allee effects are often observed in anthropogenically rare species. Optimizing selection, where the attained trait value minimizes the Allee threshold independent of population density, depended on the trade-off between search and survival, combined with monogamy when females were searching. Other scenarios led to runaway selection on the mate search rate, including evolutionary suicide. Trade-offs involved in mate search may thus be crucial to determining how density influences the evolution of Allee effects. Previous studies did not examine evolution of a trait related to the strength of Allee effects under density variation. We emphasize the crucial role that mating systems, fitness trade-offs and the evolving sex have in determining the density threshold for population persistence, in particular since evolution need not always take the Allee threshold to its minimum value., (© 2017 The Authors. Journal of Animal Ecology © 2017 British Ecological Society.)

1. Allee effects may result in negative growth rates at low population density, with important implications for conservation and management of exploited populations. Theory predicts prey populations will exhibit Allee effects when their predator exhibits a Type II functional response, but empirical evidence linking this positively density-dependent variation in predator-induced individual mortality to population growth rate and probability of extinction is lacking. 2. Here, we report a demonstration of extinction due to predator-driven Allee effects in an experimental Daphnia-Chaoborus system. A component Allee effect caused by higher predation rates at low Daphnia density led to positive density dependence in per capita growth rate and accelerated extinction rate at low density. 3. A stochastic model of the process revealed how the critical density below which population growth is negative depends on the mechanistic details of the predator-prey interaction. 4. The ubiquity of predator-prey interactions and saturating functional responses suggests predator-driven Allee effects are potentially important in determining extinction risk of a large number of species.

Objectives: To (1) describe patterns of posthospital care transitions; (2) characterize these patterns as uncomplicated or complicated; (3) identify those at greatest risk for complicated transitions., Data Sources/study Setting: The Medicare Current Beneficiary Survey was used to identify beneficiaries aged 65 and older who were discharged from an acute care hospital in 1997-1998., Study Design: Patterns of posthospital transfers were described over a 30-day time period following initial hospital discharge. Uncomplicated posthospital care patterns were defined as a sequence of transfers from higher-to lower-intensity care environments without recidivism, while complicated posthospital care patterns were defined as the opposite sequence of events. Indices were developed to identify patients at risk for complicated transitions., Principal Findings: Forty-six distinct types of care patterns were observed during the 30 days following hospital discharge. Among these patterns, 444 episodes (61.2 percent) were limited to a single transfer, 130 episodes (17.9 percent) included two transfers, 62 episodes (8.5 percent) involved three transfers, and 31 episodes (4.3 percent) involved four or more transfers. Fifty-nine episodes (8.1 percent) resulted in death. Between 13.4 percent and 25.0 percent of posthospital care patterns in the 1998 sample were classified as complicated. The area under the receiver operating curve was 0.771 for a predictive index that utilized administrative data and 0.833 for an index that used a combination of administrative and self-reported data., Conclusions: Posthospital care transitions are common among Medicare beneficiaries and patterns of care vary greatly. A significant number of beneficiaries experienced complicated care transitions-a finding that has important implications for both patient safety and cost-containment efforts. Patients at risk for complicated care patterns can be identified using data available at the time of hospital discharge.

Objective: To obtain information relevant to development of prospective payment for Medicare rehabilitation facilities (RFs) and skilled nursing facilities (SNFs): compares service utilization, length of stay (LOS), case mix, and resource consumption for Medicare patients receiving postacute institutional rehabilitation care., Data Sources/study Setting: Longitudinal patient-level and related facility-level data on Medicare hip fracture (n = 513) and stroke (n = 483) patients admitted in 1991-1994 to a sample of 27 RFs and 65 SNFs in urban areas in 17 states., Study Design: For each condition, two-group RF-SNF comparisons were made. Regression analysis was used to adjust RF-SNF differences in resource consumption per stay for patient condition (case mix) and other factors, since random assignment was not possible., Data Collection/extraction Methods: Providers at each facility were trained to collect patient case-mix and service utilization information. Secondary data also were obtained., Principal Findings: RF patients had shorter LOS, fewer total nursing hours (but more skilled nursing hours), and more ancillary hours than SNF patients. After adjustment, ancillary resource consumption per stay remained substantially higher for RF than SNF patients, particularly for stroke. The adjusted nursing resource consumption differences were smaller than the ancillary differences and not statistically significant for hip fracture. Supplemental outcome findings suggested minimal differences for hip fracture patients but better outcomes for RF than SNF stroke patients., Conclusions: Much can be gained from an integrated approach to developing prospective payment for RFs and SNFs. In that context, consideration of condition-specific per-stay payment methods applicable to both settings appears warranted.

By 1989, more than 1,100 hospitals in rural communities throughout the United States were using hospital beds as swing beds to provide both long-term and acute care. In this study, the quality of long-term care in swing-bed hospitals was compared with the quality of nursing home care, using patient outcomes along with both process and structural measures of quality. Several methodological and conceptual points on measuring and analyzing the quality of long-term care are discussed in this article. Data were analyzed on approximately 2,000 patients in four different primary data samples, three of which were longitudinal involving multiple follow-up points. An analysis of changes in patient status over time, hospitalization rates, rates of discharge to independent living, services provided, and certain structural indicators showed that (1) relative to nursing home care, swing-bed care is more effective in enhancing functional outcomes and discharge to independent living and in reducing hospitalization for long-term care patients, and (2) nursing home care appears more desirable than swing-bed care for long-stay, chronic care patients with no rehabilitation potential. Swing-bed hospitals have gravitated largely to admitting postacute long-term care patients. They do not typically compete directly with community nursing homes for chronic care patients. The greater effectiveness of swing-bed care for patients with near-acute long-term care needs suggests that this approach should be considered in urban communities and that we should scrutinize our current tendency to place in traditional nursing homes many patients who have at least some rehabilitation potential.

Case-mix differences between 653 home health care patients and 650 nursing home patients, and between 455 Medicare home health patients and 447 Medicare nursing home patients were assessed using random samples selected from 20 home health agencies and 46 nursing homes in 12 states in 1982 and 1983. Home health patients were younger, had shorter lengths of stay, and were less functionally disabled than nursing home patients. Traditional long-term care problems requiring personal care were more common among nursing home patients, whereas problems requiring skilled nursing services were more prevalent among home health patients. Considering Medicare patients only, nursing home patients were much more likely to be dependent in activities of daily living (ADLs) than home health patients. Medicare nursing home and home health patients were relatively similar in terms of long-term care problems, and differences in medical problems were less pronounced than between all nursing home and all home health patients. From the standpoint of cost-effectiveness, it would appear that home health care might provide a substitute for acute care hospital use at the end of a hospital stay, and appears to be a more viable option in the care of patients who are not severely disabled and do not have profound functional problems. The Medicare skilled nursing facility, however, is likely to continue to have a crucial role in posthospital care as the treatment modality of choice for individuals who require both highly skilled care and functional assistance.