One of the most cited hypotheses explaining the inordinate success of a small proportion of introduced plants that become pests is the 'natural enemies hypothesis'. This states that invasive introduced plants spread rapidly because they are liberated from their co-evolved natural enemies. This hypothesis had not been properly tested until recently. Previous reviews on this topic have been narrative and vote counting in nature. In this review, we carried out quantitative synthesis and meta-analysis using existing literature on plants and their herbivores to test the different components of the enemy release hypothesis. We found supporting evidence in that (1) insect herbivore fauna richness is significantly greater in the native than introduced ranges, and the reduction is skewed disproportionally towards specialists and insects feeding on reproductive parts; and (2) herbivore damage levels are greater on native plants than on introduced invasive congeners. However, herbivore damage levels are only marginally greater for plants in native than in introduced ranges, probably due to the small numbers of this type of study. Studies quantifying herbivore impacts on plant population dynamics are too scarce to make conclusions for either comparison of plants in native vs introduced ranges or of co-occurring native and introduced congeners. For future research, we advocate that more than two-way comparisons between plants in native and introduced ranges, or native and introduced congeners are needed. In addition, the use of herbivore exclusions to quantify the impacts of herbivory on complete sets of population vital rates of native vs introduced species are highly desirable. Furthermore, three-way comparisons among congeners of native plants, introduced invasive, and introduced non-invasive plants can also shed light on the importance of enemy release. Finally, simultaneously testing the enemy release hypothesis and other competing hypotheses will provide significant insights into the mechanisms governing the undesirable success of invasive species.

This paper investigates the effects of China’s New Cooperative Medical Scheme (NCMS) on health outcomes and health care expenditure of the elderly in rural China, using panel data from the 2005 and 2008 waves of the Chinese Longitudinal Healthy Longevity Survey. We employ a strategy that combines propensity score matching with a difference-in-differences approach to address selection bias. Results show that the NCMS has significantly improved the elderly enrollees’ activities of daily living and cognitive function, but has not led to better self-assessed general health status. We find no significant effect of NCMS on mortality for the previously uninsured elderly in NCMS counties, although there is moderate evidence that it is associated with reduced mortality for the elderly enrollees. We also find that the elderly participants are more likely to get adequate medical services when sick, which provides a good explanation for the beneficial health effects of NCMS. However, there is no evidence that the NCMS has reduced their out-of-pocket spending. Furthermore, we also find that low-income seniors benefit more from NCMS participation in terms of health outcomes and perceived access to health care, suggesting that the NCMS helps reduce health inequalities among the rural elderly.

c Fifty-seven carbapenem-resistant Klebsiella pneumoniae isolates belonging to ST11 (50 isolates), ST423 (5 isolates), and two other sequence types were studied. All were positive for bla KPC-2 , bla TEM-1 , and bla CTX-M-14 . SDS-PAGE analysis of six representative isolates demonstrated varied porin expression. Nevertheless, when bla KPC-2 was deleted, carbapenem resistance was markedly reduced. Additionally, SHV-12, DHA-1, and/or VIM-1 appeared to contribute to accessory carbapenemase activity. In contrast, OmpK35 and/or OmpK36 deficiency seemed to serve only as a minor cooperative factor. Table S1 in the supplemental material for primer details). Standard multilocus sequence typing (MLST) protocols were utilized, with alternative primers for gapA, mdh, rpoB, and tonB used as required. Fifty isolates belonged to ST11, five belonged to ST423, and one each belonged to ST65 and a novel MLST type, ST977. The first carbapenem-resistant isolate, derived from a urine specimen obtained in August 2006, belonged to ST423. However, only four other ST423 isolates were detected over the study period. In contrast, ST11 remained endemic throughout this period. Intriguingly, isolates belonging to ST65 and ST977 appeared only once. Except for XJ-2 and XJ-4, which exhibited lower carbapenem MICs, all 57 isolates showed high-level resistance to ampicillin, cefotaxime, ceftazidime, imipenem, meropenem, and ertapenem. PCR analysis suggested that all but two isolates produced TEM-1, KPC-2, CTX-M-14, and SHV-12; bla was not detected in XJ-1 and XJ-4. In addition, all five ST423 isolates encoded DHA-1, and the XJ-5 (ST11) isolate uniquely produced VIM-1. CIsolates XJ-1, XJ-2, and XJ-3, representative of ST977, ST65, and ST423, respectively, were chosen for further analysis together with three ST11 isolates: XJ-4 because it had relatively low carbapenem MICs, XJ-5 because it had a supplementary bla VIM-1 gene, and XJ-6 because it was typical of most ST11 isolates. SDS-PAGE analysis of outer membrane proteins extracted as described previously (10) from cells grown overnight with shaking at 37°C in nutrient broth with or without 10 g/liter NaCl showed that XJ-1 expressed smaller quantities of OmpK36, while OmpK35 production was not detected for XJ-1, XJ-4, and XJ-5 (Fig. 1). Furthermore, as the likely OmpK36 protein bands of XJ-3 and XJ-6 were shifted upwards (see below for details), the status of OmpK35 bands in these strains could not be determined (Fig. 1).Although DNA mutations relative to that of NTUH-K2044 were detected in the ompK35 sequences of XJ-4, XJ-5, and XJ-6, no amino acid changes were predicted (Fig. 2). In contrast, the predicted OmpK35 of XJ-1 exhibited 25 amino acid substitutions and a single insertion, while the corresponding sequence of XJ-2 varied by a single amino acid substitution only. The OmpK35 protein of XJ-3 lacked a five-amino-acid string (EIYNK), which mapped to the B1 ␤-sheet. This string of amino acids was strictly conserved in the OmpK35 sequences of the remaining five clinical isolates, NTUH-K2044, a...