Trophic Garnishes: Cat–Rat Interactions in an Urban Environment

BACKGROUND:Community interactions can produce complex dynamics with counterintuitive responses. Synanthropic community members are of increasing practical interest for their effects on biodiversity and public health. Most studies incorporating introduced species have been performed on islands where they may pose a risk to the native fauna. Few have examined their interactions in urban environments where they represent the majority of species. We characterized house cat (Felis catus) predation on wild Norway rats (Rattus norvegicus), and its population effects in an urban area as a model system. Three aspects of predation likely to influence population dynamics were examined; the stratum of the prey population killed by predators, the intensity of the predation, and the size of the predator population. METHODOLOGY/PRINCIPAL FINDINGS:Predation pressure was estimated from the sizes of the rat and cat populations, and the characteristics of rats killed in 20 alleys. Short and long term responses of rat population to perturbations were examined by removal trapping. Perturbations removed an average of 56% of the rats/alley but had no negative long-term impact on the size of the rat population (49.6+/-12.5 rats/alley and 123.8+/-42.2 rats/alley over two years). The sizes of the cat population during two years (3.5 animals/alley and 2.7 animals/alley) also were unaffected by rat population perturbations. Predation by cats occurred in 9/20 alleys. Predated rats were predominantly juveniles and significantly smaller (144.6 g+/-17.8 g) than the trapped rats (385.0 g+/-135.6 g). Cats rarely preyed on the larger, older portion of the rat population. CONCLUSIONS/SIGNIFICANCE:The rat population appears resilient to perturbation from even substantial population reduction using targeted removal. In this area there is a relatively low population density of cats and they only occasionally prey on the rat population. This occasional predation primarily removes the juvenile proportion of the rat population. The top predator in this urban ecosystem appears to have little impact on the size of the prey population, and similarly, reduction in rat populations doesn't impact the size of the cat population. However, the selected targeting of small rats may locally influence the size structure of the population which may have consequences for patterns of pathogen transmission

A New Technic for the Detection of Left-to-Right Cardiac Shunts by Use of an Esophageal Geiger-Müller Tube

A new technic is described for the detection of left-to-right shunts. A miniature Geiger-Müller tube is placed in the esophagus behind the left atrium and positioned by the electrocardiogram. In this position the G-M tube measures radioactivity from the left atrium. Curves are then recorded simultaneously from the precordium, lung, and left atrium. Methods of injection, monitoring, and recording are presented that provide greater diagnostic accuracy over those external detector technics currently in use. Of 23 patients studied, 11 presented left-to-right shunts. Eight of these 11 patients were submitted to surgery; all were studied preoperatively and seven were studied postoperatively. Seven of the 11 shunts were detected by both precordial and esophageal technics. Four of the 11 shunts were missed by conventional precordial technics but were correctly diagnosed preoperatively by the esophageal detector. In addition, one shunt, which remained open postoperatively, was demonstrated clearly by the esophageal technic but was not indicated by the precordial curves. In no instance was the precordial curve positive for left-to-right shunt when the esophageal curve was negative. Although the accuracy of any radioisotope detection technic with external counting may not approach that of direct cardiac catheterization, this method, because of its relative simplicity and accuracy, is useful in the demonstration of left-to-right shunts both preoperatively and postoperatively.</jats:p

Graded Exercise Stress Tests in Angiographically Documented Coronary Artery Disease

Graded exercise stress tests performed on 650 consecutive patients with proven or suspected coronary disease undergoing evaluation by cardiac catheterization were correlated with clinical, hemodynamic, and angiographic findings. Among 451 patients with significant coronary stenosis, 332 (74%) had interpretable stress tests and 65% of these were positive (sensitivity). The rate of "false positives" was 8%. The clinical syndrome of typical angina identified significant coronary disease in 89% of the patients, and 58% of that group had a positive exercise test defined by objective electrocardiographic criteria. Patients were not eliminated from this study because of recent digitalis ingestion. Although a higher frequency of uninterpretable exercise tests was found in this group (40%), the test results reflected more severe coronary disease. None of the patients with "false positive" tests were taking digitalis. It is concluded that recent digitalis ingestion should not be considered a contraindication for exercise stress testing. Among the patients with interpretable exercise tests, the angiographic severity of coronary artery disease correlates strongly with the frequency of positive tests (40%, 66%, and 76%, with 70% or greater occlusion of one, two or three vessels respectively). Left main coronary stenosis of 70% or greater was associated with more severe ST segment changes, inability to achieve target heart rate during stress, and a lower maximum heart rate during exercise. The angiographic occurrence of collateral vessels was related to the extent of coronary disease and was associated with a higher percentage of positive exercise tests; no protective effect of collateral circulation could be demonstrated. Patients with abnormal resting hemodynamics or left ventricular asynergy had no significant difference in the frequency of positive tests after adjustment for the angiographic severity of disease.</jats:p

Business Papers (MS 80-0003)

Statements given by J. H. Gillespie and F. R. Lubbock and prepared by notaries public John Donnan and F. A. Orgain attesting to a deed's authenticity