Negative relationships between species richness and temporal variability are common but weak in natural systems.

Effects of species diversity on population and community stability (or more precisely, the effects of species richness on temporal variability) have been studied for several decades, but there have been no large-scale tests in natural communities of predictions from theory. We used 91 data sets including plants, fish, small mammals, zooplankton, birds, and insects, to examine the relationship between species richness and temporal variability in populations and communities. Seventy-eight of 91 data sets showed a negative relationship between species richness and population variability; 46 of these relationships were statistically significant. Only five of the 13 positive richness-population variability relationships were statistically significant. Similarly, 51 of 91 data sets showed a negative relationship between species richness and community variability; of these, 26 were statistically significant. Seven of the 40 positive richness-community-variability relationships were statistically significant. We were able to test transferability (i.e., the predictive ability of models for sites that are spatially distinct from sites that were used to build the models) for 69 of 91 data sets; 35 and 31 data sets were transferable at the population and community levels, respectively. Only four were positive at the population level, and two at the community level. We conclude that there is compelling evidence of a negative relationship between species richness and temporal variability for about one-half of the ecological communities we examined. However, species richness explained relatively little of the variability in population or community abundances and resulted in small improvements in predictive ability.

Compensatory dynamics are rare in natural ecological communities.

In population ecology, there has been a fundamental controversy about the relative importance of competition-driven (density-dependent) population regulation vs. abiotic influences such as temperature and precipitation. The same issue arises at the community level; are population sizes driven primarily by changes in the abundances of cooccurring competitors (i.e., compensatory dynamics), or do most species have a common response to environmental factors? Competitive interactions have had a central place in ecological theory, dating back to Gleason, Volterra, Hutchison and MacArthur, and, more recently, Hubbell's influential unified neutral theory of biodiversity and biogeography. If competitive interactions are important in driving year-to-year fluctuations in abundance, then changes in the abundance of one species should generally be accompanied by compensatory changes in the abundances of others. Thus, one necessary consequence of strong compensatory forces is that, on average, species within communities will covary negatively. Here we use measures of community covariance to assess the prevalence of negative covariance in 41 natural communities comprising different taxa at a range of spatial scales. We found that species in natural communities tended to covary positively rather than negatively, the opposite of what would be expected if compensatory dynamics were important. These findings suggest that abiotic factors such as temperature and precipitation are more important than competitive interactions in driving year-to-year fluctuations in species abundance within communities.

Estimating fish consumption rates for Ontario Amerindians.

The routine assessment of human exposure to contaminants requires that exposure via consumption of freshwater fish be considered because many chemicals persist and/or bioaccumulate in fish. Estimates of fish consumption rate were determined for Ontario Amerindians from data on the concentration of mercury in the hair of 4,327 Amerindians residing in 58 reserves across the province, combined with data on mercury concentrations in three commonly consumed species of fish collected from lakes surrounding these reserves. Estimated rates of fish consumption were found to differ between sexes, with males consuming a geometric mean of 19 g of fish per day, while females were estimated to consume a geometric mean of 14 g/day. Fish consumption rate was found to increase with increasing latitude, a surrogate measure of community isolation, and to increase with age. Seasonal variation was also noted, with fish consumption rates being highest during summer months and lowest in winter. These data may provide regulatory agencies with a more statistically representative basis upon which to establish assumptions concerning fish consumption rates for risk assessment purposes. Factors such as the location of the exposed population, age and sex of exposed individuals, and time of year in which an assessment is being conducted, should also be considered as specific situations require.

Coping styles in identifiers and nonidentifiers of a breast lump as a problem.

One hundred patients referred to a teaching hospital breast clinic for as yet undiagnosed breast masses were interviewed during their first visits and prior to assessment by a surgeon. Baseline measures of mental state and coping style were obtained. Despite the purpose of their visits, 74 of the patients were "nonidentifiers" of the breast lump as a problem on their initial contact with the clinic. All patients who were non-identifiers also used denial as a coping mechanism. Nonidentifiers used more than three times the number of avoidant coping mechanisms than "identifiers." Patients with a family history of breast cancer were more likely to be identifiers than those without a family history.

A surgical experience with Crohn's disease.

From 427 histories of patients with Crohn's disease admitted to St. Michael's Hospital between 1 January 1974 and 31 March 1983, 152 patients were studied as each had at least one operation related to the disease. The age at onset of symptoms, the interval between onset of symptoms and operation, the site of disease, operations performed, the type and frequency of repeat operations and the morbidity, mortality and follow-up period were studied. The small intestine only was involved in 55 per cent of the patients, the large intestine only in 16 per cent, and both the small and large intestine in 29 per cent. The most frequent indication for operation was obstruction (29 per cent); the next was perianal disease (18 per cent). The most common procedure was resection of the lowest segment of the small intestine with adjacent colon (37 per cent). The second most common operation was perianal operation (19 per cent). There were three deaths (2 per cent mortality rate). One hundred and thirty patients (93 per cent) have been examined within the past three years. Life tables show the cumulative chance of having an operation for Crohn's disease.

Can bacteria outcompete phytoplankton for phosphorus? a chemostat test.

Although the bacterioplankton of lakes are usually considered primarily in terms of mineralization processes, recent studies suggest that they may also strongly compete for phosphorus with the phytoplankton. In the present study, we have tested in chemostat culture, and found support for the hypotheses that (1) a freshwater bacterium (Pseudomonas paucimobilis), whose carbon source is excretion from a phosphorus-limited alga (Synedra ulna var.danica), can outcompete that alga for phosphorus (P) under widely varied P supply rates; (2) exogenously-supplied organic carbon positively influences bacterial biomass and negatively influences algal biomass; (3) the ratio of bacterial to algal phosphorus uptake in short-term(32)P orthophosphate uptake experiments is an accurate predictor of their relative long-term phosphorus assimilation (i.e., growth) in mixed culture.

Complications of gastroduodenal surgery.

Postgastrectomy syndrome is too imprecise a term for the numerous complications that may follow gastroduodenal operations. A carefully taken history from a patient able to describe symptoms followed by appropriate investigations will allow accurate identification and effective treatment for most. There are many patients presently suffering these complications of gastroduodenal operations. We must remain aware of the problems in order to help them.

A method of cholecystography applicable to small laboratory animals.

A method of intraperitoneal cholecystography is described and was tested on mice with experimentally induced gallstones. The presence of stones in the gallbladder was predicted with an accuracy of 95.5%, using doses of 3 ml of 51.6% meglumine iodipamide (Cholografin) per kg diluted 10-fold, followed a few days later by a repeat dose of 5 ml per kg in cases of nonvisualization of the gallbladder. Pilot studies on guinea pigs and rabbits suggest that this method is applicable to these animals too, although a higher dose of contrast medium is required.

Retention suture technique using buttons.

The use of buttons for retention sutures is advocated as practical, inexpensive, universally available and well tolerated bolsters over which heavy nonabsorbable sutures may be secured. We have not found any disadvantages to the described techniques in the past 12 years.

Early management of the critically injured.

A plan for the early management of the critically injured patient is described with emphasis on the priorities of management of injuries to certain organ-systems. The most important priorities are the establishment and maintenance of adequate ventilation and adequate circulation. The general surgeon is best qualified to assume full responsibility for the proper care of the critically injured, of patients with multiple injuries, and of patients in traumatic shock. He must assume the risk of transfusing unmatched whole blood and of deferring non-essential radiographs. The emergency and radiology departments may have to be by-passed to save the life of the critically injured patient. The measures required to establish a clear airway, to treat complications which can impair ventilation, to manage shock and hemorrhage and the possible complications of massive transfusions of blood are reviewed.