The geography of demography: long-term demographic studies and species distribution models reveal a species border limited by adaptation.

Potential causes of species' geographic distribution limits fall into two broad classes: (1) limited adaptation across spatially variable environments and (2) limited opportunities to colonize unoccupied areas. Combining demographic studies, analyses of demographic responses to environmental variation, and species distribution models, we investigated the causes of range limits in a model system, the eastern border of the California annual plant Clarkia xantiana ssp. xantiana. Vital rates of 20 populations varied with growing season temperature and precipitation: fruit number and overwinter survival of 1-year-old seeds declined steeply, while current-year seed germination increased modestly along west-to-east gradients in decreasing temperature, decreasing mean precipitation, and increasing variation in precipitation. Long-term stochastic finite rate of increase, λ(s), exhibited a fourfold range and varied among geologic surface materials as well as with temperature and precipitation. Growth rate declined significantly toward the eastern border, falling below 1 in three of the five easternmost populations. Distribution models employing demographically important environmental variables predicted low habitat favorability beyond the eastern border. Models that filtered or weighted population presences by λ(s) predicted steeper eastward declines in favorability and assigned greater roles in setting the distribution to among-year variation in precipitation and to geologic surface material. These analyses reveal a species border likely set by limited adaptation to declining environmental quality.

Appendicitis associated with recent barium study.

There have been several reports of "barium-induced" appendicitis in the literature. When confronted with a possible case of this phenomenon, a review of the literature on the subject was carried out. The suggestion is made that there is no evidence to support a cause-effect relationship between barium retained in the appendix and appendicitis. Diseased appendices can be marked by retained barium and a higher likelihood may then exist for the subsequent development of appendicitis. Following the finding of prolonged retention of barium after contrast study, it is recommended that the patient be instructed as to the possibility of developing symptoms of acute appendicitis. Patients who present with symptoms of appendicitis should be questioned as to history of recent barium study, and x-rays should be reviewed with the possibility of finding appendoliths.

Heterotopic ossification and peripheral nerve entrapment: early diagnosis and excision.

Heterotopic ossification can occur in neurologic disorders, burns, musculoskeletal trauma, and metabolic disorders. In addition to producing the complications of contracture, skin breakdown, and pain, it can cause peripheral nerve entrapment. Nerve entrapment due to heterotopic ossification may be misdiagnosed, and it is difficult to evaluate and treat without recurrence. Computed tomography is especially useful in localization before surgical release of the entrapped nerve. Resection of heterotopic ossification can be successful using disodium etidronate to decrease the risk of recurrence, and resection can improve range of motion and nerve function. Two case studies of nerve entrapment due to heterotopic ossification are presented with the results of computed tomography localization, successful resection, and long-term follow-up. Clinicians should be aware of this complication and the potential for rapid nerve injury. If heterotopic ossification is causing clinically significant peripheral nerve entrapment, early surgical treatment may be indicated, and may be successful.