Ecological specialization and population size in a biodiversity hotspot: how rare species avoid extinction.

Species with narrow environmental niches typically have small geographic ranges. Small range size is, in turn, often associated with low local abundance. Together, these factors should mean that ecological specialists have very small total populations, putting them at high risk of extinction. But some specialized and geographically restricted species are ancient, and some ecological communities have high proportions of rare and specialized endemics. We studied niche characteristics and patterns of distribution and abundance of terrestrial vertebrates in the rainforests of the Australian Wet Tropics (AWT) to identify mechanisms by which rare species might resist extinction. We show that species with narrow environmental niches and small geographic ranges tend to have high and uniform local abundances. The compensation of geographic rarity by local abundance is exact, such that total population size in the rainforest vertebrates of the AWT is independent of environmental specialization. This effect would tend to help equalize extinction risk for specialists and generalists. Phylogenetic analysis suggests that environmental specialists have been gradually accumulating in this fauna, indicating that small range size/environmental specialization can be a successful trait as long as it is compensated for by demographic commonness. These results provide an explanation of how range-restricted specialists can persist for long periods, so that they now form a major component of high-diversity assemblages such as the AWT.

Morbidity and mortality associated with large-bore percutaneous venovenous bypass cannulation for 312 orthotopic liver transplantations.

The aim of this study is to establish the incidence of serious morbidity and mortality associated with the placement of large-bore (18 to 20 F) percutaneous bypass cannulae for venovenous bypass (VVBP) during orthotopic liver transplantation (OLT). This technique has been reported to be rapid, simple, and safe. We reviewed the case notes of 312 patients who underwent OLT in our center using this technique. We describe 4 cases of serious morbidity (incidence, 1.28%) and 1 death (incidence, 0.32%) related directly to percutaneous placement of the bypass cannula. We conclude that percutaneous cannula placement for VVBP during OLT has the potential for life-threatening complications, and this must be considered when electing to use this technique. When percutaneous cannulae are to be used, we recommend the use of the right internal jugular vein for return cannulation and the use of ultrasound guidance, particularly in those patients in whom cannulation is predictably difficult.

A central venous catheter coated with benzalkonium chloride for the prevention of catheter-related microbial colonization.

In an attempt to overcome infections associated with central venous catheters, a new antiseptic central venous catheter coated with benzalkonium chloride on the internal and external surfaces has been developed and evaluated in a clinical trial. Patients (235) randomly received either a triple-lumen central venous catheter coated with benzalkonium chloride (117) or a polyurethane non-antiseptic catheter (118). The incidence of microbial colonization of both catheters and retained antiseptic activity of the benzalkonium chloride device following removal were determined. The benzalkonium chloride resulted in a significant reduction of the incidence of microbial colonization on both the internal and external catheter surfaces. The reduction in colonization was detected at both the intradermal (21 benzalkonium chloride catheters vs. 38 controls, P = 0.0016) and distal segments of the antiseptic-coated catheters. Following catheter removal retained activity was demonstrated in benzalkonium chloride catheters which had been in place for up to 12 days. No patients developed adverse reactions to the benzalkonium chloride catheters. The findings demonstrate that the benzalkonium chloride catheter significantly reduced the incidence of catheter-associated colonization.

Survival from massive intraoperative pulmonary thromboembolism during orthotopic liver transplantation.

We report a case of massive pulmonary embolism occurring at the time of graft reperfusion in a patient undergoing orthotopic liver transplantation. The clinical diagnosis of pulmonary embolus was aided by on-table echocardiography. Cardiopulmonary bypass and surgical embolectomy prevented her death. We discuss the differential diagnosis, possible aetiology of pulmonary embolism in this context and subsequent management.