Treatment of venous thromboembolism with low-molecular-weight heparin: a synthesis of the evidence published in systematic literature reviews.

OBJECTIVE: To evaluate the methodology and cumulative evidence presented in systematic reviews of clinical trials comparing low-molecular-weight heparin (LMWH) with unfractionated heparin (UFH) for the treatment of venous thromboembolism. METHODS: We reviewed all systematic reviews of clinical trials published until March 2002. Fourteen systematic literature reviews were published between 1994 and 2000. Deficiencies in methodological quality were common, particularly in the description of search strategies, assessment of clinical trial quality, and methods used to combine results. RESULTS: Results of reviews indicate that LMWH is superior to UFH for the treatment of venous thromboembolism, particularly in reducing mortality. Patients with isolated deep venous thrombosis or deep venous thrombosis with concomitant pulmonary embolism seemed to have similar benefit. However, the benefits of LMWH over UFH were smaller in magnitude in reviews that included more recent clinical trials.

Mechanisms in the Competitive Success of an Invading Sexual Gecko over an Asexual Native.

The competitive displacement by a sexual gecko species of an asexual resident gecko has been documented over a wide geographic area. To test hypotheses concerning the detailed mechanism of this displacement, an experimental system was developed to follow populations of geckos in a duplicated, controlled environment that closely approximates the natural arena for the competitive interaction. Asymmetric competition occurred only in the presence of light, which attracts a dense concentration of insect food sources. The mechanism of competition was partly due to the behavioral dominance of the larger sexual species over the smaller asexual species in areas near the concentrated food. However, this behavior resulted from an avoidance response of subordinate asexuals rather than overt aggression by the sexual species.

The role of interspecific competition in the biogeography of island lizards.

There is increasing evidence that interspecific competition has set important constraints on the distribution, abundance and evolution of island lizards. This is surprising not because competition is rare but because for a biogeographic pattern caused by species interactions to be detectable, it must be strong enough to override the many physical and historical differences that exist among real islands. Moreover, the direct pairwise links between species, once embedded in the complicated network of species interactions in entire communities, may become diluted and confused by the indirect interactions of still other species, particularly predators. Nevertheless, if competition is strong and if communities are simple (as they are on many species-poor islands), competition leaves its fingerprint on the ecological and evolutionary trajectories taken by island lizards.