J. 2003. The distance dependence prediction of the Janzen-Connell hypothesis: a meta-analysis. -Oikos 103: 590-602.The Janzen-Connell hypothesis explains the maintenance of tropical diversity through the interacting effects of parent-centered dispersal patterns and distance-and density-dependent propagule survival. These effects were thought to support regular spacing of species within tropical forest, enhancing diversity. One of the predictions of the hypothesis is that seed and seedling survival should improve with increased parental distance. Although there are many independent tests of this hypothesis for individual species, there are few synthetic studies that have brought these data together to test its validity across species. This paper reports the results of a meta-analysis of the effect of distance on enhancing propagule survival, employing an odds-ratio effect size metric. We found no general support for the distance-dependent prediction of the hypothesis, and conclude that further testing to explore this hypothesis as a diversity-maintaining mechanism is unnecessary. However, we did find that distance from parent slightly reduces survivorship in the temperate zone, as contrasted with the tropics, and we saw stronger evidence in support of the hypothesis for seedlings than for seeds. The phenomenon of enhanced propagule survival with distance from the parent may be important for the population biology of particular species, but it is not a general phenomenon across communities, life history stages or life forms.Thirty years ago, two papers were published that proposed a suite of testable hypotheses about the processes maintaining diversity in tropical forests. At the time, it was thought that within a forest, individuals from each species of tropical tree were more regularly spaced than would be expected by a random process (Black et al.

Graduate teaching assistants (GTAs) in the sciences are a common feature of U.S. universities that have a prominent mission of research. During the past 2 decades, increased attention has been paid to the professional development of GTAs as instructors. As a result, universities have created training programs to assist GTAs in selecting instructional methods, curricular formats, and assessments when they serve as laboratory, lecture, or discussion group instructors. Unfortunately, few studies explore the educational and instructional environment of GTAs in these reformed settings. This study was conducted to address this specific need. As a constructivist inquiry, qualitative methods were used to collect and analyze the data to elucidate the educational and instructional environment of science GTAs at a doctoral/research university in which various training programs existed. We found that GTAs worked autonomously, that traditional practices and curricula existed in laboratories, and that instructors frequently held limited views of undergraduates' abilities and motivation. Findings in this initial study about GTAs suggest that developers of GTA training programs draw on the literature regarding science teacher education, and that reward systems be instituted that recognize faculty and staff for their participation in GTA training programs. © 2004 Wiley Periodicals, Inc. J Res Sci Teach 41: 211–233, 2004

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