The roles of statistical inference and historical sources in understanding landscape change: the case of feral buffalo in the freshwater floodplains of Kakadu National Park

The statistical analysis of Bowman et al. ( Journal of Biogeography , 2008, 35 , 1976–1988) revealed the weak relationship between the rate of woody cover encroachment onto the freshwater floodplains in the central section of Kakadu National Park (KNP) over a 40-year period and estimates of proximate water buffalo ( Bubalus bubalis ) density. The analysis relied on detailed mapping of buffalo tracks, the best historical record of spatial variation of buffalo density in KNP. In their reply, Petty & Werner ( Journal of Biogeography , 2009, doi: [DOI link] ) prefer to privilege an amalgam of historical sources to claim that buffalo removal is the primary driver of the woody expansion on floodplains. The contrasting weight placed on data analysis and differences of interpretation underscore a tension between statistically based historical ecology approaches and environmental history narratives, a tension that forms part of the broader cultural clash between the Sciences and Humanities.     

A method for the rapid and precise determination of acclimated phytoplankton reproduction rates

A rapid method for measuring, simultaneously, the asexual reproductionrates of hundreds of phytoplankton cultures is described. Thismethod is based on the dairy measurement of in vivo chlorophyllfluorescence read directly in the culture tubes. Hundreds ofthese culture tubes, containing specially prepared culture medium,can be maintained in identical environments in specially designedconstant environment devices. The method is capable of measuringthe acclimated reproduction rates of phytoplankton cultureswith an error of 3–4% (coefficient of variation). Completeacclimation, crucial to the detection of small genetic differencesbetween clones, takes one to three weeks, thus necessitatinglong-term experiments. Studies using the methods described indicatethat, in a constant environment, coccolithophores and dinoflagellatesreproduce at constant rates, but diatoms do not.     

Changes in Self-Efficacy and Decisional Balance for Exercise among Obese Women in a Weight Management Program

PINTO, BERNARDINE M., MATTHEW W. CLARK, DEAN G. CRUESS, LYNDA SZYMANSKI, AND VINCENT PERA. Changes in self-efficacy and decisional balance for exercise among obese women in a weight management program. Obes Res. Objective: To assess changes in eating and exercise self-efficacy and decisional balance for exercise in an obese population enrolled in a multi-disciplinary weight management program. Research Method and Procedures: Thirty-two obese women were assessed at entry and after 12 weeks of treatment. Results: Participants showed 15% mean weight loss after 12 weeks of treatment. Mean minutes of self-reported exercise increased by 229%. Participants demonstrated significant improvements in self-efficacy for both eating and exercise and health parameters but not in decisional balance for exercise adoption. Discussion: These results may have implications for the practitioner in that self-efficacy changes occur during successful weight loss, but decisional balance for exercise may not change until individuals enter maintenance. These results imply that practitioners may be advised to shift from confidence building to relapse prevention early on in treatment, and that focusing on strengthening the pros of exercise and reducing the cons of exercise may need to remain constant during treatment.     

Novel structural determinants in human SECIS elements modulate the translational recoding of UGA as selenocysteine

The selenocysteine insertion sequence (SECIS) element directs the translational recoding of UGA as selenocysteine. In eukaryotes, the SECIS is located downstream of the UGA codon in the 3′-UTR of the selenoprotein mRNA. Despite poor sequence conservation, all SECIS elements form a similar stem-loop structure containing a putative kink-turn motif. We functionally characterized the 26 SECIS elements encoded in the human genome. Surprisingly, the SECIS elements displayed a wide range of UGA recoding activities, spanning several 1000-fold in vivo and several 100-fold in vitro. The difference in activity between a representative strong and weak SECIS element was not explained by differential binding affinity of SECIS binding Protein 2, a limiting factor for selenocysteine incorporation. Using chimeric SECIS molecules, we identified the internal loop and helix 2, which flank the kink-turn motif, as critical determinants of UGA recoding activity. The simultaneous presence of a GC base pair in helix 2 and a U in the 5′-side of the internal loop was a statistically significant predictor of weak recoding activity. Thus, the SECIS contains intrinsic information that modulates selenocysteine incorporation efficiency.     

Big eucalypts grow more slowly in a warm climate: evidence of an interaction between tree size and temperature

Large trees are critical components of forest ecosystems, but are declining in many forests worldwide. We predicted that growth of large trees is more vulnerable than that of small trees to high temperatures, because respiration and tissue maintenance costs increase with temperature more rapidly than does photosynthesis and these costs may be disproportionately greater in large trees. Using 5 00 000 measurements of eucalypt growth across temperate Australia, we found that high temperatures do appear to impose a larger growth penalty on large trees than on small ones. Average stem diameter growth rates at 21 °C compared with 11 °C mean annual temperature were 57% lower for large trees (58 cm stem diameter), but only 29% lower for small trees (18 cm diameter). While our results are consistent with an impaired carbon budget for large trees at warmer sites, we cannot discount causes such as hydraulic stress. We conclude that slower growth rates will impede recovery from extreme events, exacerbating the effects of higher temperatures, increased drought stress and more frequent fire on the tall eucalypt forests of southern Australia.