An evaluation of two hands-on lab styles for plant biodiversity in undergraduate biology.

We compared learning cycle and expository formats for teaching about plant biodiversity in an inquiry-oriented university biology lab class (n = 465). Both formats had preparatory lab activities, a hands-on lab, and a postlab with reflection and argumentation. Learning was assessed with a lab report, a practical quiz in lab, and a multiple-choice exam in the concurrent lecture. Attitudes toward biology and treatments were also assessed. We used linear mixed-effect models to determine impacts of lab style on lower-order cognition (LO) and higher-order cognition (HO) based on Bloom's taxonomy. Relative to the expository treatment, the learning cycle treatment had a positive effect on HO and a negative effect on LO included in lab reports; a positive effect on transfer of LO from the lab report to the quiz; negative impacts on LO quiz performance and on attitudes toward the lab; and a higher degree of perceived difficulty. The learning cycle treatment had no influence on transfer of HO from lab report to quiz or exam; quiz performance on HO questions; exam performance on LO and HO questions; and attitudes toward biology as a science. The importance of LO as a foundation for HO relative to these lab styles is addressed.

Optimal central-place foraging by beavers: Tree-size selection in relation to defensive chemicals of quaking aspen.

At a newly occupied pond, beavers preferentially felled aspen smaller than 7.5 cm in diameter and selected against larger size classes. After one year of cutting, 10% of the aspen had been cut and 14% of the living aspen exhibited the juvenile growth form. A phenolic compound which may act as a deterrent to beavers was found in low concentrations in aspen bark, and there was no significant regression of relative concentration of this compound on tree diameter. At a pond which had been intermittently occupied by beavers for over 20 years, beavers selected against aspen smaller than 4.5 cm in diameter, and selected in favor of aspen larger than 19.5 cm in diameter. After more than 28 years of cutting at this site, 51% of the aspen had been cut and 49% of the living aspen were juvenileform. The phenolic compound was found in significantly higher concentrations in aspen bark than at the newly occupied site, and there was a significant negative regression of relative concentration on tree diameter. The results of this study show that responses to browsing by trees place constraints on the predictive value of standard energy-based optimal foraging models, and limitations on the use of such models. Future models should attempt to account for inducible responses of plants to damage and increases in concentrations of secondary metabolites through time.