Abstract. The literature is inconsistent regarding the ability of herbivory to control or reduce densities of a major invasive plant species of North America, spotted knapweed (Centaurea stoebe). Here, findings from experimental manipulations of spotted knapweed and long-term monitoring of seed production and insect abundance were used to parameterize a population matrix model for this species. Model predictions were compared against spotted knapweed densities observed in permanent transects, which were established after the release of biological controls. The model incorporated population-level compensation for adult mortality (increased growth from juveniles to adults). The model also incorporated newly reported results showing an interaction between precipitation and biological control impacts. We compared predictions from four alternate models against the observed population densities; models were: conspecific densitydependence, the effects of biological controls, precipitation, and biological control-precipitation interaction. The best model to explain population declines included the effects of biological control agents. Declines in population growth rates (k , 1) were only predicted when reduced seed production and increased plant mortality due to biological controls were included. Results suggest that biological controls contributed to declines observed in field studies, and support the contention that biological control attenuates the ability of spotted knapweed to exploit favorable climatic conditions. The results also demonstrate that spotted knapweed control (i.e., conditions where k , 1) depends upon a relatively large impact of biological control agents through high densities or large per capita impact; both of which are known to vary at our site and elsewhere. At our site spotted knapweed in certain habitats (e.g., disturbed riparian areas) is unlikely to be eradicated by insect herbivory, but spotted knapweed densities found in most other habitats can be reduced by biological control agents. Regardless, the management implications from these findings are that biological controls can intensify the efficacy of other control methods.

Background: Commonplace biodiversity labs in introductory undergraduate biology typically emphasize declarative knowledge. We contend that shifting these labs to emphasize evolution, higher-order cognition, and science reasoning would benefit student learning. Four factors that likely make evolution-based higher-order learning goals difficult to achieve in these labs are: the novelty and quantity of required declarative knowledge, the number of integrated concepts, the theoretical nature of evolution, and limitations on working memory. Thus, we propose that a model to shift learning from lower-order declarative knowledge to evolution-based higher-order integration in these labs would reduce overall lower-order content, increase time efficiency through hands-on pre-lab activities, and increase evidence-based reasoning through written post-labs that emphasize evolution-based higher-order integration. We tested this contention by comparing exam performances of students who did and did not participate in the redesigned lab. Methods: A new plant biodiversity lab design was implemented in an introductory undergraduate biology lab class. The lab class was a separate class from the complementary lecture class, but the content-oriented learning goals were similar between the lecture and lab. We compared achievement of students in lecture + lab to those in lecture only with a pre-assessment and a mid-semester exam which contained questions that were both related and unrelated to the plant biodiversity lab learning goals. Results: Students in 'lecture + lab' relative to 'lecture only' did not perform significantly different on the pre-assessment lower or higher-order questions. On the post-assessment, students in lab + lecture performed significantly better on knowledge questions that were unrelated to lab with an improvement of 5.9%. Moreover, students in lab + lecture also performed significantly better on lab-related knowledge questions and lab-related evolution-based integrative reasoning questions with a range of 6.3 to 11% improvement, compared to students in the lecture only group. Conclusions: The proposed framework was successful in improving student learning for both lower-order declarative knowledge questions and evolution-based questions involving higher-order integration of concepts. In addition, because students in lecture + lab outperformed students in lecture only on questions unrelated to lab content, our proposed model highlights the importance of multiple inquiry-oriented lab experiences in higher education.

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Predicting site vulnerability to nonnative plant establishment remains a difficult goal. Seedling survival is an important component of population dynamics and can affect the success of control strategies. Field manipulations allow potential causal mechanisms of site vulnerability to be evaluated under realistic environmental conditions. We conducted field studies to determine the effects of plant competition and differing precipitation regimes on spotted knapweed seedling survival. We also examined the effect of herbivory on rosette survival and growth. Seeds were sown into plots with vegetation intact or removed at three sites. Seeds were also sown into plots where plant competition and precipitation were manipulated in a factorial design at a single site. Field studies demonstrated that site accounted for much of the variation in emergence rate, while herbivory and plant competition affected seedling survival rates. We observed a wide range in emergence rates, with site averages ranging from 13.1 to 42.5%. Survival the following year ranged from 0.5 to 9.4% of sown seeds. Rosette survival was significantly higher when herbivores were excluded from plots. Below average precipitation reduced seedling survival; however, even with supplemental water, dry-down of exposed sites resulted in low seedling survival. Of the 8,000 seeds added to plots in one study, by autumn, only eight plants resulted, seven of which survived in watered plots with intact vegetation. Collectively, these results show that seedling survival is a critical phase in spotted knapweed population dynamics and can vary among habitats on the basis of plant competition and precipitation. Furthermore, herbivory affects all stages of the lifecycle from the seedling onward. The observed differences help explain the reported variability in seedling survival in the literature and inform efforts to control spotted knapweed using plant competition and biological controls.