Ecosystem engineering and leaf quality together affect arthropod community structure and diversity on white oak (Quercus alba L.).

Shelter building caterpillars act as ecosystem engineers by creating and maintaining leaf shelters, which are then colonized by other arthropods. Foliage quality has been shown to influence initial colonization by shelter-building caterpillars. However, the effects of plant quality on the interactions between ecosystem engineers and their communities have yet to be studied at the whole plant level. We examined how leaf tying caterpillars, as ecosystem engineers, impact arthropod communities on Quercus alba (white oak), and the modifying effect of foliage quality on these interactions. We removed all leaf tying caterpillars and leaf ties on 35 Q. alba saplings during the season when leaf tying caterpillars were active (June-September), and compared these leaf tie removal trees to 35 control trees whose leaf ties were left intact. Removal of these ecosystem engineers had no impact on overall arthropod species richness, but reduced species diversity, and overall arthropod abundance and that of most guilds, and changed the structure of the arthropod community as the season progressed. There was an increase in plant-level species richness with increasing number of leaf ties, consistent with Habitat Diversity Hypothesis. In turn, total arthropod density, and that of both leaf tying caterpillars and free-feeding caterpillars were affected by foliar tannin and nitrogen concentrations, and leaf water content. The engineering effect was greatest on low quality plants, consistent with the Stress-Gradient Hypothesis. Our results demonstrate that interactions between ecosystem engineering and plant quality together determine community structure of arthropods on Q. alba in Missouri.

Assessing the current and potential future distribution of four invasive forest plants in Minnesota, U.S.A., using mixed sources of data.

Invasive plants are an ongoing subject of interest in North American forests, owing to their impacts on forest structure and regeneration, biodiversity, and ecosystem services. An important component of studying and managing forest invaders involves knowing where the species are, or could be, geographically located. Temporal and environmental context, in conjunction with spatially-explicit species occurrence information, can be used to address this need. Here, we predict the potential current and future distributions of four forest plant invaders in Minnesota: common buckthorn (Rhamnus cathartica), glossy buckthorn (Frangula alnus), garlic mustard (Alliaria petiolata), and multiflora rose (Rosa multiflora). We assessed the impact of two different climate change scenarios (IPCC RCP 6.0 and 8.5) at two future timepoints (2050s and 2070s) as well as the importance of occurrence data sources on the potential distribution of each species. Our results suggest that climate change scenarios considered here could result in a potential loss of suitable habitat in Minnesota for both buckthorn species and a potential gain for R. multiflora and A. petiolata. Differences in predictions as a result of input occurrence data source were most pronounced in future climate projections.

Physical Fighting Among Male and Female Adolescents of Military Families: Results From a Representative Sample of High School Students.

The impact of family military involvement on adolescent mental health and substance abuse is well established, but little is known about other behavioral health outcomes such as physical fighting. We assessed the relationship between family military involvement and physical fighting in a representative sample of 3,928 high school students. Weighted logistic regression was used to determine whether adolescents from military families had higher odds of fighting and fighting on school property compared with adolescents of non-military families after controlling for demographics, substance use, depressive symptoms, and bullying victimization. We also assessed the cumulative impact of multiple risk factors on fighting outcomes. Overall, 23.5% of high school students reported physical fighting and 7.0% reported physical fighting at school. Youth from military families had higher odds of physical fighting (adjusted odds ratios [AOR] = 1.69; 95% confidence interval [CI] = [1.27, 2.25]) and physical fighting on school property (AOR = 1.98; 95% CI = [1.16, 3.39]). In models stratified by gender, family military involvement remained independently associated with physical fighting and physical fighting at school for males (AOR = 1.74; 95% CI = [1.15, 2.65] and AOR = 2.21; 95% CI = [1.03, 4.74]) and females (AOR = 1.65; 95% CI = [1.11, 2.45] and AOR = 1.88; 95% CI = [1.01, 3.50]). The odds of engaging in each physical fighting outcome increased as the cumulative number of risk factors increased. School-based interventions aimed at addressing fighting should be tailored to fit the unique needs of adolescents in military families, particularly those with additional risk factors.

Ode to Ehrlich and Raven or how herbivorous insects might drive plant speciation.

Fifty years ago, Ehrlich and Raven proposed that insect herbivores have driven much of plant speciation, particularly at tropical latitudes. There have been no explicit tests of their hypotheses. Indeed there were no proposed mechanisms either at the time or since by which herbivores might generate new plant species. Here we outline two main classes of mechanisms, prezygotic and postzygotic, with a number of scenarios in each by which herbivore-driven changes in host plant secondary chemistry might lead to new plant lineage production. The former apply mainly to a sympatric model of speciation while the latter apply to a parapatric or allopatric model. Our review suggests that the steps of each mechanism are known to occur individually in many different systems, but no scenario has been thoroughly investigated in any one system. Nevertheless, studies of Dalechampia and its herbivores and pollinators, and patterns of defense tradeoffs in trees on different soil types in the Peruvian Amazon provide evidence consistent with the original hypotheses of Ehrlich and Raven. For herbivores to drive sympatric speciation, our findings suggest that interactions with both their herbivores and their pollinators should be considered. In contrast, herbivores may drive speciation allopatrically without any influence by pollinators. Finally, there is evidence that these mechanisms are more likely to occur at low latitudes and thus more likely to produce new species in the tropics. The mechanisms we outline provide a predictive framework for further study of the general role that herbivores play in diversification of their host plants.

Asteroid Risk Assessment: A Probabilistic Approach.

Following the 2013 Chelyabinsk event, the risks posed by asteroids attracted renewed interest, from both the scientific and policy-making communities. It reminded the world that impacts from near-Earth objects (NEOs), while rare, have the potential to cause great damage to cities and populations. Point estimates of the risk (such as mean numbers of casualties) have been proposed, but because of the low-probability, high-consequence nature of asteroid impacts, these averages provide limited actionable information. While more work is needed to further refine its input distributions (e.g., NEO diameters), the probabilistic model presented in this article allows a more complete evaluation of the risk of NEO impacts because the results are distributions that cover the range of potential casualties. This model is based on a modularized simulation that uses probabilistic inputs to estimate probabilistic risk metrics, including those of rare asteroid impacts. Illustrative results of this analysis are presented for a period of 100 years. As part of this demonstration, we assess the effectiveness of civil defense measures in mitigating the risk of human casualties. We find that they are likely to be beneficial but not a panacea. We also compute the probability-but not the consequences-of an impact with global effects ("cataclysm"). We conclude that there is a continued need for NEO observation, and for analyses of the feasibility and risk-reduction effectiveness of space missions designed to deflect or destroy asteroids that threaten the Earth.

Invasive plant species alters consumer behavior by providing refuge from predation.

Understanding the effects of invasive plants on native consumers is important because consumer-mediated indirect effects have the potential to alter the dynamics of coexistence in native communities. Invasive plants may promote changes in consumer pressure due to changes in protective cover (i.e., the architectural complexity of the invaded habitat) and in food availability (i.e., subsidies of fruits and seeds). No experimental studies have evaluated the relative interplay of these two effects. In a factorial experiment, we manipulated cover and food provided by the invasive shrub Amur honeysuckle (Lonicera maackii) to evaluate whether this plant alters the foraging activity of native mammals. Using tracking plates to quantify mammalian foraging activity, we found that removal of honeysuckle cover, rather than changes in the fruit resources it provides, reduced the activity of important seed consumers, mice in the genus Peromyscus. Two mesopredators, Procyon lotor and Didelphis virginiana, were also affected. Moreover, we found rodents used L. maackii for cover only on cloudless nights, indicating that the effect of honeysuckle was weather-dependent. Our work provides experimental evidence that this invasive plant species changes habitat characteristics, and in so doing alters the behavior of small- and medium-sized mammals. Changes in seed predator behavior may lead to cascading effects on the seeds that mice consume.