Population models reveal synergistic fitness effects of climate change and urbanization on poison ivy (Toxicodendron radicans) via disruption of seed dispersal interactions

Urban Ecosystems - Two of the most important human disturbances on natural ecosystems are urbanization and climate change. While their individual effects are well-documented, how the combined...     

Multi-Stage Model Estimates of Lung Cancer Risk from Exposure to Diesel Exhaust, Based on a U.S. Railroad Worker Cohort

A California Environmental Protection Agency (Cal/EPA) report concluded that a reasonable and likely explanation for the increased lung cancer rates in numerous epidemiological studies is a causal association between diesel exhaust exposure and lung cancer. A version of the present analysis, based on a retrospective study of a U.S. railroad worker cohort, provided the Cal/EPA report with some of its estimates of lung cancer risk associated with diesel exhaust. The individual data for that cohort study furnish information on age, employment, and mortality for 56,000 workers over 22 years. Related studies provide information on exposure concentrations. Other analyses of the original cohort data reported finding no relation between measures of diesel exhaust and lung cancer mortality, while a Health Effects Institute report found the data unsuitable for quantitative risk assessment. None of those three works used multistage models, which this article uses in finding a likely quantitative, positive relations between lung cancer and diesel exhaust. A seven-stage model that has the last or next-to-last stage sensitive to diesel exhaust provides best estimates of increase in annual mortality rate due to each unit of concentration, for bracketing assumptions on exposure. Using relative increases of risk and multiplying by the background lung cancer mortality rates for California, the 95% upper confidence limit of the 70-year unit risks for lung cancer is estimated to be in the range 2.1 x 10(-4) (microg/m3)(-1) to 5.5 x 10(-4) (microg/m3)(-1). These risks constitute the low end of those in the Cal/EPA report and are below those reported by previous investigators whose estimates were positive using human data.     

Bat ecology and public health surveillance for rabies in an urbanizing region of Colorado

We describe use of Fort Collins, Colorado, and nearby areas by bats in 2001–2005, and link patterns in bat ecology with concurrent public health surveillance for rabies. Our analyses are based on evaluation of summary statistics, and information-theoretic support for results of simple logistic regression. Based on captures in mist nets, the city bat fauna differed from that of the adjacent mountains, and was dominated by big brown bats (Eptesicus fuscus). Species, age, and sex composition of bats submitted for rabies testing locally and along the urbanizing Front Range Corridor were similar to those of the mist-net captures and reflected the annual cycle of reproduction and activity of big brown bats. Few submissions occurred November- March, when these bats hibernated elsewhere. In summer females roosted in buildings in colonies and dominated health samples; fledging of young corresponded to a summer peak in health submissions with no increase in rabies prevalence. Roosting ecology of big brown bats in buildings was similar to that reported for natural sites, including colony size, roost-switching behavior, fidelity to roosts in a small area, and attributes important for roost selection. Attrition in roosts occurred from structural modifications of buildings to exclude colonies by citizens, but without major effects on long-term bat reproduction or survival. Bats foraged in areas set aside for nature conservation. A pattern of lower diversity in urban bat communities with dominance by big brown bats may occur widely in the USA, and is consistent with national public health records for rabies surveillance.     

Measures of Disadvantage: is Car Ownership a Good Indicator?

A need to better understand the multidimensional nature of disadvantage is leading to the adoption of a wider range of measurement variables. One variable now commonly adopted is zero car ownership. This paper challenges the logic of including ‘not having a car’ as an indicator of disadvantage. It argues that this can distort the real picture of disadvantage. It presents evidence to show that zero car ownership can be a positive feature of low income households and that conversely high car ownership can put significant financial stress on households with low income.     

Effects of urbanization on trophic dynamics of arthropod communities on a common desert host plant

Urbanization is a dominant demographic trend that radically alters ecological patterns. Most urban ecology studies, however, are strictly observational, and the mechanisms underlying these patterns have not been experimentally examined in cities. We manipulated vertebrate and invertebrate predators and water availability of a common native shrub to investigate the mechanisms controlling trophic dynamics of associated arthropod communities in an outlying desert, an urban desert remnant, and a mesic yard. The outlying desert had higher diversity and greater evenness but lower abundances than urban sites. The desert remnant resembled the mesic yard in terms of arthropod seasonality, abundances, and diversity. Surprisingly, top-down pressures on arthropods were stronger in urbanized areas and controlled already elevated herbivore abundances. Predators were especially sensitive to water availability, suggesting that stress plays an important role in this trophic system. Shifts in trophic dynamics are likely common in cities and preserved remnants may not mimic the trophic structure and function of their more pristine counterparts. If these patterns hold in other urbanized areas, they would have broad implications for conservation biology given that simply preserving natural habitats in urbanizing areas may not be enough to ensure an associated fauna that reflects the more intact and less urbanized habitat.