Use of tree aggregations in forest ecology and management

Two recent studies using tree aggregations to analyze forest age-structure stability and past forest structure are flawed. A better understanding of aggregation dynamics is needed before aggregation analysis is used in forest management.     

LACTOSE NEGATIVE ESCHERICHIA COLI FROM RANGELAND STREAMS: SOURCE,ANTIBIOTIC RESISTANCE,AND COLICINOGENICITY1

ABSTRACT: Lactose-negative Escherichia coil from cattle feces appeared as yellow, atypical colonies on m-FC medium plates with water samples from rangeland streams. The lactose-negative E. coil may impact stream water quality analyses if infrequent samples are collected; are less antibiotic resistant than the lactose-positive E. coili isolated from rangeland streams; and are colicinogenic toward all the laboratory strains of E. coil examined and toward 61 percent of the lactose-positive E. coil rangeland-stream isolates that were tested. This latter result could explain the potentially low degree of antibiotic resistance transfer from lactose-positive to lactose-negative E. coil. In addition, the colicinogenicity of the lactose-negative E. coil may interfere with microbiological water quality analyses that depend upon lactose fernientations with mixed populations of coliforms.     

Graduated driver licensing: the New Zealand experience

In New Zealand, on 1 August 1987, a three-stage graduated driver licensing (GDL) system that applied to all new drivers aged 15-24 years was introduced. The essential elements of GDL were a 6-month learner license (supervised driving) and an 18-month restricted license stage (with restrictions on night driving and carrying passengers). A blood alcohol limit of 0.03 mg% applied at both stages. EVALUATION STUDIES: Early studies indicated that young people were reasonably accepting of the restrictions, with the passenger restriction being the least acceptable. Problems of compliance with the restricted license driving restrictions were reported. Evaluations of the impact of the graduated driver licensing (GDL) on serious traffic-related injury showed that up until 1991-1992, an 8% reduction could be attributed to GDL. At this time, it was considered that reduced exposure was the main reason for this reduction. However, the number of fatalities and hospital admissions among young people continued to decline, as did the population rate and the rate per number of licensed drivers among the young driver age group. A further evaluation study showed that drivers with a restricted license had a smaller proportion of crashes at night, and with passengers, compared with drivers licensed before GDL. IMPACT OF GDL: These results suggested that GDL restrictions had contributed to the reduction in crashes among young people and that it was not simply a case of reduced exposure to risk. An update of the most recent crash statistics indicated that, compared with older age groups, the fatal and serious injury crash rate among young people has remained substantially below the pre-GDL level. This suggests that the impact of GDL has not diminished over time.     

Stable carbon isotope variability in marine macrophytes and its implications for food web studies

Stable carbon isotope ratios (¹³C) of eelgrass Zostera marina and of kelp Laminaria longicruris showed considerable variation in time and space. The isotopic composition of Z. marina varied seasonally from a mean of-6 for leaves formed in June to a mean of-10 for leaves formed in February. The maximum range for individual leaves was from-5 to-11.4. Once a leaf was fully formed, its isotopic composition appeared not to change. In L. longicruris there was no clear seasonal pattern of variation, but in any given blade there was a spatial pattern of variation, with the thickened central band tending to be least negative and the margins most negative. In one blade the range was from-12 to-20. Since this range overlaps values that are found in various other macrophytes and in seston, the value of the stable carbon isotope ratio as a tracer in food webs involving macroalgae is questioned. For Z. marina, in which the values are seasonally predictable, the technique may be useful if interpreted with care. The most probable explanation of variation in the ratios is differential storage of biochemical components of different isotopic compostion.     

Conceptual approaches for the development of dynamic specific activity models of 14C transfer from surface water to humans

Carbon-14 is a particularly interesting radionuclide from the perspective of dose estimation. Many nuclear facilities, including power reactors, release 14C into the environment, and much of this is as 14CO2. This mixes readily with stable CO2, and hence enters the food chain as fundamental biomolecules. This isotopic mixing is often used as the basis for dose assessment models. The present model was developed for the situation of 14C releases to surface waters, where there are distinct changes in the water 14C activity concentrations throughout the year. Complete isotopic mixing (equilibrium) cannot be assumed. The model computes the specific activity (activity of 14C per mass of total C) in water, phytoplankton, fish, crops, meat, milk and air, following a typical irrigation-based food-chain scenario. For most of the biotic compartments, the specific activity is a function of the specific activity in the previous time step, the specific activity of the substrate media, and the C turnover rate in the tissue. The turnover rate is taken to include biochemical turnover, growth dilution and mortality, recognizing that it is turnover of C in the population, not a tissue or an individual, that is relevant. Attention is paid to the incorporation of 14C into the surface water biota and the loss of any remaining 14CO2 from the surface water-air interface under its own activity concentration gradient. For certain pathways, variants in the conceptual model are presented, in order to fully discuss the possibilities. As an example, a new model of the soil-to-plant specific activity relationship is proposed, where the degassing of both 14C and stable C from the soil is considered. Selection of parameter values to represent the turnover rates as modeled is important, and is dealt with in a companion paper.     

Assessing ecological function in the context of species recovery

Species interactions matter to conservation. Setting an ambitious recovery target for a species requires considering the size, density, and demographic structure of its populations such that they fulfill the interactions, roles, and functions of the species in the ecosystems in which they are embedded. A recently proposed framework for an International Union for Conservation of Nature Green List of Species formalizes this requirement by defining a fully recovered species in terms of representation, viability, and functionality. Defining and quantifying ecological function from the viewpoint of species recovery is challenging in concept and application, but also an opportunity to insert ecological theory into conservation practice. We propose 2 complementary approaches to assessing a species’ ecological functions: confirmation (listing interactions of the species, identifying ecological processes and other species involved in these interactions, and quantifying the extent to which the species contributes to the identified ecological process) and elimination (inferring functionality by ruling out symptoms of reduced functionality, analogous to the red-list approach that focuses on symptoms of reduced viability). Despite the challenges, incorporation of functionality into species recovery planning is possible in most cases and it is essential to a conservation vision that goes beyond preventing extinctions and aims to restore a species to levels beyond what is required for its viability. This vision focuses on conservation and recovery at the species level and sees species as embedded in ecosystems, influencing and being influenced by the processes in those ecosystems. Thus, it connects and integrates conservation at the species and ecosystem levels.