Theoretical analysis of the weight-length relationship in fish juveniles

The weight-length relationship in fish juveniles was investigated theoretically, to assess the significance of the allometric factor and the validity of the condition factor; these biological factors often remain undetermined, because most fishery studies have been conducted for commercial-sized and/or adult populations. The exponent b (allometric factor) seemed to be the main parameter, performing a key role in the equation W=aL ^b , where W=weight, a is a constant and L=length. The parameters a (condition factor) and K (ponderal index; K=10³ W/L ³) were judged to be less important in comparative studies, since these parameters were closely correlated with b. It is recommended that the assumed theoretical value of b=3 not be used in applied ichthyological surveys, since this value was rarely obtained in the studies, and since a much wider range is usually seen. These analyses led to a new working hypothesis — not yet verified — which opens a new approach to understanding the biological significance of the allometric factor. This approach involves the fractal theory (where b may be considered as a fractal dimension equivalent) linked to the theory of saltatory ontogeny [where b is a threshold characteristic in the (early) life history of fishes].     

Environmental Cleanliness as a Public Good: Welfare and Policy Implications of Nonconvex Preferences

This paper explores the implications of a form of nonconvexity in individual preferences over the public good “cleanliness.” The implications of this nonconvexity on equilibrium outcomes, welfare analysis, the process of development, and optimal government policy are examined. The nonconvexity can imply a role for government in providing a commitment to a clean environment even if the government has a cost disadvantage in cleaning compared with individuals. By providing a credible commitment to a clean environment the government can induce private individuals to undertake optimal levels of cleaning on their own.     

An Age-Structured Demographic Model for the Endangered Stephens' Kangaroo Rat

Effective conservation of endangered species often is hampered by inadequate knowledge of demography. We extracted information on survival and fecundity from an 18-month, live-trapping study of Dipodomys stephensi , and from this we developed an age-structured demographic model to assess population viability. Adult Stephens' kangaroo rats persisted longer than juveniles, and adult females persisted longer than adult males. Disappearance rates were high in the first months after initial capture. Thereafter, the fraction of animals persisting decreased slowly and in an approximately linear fashion on a semilogarithmic scale, suggesting age-independent mortality factors such as predation. Juvenile persistence did not differ substantially between two years of strikingly different rainfall. Onset of breeding followed the start of winter rains. Length of the breeding season, average number of litters per female, and the fraction of first-year females breeding were much greater in the year of higher rainfall. We propose a birth-pulse demographic model for D. stephensi that distinguishes juvenile and adult age classes. Temporal environmental variation can be modeled adequately with a constant survivorship schedule and variable fecundity determined by yearly precipitation. Several issues should be resolved, however, before conservation decisions are based on the model. Better estimates of juvenile survivorship are critical, the quantitative relationship between precipitation and fecundity must be determined, and the potential for density dependence and source-sink population dynamics must be evaluated.     

The effect of perceived intruder proximity and resident body size on the aggressive responses of male green frogs, Rana clamitans (Anura: Ranidae)

We examined variation in aggressive responses within and among individuals in the green frog, Rana clamitans. We tested the hypothesis that resident males respond in a graded fashion to changes in perceived intruder proximity (stimulus intensity). We also investigated how response level varied with responder body size. We found that green frogs differentially alter aggressive responses (increasing movement and calling rates while decreasing the duration and dominant frequency of their calls) with an increase in stimulus intensity. Body size did not appear to be a significant influence on most response levels. We suggest that aggressive responses are graded, and advertisement and aggressive calls represent opposite ends of a continuum. Green frogs do not exhibit clearly defined thresholds for responses like those reported for some other frogs. By using graded responses rather than discrete all-or-nothing responses, males may reduce the potential costs of aggressive encounters.     

Staff burnout in a psychiatric hospital: A cross-lagged panel design

Previous research has shown that burnout in staff members at psychiatric hospitals is significantly associated with state anxiety and collegial support. The directionality of these relationships may be inferred using a cross-lagged panel design. To do this, 35 staff members representing various clinical disciplines completed measures of burnout, support, and anxiety twice, eight months apart. Burnout comprised three factors: emotional exhaustion, depersonalization, and personal accomplishment. Findings from one cross-lagged panel suggested that emotional exhaustion causes state anxiety. The second panel showed that lack of collegial support caused depersonalization. Understanding causes and effects of burnout for inpatient psychiatric staff may lead to training and resource development that will improve the quality of their work environment.     

Human impact on the Falkland Islands environment

Summary A historic analysis of human-initiated influences on the Falkland Islands ecologies is presented. Ecosystems were extensively altered by the destruction of seal and penguin communities in the late eighteenth and nineteenth centuries; and by the introduction of domesticated animals and exotic plants, the proliferation of fires, and the hunting to extinction, or near extinction, of certain animals. The harsh Falklands climate has permitted only limited recovery from some of these ravages. No island ecosystems, however remote, are spared the effects of economic and political changes influencing the rest of the world.He has published a previous article on island ecologies inThe Environmentalist (1992).     

In-situ biological treatment of vinyl acetate-contaminated soil: An emergency response action

In-situ biological solid-phase (or land) treatment was cost-effectively used to remediate 1,500 cubic yards (1,100 m³) of contaminated soil within three months of field operation following spillage of an estimated 12,000 gallons (45,000 L) of vinyl acetate from a railroad tank car onto surface soil. The vinyl acetate rapidly hydrolyzed to acetate and acetaldehyde with concentrations ranging up to 22,000 and 3,000 mg/kg, respectively. Ethanol, a metabolic intermediate, was found to accumulate in soil to concentrations as high as 280 mg/kg. The estimate for excavation, transportation, and disposal of the contaminated soil as a special waste, and for backfilling of the excavated area, was $850,000. The cost for biological remediation of the contaminated soil was $400,000, which was less than half the cost of excavation. In-situ biological treatments have been used to readily remove contaminants, such as acrylonitrile, styrene, butylcellosolve, ethylacrylate, and n-butylacrylate, at other sites involving railroad incidents.     

Turkey vultures foraging at experimental food patches: a test of information transfer at communal roosts

Summary Experimental food patches were used to assess the importance of food information transfer in communally roosting turkey vultures (Cathartes aura) in southern Ontario. Feeding trials failed to provide evidence of recruitment due to information transfer. Overall, fewer birds arrived at novel food patches on the days following discovery than was expected, had information transfer been operating. Earlier arrivals on second days were more likely due to local enhancement rather than information transfer since the size of groups arriving at food patches did not differ between the 2 days. These results indicate that turkey vulture roosts in Ontario do not operate as centers for food information transfer. Intraspecific competition, preferential selection of small-sized carrion, and a low degree of kin association make the proposed benefits of information transfer much less applicable to turkey vultures than has been found for other scavenging species.Offprint requests to: P.J. Weatherhead