A Carbon-balance Model of Stand Growth: a Derivation Employing Pipe-model Theory and the Self-thinning Rule

A carbon-balance model of the growth of an even-aged, self-thinning,mono-specific stand of trees is derived using a structural frameworkbased on pipe-model theory. Within the pipe-model framework,dry matter arising from extension of roots and shoots is separablefrom that arising from the cross-sectional expansion of stems.This permits the derivation of models describing the growthof average stem length, total basal area, and total volume ofthe stand. Variations of these models are described for twosituations: (1) where the annual rates of substrate productionand feeder-root turnover can be assumed constant over time;and (2) where these rates are expected to change over time,such as in polluted environments. The model describing the growthof stand volume for the first situation fits published yieldtables. Growth-rate models applicable to individual trees arealso described. Carbon-balance model, dry-matter partitioning, pipe-model theory, stand growth, self-thinning     

Immunoparasitology in Avian Species

There has been no work on the immunological response of birdsto helminth infections since the late 1960s, an area of investigationthat has been too long ignored. Similarly, studies of arthropod-mediatedresponses in birds are lacking except for a few scattered investigations.Recently, a serum antibody response has been seen against onearthropod, the northern fowl mite. The appearance of antibodiesrecognizing an 8–10 kilodalton mite antigen seems to correlatewith a reduction in the mite population on infested chickens.Most of the studies on parasite immunity in avian species havecentered on the economically important Eimeria species, protozoanparasites that infect the intestine of chickens and turkeys.These investigations encompass wide areas of interest includingthe effect of immunity on parasite invasion, development ofT-cell proliferation assays and T-cell clones, inhibition ofparasite penetration and development by hybridoma antibody treatment,production of genetically engineered Eimeria antigens used inbird immunization studies, and studies using inbred or congeniclines of birds to determine what effect the major histocompatibilitycomplex has on parasite immunity. From these efforts it hasbeen learned that not only is the immunity species-specific,but also depending on where in the intestine the parasite invades,penetration is either not affected or inhibited by as much as50%. The T-cell proliferation assays suggest that this specificitymay be due to a species-specific T-cell response. Immunizationstudies using a genetically engineered antigen have indicatedthat at least partial protection against one species of Eimeriais possible. Studies done with the inbred congenic lines ofbirds have shown that the genetic makeup of the bird is importantin how it responds to either a natural infection or to immunizationwith a genetically engineered antigen. Clearly, these resultsshow not only the complexity of the bird response to parasiteinfection, but also the amount of work still undone.     

Comparison of adult mosquito community structure on various habitats

The community structure of adult mosquitoes was compared from New Jersey light trap collections in six different types of habitats in Citrus County, Florida, USA. From October 1998 to December 2000, mosquitoes were collected three times a week from the following habitats (swamps, swamps and freshwater marshes, pine fiat-woods, pine fiat-woods and scrub, salt marshes, and salt marshes and mangroves). Mosquito density was highest in the swamps and freshwater marshes habitat, with an average of 95.65 specimens per trap.Density was lowest in the flatwoods and scrub habitat, with an average of 14.38 specimens per trap. Species dominance differed among habitats. Salt marshes produced the greatest aggregation index, while pine flatwoods produced the lowest. Conversely, diversity analysis showed that pine flatwoods had the greatest diversity, while salt marshes the lowest diversity. Similarity indices indicated that the adult mosquito communities from pine flatwoods and pine flatwoods and scrub were very similar (0.8583). The adult mosquito community of salt marshes was different from that of swamps and freshwater marshes (the similar index was 0.0217).     

SOURCES OF ERROR AND THE NO-PREFERENCE OPTION IN DAIRY PRODUCT TESTING

When products are physically identical, consumers will choose a no‐preference option in a paired preference test only about 30% of the time, giving a nonintuitive result. We evaluated the no‐preference false alarm rate in dairy products and the potential sources of error in panelist behavior, including discrimination problems and poor repeatability of judgments. Paired preference tests were conducted with milk (2% versus nonfat or skim), with cottage cheese (4% versus nonfat) and with identical samples. Triangle, dual standard and same/different discrimination tests were also conducted. The no‐preference option was chosen by about 30% of the consumers when samples were identical, and less frequently when samples were different. Discrimination performance, although statistically significant, was poorer than expected with about 30% discriminators (d′ of 1.7) in most tests. Even in the dual standard tests on milk (visually obvious and with references present), performance was only 88% correct (76% discriminators). Repeatability in preference tests was also poorer than expected, with only 56% choosing the same preference option for different samples on repeat trials although the group preferences were stable. Same/different tests indicated that over 50% of the consumers called identical samples different, although this fell short of explaining the 70% average false alarm rate in preferences. Even with apparently discriminable consumer products, accurate discrimination of the samples and repeatability of preferences should not be assumed. Random responding may contribute to error variance and produce nonsensical results such as the expression of choice between identical samples.     

Excitation-Contraction Coupling in Crayfish

High-sensitivity recording techniques demonstrate a continuousrelation between the onset and magnitude ot tension and themembrane depolarization that is induced by increasing K in thebathing medium or by intracellularly applied outward currents.This finding is not consistent with the mechanism of signallinge-c coupling by electrotonic spread of a "critical" depolarizationinward along the membrane of the transverse tubular system.It is in accord, however, with the channelled current mechanismthat is based on the known anion-permselectivity of the membranein the terminals of the TTS. The channelled-current model alsopredicts a direct role of Cl and a possible interaction betweenCa and CI in e-c coupling. The initiation and maintenance oftension as well as its magnitude, are in fact dependent uponthe concentrations of Ca and Cl in the medium. Thus, both thesignalling to, and the activation of, the contractile systemappear to be performed by a flow of current in the loop: cellmembrane – cell interior – TTS membrane –TTS channels – exterior, as is envisaged in the channelled-currentmodel of e-c coupling.     

LOGARITHMIC TRANSFORMATION OF MAGNITUDE ESTIMATION DATA AND COMPARISONS OF SCALING METHODS

Recent studies comparing magnitude estimation to other scaling methods have been criticized for failure to submit the data to logarithmic transformation before statistical analysis, a procedure which can improve the ability of magnitude estimation scaling to differentiate among products. Data from one of these studies was available for re-analysis, which was conducted both with and without logarithmic transformation of magnitude estimation, category scales and line scales. The ability of magnitude estimation to differentiate among products was improved by log transformation, while the other methods were not. Improvements were associated in pan with reductions in positive skew and improved approximation of the normal distribution. In spite of this improvement, magnitude estimation remained slightly inferior to the other methods especially in the hands of an untrained consumer sample.     

Succession following wildfire in coastal heathland (Nadgee Nature Reserve N.S.W.)

Changes in coastal heath vegetation were measured for 6 years following a wildfire and the data compared with the pre-fire vegetation. For the first 2 years changes were related to time; after that environmental factors dominated the process of regeneration. During the first 4 years plant species spread rapidly and maximum species diversity per plot was reached 4 years after the fire. About the same time many species consolidated their position in the community; this being shown by cover levels greater than before the fire for some species. Six years after the fire the vegetation is still dynamic and very different when compared with the heath before burning.