Invasive Exotic Plants in the Tropical Pacific Islands: Patterns of Diversity

Oceanic islands are good model systems with which to explore factors affecting exotic species diversity. Islands vary in size, topography, substrate type, degree of isolation, native species diversity, history, human population characteristics, and economic development. Moreover, islands are highly vulnerable to exotic species establishment. We used AICc analyses of data on 1132 vascular plant species for 15 countries and 114 islands from the Pacific Island Ecosystems at Risk (PIER) project to examine biological, geographical, and socioeconomic correlates of exotic species richness. PIER provides data on the distribution of naturalized non-native plant species thought to pose environmental or economic risk. We hypothesized that the numbers of PIER-listed species would be positively correlated with island size, habitat diversity, and proximity to major source pools for propagules. Further, we expected numbers of PIER-listed exotic species to be similar among islands in the same country and to be greater where human populations were larger and where economic activity was high. Most species (908) were found on ≤ 10 islands. Species number was significantly correlated with island and country areas and with native plant species richness. The strongest model revealed by AICc analyses of island data included log (area) and maximum elevation as well as country membership, substrate type, and presence of an airport with paved runway (an index of economic activity). By country, AICc analyses revealed two equivalent models, both of which included log (area) and per capita gross domestic product as well as a measure of population size (either log (population size) or (population density)). Our analyses provide strong evidence of the roles of biogeographic, environmental, and socioeconomic impacts on the distribution and spread of exotic species.     

Variation in stand structure,light and seedling abundance across a tropical moist forest chronosequence,Panama

Abstract. We asked whether forest structure and understory light environments across a tropical moist forest chronosequence followed predictions of a 4‐phase model of secondary succession (establishment, thinning, transition and steady‐state) and whether seedling density and diversity were functions of light availability as predicted by this model. Using aerial photographs, we identified eight second‐growth stands (two each aged ca. 20, 40, 70, and 100 yr) and two old‐growth stands within Barro Colorado Nature Monument, Panama. Trees and seedlings were sampled in nested, contiguous quadrats in 2 160‐m transects in each stand. Light was measured as percent transmittance of diffuse photosynthetically active radiation (TPAR) at each seedling quadrat and by estimation of percent total incident radiation during the growing season from hemispherical canopy photographs. Basal area, tree density, and canopy height followed predictions of the 4‐phase model. Percent total radiation, but not TPAR, declined with stand age as did seedling density. While seedlings were more likely to occur in quadrats at higher light levels, much variation in seedling density was not related to light availability. Seedling patch sizes were small irrespective of light patches, estimated as semivariance ranges. Seedling species richness was a function of seedling density; estimates of species diversity unbiased by density did not vary systematically as a function of stand age. Proximate seed sources, efficient dispersal mechanisms, and appropriate establishment conditions can promote establishment of species‐rich communities early in successions of heterogeneous tropical moist forest.     

Wall thickness referenced to myocardial volume: a new noninvasive framework for cardiac mechanics.

Dimensional variables measured for study of left ventricular mechanics are subject to errors arising from difficulty in determining zero-stress dimensions for use as a reference. Based on a method validated for measurements within individuals, we have devised an approach that facilitates comparison between individuals while minimizing random scatter. We define an exact mathematical index of strain, ln(h(0)/h), using wall thickness (h) referenced to extrapolated wall thickness at zero-luminal volume (h(0)). Noninvasive data from rabbits, pigs, and humans all yielded highly similar myocardial stress, ln(h(0)/h), and work values. The stress-ln(h(0)/h) relationship during afterload variation was constant among individual pigs with a twofold variation in ventricular mass. Stress-ln(h(0)/h) data from our analysis displayed lower scatter than either pressure-volume data normalized to myocardial mass or stress-ln(h(0)/h) data referenced to end-diastolic dimensions. A Frank-Starling-like curve with high correlation (r(2) = 0.96) was constructed from single points from different pigs, suggesting a low level of size and intersubject scatter. This method offers high precision for noninvasive characterization of ventricular and myocardial mechanics and for comparisons between subjects and between species.     

ABRF ESRG 2005 study: identification of seven modified amino acids by Edman sequencing.

Identification of modified amino acids can be a challenging part for Edman degradation sequence analysis, largely because they are not included among the commonly used phenylthiohydantion amino acid standards. Yet many can have unique retention times and can be assigned by an experienced researcher or through the use of a guide showing their typical chromatography characteristics. The Edman Sequencing Research Group (ESRG) 2005 study is a continuation of the 2004 study, in which the participating laboratories were provided a synthetic peptide and asked to identify the modified amino acids present in the sequence. The study sample provided an opportunity to sequence a peptide containing a variety of modified amino acids and note their retention times relative to the common amino acids. It also allowed the ESRG to compile the chromatographic properties and intensities from multiple instruments and tabulate an average elution position for these modified amino acids on commonly used instruments. Participating laboratories were given 2000 pmoles of a synthetic peptide, 18 amino acids long, containing the following modified amino acids: dimethyl- and trimethyl-lysine, 3-methyl-histidine, N-carbamyl-lysine, cystine, N-methyl-alanine, and isoaspartic acid. The modified amino acids were interspersed with standard amino acids to help in the assessment of initial and repetitive yields. In addition to filling in an assignment sheet, which included retention times and peak areas, participants were asked to provide specific details about the parameters used for the sequencing run. References for some of the modified amino acid elution characteristics were provided and the participants had the option of viewing a list of the modified amino acids present in the peptide at the ESRG Web site. The ABRF ESRG 2005 sample is the seventeenth in a series of studies designed to aid laboratories in evaluating their abilities to obtain and interpret amino acid sequence data.     

Cloning and nucleotide sequence of the Vibrio proteolyticus aminopeptidase gene.

The gene encoding the Vibrio proteolyticus aminopeptidase was cloned and sequenced and its amino acid sequence was deduced. The gene encodes a 54 kDa protein, larger than the previously reported size of 30 kDa for the purified aminopeptidase. Sequence alignments revealed a 43-45% homology with two other Vibrio sp. extracellular proteinases.