Effects of grazing and topography on long-term vegetation changes in a Mediterranean ecosystem in Israel

The dynamics of Mediterranean vegetation over 28 years was studied in the Northern Galilee Mountains, Israel, in order to identify and quantify the major factors affecting it at the landscape scale. Image analysis of historical and current aerial photographs was used to produce high resolution digital vegetation maps (pixel size = 30 cm) for an area of 4 km² in the Galilee Mountains, northern Israel. GIS tools were used to produce corresponding maps of grazing regime, topographic indices and other relevant environmental factors. The effects of those factors were quantified using a multiple regression analyses. Major changes in the vegetation occurred during the period studied (1964–1992); tree cover increased from 2% in 1964 to 41% in 1992, while herbaceous vegetation cover decreased from 56% in 1964 to 24% in 1992. Grazing, topography and initial vegetation cover were found to significantly affect present vegetation patterns. Both cattle grazing and goat grazing reduced the rate of increase in tree cover, yet even intensive grazing did not halt the process. Grazing affected also the woody-herbaceous vegetation dynamics, reducing the expansion of woody vegetation. Slope, aspect, and the interaction term between these two factors, significantly affected vegetation pattern. Altogether, 56% and 72% of the variability in herbaceous and tree cover, respectively, was explained by the regression models. This study indicates that spatially explicit Mediterranean vegetation dynamics can be predicted with fair accuracy using few biologically important environmental variables.     

CO2激光对西瓜种子最佳辐射剂量的筛选及其数学模拟

采用功率密度为８９８ｍ ｗ ／ｃｍ ２ 的ＣＯ２ 激光对西瓜种子进行不同时间的辐射处理,筛选出了最佳刺激剂量,并应用多项式回归进行数学模拟,得到了比较理想的结论。     

MONITORING THE TREND OF HARBOR SEALS IN PRINCE WILLIAM SOUND,ALASKA, AFTER THE EXXON VALDEZ OIL SPILL

We used aerial counts to monitor the trend in numbers of harbor seals, Phoca vitulina richardsi, in Prince William Sound, Alaska, following the 1989 Exxon Valdez oil spill. Repetitive counts were made at 25 haul-out sites during the annual molt period each year from 1990 through 1997. A generalized linear model indicated that time of day, date, and time relative to low tide significantly affected seal counts. When Poisson regression was used to adjust counts to a standardized set of survey conditions, results showed a highly significant decline of 4.6% per year. Unadjusted counts indicated a slight, but not statistically significant, decline in the number of seals. The number of harbor seals on the trend-count route in eastern and central PWS has been declining since at least 1984, with an overall population reduction of 63% through 1997. Programs to monitor long-term changes in animal population sizes should account for factors that can cause short-term variations in indices of abundance. The inclusion of such factors as covariates in models can improve the accuracy of monitoring programs.     

Why the Phylogenetic Species Concept?—Elementary

Although species play a number of unique and necessary roles in biology, none are more important than as the elements of phylogeny, nomenclature, and biodiversity study. Species are not divisible into any smaller units among which shared derived characters can be recognized with fidelity. Biodiversity inventory, assessment, and conservation are dependent upon a uniformly applicable species concept. Species are the fundamental units in formal Linnaean classification and zoological nomenclature. The Biological Species Concept, long given nominal support by most zoologists, forced an essentialy taxonomic problem (what are species?) into a population genetics framework (why are there species?). Early efforts at a phylogenetic species concept focused on correcting problems in the Biological Species Concept associated with ancestral populations, then applying phylogenetic logic to species themselves. Subsequently, Eldredge and Cracraft, and Nelson and Platnick, each proposed essentially identical and truly phylogenetic species concepts that permitted the rigorous recognition of species prior to and for the purposes of phylogenetic analysis, yet maintained the integrity of the Phylogenetic Species Concept outside of cladistic analysis. Such phylogenetic elements have many benefits, including giving to biology a unit species concept applicable across all kinds of living things including sexual and asexual forms. This is possible because the Phylogenetic Species Concept is based on patterns of character distributions and is therefore consistent with the full range of possible evolutionary processes that contribute to species formation, including both biotic and abiotic (even random) factors.     

Online Calculation of Efficient Designs for Multi‐Factor Models

A class of “incomplete” multivariate polynomial regression models on the q‐cube is considered. A simple algorithm for the determination of D‐optimal product designs is developed and illustrated by specific examples. The methods are implemented on an IBM compatible PC under MS‐DOS and provide an effective method for the numerical solution of an optimal design problem, which was unsolved in nearly all cases of practical interest.     

Opposing community assembly patterns for dominant and nondominant plant species in herbaceous ecosystems globally

Biotic and abiotic factors interact with dominant plants—the locally most frequent or with the largest coverage—and nondominant plants differently, partially because dominant plants modify the environment where nondominant plants grow. For instance, if dominant plants compete strongly, they will deplete most resources, forcing nondominant plants into a narrower niche space. Conversely, if dominant plants are constrained by the environment, they might not exhaust available resources but instead may ameliorate environmental stressors that usually limit nondominants. Hence, the nature of interactions among nondominant species could be modified by dominant species. Furthermore, these differences could translate into a disparity in the phylogenetic relatedness among dominants compared to the relatedness among nondominants. By estimating phylogenetic dispersion in 78 grasslands across five continents, we found that dominant species were clustered (e.g., co‐dominant grasses), suggesting dominant species are likely organized by environmental filtering, and that nondominant species were either randomly assembled or overdispersed. Traits showed similar trends for those sites (<50%) with sufficient trait data. Furthermore, several lineages scattered in the phylogeny had more nondominant species than expected at random, suggesting that traits common in nondominants are phylogenetically conserved and have evolved multiple times. We also explored environmental drivers of the dominant/nondominant disparity. We found different assembly patterns for dominants and nondominants, consistent with asymmetries in assembly mechanisms. Among the different postulated mechanisms, our results suggest two complementary hypotheses seldom explored: (1) Nondominant species include lineages adapted to thrive in the environment generated by dominant species. (2) Even when dominant species reduce resources to nondominant ones, dominant species could have a stronger positive effect on some nondominants by ameliorating environmental stressors affecting them, than by depleting resources and increasing the environmental stress to those nondominants. These results show that the dominant/nondominant asymmetry has ecological and evolutionary consequences fundamental to understand plant communities.     

Technical note: Regression analysis in adult age estimation

Accurate estimation of human adult age has always been a problem for anthropologists, archaeologists and forensic scientists. The main factor contributing to the difficulties is the high variability of physiological age indicators. However, confounding this variability in many age estimation applications is a systematic tendency for age estimates, regardless of physiological indicator employed, to assign ages which are too high for young individuals, and too low for older individuals. This paper shows that at least part of this error is the inevitable consequence of the statistical procedures used to extract an estimate of age from age indicators, and that the magnitude of the error is inversely related to how well an age indicator is correlated with age. The use of classical calibration over inverse calibration is recommended for age estimation. Am J Phys Anthropol 104:259–265, 1997. © 1997 Wiley-Liss, Inc.     

A novel β-thymosin from the sea urchin: extending the phylogenetic distribution of β-thymosins from mammals to echinoderms

The study of the phylogenetic distribution of the β-thymosin family is important to elucidate its biological function further. A new thymosin, designated as thymosin β₁₄, consisting of 40 amino acid residues and with a molecular weight of 4537 Da as determined by ion spray mass spectrometry, was isolated from the sea urchin. The N-terminus of this polypeptide is blocked by an acetyl group as found by matrix-assisted laser desorption mass spectrometric and amino acid analysis. The primary structure was elucidatd by Edman degradation of the HPLC-purified thymosin β₁₄ fragments produced by digestion with endoproteinase Asp-N and trypsin. Sequence comparison reveals that thymosin β₁₄ is 73% homologous to thymosin β₄, obtained from calf thymus. By isolating and characterising the structure of thymosin β₁₄ from the sea urchin, an invertebrate, substantial knowledge about the phylogenetic distribution and evolution of β-thymosins is gained. © 1997 European Peptide Society and John Wiley & Sons Ltd.