The land–atmosphere water flux in the tropics

Tropical vegetation is a major source of global land surface evapotranspiration, and can thus play a major role in global hydrological cycles and global atmospheric circulation. Accurate prediction of tropical evapotranspiration is critical to our understanding of these processes under changing climate. We examined the controls on evapotranspiration in tropical vegetation at 21 pan-tropical eddy covariance sites, conducted a comprehensive and systematic evaluation of 13 evapotranspiration models at these sites, and assessed the ability to scale up model estimates of evapotranspiration for the test region of Amazonia. Net radiation was the strongest determinant of evapotranspiration (mean evaporative fraction was 0.72) and explained 87% of the variance in monthly evapotranspiration across the sites. Vapor pressure deficit was the strongest residual predictor (14%), followed by normalized difference vegetation index (9%), precipitation (6%) and wind speed (4%). The radiation-based evapotranspiration models performed best overall for three reasons: (1) the vegetation was largely decoupled from atmospheric turbulent transfer (calculated from Ω decoupling factor), especially at the wetter sites; (2) the resistance-based models were hindered by difficulty in consistently characterizing canopy (and stomatal) resistance in the highly diverse vegetation; (3) the temperature-based models inadequately captured the variability in tropical evapotranspiration. We evaluated the potential to predict regional evapotranspiration for one test region: Amazonia. We estimated an Amazonia-wide evapotranspiration of 1370 mm yr⁻¹, but this value is dependent on assumptions about energy balance closure for the tropical eddy covariance sites; a lower value (1096 mm yr⁻¹) is considered in discussion on the use of flux data to validate and interpolate models.     

Culling Versus Density Effects in Management of a Deer Population

Abstract: Wildlife managers often manipulate hunting regulations to control deer populations. However, few empirical studies have examined the level of hunting effort (hunter-days) required to limit population growth and demographic effects through harvesting of females. Moreover, the relative importance of density effects on population growth has not been quantified. We reconstructed a sika deer [Cervus nippon] population over a period of 12 years (1990–2001) using age- and sex-specific harvest data. Using cohort analysis, we analyzed population dynamics, focusing on 1) the relationship between hunting effort and hunting-induced mortality rate, 2) relative contributions of hunting mortality and recruitment of yearlings to annual changes in population growth rate, and 3) annual variation in recruitment rate. Population size increased until 1998 and declined thereafter. The population growth rate changed more in response to annual changes in recruitment rate than hunting mortality rate. Temporal variation in recruitment rate was not controlled by birth rate alone; direct density dependence, intensities of hunting mortality for fawns, and for females (≥2 yr of age), which accounted for the fawn survival rate, were required as factors to explain temporal variation. Density effects on the recruitment rate were not strong enough to regulate the population within the study period; high hunting mortality, with intensive female harvesting, was necessary to prevent population growth. Hunting effort was a good predictor of the hunting mortality rate, and female harvest had a negative effect on the recruitment rate through fawn survival. We suggest that >3,500 hunter-days and prioritization of female harvesting are required to prevent increases in this deer population.     

Receptors to Dolichos biflorus Agglutinin

Dolichos biflorus agglutinin (DBA), a lectin specific to N-acetylgalactosamine residue, identifies cell surface markers on teratocarcinoma cells. These receptors are found in very limited types of adult tissues. In the present investigation, mouse embryos collected on days 1 (2-cell) to 3 (early blastocyst) were shown to be stained with FITC-conjugated DBA. Embryos homozygous for t ^w32 were also positively stained. These results suggest that receptors for DBA on preimplantation embryos include components distinct from Forssman, F9, and SSEA-1 antigens.     

Age‐dependent investment in death‐feigning behaviour in the sweetpotato weevil Cylas formicarius

Because life‐history theory predicts that risky behaviours such as mating should increase as life expectancy decreases, predatory avoidance is expected to decrease with age. However, this prediction has not been examined. In the present study, the effect of age on death‐feigning behaviour, a form of predatory avoidance behaviour in the sweetpotato weevil Cylas formicarius (Summers) (Coleoptera: Brentidae), is investigated by performing a longitudinal study. Because the effects of mating history and age usually cannot be distinguished, mating history is controlled. The results show that only female weevils decrease the investment in death‐feigning behaviour with age, whereas male weevils do not show any age‐related change. In addition, death‐feigning behaviour of mated females is longer than that of virgin females, possibly because additional mating partners would be not needed by mated females.     

Proliferation and Neoplastic Transformation of Pigment Cells in Metallothionein/ret Transgenic Mice

Although melanoma is a common human disease, there were few animal models in which melanoma developed at high incidence. To date, the Xiphophorus fish has been used as a model system to study melanoma formation. Studies on this fish showed the presence of a dominant oncogene, Tu, which encodes a transmembrane, tyrosine kinase of epidermal growth factor receptor type (Wittbrodt et al., Nature, 341:415–421, 1989). Recently, we succeeded in establishing novel transgenic mouse lines in which melanosis and melanocytic tumors developed stepwise by introducing another transmembrane tyrosine kinase oncogene, ret (Iwamoto et al., EMBO J., 10:3167–3175, 1991). In our transgenic mice, high levels of expression of the ret transgene induced proliferation and neoplastic transformation of melanin-producing cells. In addition, crossbreeding experiments between transgenic mice and W^v mice showed that the ret oncogene can also induce melanogenesis and melanocyte development in W^v/W^v mice.     

Effects of elevated CO2 on the size structure in even-aged monospecific stands of Chenopodium album

To investigate the effect of elevated CO₂ on the size inequality and size structure, even‐aged monospecific stands of an annual, Chenopodium album, were established at ambient and doubled CO₂ with high and low nutrient availabilities in open top chambers. The growth of individual plants was monitored non‐destructively every week until flowering. Elevated CO₂ significantly enhanced plant growth at high nutrients, but did not at low nutrients. The size inequality expressed as the coefficient of variation tended to increase at elevated CO₂. Size structure of the stands was analyzed by the cumulative frequency distribution of plant size. At early stages of plant growth, CO₂ elevation benefited all individuals and shifted the whole size distribution of the stand to large size classes. At later stages, dominant individuals were still larger at elevated than at ambient CO₂, but the difference in small subordinate individuals between two CO₂ levels became smaller. Although these tendencies were found at both nutrient availabilities, difference in size distribution between CO₂ levels was larger at high nutrients. The CO₂ elevation did not significantly enhance the growth rate as a function of plant size except for the high nutrient stand at the earliest stage, indicating that the higher biomass at elevated CO₂ at later stages in the high nutrient stand was caused by the larger size of individuals at the earliest stage. Thus the effect of elevated CO₂ on stand structure and size inequality strongly depended on the growth stage and nutrient availabilities.