Is productivity of mesic savannas light limited or water limited? Results of a simulation study

A soil–plant–atmosphere model was used to estimate gross primary productivity (GPP) and evapotranspiration (ET) of a tropical savanna in Australia. This paper describes model modifications required to simulate the substantial C4 grass understory together with C3 trees. The model was further improved to include a seasonal distribution of leaf area and foliar nitrogen through 10 canopy layers. Model outputs were compared with a 5‐year eddy covariance dataset. Adding the C4 photosynthesis component improved the model efficiency and root‐mean‐squared error (RMSE) for total ecosystem GPP by better emulating annual peaks and troughs in GPP across wet and dry seasons. The C4 photosynthesis component had minimal impact on modelled values of ET. Outputs of GPP from the modified model agreed well with measured values, explaining between 79% and 90% of the variance and having a low RMSE (0.003–0.281 g C m^?2 day^?1). Approximately, 40% of total annual GPP was contributed by C4 grasses. Total (trees and grasses) wet season GPP was approximately 75–80% of total annual GPP. Light‐use efficiency (LUE) was largest for the wet season and smallest in the dry season and C4 LUE was larger than that of the trees. A sensitivity analysis of GPP revealed that daily GPP was most sensitive to changes in leaf area index (LAI) and foliar nitrogen (N_f) and relatively insensitive to changes in maximum carboxylation rate (V_cmax), maximum electron transport rate (J_max) and minimum leaf water potential (ψ_min). The modified model was also able to represent daily and seasonal patterns in ET, (explaining 68–81% of variance) with a low RMSE (0.038–0.19 mm day^?1). Current values of N_f, LAI and other parameters appear to be colimiting for maximizing GPP. By manipulating LAI and soil moisture content inputs, we show that modelled GPP is limited by light interception rather than water availability at this site.     

BIOCHEMICAL GENETICS AND SPECIES RELATIONSHIPS WITHIN THE GENUS HALIOTIS (GASTROPODA: HALIOTIDAE)

The marine gastropod genus Haliotis includes 60–70 describedspecies distributed along the coastlines of most continentsand of islands in the Pacific, Indian and Atlantic Oceans. Theyoccur in tropical and temperate regions of both hemispheres.Protein gel electrophoresis revealed genetic relationships amongseventeen temperate species; Haliotis rubra, H. conicopora,H. laevigata, H. roei, H. scalaris, H. cyclobates, H. coccoradiata,H. midae, H. iris, H, austrails, H. virginea, H. discus hannai,H. kamtschaktkana, H. rufescens, H. corrugata, H. cracherodii,and H. fulgens. Northern temperate species clustered together, but northernand southern species shared so few allelic states that theycould not be united on a single genetic distance diagram. Nordid all the southern temperate species form a single cluster.In addition, genetic characters do not support previous sub-genericdivisions within Haliotis. The observed genetic distances betweensome species were found to be large, and in some cases larger,than those normally associated with species in the same genus.These relationships provide insight into the evolutionary historyand biogcography of the group and emphasize the need for taxonomicreview based on both morphological and genetic information. (Received 8 September 1992; accepted 1 February 1993)     

A visual DNA probe for detection of enterotoxigenic Escherichia coli by colony hybridization

A colony hybridization method for visual detection of heat-labile enterotoxin (LT)-producing Escherichia coli has been developed. The interchangeability of probe DNA in the system offers the advantage of a more definitive indicator and detection procedure over current plating procedures. Preliminary studies have demonstrated complete specificity of the visual probe for target DNA. This model system has potential for use as a more definitive indicator method for the examination of foods and wastewater for LT toxin genes.     

Emergence of Zoonotic Canine Leishmaniasis in the United States: Isolation and Immunohistochemical Detection of Leishmania infantum from Foxhounds from Virginia.

ABSTRACT. Previously considered an exotic disease, canine leishmaniasis caused by Leishmania infantum has recently been detected within the foxhound population in the United States and parts of Canada. Leishmania infantum is the etiologic agent of visceral leishmaniasis in many areas of the world and dogs are considered a major reservoir host for human Leishmania infections. Human visceral leishmaniasis has recently emerged as an opportunistic infection among individuals co-infected with HIV/AIDS and in persons taking immunosuppressive drugs. We report the isolation of L. infantum from 3 naturally infected foxhounds from Virginia by culture of popliteal lymph node and bone marrow, and the development of an immunohistochemical test to detect the parasite in tissues.     

Effects of fungicides applied to seed potato tubers at harvest or after grading on fungal storage diseases and plant development

An assessment was made over 3 years of the efficacy of thiabendazole, 2–aminobutane and a formulation of a mixture of thiabendazole and 2–aminobutane in controlling gangrene, skin spot and dry rot when applied either at harvest or after grading at different dates during the storage season.
After harvest applications, the incidence of gangrene was least on tubers treated with the mixture and generally greatest with thiabendazole. When applied after grading the efficacy of the fungicides was not affected by date of grading. Although 2–aminobutane applications at harvest or after grading were equally effective in controlling gangrene, thiabendazole and the mixture were less effective after grading where gangrene was prevalent in a stock. Thiabendazole and the mixture gave good control of dry rot when applied at harvest but were less effective when applied after grading, particularly late in the storage season. Dry rot was sometimes more prevalent on tubers fumigated with 2–aminobutane, especially those treated after grading. Skin spot was more effectively controlled by the mixture and 2–aminobutane than by thiabendazole but, with applications after grading, the efficacy of all fungicides declined the later the date of grading.
Plants grown from tubers treated with the mixture or its 2–aminobutane glycollate constituent exhibited characteristics associated with genetic variation.     

Infestation of Chocolate-based Products: Insects Responsible and Origins of Contamination

In response to on-going consumer complaints regarding insect infestation of chocolate-based products manufactured at a factory in southern Australia, research was undertaken to determine the insects responsible for infestation and locate the points along the manufacture/distribution network where insect pests were most likely to be entering the produce. Phycitine moths were responsible for almost all cases of product infestation, with most infestation occurring after goods had been packaged. Methods of identifying storage environments suspected of unknowingly harbouring phycitine populations or of regularly handling infested goods are discussed. the detrimental consequences for the manufacturer, and for the processed food industry in general, of the presence of stored product insects in wholesale and retail outlets are also considered.     

Expanding northward: influence of climate change,forest connectivity,and population processes on a threatened species' range shift

Species' ranges are dynamic, shifting in response to a large number of interrelated ecological and anthropogenic processes. Climate change is thought to be one of the most influential drivers of range shifts, but the effects of other confounded ecological processes are often ignored even though these processes may modify expected range responses to climate change. To determine the relative effects of climate, forest availability, connectivity, and biotic processes such as immigration and establishment, we examine range changes occurring in a species of bird, the Hooded Warbler (Wilsonia citrina). We focus predominantly on the periphery of the species' northern range in Canada but we also examine data from the entire species' range. Nesting records in southern Ontario were obtained from two breeding bird Atlases of Ontario separated by a period of 20 years (1981–1985 and 2001–2005), and the rate of range expansion was estimated by comparing the number of occupied areas in each Atlas. Twelve hypotheses of the relationship between the rate of range expansion and factors known to influence range change were examined using model‐selection techniques and a mixed modeling approach (zero‐inflated Poisson's regression). Cooler temperatures were positively related to a lack of range expansion indicating that climate constrained the species' distribution. Establishment probability (based on the number of occupied, neighboring Atlas squares) and immigration from populations to the south (estimated using independent data from the North American Breeding Bird Survey) were also important predictors of range expansion. These biotic process variables can mask the effects of forest availability and connectivity on range expansion. Expansion due to climate change may be slower in fragmented systems, but the rate of expansion will be influenced largely by biotic processes such as proximity to neighboring populations.