A Comparison of Two Modeling Approaches for Evaluating Wildlife-Habitat Relationships

ABSTRACT Studies of resource selection form the basis for much of our understanding of wildlife habitat requirements, and resource selection functions (RSFs), which predict relative probability of use, have been proposed as a unifying concept for analysis and interpretation of wildlife habitat data. Logistic regression that contrasts used and available or unused resource units is one of the most common analyses for developing RSFs. Recently, resource utilization functions (RUFs) have been developed, which also predict probability of use. Unlike RSFs, however, RUFs are based on a continuous metric of space use summarized by a utilization distribution. Although both RSFs and RUFs predict space use, a direct comparison of these 2 modeling approaches is lacking. We compared performance of RSFs and RUFs by applying both approaches to location data for 75 Rocky Mountain elk (Cervus elaphus) and 39 mule deer (Odocoileus hemionus) collected at the Starkey Experimental Forest and Range in northeastern Oregon, USA. We evaluated differences in maps of predicted probability of use, relative ranking of habitat variables, and predictive power between the 2 models. For elk, 3 habitat variables were statistically significant (P < 0.05) in the RSF, whereas 7 variables were significant in the RUF. Maps of predicted probability of use differed substantially between the 2 models for elk, as did the relative ranking of habitat variables. For mule deer, 4 variables were significant in the RSF, whereas 6 were significant in the RUF, and maps of predicted probability of use were similar between models. In addition, distance to water was the top-ranked variable in both models for mule deer. Although space use by both species was predicted most accurately by the RSF based on cross-validation, differences in predictive power between models were more substantial for elk than mule deer. To maximize accuracy and utility of predictive wildlife-habitat models, managers must be aware of the relative strengths and weaknesses of different modeling techniques. We conclude that although RUFs represent a substantial advance in resource selection theory, techniques available for generating RUFs remain underdeveloped and, as a result, RUFs sometimes predict less accurately than models derived using more conventional techniques.     

Resistance to halo-blight in the Cambridge accessions V4604 and V4058 of Phaseolus beans

V4604, a Cambridge University accession of Phaseolus vulgaris, had a high degree of leaf resistance to race 1 of Pseudomonas phaseolicola and partial resistance to race 2. Genetic control of resistance to race 1 was by a major dominant gene which is also present in the cv. Red Mexican. The partial resistance of V4604 to race 2 was under polygenic control, as was the low level resistance to race 2 in V4058.     

The Effect of Sugars and Polyols on the Heat Resistance and Morphology of Osmophilic Yeasts

Heat resistance at 65· of Saccharomyces rouxii and Schizosaccharomyces pombe was enhanced in solutions of sugars and polyols, containing 0·1 M-phosphate buffer, pH 6·5, at a water activity of 0·95. Resistance was maximum in solutions of sucrose, less in sorbitol and least in solutions of glucose, fructose and glycerol. Examination of the yeast cells by phase contrast microscopy showed shrinkage of cells in all solutions. Electron microscopy of freeze-etched preparations of Sacch. rouxii indicated plasmolysis of cells in sucrose and sorbitol solutions only.     

The Influence of Light and Potassium Nitrate on the Dormancy and Germination of Avena fatua L. (wild oat) Seed Stored Buried Under Natural Conditions

The influence of light and potassium nitrate on the dormancyand germination of Avena fatua L. seed stored buried under naturalconditions was studied over a 13 month period. Natural emergenceof seedlings from buried seed in relation to rainfall and temperatureregimes and fluctuation was also monitored. The present findingsshow that potassium nitrate is stimulatory to germination onlyin the light and, further, that seeds from two positions inthe spikelet respond differently. Key words: Dormancy, Light, Nitrate     

Anatomical and molecular systematics of Asteliaceae and Hypoxidaceae

The astelioid group of asparagoid lilies (Lilianae - Asparagales) comprises Hypoxidaceae, Asteliaceae, Blandfordia and Lanaria. New information is presented on astelioid anatomy, together with a review of other systematic characters. These data are analysed in the context of recent evidence from rbc L nucleotide sequences that astelioids are related to orchids, and that astelioids and orchids (plus Alania and Borya ) form a clade that is sister to all other asparagoid taxa. Hypoxidaceae and Asteliaceae differ from each other in several respects, but there are certain characters linking the two families, notably branched hairs and mucilage canals, unusual characters in Lilianae. Family diagnoses are upheld, but the precise relationships of Blandfordia and Lanaria are still poorly supported within the astelioid clade.     

Ethirimol-sensitivity in populations of Erysiphe graminis from plots of spring barley

Barley plots, cv. Proctor were sown with either ethirimol-treated or untreated seed. At seedling emergence, plots were inoculated with isolates of Erysiphe graminis either sensitive or insensitive to ethirimol, or left uninoculated. Mildew samples taken from the coleoptile leaves of seedlings, and later from leaf 6 (next but one to the flag leaf) were compared for ethirimol sensitivity using probit analysis. Probit lines were derived using ‘Wadley's analysis’. This analysis uses the number of survivors to estimate the total number of individuals originally present. In the test for ethirimol sensitivity a count of colonies on inoculated test leaves was taken to represent survivors. Microscopic counting of the original inoculum was thus avoided. The analyses snowed that the initial leaf inoculation treatments established mildew populations in the plots, which differed considerably in ethirimol sensitivity. Some 6 wk after inoculation the levels of sensitivity in these populations remained unchanged even though inoculum coming into the experiment from external sources was often much more insensitive than the mildew in some plots. Probit lines of response to ethirimol had shallow slopes, showing that large variability exists in the pathogen for this character.     

Development of N2-fixing nodules on the wetland legume Lotus uliginosus exposed to conditions of flooding

Seeds of the wetland legume, Lotus uliginosus , were germinated and grown in vermiculite which was either continuously flooded or well-drained. Plants from both treatments were infected by Mesorhizobium loti strain DUS341 via a 'classical' root hair pathway, although some flooded plants appeared to be infected via enlarged epidermal cells. Subsequent to infection by M. loti , nodule meristems, which had developed within the root outer cortex, were penetrated by infection threads that released bacteria into the meristematic cells. The infection threads and infection droplets were immunogold labelled with monoclonal antibodies (MAC265 and MAC236) that recognize epitopes (at approx. 155/170 and 170/210 kDa, respectively) on a glycoprotein component of the matrix that surrounded the bacteria within the threads or droplets. Although labelling of infection threads or infection droplets with MAC236 was stronger than that with MAC265, both antibodies strongly labelled material occluding intercellular spaces in the cortices of developing nodules that had not yet expressed nitrogenase (as determined by a lack of signal after immunogold labelling with an antibody raised against nitrogenase component II). After 60 d, nitrogenase activity, shoot and root dry weights, and nodule fresh weight per plant did not differ between the treatments. After a further 30 d submergence, the flooded stems developed extensive aerenchyma and there was profuse development of (nodulated) adventitious roots. Nodules also formed at the junction of adventitious roots and the subtending stem and these were connected vascularly to a small stalk of tissue which gave rise to both a nodule and an adventitious root. The flooded nodules had prominent lenticels, and possible air pathways from the atmosphere to the nitrogen-fixing bacteroids are discussed.     

Resistance management strategies in malaria vector mosquito control. Baseline data for a large-scale field trial against Anopheles albimanus in Mexico

Abstract. A high level of DDT resistance and low levels of resistance to organophosphorus, carbamate and pyrethroid insecticides were detected by discriminating dose assays in field populations of Anopheles albimanus in Chiapas, southern Mexico, prior to a large-scale resistance management project described by Hemingway et al. (1997) . Biochemical assays showed that the DDT resistance was caused by elevated levels of glutathione S-transferase (GST) activity leading to increased rates of metabolism of DDT to DDE. The numbers of individuals with elevated GST and DDT resistance were well correlated, suggesting that this is the only major DDT resistance mechanism in this population. The carbamate resistance in this population is conferred by an altered acetylcholinesterase (AChE) -based resistance mechanism. The level of resistance observed in the bioassays correlates with the frequency of individuals homozygous for the altered AChE allele. This suggests that the level of resistance conferred by this mechanism in its heterozygous state is below the level of detection by the WHO carbamate discriminating dosage bioassay. The low levels of organophosphate (OP) and pyrethroid resistance could be conferred by either the elevated esterase or monooxygenase enzymes. The esterases were elevated only with the substrate pNPA, and are unlikely to be causing broad spectrum OP resistance. The altered AChE mechanism may also be contributing to the OP but not the pyrethroid resistance. Significant differences in resistance gene frequencies were obtained from the F₁ mosquitoes resulting from adults obtained by different collection methods. This may be caused by different insecticide selection pressures on the insects immediately prior to collection, or may be an indication that the indoor- and outdoor-resting A. albimanus collections are not from a randomly mating single population. The underlying genetic variability of the populations is currently being investigated by molecular methods.