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.     

Towards an understanding of how phloem amino acid composition shapes elevated CO2‐induced changes in aphid population dynamics

1. The performance of foliage feeders tends to decrease under elevated CO₂, but the responses of phloem‐feeding insects have been much more equivocal. As phloem tissues are less accessible than whole‐plant tissues, much less is known about how phloem composition is altered under elevated CO₂ and the mechanisms driving changes in aphid performance. 2. In this study, the plant mechanisms underlying the performance of Rhopalosiphum padi aphids on Hordeum vulgare (barley) grown under ambient (390 ppm) and elevated (700 ppm) CO₂ were examined. We used aphid stylectomy to sample pure phloem from plants in CO₂‐controlled conditions and high‐performance liquid chromatography to analyse phloem samples for amino acid concentrations. 3. Aphid abundance significantly increased by 127% under elevated CO₂. Consequently, plant biomass decreased under elevated CO₂ in trials with herbivores present, possibly due to the increased herbivore load, but increased when aphids were absent. The intrinsic rate of population increase (r_m) was significantly higher under elevated CO₂; however, there were no statistically significant effects on aphid fecundity or development time. The concentration of individual amino acids tended to increase, although these increases were statistically significant in only a few cases. A principal components analysis revealed that the relative abundance (mol %) of those amino acids considered essential for aphids tended to increase under elevated CO₂. 4. These results indicate that CO₂ may affect nutrient translocation in plants in ways that are contrary to predictions about nitrogen metabolite responses to CO₂. Such plant biochemical responses may underlie observations of improved phloem feeder performance under elevated CO₂.     

A Single-Sampling Hair Trap for Mesocarnivores

Abstract Although techniques to analyze and quantify DNA-based data have progressed, methods to noninvasively collect samples lag behind. Samples are generally collected from devices that permit coincident sampling of multiple individuals. Because of cross-contamination, substantive genotyping errors can arise. We developed a cost-effective (US$4.60/trap) single-capture hair trap for American martens (Martes americana). In the field, traps effectively targeted martens; >75% of all hair samples were identified as marten. Eighty percent of marten hair (n = 180) contained sufficient quality for DNA-based analyses. This effective and affordable trap can be used by managers to monitor mesocarnivore populations noninvasively.     

Residence Probability and Population Size of Red Knots During Spring Stopover in the Mid-Atlantic Region of the United States

ABSTRACT Weekly counts of western Atlantic red knots (Calidris canutus rufa) at their Delaware Bay migration stopover site have suggested a major decline since the 1980s. We estimated red knot spring passage population size in the New Jersey Coast-Delaware Bay region (DENJ; 2004 and 2006) and Virginia (VA; 2006 and 2007), USA, by correcting weekly aerial counts for mean daily residence probability between counts in a Monte-Carlo simulation. We used daily telemetry relocations in mark-resight models to estimate mean daily residence probability. Average daily residence probability was approximately 1.0 in mid-May, 0.96–0.97 in the week of 22 May, and 0.64–0.77 after May 28 in DENJ in 2004 and 2006 and in VA in 2006. Average daily residency was approximately 0.88 in VA in 2007 from 22 May to 5 June. No birds moved from VA to DENJ in 2006 and only 2 birds (5.5%) moved in 2007. Stopover population sizes (±SE) in DENJ were 17,108 ± 1,322 in 2004 and 19,555 ± 831 in 2006, and in VA were 7,224 ± 389 in 2006 and 8,332 ± 718 in 2007, significantly greater than peak aerial counts. Years with similar peak counts had different residence probabilities; hence, adjustments for turnover should be used in the future to assess annual population changes. Our results suggest that VA can support a significant portion of this red knot subspecies during migration in at least some years. Managing red knots for recovery should entail improving our understanding of the use of other Atlantic Coast sites and protecting key coastal habitat from disturbance and development.     

Patterns of Root Respiration Associated with the Induction of Aluminium Tolerance in Phaseolus vulgaris L.

Aluminium (Al) tolerance in an Al-tolerant cultivar of Phaseolusvulgaris L. (‘Dade’) was found to be an inducibletrait. Upon exposure to 10 µM Al, the rate of root elongationwas inhibited in comparison to controls. During the following72 h, the rate of elongation returned to levels comparable tocontrols. In contrast, root elongation of an Al-sensitive cultivar(‘Romano’) did not recover after exposure to Al.In Dade, the resumption of root elongation following exposureto Al was accompanied by increased rates of root respiration,whereas respiration rates slowly declined over the 72 h treatmentperiod in Romano. When partitioned into growth and maintenanceexpenditures, a larger proportion of root respiration of Dadeexposed to Al was allocated to maintenance processes, potentiallyreflecting diversion of energy to metabolic pathways that offsetthe adverse effects of Al toxicity. Romano did not show sucha pattern and respiration associated with both growth and maintenancewas reduced after exposure to Al. Root and shoot growth of bothcultivars were also measured to determine the effects of long-term(21 d) exposure to 10 µM Al. Dade plants exposed to Alexhibited enhanced growth in comparison to controls, whereasRomano plants were characterized by reduced shoot and root growth.Modelling the time-course of root respiration and measuringthe long-term growth responses to Al is a valuable method ofelucidating respiratory costs of stress tolerance. Key words: Aluminium, differential tolerance, maintenance respiration, Phaseolus vulgaris, root respiration     

Characterization of the Galactose-Specific Binding Activity of a Purified Soluble Entamoeba histolytica Adherence Lectin

ABSTRACT. We studied galactose (Gal)-specific binding of the soluble purified 260-kDa Entamoeba histolytica adherence protein to glycosylation deficient Chinese hamster ovary (CHO) cell mutants. Our goal was to further define the lectin's functional activity and carbohydrate receptor specificity. The adherence protein was purified by acid elution from an immunoaffnity column; however, exposure of the surface membrane lectin on viable trophozoites to identical acid pH conditions had no effect on carbohydrate binding activity. Saturable Gal-specific binding of soluble lectin to parental CHO cells was demonstrated at 4°C by radioimmunoassay; the dissociation coefficient (Kd was 2.39 × 10^?8 M^?1 with 5.97 × 10⁴ lectin receptors present per CHO cell. Gal-specific binding of lectin to Lec2 CHO cell mutants, which have increased N- and O-linked terminal Gal residues on cell surface carbohydrates, was increased due to an enhanced number of receptors (2.41 × 10⁵/cell) rather than a significantly reduced dissociation constant (4.93 × 10^?8 M^?1). At 4°C, there was no measurable Gal-specific binding of the adherence protein to the Lec and IdlD.Lecl CHO mutants, which contain surface carbohydrates deficient in terminal Gal residues. Binding of lectin (20 μg/ml) to CHO cells was equivalent at 4°C and 37°C and unaltered by adding the microfilament inhibitor, Cytochalasin D (10 μg/ml). Gal-specific binding of the lectin at 4°C was calcium independent and reduced by 81% following adsorption of only 0.2% of the lectin to CHO cells. In summary, these findings indicate that the purified E. histolytica adherence lectin demonstrates saturable Gal-specific binding to 1–6 branched-N-linked and not O-linked galactose terminal cell surface carbohydrates; however, apparently only a small percentage of purified amebic lectin molecules actually possess galactose binding activity.     

Flagellar Morphology in Stumpy-Flagella Mutants of Chlamydomonas reinhardtii1

Sixteen new mutants of the biflagellate green alga Chlamydomonas reinhardtii with either stumpy-flagella or no flagella at all were examined by electron microscopy. Four of the mutants were found to carry short bulbous flagella containing amorphous electron-dense material which may represent unassembled flagellar protein. Basal bodies of normal ultrastructure were present in all mutants. Dikaryon dominance tests indicated that the stumpy mutations were recessive to wild-type in all cases tested. Stumpy mutations also conferred a measure of detergent resistance to Chlamydomonas, apparently by affecting the detergent-solubility of the flagellar membrane.