Effects of tree height on branch hydraulics, leaf structure and gas exchange in California redwoods

We examined changes in branch hydraulic, leaf structure and gas exchange properties in coast redwood ( Sequoia sempervirens ) and giant sequoia ( Sequoiadendron giganteum ) trees of different sizes. Leaf-specific hydraulic conductivity ( k _L) increased with height in S. sempervirens but not in S. giganteum , while xylem cavitation resistance increased with height in both species. Despite hydraulic adjustments, leaf mass per unit area (LMA) and leaf carbon isotope ratios ( δ ¹³C) increased, and maximum mass-based stomatal conductance ( g _mass) and photosynthesis ( A _mass) decreased with height in both species. As a result, both A _mass and g _mass were negatively correlated with branch hydraulic properties in S. sempervirens and uncorrelated in S. giganteum . In addition, A _mass and g _mass were negatively correlated with LMA in both species, which we attributed to the effects of decreasing leaf internal CO₂ conductance ( g _i). Species-level differences in wood density, LMA and area-based gas exchange capacity constrained other structural and physiological properties, with S. sempervirens exhibiting increased branch water transport efficiency and S. giganteum exhibiting increased leaf-level water-use efficiency with increasing height. Our results reveal different adaptive strategies for the two redwoods that help them compensate for constraints associated with growing taller, and reflect contrasting environmental conditions each species faces in its native habitat.     

Estimating Detection Probabilities of Waterfowl Broods From Ground-Based Surveys

ABSTRACT Brood:pair ratios could provide an economical method for assessing spatial or temporal variation in waterfowl productivity, but such estimators are severely biased by incomplete detection of broods. We conducted 3 sequential counts of 1,357 waterfowl broods in northeastern North Dakota, USA, and used closed-population mark-recapture models to estimate total brood abundance while controlling for variation in detection probabilities (p). Blue-winged teal (Anas discors) broods had the lowest average detection probability (p = 0.305), whereas diving-duck broods had the highest average detectability (p = 0.571). Detection was generally highest in morning or evening, but temporal patterns varied among species and there was no survey window that maximized detection probabilities for all species. Detection probabilities averaged 0.108 (SD = 0.056) higher for an experienced observer versus an inexperienced observer. Detection probabilities were 0.044 higher for roadside versus walk-up surveys and increased with increasing brood size, total brood abundance, survey date, wind speed, temperature, cloud cover, and amount of time spent surveying each wetland. Detection probabilities declined with increasing wetland size and amount of tall peripheral vegetation. Our mark-recapture results indicated that a traditional unreplicated brood survey would have missed 67.5% of estimated broods, summed over all species. Use of closed-population mark-recapture techniques provided an effective method for reducing this bias and identifying and quantifying factors that reduce detection probabilities of waterfowl broods. We recommend that future brood surveys incorporate 2 or 3 temporally segregated replicate counts to allow for formal estimation of detection probabilities.     

Assessing Ecoregional-Scale Habitat Suitability Index Models for Priority Landbirds

ABSTRACT Emerging methods in habitat and wildlife population modeling promise new horizons in conservation but only if these methods provide robust population-habitat linkages. We used Breeding Bird Survey (BBS) data to verify and validate newly developed habitat suitability index (HSI) models for 40 priority landbird species in the Central Hardwoods and West Gulf Coastal Plain/Ouachitas Bird Conservation Regions. We considered a species’ HSI model verified if there was a significant rank correlation between mean predicted HSI score and mean observed BBS abundance across the 88 ecological subsections within these Bird Conservation Regions. When we included all subsections, correlations verified 37 models. Models for 3 species were unverified. Rank correlations for an additional 5 species were not significant when analyses included only subsections with BBS abundance >0. To validate models, we developed generalized linear models with mean observed BBS abundance as the response variable and mean HSI score and Bird Conservation Region as predictor variables. We considered verified models validated if the overall model was an improvement over an intercept-only null model and the coefficient on the HSI variable in the model was >0. Validation provided a more rigorous assessment of model performance than verification, and models for 12 species that we verified failed validation. Species whose models failed validation were either poorly sampled by BBS protocols or associated with woodland and shrubland habitats embedded within predominantly open landscapes. We validated models for 25 species. Habitat specialists and species reaching their highest densities in predominantly forested landscapes were more likely to have validated models. In their current form, validated models are useful for conservation planning of priority landbirds and offer both insight into limiting factors at ecoregional scales and a framework for monitoring priority landbird populations from readily available national data sets.     

Can limited dispersal or biotic interaction explain the declining abundance of the whelk,Morula marginalba,at the edge of its range?

The southern range limit of the planktotrophic, intertidal whelk, Morula marginalba, occurs immediately to the north of the south‐east Australian biogeographical barrier and we predict that its range may be limited by dispersal and biotic interactions. The barrier includes several hundred kilometers without suitable habitat and is the convergence zone of major ocean currents. Within the barrier region, along‐shore larval transport is expected to be erratic, with water moving offshore to form long‐lived eddies. Through comparison of central and range edge populations, we test for evidence of recruitment limitation and interspecific competition with the whelk, Haustrum vinosum, which occurs sympatrically at the range edge. We found similar levels of recruitment and allozyme genetic variation within centre and edge populations where H. vinosum was absent, implying that populations are strongly interconnected. Nevertheless, recruitment and abundance of M. marginalba were lower at its extreme range limit, where it occurs with H. vinosum. Indeed, we detected significant inverse correlations between the abundance of these species, although their habitat use was similar and they consumed similar prey. These lines of evidence suggest a restricted recruitment across the barrier limits the range of M. marginalba but emphasize that multiple factors may act to set species range limits. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103 , 849–862.     

Foggy days and dry nights determine crown‐level water balance in a seasonal tropical montane cloud forest

The ecophysiology of tropical montane cloud forest (TMCF) trees is influenced by crown‐level microclimate factors including regular mist/fog water inputs, and large variations in evaporative demand, which in turn can significantly impact water balance. We investigated the effect of such microclimatic factors on canopy ecophysiology and branch‐level water balance in the dry season of a seasonal TMCF in Veracruz, Mexico, by quantifying both water inputs (via foliar uptake, FU) and outputs (day‐ and night‐time transpiration, NT). Measurements of sap flow, stomatal conductance, leaf water potential and pressure–volume relations were obtained in Quercus lanceifolia, a canopy‐dominant tree species. Our results indicate that FU occurred 34% of the time and led to the recovery of 9% (24 ± 9.1 L) of all the dry‐season water transpired from individual branches. Capacity for FU was independently verified for seven additional common tree species. NT accounted for approximately 17% (46 L) of dry‐season water loss. There was a strong correlation between FU and the duration of leaf wetness events (fog and/or rain), as well as between NT and the night‐time vapour pressure deficit. Our results show the clear importance of fog and NT for the canopy water relations of Q. lanceifolia.     

Effects of different mesenchymal stromal cell sources and delivery routes in experimental emphysema

We sought to assess whether the effects of mesenchymal stromal cells (MSC) on lung inflammation and remodeling in experimental emphysema would differ according to MSC source and administration route. Emphysema was induced in C57BL/6 mice by intratracheal (IT) administration of porcine pancreatic elastase (0.1 UI) weekly for 1 month. After the last elastase instillation, saline or MSCs (1×10⁵), isolated from either mouse bone marrow (BM), adipose tissue (AD) or lung tissue (L), were administered intravenously (IV) or IT. After 1 week, mice were euthanized. Regardless of administration route, MSCs from each source yielded: 1) decreased mean linear intercept, neutrophil infiltration, and cell apoptosis; 2) increased elastic fiber content; 3) reduced alveolar epithelial and endothelial cell damage; and 4) decreased keratinocyte-derived chemokine (KC, a mouse analog of interleukin-8) and transforming growth factor-β levels in lung tissue. In contrast with IV, IT MSC administration further reduced alveolar hyperinflation (BM-MSC) and collagen fiber content (BM-MSC and L-MSC). Intravenous administration of BM- and AD-MSCs reduced the number of M1 macrophages and pulmonary hypertension on echocardiography, while increasing vascular endothelial growth factor. Only BM-MSCs (IV > IT) increased the number of M2 macrophages. In conclusion, different MSC sources and administration routes variably reduced elastase-induced lung damage, but IV administration of BM-MSCs resulted in better cardiovascular function and change of the macrophage phenotype from M1 to M2.     

Changes in Ribonuclease Activity of Wheat Plants during Water Stress

RNases from control and water-stressed wheat seedlings were purified by ion exchange chromatography, gel filtration and gel electrophoresis. The enzyme appeared to be identical from both treatments and only one species was found. Subcellular distribution between soluble and particulate fractions was not changed by water stress treatment. Total quantity of RNase per plant was similar in control and water-stressed plants, although since the dry weight of treated plants was less, the activity per gram was significantly higher. Crude homogenates of leaf extracts contained an RNase inhibitor with a greater amount being present in control leaves. No evidence was found to indicate that new types of RNases are synthesized during water stress.     

Assessment of Canada Lynx Research and Conservation Needs in the Southern Range: Another Kick at the Cat

Abstract The ecology of Canada lynx (Lynx canadensis) and their main prey, snowshoe hares (Lepus americanus), is poorly understood in southern Canada and the contiguous United States compared to the boreal forest of Canada and Alaska, USA, where both species are well studied. However, given recent listing of lynx under the Endangered Species Act, accurate understanding of lynx and snowshoe hare ecology and conservation requirements in the United States is a high priority. We critically examined unchallenged perceptions and important research needs related to lynx and hare ecology and conservation at the southern extent of their range. Contrary to popular dogma, lynx do not require old-growth forest for denning, but further research on lynx and hare use of fragmented landscapes at lower latitudes is required. The contention that southern lynx are subject to higher interference or exploitative competition compared to their northern counterparts remains without strong empirical support. Lynx rely more on red squirrels (Tamiasciurus hudsonicus) and possibly other alternate prey at lower latitudes, but hares are the predominant food type for lynx across their range. Southern lynx and hare populations do not exhibit periodic cyclicity, but harvest statistics suggest that lynx abundance in the southern range is highly variable, implying that numerical fluctuations likely are fueled by immigration from Canada. Southern lynx population viability in the absence of ingress is suspect and thus maintaining connectivity with northern areas of occupancy should be a priority. Successful conservation of lynx populations in the contiguous United States will require 1) improved understanding of lynx population and habitat ecology at lower latitudes, 2) protection and management of large tracts of lynx and snowshoe hare habitat, and 3) ensured connectivity between lynx populations at the core and periphery of the species' range. However, in light of the numerous challenges facing conservation of populations of many species at their southern distributional limit, the long-term prognosis for lynx in the southern range currently is uncertain.     

Budding yeast Rif1 binds to replication origins and protects DNA at blocked replication forks

Despite its evolutionarily conserved function in controlling DNA replication, the chromosomal binding sites of the budding yeast Rif1 protein are not well understood. Here, we analyse genome‐wide binding of budding yeast Rif1 by chromatin immunoprecipitation, during G1 phase and in S phase with replication progressing normally or blocked by hydroxyurea. Rif1 associates strongly with telomeres through interaction with Rap1. By comparing genomic binding of wild‐type Rif1 and truncated Rif1 lacking the Rap1‐interaction domain, we identify hundreds of Rap1‐dependent and Rap1‐independent chromosome interaction sites. Rif1 binds to centromeres, highly transcribed genes and replication origins in a Rap1‐independent manner, associating with both early and late‐initiating origins. Interestingly, Rif1 also binds around activated origins when replication progression is blocked by hydroxyurea, suggesting association with blocked forks. Using nascent DNA labelling and DNA combing techniques, we find that in cells treated with hydroxyurea, yeast Rif1 stabilises recently synthesised DNA. Our results indicate that, in addition to controlling DNA replication initiation, budding yeast Rif1 plays an ongoing role after initiation and controls events at blocked replication forks.     

Chemorepellents in Paramecium and Tetrahymena

Although Paramecium has been widely used as a model sensory cell to study the cellular responses to thermal, mechanical and chemoattractant stimuli, little is known about their responses to chemorepellents. We have used a convenient capillary tube repellent bioassay to describe 4 different compounds that are chemorepellents for Paramecium and compared their response with those of Tetrahymena. The classical Paramecium t-maze chemokinesis test was also used to verify that this is a reliable chemorepellent assay. The first two compounds, GTP and the oxidant NBT, are known to be depolarizing chemorepellents in Paramecium but this is the first report of them as repellents in Tetrahymena. The second two compounds, the secretagogue alcian blue and the dye cibacron blue, have not previously been described as chemorepellents in either of these ciliates. Two other compounds, the secretagogue AED and the oxidant cytochrome c, were found to be repellents to Paramecium but not to Tetrahymena. The repellent nature of each of these compounds is not related to toxicity because cells are completely viable in all of them. More importantly, all of these repellents are effective at micromolar to nanomolar concentrations, providing an opportunity to use them as excitatory ligands in future works concerning their membrane receptors and possible receptor operated ion channels.