Subtle Environmental Differences Research Articles

Understory palms are not canopy palms writ small: Factors affecting Amazonian understory palms within riparian zones and across the landscape

Understory palms are subject to different ecological pressures than those experienced by canopy palms, but most studies do not distinguish between understory and canopy palms, or include only canopy palms. Much of the variation in the taxonomic composition of understory palms in the Amazon is concentrated in riparian zones. However, abiotic characteristics of the riparian zone that influence this variation are underexplored or have been modeled only through additive relationships. Our objectives were to determine (1) if the abundance of understory palms is related to the abundance of canopy palms, (2) how topographic and soil variables, and their interactions, affect variation in composition of understory-palm assemblages across the entire landscape, which includes riparian and non-riparian zones, and (3) how understory-palm assemblages vary in species composition along streams as a result of variation in abiotic factors and their interactions within the riparian zone. We sampled 40 riparian areas and analyzed the data in combination with existing data from 72 non-riparian plots. Plots (250 m × 4 m) were distributed across 64 km2 of a terra-firme forest (Reserva Ducke) covering two major drainage basins that differ in topography and soil characteristics. Abundances of understory and canopy palms have opposite relationships to the same environmental variables and, therefore, should not be treated as a single group. In addition, interactions among environmental factors at the mesoscale (entire landscape) and at the local scale (riparian zone), generate compositional turnover even among sites with only subtle environmental differences. Stream discharge and soil structure are among the first variables to be affected by human occupation of riparian zones, which indicates that a better understanding of interactions between environmental predictors and a landscape approach will be necessary to conserve Amazonian understory palms.

Non‐Chained, Non‐Interacting, Stable Single‐Domain Magnetite Octahedra in Deep‐Sea Red Clay: A New Type of Magnetofossil?

AbstractMagnetic detection and classification of magnetofossils have been proposed as potential tools for paleoenvironmental studies. Magnetosomes in bacterial species living in different environmental conditions exhibit different grain morphologies and chain configurations, which determine their magnetic properties. Recently, abundant magnetofossils have been reported from unfossiliferous pelagic red clay. However, little is known about their geometry and magnetic properties. Here we report very low coercivity biogenic magnetite in red clay from Ocean Drilling Program (ODP) Site 777 in the northern Mariana Basin. Analyzed sediment showed non‐interacting, stable single‐domain‐like magnetic behaviors. Acquisition of isothermal remanence was decomposed into five components, and a component with mean coercivity below 10 mT accounted for around 25 % of the remanence in some samples. Based on comparisons with semi‐quantitative transmission electron microscopy observations of magnetic extracts, this component appears to be carried by octahedral grains with size and shape very similar to biogenic magnetite in red clay from other sites. Micromagnetic calculations indicated that isolated maghemite octahedra may be responsible for the observed low coercivity component. Based on these results, we conclude that the low coercivity component represents non‐chained biogenic magnetite that has been oxidized to maghemite. The crystal morphology, geological setting, and lithology do not suggest unusual environmental conditions for ODP Site 777, so the relative amount of chained versus non‐chained grains may represent subtle environmental differences. We suggest that non‐chained magnetofossils may be widespread in deep‐sea sediments. Some methods could overlook the presence of non‐chained magnetite, affecting the identification and quantification of magnetofossils.

Incipient speciation in Oncocyclus irises: Eco-geographic isolation and genetic divergence with no reproductive isolation?

The establishment of reproductive isolation is considered to be an ultimate result of ecological speciation, but empirical evidence for the latter is limited. We hypothesized that in the absence of inter-specific gene flow and with subtle environmental differences, local adaptation will not require trade-offs in performance across environments and therefore will not result in reproductive isolation. We tested this hypothesis on four iris species, Iris atrofusca, I. atropurpurea, I. petrana and I. mariae, which have non-overlapping geographical distributions, grow naturally in different environmental conditions with respect to amount of rainfall and soil type, and possess suites of diagnostic traits that previously were assumed to result from local selection. We analyzed their genetic (AFLP) and quantitative trait divergence (by means of a common garden experiment), conducted a habitat suitability analysis, examined experimentally the effects of soil type and water availability on plant performance, and tested for postzygotic reproductive isolation using a crossing experiment. Our results supported the hypothesis that eco-geographical isolation does not necessarily lead to local adaptation or to postzygotic reproductive isolation when environmental differences are subtle. Thus, we obtained some evidence that the desert I. atrofusca was reproductively isolated from coastal I. atropurpurea, but not from desert I. mariae, although genetically the first two are more similar to each other than I. atrofusca is to I. mariae.

Understanding Protein Function Through an Ensemble Description: Characterization of Functional States by 19F NMR.

Protein function is a consequence of a complex and dynamic equilibrium between allosterically coupled functional states. However, it is often difficult to distinguish the representative members of an ensemble by spectroscopic means. 19F NMR is particularly useful in this regard owing to the sensitivity of its chemical shift to subtle differences in environment. Here, we address aspects of 19F NMR relevant to the study of ensembles. In particular, we discuss current trends toward: (1) 19F-reporters that can be biosynthetically incorporated into proteins, (2) Approaches to chemical tagging of proteins by 19F reporters, (3) Improving delineation of states by 19F NMR, (4) Distinguishing states by (19F NMR-based) topology measurements that focus on solvent exposure and hydrophobicity, (5) Relaxation experiments and simple approaches to delineating states in fast and slow exchange, (6) Extending resolution of states by 19F NMR, and (7) Validating 19F NMR spectroscopy by computational methods. Many of these advances are demonstrated through recent 19F NMR studies of a homodimeric enzyme, fluoroacetate dehalogenase.

Accurate Quantification of N-Glycolylneuraminic Acid in Therapeutic Proteins Using Supramolecular Mass Spectrometry.

Practical applications of innovative host-guest systems are challenging because of unexpected guest competitors and/or subtle environmental differences. Herein, a supramolecular mass spectrometry (MS)-based method using a synthetic host, cucurbit[7]uril (CB[7]), was developed for identifying and quantifying N-glycolylneuraminic acid (Neu5Gc) in therapeutic glycoproteins, which critically reduces drug efficacy. The development of a reliable derivatization-free analytical method for Neu5Gc is highly challenging because of the interference by the abundant N-acetylneuraminic acid (Neu5Ac). CB[7] recognized the subtle structural differences between Neu5Gc and Neu5Ac. Distinct host-guest interactions between CB[7] and the two sialic acids produced a highly linear relationship between the complexation and concentration proportions of the two sialic acids in MS. Furthermore, the developed method had sub-picomolar quantification limits and a wide range of applicability for diverse glycoproteins, demonstrating the potential utility of this method as a reliable assay of Neu5Gc in therapeutic glycoproteins.

Relationships Between Maternal Engorgement Weight and the Number, Size, and Fat Content of Larval Ixodes scapularis (Acari: Ixodidae).

The relationship between engorgement weight of female Ixodes scapularis Say and characteristics of offspring was studied using field-collected females fed on rabbits in the laboratory. The number of eggs laid was positively related to maternal engorgement weight in one trial, and larval size (estimated by scutal area) was positively related to maternal engorgement weight in the other. These results suggest a trade-off in number of eggs produced versus average size of offspring, possibly determined during late engorgement. The adults for the two trials were collected from different sites in southern Rhode Island and in different seasons (the fall adults were newly emerged, while the spring adults had presumably lived through the winter), so it is not clear whether these results reflect genetic differences or subtle environmental differences between trials. Percent egg hatch and average fat content of larvae were not related to female engorgement weight. We present a modified method to measure lipid content of pooled larval ticks.

Insect prey characteristics affecting regional variation in chimpanzee tool use

It is an ongoing interdisciplinary pursuit to identify the factors shaping the emergence and maintenance of tool technology. Field studies of several primate taxa have shown that tool using behaviors vary within and between populations. While similarity in tools over spatial and temporal scales may be the product of socially learned skills, it may also reflect adoption of convergent strategies that are tailored to specific prey features. Much has been claimed about regional variation in chimpanzee tool use, with little attention to the ecological circumstances that may have shaped such differences. This study examines chimpanzee tool use in termite gathering to evaluate the extent to which the behavior of insect prey may dictate chimpanzee technology. More specifically, we conducted a systematic comparison of chimpanzee tool use and termite prey between the Goualougo Triangle in the Republic of Congo and the La Belgique research site in southeast Cameroon. Apes at both of these sites are known to use tool sets to gather several species of termites. We collected insect specimens and measured the characteristics of their nests. Associated chimpanzee tool assemblages were documented at both sites and video recordings were conducted in the Goualougo Triangle. Although Macrotermitinae assemblages were identical, we found differences in the tools used to gather these termites. Based on measurements of the chimpanzee tools and termite nests at each site, we concluded that some characteristics of chimpanzee tools were directly related to termite nest structure. While there is a certain degree of uniformity within approaches to particular tool tasks across the species range, some aspects of regional variation in hominoid technology are likely adaptations to subtle environmental differences between populations or groups. Such microecological differences between sites do not negate the possibility of cultural transmission, as social learning may be required to transmit specific behaviors among individuals.

Methane Emissions and Production Potentials of Forest Swamp Wetlands in the Eastern Great Xing’an Mountains, Northeast China

Measurements of methane flux at a few inundated sites in China have been extrapolated to obtain estimates on a national scale. To enable those national estimates to be refined and to compare flux from geographically separated sites comprising the same wetland types, we used a closed chamber method to measure methane flux in uninundated Betula platyphylla-and Larix gmelinii-dominated peatlands in the Northeast China. Our measurements were taken from both vegetated and bare soil surfaces, and we compared flux with environmental measures including vegetation biomass, soil temperature and soil characteristics. We found that methane flux was low, and that there were no significant differences between wetland types, indicating that environmental influences were dominant. We found that flux was positively correlated to temperature in the surface layers of the soil, the above-ground biomass of the shrub and herb layers, total soil carbon and total soil nitrogen; and we suggest that emissions may be due to anaerobic microcosms in the surface layers. The methane production potentials of the soils were low and similar between both sites but inconsistent with the differences between fluxes, and inconsistent with production potentials and fluxes reported from the same wetland types elsewhere, indicating that there were subtle environmental differences between wetlands classed as being of the same type. Differences between fluxes in vegetated chambers with bare soil chambers were insignificant, indicating that no methane emission through aerenchyma occurred at our sites. We concluded that wetland type was not an accurate predictor of methane flux.

An Estuarine Habitat Classification for a Complex Fjordal Island Archipelago

Spatial patterns of estuarine biota suggest that some nearshore ecosystems are functionally linked to interacting processes of the ocean, watershed, and coastal geomorphology. The classification of estuaries can therefore provide important information for distribution studies of nearshore biodiversity. However, many existing classifications are too coarse-scaled to resolve subtle environmental differences that may significantly alter biological structure. We developed an objective three-tier spatially nested classification, then conducted a case study in the Alexander Archipelago of Southeast Alaska, USA, and tested the statistical association of observed biota to changes in estuarine classes. At level 1, the coarsest scale (100–1000’s km2), we used patterns of sea surface temperature and salinity to identify marine domains. At level 2, within each marine domain, fjordal land masses were subdivided into coastal watersheds (10–100’s km2), and 17 estuary classes were identified based on similar marine exposure, river discharge, glacier volume, and snow accumulation. At level 3, the finest scale (1–10’s km2), homogeneous nearshore (depths <10 m) segments were characterized by one of 35 benthic habitat types of the ShoreZone mapping system. The aerial ShoreZone surveys and imagery also provided spatially comprehensive inventories of 19 benthic taxa. These were combined with six anadromous species for a relative measure of estuarine biodiversity. Results suggest that (1) estuaries with similar environmental attributes have similar biological communities, and (2) relative biodiversity increases predictably with increasing habitat complexity, marine exposure, and decreasing freshwater. These results have important implications for the management of ecologically sensitive estuaries.

Distribution of diatoms and mollusks in shallow lakes from the semiarid Pampa region, Argentina: Their relative paleoenvironmental significance

The aim of this study was to assess the potential of diatoms and mollusks as paleoenvironmental indicators in semiarid lakes of the Argentinean Pampas. At each lake, physical and chemical variables were quantified, and diatoms and mollusks collected. The relationships between environmental variables and biological assemblages were explored through ordination techniques. Lakes were highly alkaline (pH 9.5–10.5), and varied significantly in conductivity (0.2–15.7mS/cm) and hardness (120–1874mg/l CaCO3). A total of 79 diatom and two mollusk species were identified. The highest percentage variance in diatom data was explained by hardness, conductivity, and mud percentage. Mollusk variability was significantly related to conductivity, hardness, and vegetation cover. Diatom-based ordination of sites accurately reflected the main environmental gradients characteristic of the region, while the resolution provided by mollusk-based ordinations was lower, mainly as consequence of the wide ranges of tolerance to hardness and conductivity exhibited by the two species represented. Hence, while the use of mollusks as paleoenvironmental indicators is only valid at a large, regional scale, diatoms allow discriminating local conditions and subtle environmental differences. As a consequence, the results emphasize the use of mollusks as qualitative and semi-quantitative indicators, while the strong statistical relationship between diatoms and climate-driven environmental parameters highlights their potential use as quantitative indicators of Quaternary climatic changes in the semiarid Pampas.

Daily variation in plasma electrolyte and acid–base status in fasted horses over a 25 h period of rest

AbstractMeasurement and interpretation of acid–base status are important in clinical practice and among racing jurisdictions to determine if horses have been administered alkalinizing substances for the purpose of enhancing performance. The present study used the physicochemical approach to characterize the daily variation in plasma electrolytes and acid–base state that occurs in horses in the absence of feeding and exercise. Jugular venous blood was sampled every 1–2 h from two groups (n=4 andn=5) of Standardbred horses over a 25 h period where food and exercise were withheld. One group of horses was studied in October and one in December. The time course and magnitude of circadian responses differed between the two groups, suggesting that subtle differences in environment may manifest in acid–base status. Significant daily variation occurred in plasma weak acid concentration ([Atot]) and strong ion difference ([SID]), [Cl−], [K+], [Na+] and [lactate−], which contributed to significant changes in [H+] and TCO2. The night-time period was associated with a mild acidosis, marked by increases in plasma [H+] and decreases in TCO2, compared with the morning hours. The night-time acidosis resulted from an increased plasma [Atot] due to an increased plasma protein concentration ([PP]), and a decreased [SID] due to increases in [Cl−] and decreases in [Na+]. An increased plasma [K+] during the night-time had a mild alkalotic effect. There were no differences inpCO2. It was concluded that many equine plasma electrolyte and acid–base parameters exhibit fluctuations in the absence of feeding and exercise, and it is likely that some of these changes are due to daily variation.

Subtle differences in environmental stress along a flooding gradient affect the importance of inter-specific competition in an annual plant community

Empirical evidence suggests that the direction and intensity of plant–plant interactions may depend on the favourability of the environment. Previous studies have mainly focused on steep gradients of environmental stress or disturbance, while the interplay of competition and environment has not been tested for subtle environmental differences. Here, we present results from a study on plant communities of temporary wetlands in East-German farmland. Due to yearly ploughing in autumn, the vegetation is composed of annual species. Flooding does not affect adult plants and the elevation on the gradient expresses differences in the length of the growing season rather than in disturbance intensity or severe environmental stress. We tested whether such subtle differences in environmental stress may affect the importance of interspecific competition by the dominant species. Two treatments were applied at two elevations: removal of the dominant species (Matricaria maritima ssp. inodora) and reciprocal transplants of the seed-bank of the two elevations. At both elevations, removal of Matricaria inodora led to an increase in total species richness and number of wetland species, but the effects were substantially stronger at high elevations. Removal and the elevation on the flooding gradient significantly influenced the plant community composition. In particular, the weed communities became more similar to the wetland communities after the removal. Transplanted weed species did not emerge at low elevations. While two of four target species had significantly higher densities after the removal at high elevations, none of them was influenced by removal at low elevations. This indicates that, consistent with previous studies from other habitat types, competition by the dominant species was more intense under conditions of low environmental stress. The overall results suggest that both flooding as well as interspecific competition are important in structuring the plant communities along the freshwater gradient studied.

PALEOECOLOGY AND TAPHONOMY OF TWO NEW EDRIOASTEROIDS FROM A MISSISSIPPIAN HARDGROUND IN KENTUCKY

A recently discovered series of hardground surfaces in the lower Salem Limestone (Meramecian, Mississippian) and upper Muldraugh Member of the Borden Formation (upper Osagean to lower Meramecian, Mississippian), in Hardin County, Kentucky is colonized by a hard substrate community that includes three species of pyrgate edrioasteroids. Torquerisediscus kypsi n. gen. and n. sp. differs from other edrioasteroids by bearing a cyclic pattern of twelve ambulacral cover plates and meandering distal ambulacra. Ulrichidiscus spinosus n. sp. differs from other species of Ulrichidiscus by the presence of large spines on the ambulacral cover plates, anal pyramid plates, and hydropore orals. Two small specimens are assigned tentatively to Ulrichidiscus aff. pulaskiensis. Edrioasteroid populations occurring on several surfaces show marked differences in size frequency distribution. Three of the surfaces only have large individuals of Torquerisediscus kypsi whereas a fourth surface is colonized by only juvenile specimens of T. kypsi as well as both species of Ulrichidiscus suggesting subtle differences in environment and duration of surface colonization prior to burial. Furthermore, taphonomic pathways differ among these four surfaces with some containing only disrupted individuals and others con- taining only fully articulated individuals suggesting either differences in burial depth, or some differences in decomposition of edrioas- teroid carcasses prior to final burial.

Paleoecology and taphonomy of two new edrioasteroids from a Mississippian hardground in Kentucky

A recently discovered series of hardground surfaces in the lower Salem Limestone (Meramecian, Mississippian) and upper Muldraugh Member of the Borden Formation (upper Osagean to lower Meramecian, Mississippian), in Hardin County, Kentucky is colonized by a hard substrate community that includes three species of pyrgate edrioasteroids. Torquerisediscus kypsi n. gen. and n. sp. differs from other edrioasteroids by bearing a cyclic pattern of twelve ambulacral cover plates and meandering distal ambulacra. Ulrichidiscus spinosus n. sp. differs from other species of Ulrichidiscus by the presence of large spines on the ambulacral cover plates, anal pyramid plates, and hydropore orals. Two small specimens are assigned tentatively to Ulrichidiscus aff. pulaskiensis.Edrioasteroid populations occurring on several surfaces show marked differences in size frequency distribution. Three of the surfaces only have large individuals of Torquerisediscus kypsi whereas a fourth surface is colonized by only juvenile specimens of T. kypsi as well as both species of Ulrichidiscus suggesting subtle differences in environment and duration of surface colonization prior to burial. Furthermore, taphonomic pathways differ among these four surfaces with some containing only disrupted individuals and others containing only fully articulated individuals suggesting either differences in burial depth, or some differences in decomposition of edrioasteroid carcasses prior to final burial.

Effects of an Activity-Correlated Feeding Regime on Circadian Locomotor Activity Rhythms in LEW/Ztm Rats

The aim of the present study was to examine the possible feedback effect of activity on the circadian system in rats. The animals were housed in running wheel cages equipped with food dispensers and were forced to run for their food during parts of the study. Overall level and free-running period θ of wheel-running activity were recorded continuously to quantify the relationship between θ and the level of activity. Surprisingly, the activity-dependent feeding regime failed to increase the level of wheel-running activity and did not affect the activity pattern. Nevertheless, the period of wheel-running activity was shortened in 50% of the animals subjected to food dispensers and in 38% of the animals fed only once a day at irregular times, indicating that subtle environmental differences can affect the circadian pacemaker system without changing the level or the pattern of activity. In addition, 26% of the animals showed a shortening of θ after 3 weeks, i.e., before any change in the experimental setup. This shortening was probably caused by the access to the running wheel at the beginning of the experiment. The present results suggest that the effect on the circadian pacemaker common to both of these experimental manipulations is a change in the physiological or emotional state of the animal rather than an increase of the overall level of activity.

Characteristics of a white-footed mouse (Peromyscus leucopus) population inhabiting a polychlorinated biphenyls contaminated site

Demographic characteristics of a white-footed mouse (Peromyscus leucopus) population inhabiting a woodland containing a low level of PCBs contamination were compared to an uncontaminated reference site. Although population density was higher on the PCBs-contaminated grid, the population exhibited greater temporal variability among years and had a higher number of transient animals. These population trends are consistent with those observed in structurally suboptimal habitats, indicating that the PCBs-contaminated grid is functioning as a suboptimal habitat. However, the data are not compelling enough to firmly conclude that the differences are due to contamination rather than to undetected environmental variation between sites. If demographic differences due to contamination are slight, they will be difficult to detect against a background of demographic variation resulting from subtle environmental differences. We conclude that animals at this site experienced a level of contamination that was below threshold for unequivocal detection of demographic effects.

Community Structure in Grazed and Ungrazed Grassland Sites in the Flooding Pampa, Argentina

-We compared the community structure and composition of two contiguous grasslands, one that had been continuously grazed and one that had remained ungrazed since 1972. Basal cover was measured at both sites in 1976 and 1985. The structure of the grazed area was affected by grazing during these 9 years, which was indicated by the reduction of the cover of grasses and the increase of the cover of forbs and exotic species. In the ungrazed site more than 95% of the basal cover was due to monocots, and the species that dominated this site were seldom found in the grazed site. Large tussocks replaced smaller ones in the absence of cattle. The grazed community was more diverse than the ungrazed one at a small scale (5 m), but less diverse at a larger scale (20 m). Cool season species were always dominant in the grazed site, but in the ungrazed site warm season species dominated some patches and cool season species, others. We concluded that in the absence of grazing, different competitive equilibria may be attained in different patches, probably due to subtle environmental differences. In the grazed area, the effects of cattle upon the community may override environmental heterogeneity and prevent the achievement of competitive equilibrium.

Increased parasitic pressure as a major factor in the evolution of social behavior in halictine bees

Mutillid parasites,Pseudomethoca frigida (Smith), were frequently found in a nest aggregation ofLasioglossum zephyrum (Smith), and were observed in combat with the bees, thereby indicating their importance (and that of parasites and predators in general) in the evolution of nest guarding and supporting Michener's hypothesis that one of the important factors in the evolution of social behavior was the opportunity for defense by guards in nests containing more than one bee. Nesting aggregations may have evolved in several ways, one being selection of bees nesting in areas already proven successful. Such selection might be expected where subtle environmental differences are critical, and may take the form of return to the parental nest sites or joining some other nest aggregation. Aggregation probably increases parasite and predator pressure, thus perhaps providing the necessary selective pressure for colony formation with nest guarding, as well as providing the potentiality for colony formation by allowing females to enter different nests. The seemingly greater success in nest defense by larger colonies suggests that this is one of of the factors responsible for the evolution of increased colony size. The behavior of the bees in nest defense and of their mutillid parasites is described.