Pervasive influence of large-scale climate in the dynamics of a terrestrial vertebrate community.
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BACKGROUND: Large-scale climatic variability has been implicated in the population dynamics of many vertebrates throughout the Northern Hemisphere, but has not been demonstrated to directly influence dynamics at multiple trophic levels of any single system. Using data from Isle Royale, USA, comprising time series on the long-term dynamics at three trophic levels (wolves, moose, and balsam fir), we analyzed the relative contributions of density dependence, inter-specific interactions, and climate to the dynamics of each level of the community. RESULTS: Despite differences in dynamic complexity among the predator, herbivore, and vegetation levels, large-scale climatic variability influenced dynamics directly at all three levels. The strength of the climatic influence on dynamics was, however, strongest at the top and bottom trophic levels, where density dependence was weakest. CONCLUSIONS: Because of the conflicting influences of environmental variability and intrinsic processes on population stability, a direct influence of climate on the dynamics at all three levels suggests that climate change may alter stability of this community. Theoretical considerations suggest that if it does, such alteration is most likely to result from changes in stability at the top or bottom trophic levels, where the influence of climate was strongest. (+info)
Wind-dispersed pollen mediates postglacial gene flow among refugia.
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A long-term genetic legacy of refugial isolation has been postulated and was demonstrated for maternal refugial lineages for numerous plant and animal species. The lineages were assumed to have remained separated from each other for several glacial periods. The conifer Abies alba Miller, silver fir, is an excellent model to test whether pollen-mediated gene flow may eliminate the genetic imprints of Pleistocene refugial isolation. Two DNA markers with contrasting modes of inheritance were applied to 100 populations covering the entire range of silver fir in Europe. The markers exhibited each two highly conserved alleles based on an insertion/deletion of 80 bp in the fourth intron of the mitochondrial nad5 gene and on a synonymous substitution in the chloroplast psbC gene. The geographical distribution of the maternally inherited mitochondrial variation supported the existence of at least two refugia with two recolonizing maternal lineages remaining largely separated throughout the range. The cline of the nad5 allele frequencies was much steeper than the one of the two psbC alleles. The psbC cline was as wide as the whole range of the species. Our results provide striking evidence that even a species with very long generation times and heavy pollen grains was able to establish a highly efficient pollen-mediated gene flow between refugia. Therefore we postulate that an exchange of genetic information between refugia by range-wide paternal introgression is possible in wind-pollinated plant species. (+info)
Seasonal and perennial changes in the distribution of water in the sapwood of conifers in a sub-frigid zone.
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An analysis was made of progressive changes in patterns of cavitation in the sapwood of three species of conifer (Larix kaempferi, Abies sachalinensis, and Picea jezoensis) that were growing in a sub-frigid zone. In all three conifers, all tracheids of the newly forming outermost annual ring were filled with water or cytoplasm during the period from May to August. However, many tracheids in the transition zone from earlywood to latewood lost water in September, presumably through drought-induced cavitation. Cavitated tracheids tended to be continuously distributed in a tangential direction. Subsequently, some earlywood tracheids of the outermost annual ring lost water during the period from January to March. This was associated with freeze-thaw cycles. In the second and third annual rings from the cambium of all three conifers, the lumina of most tracheids in the transition zone from earlywood to latewood contained no water. In contrast, some latewood tracheids near the annual ring boundary and many earlywood tracheids retained water in their lumina. The third annual ring had more cavitated tracheids than the second annual ring. Our observations indicated that cavitation progressed gradually in the tracheids of the conifers and that they were never refilled once cavitation had occurred. The region involved in water transport in conifers did not include the entire sapwood and differed among annual rings. (+info)
Modeling current and future potential wintering distributions of eastern North American monarch butterflies.
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Monarch butterflies overwinter in restricted areas in montane oyamel fir forests in central Mexico with specific microclimates that allow the butterflies to survive for up to 5 months. We use ecological niche modeling (ENM) to identify areas adequate for overwintering monarch colonies under both current and future climate scenarios. The ENM approach permits testing and validation of model predictivity, and yields quantitative, testable predictions regarding likely future climate change effects. Our models predicted monarch presence with a high degree of accuracy, and indicated that precipitation and diurnal temperature range were key environmental factors in making locations suitable for monarchs. When we projected monarch distribution onto future climate scenarios (Hadley Centre climate models), we found that conditions were likely to be inadequate across the entire current winter range, particularly owing to increased cool-weather precipitation that could cause increased mortality. This study applies ENM to understanding the seasonal dynamics of a migratory species under climate change, and uses ENM to identify key limiting environmental parameters in species' responses to climate change. (+info)
The influence of top-down, bottom-up and abiotic factors on the moose (Alces alces) population of Isle Royale.
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Long-term, concurrent measurement of population dynamics and associated top-down and bottom-up processes are rare for unmanipulated, terrestrial systems. Here, we analyse populations of moose, their predators (wolves, Canis lupus), their primary winter forage (balsam fir, Abies balsamea) and several climatic variables that were monitored for 40 consecutive years in Isle Royale National Park (544 km2), Lake Superior, USA. We judged the relative importance of top-down, bottom-up and abiotic factors on moose population growth rate by constructing multiple linear regression models, and calculating the proportion of interannual variation in moose population growth rate explained by each factor. Our analysis indicates that more variation in population growth rate is explained by bottom-up than top-down processes, and abiotic factors explain more variation than do bottom-up processes. Surprisingly, winter precipitation did not explain any significant variation in population growth rate. Like that detected for two Norwegian ungulate populations, the relationship between population growth rate and the North Atlantic Oscillation was nonlinear. Although this analysis provides significant insight, much remains unknown: of the models examined, the most parsimonious explain little more than half the variation in moose population growth rate. (+info)
Respiratory symptoms and peak expiratory flow rates among furniture-decoration students.
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This study was designed to evaluate the effects of furniture production, mainly including fir tree (aberia mulleriana), on respiratory health of young workers and to compare the results with those obtained from previous studies. Sixty-four furniture-decoration students (57 males and 7 females) and 62 controls (54 male, 8 female) from different departments in the same school were included into the study. All participants were assessed with a questionnaire (concerning history of occupational exposure, work-related respiratory and other symptoms, smoking history, previous asthma history), full physical examination, spirometric evaluation and chest radiograph. Participants then performed serial monitoring of peak expiratory flow rates (PEFR) at work and away from work within a month. Mean age of students was 20.9 +/- 3.7 years, 20.5 +/- 2.6 years in controls. There was no difference between study and control groups with regard to age, gender, smoking status and previous asthma history. Reported cough (23.4 % vs. 8.1 %) and shortness of breath (18.8 % vs. 6.5 %) were significantly higher in furniture-decoration students than in controls (p = 0.016 and p = 0.034, respectively). Furniture-decoration students had higher conjunctivitis (34.4 % vs. 9.7 %, p = 0.001) and rhinitis (34.4 % vs. 19.4 %, p = 0.044) history when compared with controls. Both students and controls were normal in terms of respiratory examination. PEF recordings were performed for approximately one month. Diurnal variability greater than 20 % was seen in 12/64 (18.7 %) of students at work, whereas it was detected in 4/62 (6.4 %) of controls (p = 0.034). When comparing for the presence of diurnal variability greater than 20 % in weekends, no difference was found between groups (p = 0.457). In conclusion, early detection of work-related respiratory changes by serial monitoring of peak expiratory flows should save the workers from hazardous respiratory effects of the furniture production, especially in young population. (+info)
Differentiation of terminal latewood tracheids in silver fir trees during autumn.
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BACKGROUND AND AIMS: The differentiation of terminal latewood tracheids of silver fir (Abies alba) trees grown in Slovenia was investigated in autumn/winter 2001/2002. METHODS: The experimental trees were divided into three groups: one with narrow annual rings, width less than 1 mm; one with annual ring widths between 1 and 4 mm; and one group with broad rings larger than 4 mm. The differentiation of terminal latewood tracheids was investigated by light-, electron- and UV-microscopy in tissues sampled in October and November 2001 and March 2002. KEY RESULTS: In the middle of October, cambial divisions did not occur any more in any of the trees. In trees with narrow annual rings, cell wall deposition as well as lignification were completed in terminal latewood tracheids at this date, whereas in trees with annual ring widths of more than 1 mm these processes still continued. Electron microscopy as well as UV microscopy revealed an unlignified inner S(2) layer and the absence of S(3) and warty layers. With increasing distance from the cambium, wall formation and lignification gradually appeared to be completed. Samples of all trees taken in the middle of November only contained differentiated terminal latewood tracheids. At the structural and lignin topochemical level, November and March samples showed completed differentiation of walls of terminal latewood tracheids. CONCLUSIONS: In trees with broader annual rings, the final steps of differentiation of the youngest latewood tracheids near the cambium still continued during autumn, but were finished prior to winter. It was concluded from structural observations that duration of cambial activity is longer in trees with broad annual rings than in trees with narrow rings. (+info)
Unexpectedly high bacterial diversity in arctic tundra relative to boreal forest soils, revealed by serial analysis of ribosomal sequence tags.
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Arctic tundra and boreal forest soils have globally relevant functions that affect atmospheric chemistry and climate, yet the bacterial composition and diversity of these soils have received little study. Serial analysis of ribosomal sequence tags (SARST) and denaturing gradient gel electrophoresis (DGGE) were used to compare composite soil samples taken from boreal and arctic biomes. This study comprises an extensive comparison of geographically distant soil bacterial communities, involving the analysis of 12,850 ribosomal sequence tags from six composite soil samples. Bacterial diversity estimates were greater for undisturbed arctic tundra soil samples than for boreal forest soil samples, with the highest diversity associated with a sample from an extreme northern location (82(o)N). The lowest diversity estimate was obtained from an arctic soil sample that was disturbed by compaction and sampled from a greater depth. Since samples from the two biomes did not form distinct clusters on the basis of SARST data and DGGE fingerprints, factors other than latitude likely influenced the phylogenetic compositions of these communities. The high number of ribosomal sequences analyzed enabled the identification of possible cosmopolitan and endemic bacterial distributions in particular soils. (+info)