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91.
Karen L. Overholtzer-McLeod 《Coral reefs (Online)》2005,24(2):283-291
Understanding the dynamics of open marine populations is inherently complex, and this complexity has led to decades of debate regarding the relative importance of pre- versus post-settlement processes in structuring these populations. Movement between patches may be an important modifier of patterns established at settlement, yet local immigration and emigration have received less attention than other demographic rates. I examined loss rates from tagged populations of juvenile wrasses (yellowhead wrasse Halichoeres garnoti and bluehead wrasse Thalassoma bifasciatum) at two sites in the Bahamas. Assuming that all losses were due solely to mortality would have significantly underestimated survivorship of yellowhead wrasse by 29% and bluehead wrasse by 14%. On average, per capita mortality and emigration rates were higher for yellowhead than bluehead wrasse, but neither demographic rate differed between sites for either species. With respect to within-species density, bluehead wrasse mortality was density-dependent at the patch reef site, but mortality rates of yellowhead wrasse were consistently density-independent. Evaluating the effects of between-species density, yellowhead wrasse mortality increased with a decrease in bluehead wrasse density, but this effect was limited to the patch reef site. Emigration rates were not a function of either within-species or between-species density, but instead varied inversely with isolation distance. Numerous previous studies of coral-reef fish, conducted on patch reefs separated by only a few meters of sand and often using untagged fish, may have confounded losses due to emigration with those due to mortality. A better understanding of the factors affecting emigration in marine fishes is important to their effective management using spatial tools such as marine protected areas. 相似文献
92.
FrancisLEMCKERT 《动物学报》2005,51(3):393-400
在澳大利亚新南威尔士南部沿海,作者搜集了一个池塘繁殖的斑索蟾(Crinia signifera)的种群统计资料。通过捕捉进出池塘的1 612只个体,获得种群大小、结构、生长率、性成熟时的大小和年龄、死亡率及寿命资料。迁移高峰从6月持续到11月,蛙的最高、最低遇见数量分别出现在春季和秋季。但第2年,该池塘蛙的数量明显减少,可能是由于补充到种群中的幼体数量很少的缘故。6个月后个体的重捕率很低;但距第一次捕获18个月以后,仍有个别个体再次被捕获。性成熟时,雌性比雄性的身体大一些。生长曲线显示,雌性比雄性的生长更快,所以更早地达到性成熟。研究种群的数量、结构和死亡率趋势等与已知的其它Crinia signifera种群基本一致。但研究种群迁移活动的高峰出现较晚,并且夏季的活动水平明显很高。这种长的活动时间可能会导致存活率的下降,同时有利于选择迅速性成熟的雌性[动物学报51 (3) : 393 -400 , 2005]。 相似文献
93.
Questions: Are there interspecific differences in mortality and recruitment rates across life stages between two shade‐tolerant dominant trees in a sub‐alpine old‐growth forest? Do such differences in demography contribute to the coexistence and co‐dominance of the two species? Location: Sub‐alpine, old‐growth forest on Mt. Ontake, central Honshu, Japan. Methods: From 1980 to 2005, we recorded DBH and status (alive or dead) of all Abies mariesii and A. veitchii individuals (DBH ≥ 5 cm) in a 0.44‐ha plot. Based on this 25 year census, we quantified mortality and recruitment rates of the two species in three life stages (small tree, 5 cm ≤ DBH < 10 cm; subcanopy tree, 10 cm ≤ DBH < 20 cm; canopy tree, DBH ≥ 20 cm). Results: Significant interspecific differences in mortality and recruitment rates were observed in both the small tree and sub‐canopy tree stages. In this forest, saplings (< 5 cm DBH) are mostly buried by snow‐pack during winter. As a consequence, saplings of A. mariesii, which is snow and shade tolerant, show higher rates of recruitment into the small tree stage than do those of A. veitchii. Above the snow‐pack, trees must tolerate dry, cold temperatures. A. veitchii, which can more readily endure such climate conditions, showed lower mortality rate at the subcanopy stage and a higher recruitment rate into the canopy tree stage. This differential mortality and recruitment among life‐stages determines relative dominance of the two species in the canopy. Conclusion: Differential growth conditions along a vertical gradient in this old forest determine survival of the two species prior to reaching the canopy, and consequently allow co‐dominance at the canopy stage. 相似文献
94.
Since the late 1990s, the Pacific oyster (Crassostrea gigas) has spread into the East Frisian Wadden Sea (Germany). This invasion provided an opportunity to study the population dynamics
and the patterns of spread during the initial bioinvasion process. With its source area in The Netherlands, the bioinvasion
continues in an eastward direction, as documented by a gradient of high abundances in the west and low abundances in the east
during the first study year. One year later, abundances of the Pacific oyster were more heterogenic and differed between adjacent
tidal basins. The increase in population sizes at all study sites was very high, reaching levels similar to native occurrence
populations. The growth constant (K) varied between 0.300 and 0.990 year−1. The mussel bed with the highest densities had a mean abundance of >300 ind. m−2, and a maximum of 1,460 ind. m−2. Furthermore, the bioinvasion was facilitated by a low mortality (Z) found for populations between 0.5 and 1.5 years old (Z = 0.03–0.13 year−1). At present, Pacific oysters are well established at several locations in the East Frisian Wadden Sea and may become with
these reproductive potential self-sustaining populations. 相似文献
95.
After considering the observed long-term trends in average monthly temperatures distribution in Moscow, the authors evaluated
how acute mortality responded to changes in daily average, minimum and maximum temperatures throughout the year, and identified
vulnerable population groups, by age and causes of death. A plot of the basic mortality–temperature relationship indicated
that this relationship was V-shaped with the minimum around 18°C. Each 1°C increment of average daily temperature above 18°C
resulted in an increase in deaths from all non-accidental causes by 2.8%, from coronary heart disease by 2.7%, from cerebrovascular
diseases by 4.7%, and from respiratory diseases by 8.7%, with a lag of 0 or 1 day. Each 1°C drop of average daily temperature
from +18°C to −10°C resulted in an increase in deaths from all non-accidental causes by 0.49%, from coronary heart disease
by 0.57%, from cerebrovascular diseases by 0.78%, and from respiratory diseases by 1.5%, with lags of maximum association
varying from 3 days for non-accidental mortality to 6 days for cerebrovascular mortality. In the age group 75+ years, corresponding
risks were consistently higher by 13–30%. The authors also estimated the increase in non-accidental deaths against the variation
of daily temperatures. For each 1°C increase of variation of temperature throughout the day, mortality increased by 0.3–1.9%,
depending on other assumptions of the model. 相似文献
96.
Summary . A distributed lag model (DLagM) is a regression model that includes lagged exposure variables as covariates; its corresponding distributed lag (DL) function describes the relationship between the lag and the coefficient of the lagged exposure variable. DLagMs have recently been used in environmental epidemiology for quantifying the cumulative effects of weather and air pollution on mortality and morbidity. Standard methods for formulating DLagMs include unconstrained, polynomial, and penalized spline DLagMs. These methods may fail to take full advantage of prior information about the shape of the DL function for environmental exposures, or for any other exposure with effects that are believed to smoothly approach zero as lag increases, and are therefore at risk of producing suboptimal estimates. In this article, we propose a Bayesian DLagM (BDLagM) that incorporates prior knowledge about the shape of the DL function and also allows the degree of smoothness of the DL function to be estimated from the data. We apply our BDLagM to its motivating data from the National Morbidity, Mortality, and Air Pollution Study to estimate the short-term health effects of particulate matter air pollution on mortality from 1987 to 2000 for Chicago, Illinois. In a simulation study, we compare our Bayesian approach with alternative methods that use unconstrained, polynomial, and penalized spline DLagMs. We also illustrate the connection between BDLagMs and penalized spline DLagMs. Software for fitting BDLagM models and the data used in this article are available online. 相似文献
97.
Ayşegül Bayır Ahmet Ak Hasan Kara Tahir Kemal Şahin 《Biological trace element research》2009,130(1):7-12
The aim of this study was to determine the relationship between serum and cerebrospinal fluid (CSF) magnesium (Mg+2) levels, Glasgow Coma Scores (GCS), and 7-day mortality in acute stroke patients. Patients with acute ischemic or hemorrhagic
stroke arriving within the first 3 h of symptoms were included in the study. The control group consisted of healthy volunteers.
GCS was determined, and blood and CSF samples were taken in order to establish serum and CSF glucose, Mg+2, sodium, potassium, calcium, and chlorine levels. Mortality was recorded at 7 days after admission. CSF Mg+2 in the ischemic infarct group was significantly lower than in the control group (p = 0.006). CSF Mg+2 in the ischemic infarct patients with a GCS ≤ 8 were significantly lower (p = 0.002) than controls and in ischemic infarct patients with a GCS ≥9. In the ischemic stroke patients, CSF Mg+2 and GCS were significantly correlated (r = 55, p = 0.031). CSF Mg+2 levels in ischemic stroke patients who died within 7 days were significantly lower than controls, ischemic stroke patients
who survived, and hemorrhagic stroke patients who died (p = 0.002, p = 0.042, and p = 0.005, respectively). Low CSF Mg+2 levels in patients with acute ischemic stoke at admission predicted a higher 1-week mortality. 相似文献
98.
Jameal F. Samhouri Richard R. Vance Graham E. Forrester Mark A. Steele 《Oecologia》2009,160(2):257-265
Structural refuges within which prey can escape from predators can be an important limiting resource for the prey. In a manner
that resembles the childhood game of musical chairs, many prey species rapidly retreat to shared, unguarded refuges whenever
a predator threatens, and only when refuges are relatively abundant do all prey individuals actually escape. The key feature
of this process is that the per capita prey mortality rate depends on the ratio of prey individuals to refuges. We introduce
a new class of mortality functions with this feature and then demonstrate statistically that they describe field mortality
data from a well-studied coral reef fish species, the Caribbean bridled goby Coryphopterus glaucofraenum, substantially better than do several mortality functions of more conventional form.
J. F. Samhouri and R. R. Vance contributed equally to this work. 相似文献
99.
Atmospheric carbon dioxide (CO2) and ozone (O3) concentrations are rising, which may have opposing effects on tree C balance and allocation to fine roots. More information
is needed on interactive CO2 and O3 effects on roots, particularly fine-root life span, a critical demographic parameter and determinant of soil C and N pools
and cycling rates. We conducted a study in which ponderosa pine (Pinus ponderosa) seedlings were exposed to two levels of CO2 and O3 in sun-lit controlled-environment mesocosms for 3 years. Minirhizotrons were used to monitor individual fine roots in three
soil horizons every 28 days. Proportional hazards regression was used to analyze effects of CO2, O3, diameter, depth, and season of root initiation on fine-root survivorship. More fine roots were produced in the elevated
CO2 treatment than in ambient CO2. Elevated CO2, increasing root diameter, and increasing root depth all significantly increased fine-root survivorship and median life span.
Life span was slightly, but not significantly, lower in elevated O3, and increased O3 did not reduce the effect of elevated CO2. Median life spans varied from 140 to 448 days depending on the season of root initiation. These results indicate the potential
for elevated CO2 to increase the number of fine roots and their residence time in the soil, which is also affected by root diameter, root
depth, and phenology. 相似文献
100.
Short-term experiments were used to isolate the detrimental effects of grazer disturbance on young corals, and determine the
stage of development at which recruits are no longer susceptible to this disturbance. Artificial substrata containing an algal
matrix and coral recruits of different life stages were exposed to grazing by epilithic algal matrix (EAM) feeding combtoothed
blennies, Salarias fasciatus. Single polyp recruits were vulnerable to grazer disturbance, while multi-polyp recruits (ca. 6–8 polyps) survived with evidence of minor damage in the form of tissue and polyp loss. The result indicates that blennies,
although small and possessing weak dentition, can negatively influence the survival of young coral recruits. The protruding
structure of micro-nubbins, representing juvenile corals were not damaged, suggesting that coral achieving that size and form
can escape such damage.
Communicated by Ecology Editor Prof. Peter Mumby 相似文献