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71.
G. Lankin‐Vega S. P. Worner D. A. J. Teulon 《Entomologia Experimentalis et Applicata》2008,129(3):308-315
A novel modeling method is proposed to predict the abundance of the main vector of barley yellow dwarf virus in autumn sown cereal crops. An ensemble model based on artificial neural networks (ANN) was developed to predict the number of Rhopalosiphum padi (L.) (Homoptera: Aphididae) caught in traps during the autumn flight period at Lincoln, Canterbury, New Zealand, over the period 1982–2003. Artificial neural networks were trained using historical weather data and aphid data collected from a suction trap. Model results were compared with those obtained using multiple regression (MR) models using the same independent variables. Both ANN and MR models were validated by leave‐one‐out validation, in other words, by sequentially jackknifing each year out of the data set, fitting a model to the remaining data, then using that model to predict the number of aphids for each jackknifed year. A linear ensemble of ANN models further improved the predictions and represented the trends in the number of aphids over the 22‐year period very well. The r2 between the predicted and observed numbers of aphids for the ANN models changed from 0.68 to 0.83 using the linear ensemble model, but the ensemble approach did not change the prediction for the MR models. The absolute mean error (ABSME) of prediction was much lower for the ANN ensemble predictions compared to that for the MR models. The ABMSE for the ANN models dropped from 109 to 86 aphids compared to an ABMSE reduction from 245 to 220 aphids for the MR models. We discuss the potential for ensemble models for predicting insect abundance when long‐term historical data are available. 相似文献
72.
Forecasting Environmental Responses to Restoration of Rivers Used as Log Floatways: An Interdisciplinary Challenge 总被引:1,自引:0,他引:1
Christer Nilsson Fabio Lepori Björn Malmqvist Erik Törnlund Niclas Hjerdt James M. Helfield Daniel Palm Johan Östergren Roland Jansson Eva Brännäs Hans Lundqvist 《Ecosystems》2005,8(7):779-800
Log floating in the 19th to mid 20th centuries has profoundly changed the environmental conditions in many northern river
systems of the world. Regulation of flow by dams, straightening and narrowing of channels by various piers and wing dams,
and homogenization of bed structure are some of the major impacts. As a result, the conditions for many riverine organisms
have been altered. Removing physical constructions and returning boulders to the channels can potentially restore conditions
for these organisms. Here we describe the history of log driving, review its impact on physical and biological conditions
and processes, and predict the responses to restoration. Reviewing the literature on comparable restoration efforts and building
upon this knowledge, using boreal Swedish rivers as an example, we address the last point. We hypothesize that restoration
measures will make rivers wider and more sinuous, and provide rougher bottoms, thus improving land-water interactions and
increasing the retention capacity of water, sediment, organic matter and nutrients. The geomorphic and hydraulic/hydrologic
alterations are supposed to favor production, diversity, migration and reproduction of riparian and aquatic organisms. The
response rates are likely to vary according to the types of processes and organisms. Some habitat components, such as beds
of very large boulders and bedrock outcrops, and availability of sediment and large woody debris are believed to be extremely
difficult to restore. Monitoring and evaluation at several scales are needed to test our predictions. 相似文献
73.
Information from four archival literature sources from the late 19th century was matched to present-day plant species distribution data for the region of Turnhout (Belgium) and for 15 smaller sub-regions within this region. In the entire study area 25% of the species recorded in the late 19th century went extinct during the 20th century and the extinction rate doubled at the more detailed sub-region level. Binary survival-extinction data and continuous residuals from a linear regression between historical and present-day abundance categories were used to investigate underlying ecological factors of change including habitat preference, ecological amplitude and life strategy. Species increasing relative to the overall trend were generally correlated with nutrient-rich habitats while declining species were more associated with nutrient-poor situations. Generalist species have become relatively more common whilst habitat specialists have strongly declined, resulting in a flora with many ‘losers’ and a few tolerant ‘winners’. The winners are often competitive species while the losers are mainly stress-tolerating species and species with combined life strategies (e.g. SC, SR). Correlations between the decline of historically present habitats and extinction rates of related habitat specialist species show clear trends. We suggest the most important factors involved in changes in flora diversity and vegetation composition are habitat loss due to urbanization and habitat deterioration, mainly due to agricultural intensification. 相似文献
74.
75.
KenSUGIMURA FumioYAMADA 《动物学报》2004,50(4):519-526
为了测量奄美岛上濒危物种琉球兔 (Pentalagusfurnessi)的丰盛度 ,我们计数了森林中道路、溪流和森林地被物中的粪堆数量。计算用的模型包括新粪堆的数量及其年龄、总粪堆数量、每天产生的平均粪堆数 ,以及在森林地被物和溪边的粪堆数量的回归方程。估计在 1 993- 1 994年期间该岛上有 2 5 0 0 - 6 1 0 0只琉球兔 ,在 2 0 0 2 - 2 0 0 3年间有 2 0 0 0 - 4 80 0只。通过比较粪便丰盛度和在森林道路旁观察到的琉球兔数量 ,我们考察了该模型的有效性 ,最后将以前调查的数据应用于该模型以确定种群下降的程度 相似文献
76.
77.
Atmospheric Deposition to the Turkey Lakes Watershed: Temporal Variations and Characteristics 总被引:3,自引:0,他引:3
We investigated the atmospheric concentrations and deposition fluxes of major ions to the Turkey Lakes Watershed (TLW) between
1980 and 1996. During that time, daily SO4
2− concentrations in precipitation decreased markedly, while NO3
−, NH4
+, and H+ concentrations remained roughly constant. It appears that precipitation acidity did not decrease in spite of declining SO4
2− concentrations due to a concurrent and counterbalancing decrease in the concentrations of Ca2+, Mg2+, and K+ in precipitation. The reasons for the decline in base cations are unknown, but this decline is probably related to decreasing
emissions of soil-derived particles from agricultural, industrial, and road sources. A similar situation was seen during the
same period in other parts of Canada, the eastern United States, and Europe. Wet, dry, and total (wet + dry) deposition fluxes
of sulphur (S) and nitrogen (N) were estimated annually for the years 1980–96. The 17-year mean annual total (wet + dry) deposition
of S to the watershed was estimated at 38.5 mmol m−2 y−1 (range 24.3–50.3). Total S deposition decreased by 35% from the early 1980s (1982–84) to the mid-1990s (1994–96), a decline
consistent with the 23% decline in annual SO2 emissions in eastern North America during the same period. In contrast, the annual total (wet + dry) deposition of oxidized
N ranged from 39.8 to 60.4 mmol m−2 y−1, with a 15-year mean of 50.1 mmol m−2 y−1 and a net increase of 10% between the early 1980s (1983–85) and the mid-1990s (1994–96). This is in keeping with a 10% increase
in NOx emissions in eastern North America during the same period. For both S and N (oxidized), wet deposition dominated over dry
deposition as the major mechanism for atmospheric input to the watershed. Annually, wet deposition accounted for approximately
two-thirds of the total atmospheric deposition of both S and N. Dry S deposition was due more to gaseous SO2 deposition (two-thirds of dry S deposition) than to particulate SO4
2− deposition (one-third of dry S deposition). Dry deposition of oxidized N, however, was dominated (95%) by gaseous HNO3 deposition, with minimal input from particulate NO3
− deposition. Compared to several selected watershed/forest sites in Canada, the United States, and Europe, the estimated total
deposition of S and N at the TLW was relatively high during the measurement period.
Received 5 October 1999; accepted 1 March 2001. 相似文献
78.
The effect of temperature on egg development of the apple sawfly Hoplocampa testudinea Klug was studied under controlled conditions. Based on a linear model describing the relationship between temperature and developmental rates a thermal threshold of 6.9 °C and a thermal constant of 85 day-degrees were established. The experimental results were used to expand and parameterise an existing phenology model to include egg development and hatching of first instar larvae. The model thus became a valuable forecasting tool not only for adult emergence and the optimal monitoring period but also for egg hatch and the best timing of control measures against first instar larvae. The model was validated by comparing predictions with independent observations on egg-laying and subsequent hatching of first instar larvae under semi-field conditions. 相似文献
79.
Climatic harshness is expected to increase at higher elevations; however, elevational trends of tree radial growth response of high-elevation forests to climate change need to be investigated at different locations because of existing local variability in site-specific climatic conditions. We developed tree-ring width chronologies of Yunnan fir (Abies georgei) along elevation gradients at two sites in the central Hengduan Mountains (HM). High-elevation forests of A. georgei showed growth synchronicity and common growth signals along elevation gradients, indicating a common climatic forcing, although tree radial growth rates decreased with increasing elevation. Radial growth of Yunnan fir showed positive correlations with summer temperatures and February precipitation and moisture availability, but were negatively correlated with spring temperatures. The strongest positive relationship indicated summer (July) mean and minimum temperatures are the most important growth determining climatic factors for tree radial growth in the cold environment of HM, and this relationship revealed a clear elevational trend with stronger correlations at higher altitudes. In contrast, tree radial growth was negatively correlated with June precipitation and moisture availability. The whole study period 1954–2015 was split in two sub-periods of equal length. Comparing the early sub-period (1954–1984) to the later sub-period (1985–2015), tree growth response to the summer temperatures strongly increased, while it became weaker to June precipitation and moisture availability. High-elevation Yunnan fir forests in the HM currently benefit from elevated growing season temperatures under humid summer conditions. However, increasing temperatures may induce drought stress on tree radial growth if the observed decreasing trend in humidity and precipitation continues. 相似文献
80.
A three-dimensional operational hydrodynamic model, developed at the Institute of Oceanography, University of Gdańsk was used
to forecast hydrological conditions in the Oder Estuary. The model was based on the coastal ocean circulation model known
as the Princeton Ocean Model (POM). Because of wind-driven water backup in the Oder mouth, a simplified operational model
of river discharge, based on water budget in a stream channel, was developed. Linking these two models into a single system
made it possible to forecast water levels, currents, water temperature, and salinity in the estuary. A good fit between the
observed and computed data allowed to consider the model as a reliable environmental tool. Obtaining a hydrological forecast
via a quick website access gives potential users an opportunity to predict the day-by-day course of processes that may affect
different areas of human life and activities, e.g., navigation, port operations, flood protection of coastal areas; the predictions
may also be used in studies of coastal processes in the estuary. 相似文献