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131.
Forecasting impacts of future climate change is an important challenge to biologists, both for understanding the consequences of different emissions trajectories and for developing adaptation measures that will minimize biodiversity loss. Existing variation provides a window into the effects of climate on species and ecosystems, but in many places does not encompass the levels or timeframes of forcing expected under directional climatic change. Experiments help us to fill in these uncertainties, simulating directional shifts to examine outcomes of new levels and sustained changes in conditions. Here, we explore the translation between short‐term responses to climate variability and longer‐term trajectories that emerge under directional climatic change. In a decade‐long experiment, we compare effects of short‐term and long‐term forcings across three trophic levels in grassland plots subjected to natural and experimental variation in precipitation. For some biological responses (plant productivity), responses to long‐term extension of the rainy season were consistent with short‐term responses, while for others (plant species richness, abundance of invertebrate herbivores and predators), there was pronounced divergence of long‐term trajectories from short‐term responses. These differences between biological responses mean that sustained directional changes in climate can restructure ecological relationships characterizing a system. Importantly, a positive relationship between plant diversity and productivity turned negative under one scenario of climate change, with a similar change in the relationship between plant productivity and consumer biomass. Inferences from experiments such as this form an important part of wider efforts to understand the complexities of climate change responses. 相似文献
132.
Environmental change influences the life history of salmon Salmo salar in the North Atlantic Ocean
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Annual mean total length (LT) of wild one‐sea‐winter (1SW) Atlantic salmon Salmo salar of the Norwegian River Imsa decreased from 63 to 54 cm with a corresponding decrease in condition factor (K) for cohorts migrating to sea from 1976 to 2010. The reduction in LT is associated with a 40% decline in mean individual mass, from 2 to 1·2 kg. Hatchery fish reared from parental fish of the same population exhibited similar changes from 1981 onwards. The decrease in LT correlated negatively with near‐surface temperatures in the eastern Norwegian Sea, thought to be the main feeding area of the present stock. Furthermore, S. salar exhibited significant variations in the proportion of cohorts attaining maturity after only one winter in the ocean. The proportion of S. salar spawning as 1SW fish was lower both in the 1970s and after 2000 than in the 1980s and 1990s associated with a gradual decline in post‐smolt growth and smaller amounts of reserve energy in the fish. In wild S. salar, there was a positive association between post‐smolt growth and the sea survival back to the River Imsa for spawning. In addition, among smolt year‐classes, there were significant positive correlations between wild and hatchery S. salar in LT, K and age at maturity. The present changes may be caused by ecosystem changes following the collapse and rebuilding of the pelagic fish abundance in the North Atlantic Ocean, a gradual decrease in zooplankton abundance and climate change with increasing surface temperature in the Norwegian Sea. Thus, the observed variation in the life‐history traits of S. salar appears primarily associated with major changes in the pelagic food web in the ocean. 相似文献
133.
Identification of coding regions in DNA sequences remains challenging. Various methods have been proposed, but these are limited by species-dependence and the need for adequate training sets. The elements in DNA coding regions are known to be distributed in a quasi-random way, while those in non-coding regions have typical similar structures. For short sequences, these statistical characteristics cannot be extracted correctly and cannot even be detected. This paper introduces a new way to solve the problem: balanced estimation of diffusion entropy (BEDE). 相似文献
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137.
Random field models for fitness landscapes 总被引:1,自引:0,他引:1
In many cases fitness landscapes are obtained as particular instances of random fields by randomly assigning a large number
of parameters. Models of this type are often characterized reasonably well by their covariance matrices. We characterize isotropic
random fields on finite graphs in terms of their Fourier series expansions and investigate the relation between the covariance
matrix of the random field model and the correlation structure of the individual landscapes constructed from this random field.
Correlation measures are a good characteristic of “rugged landscapes” models as they are closely related to quantities like
the number of local optima or the length of adaptive walks. Our formalism suggests to approximate landscape with known autocorrelation
function by a random field model that has the same correlation structure.
Received: 10 November 1995 / Revised version: 19 February 1996 相似文献
138.
J.-R. Martin R. Ernst M. Heisenberg 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1999,184(1):73-84
The temporal pattern of locomotor activity of single Drosophila melanogaster flies freely walking in small tubes is described. Locomotor activity monitored by a light gate has a characteristic time-course
that depends upon age and the environmental conditions. Several methods are applied to assess the complexity of the temporal
pattern. The pattern varies according to sex, genotype, age and environmental conditions (food; light). Activity occurs clustered
in bouts. The intrinsic bout structure is quantified by four parameters: number of light gate passages (counts) per bout,
duration of a bout, pause between two successive bouts and mean bout period. In addition, the distribution of the periods
between light-gate crossings (inter-count intervals) as function of inter-count interval duration reveals a power law, suggesting
that the overall distribution of episodes of activity and inactivity has a fractal structure. In the dark without food, the
fractal dimension which represents a measure of the complexity of the pattern is sex, genotype and age specific. Fractality
is abolished by additional sensory stimulation (food; light). We propose that time-course, bout structure and fractal dimension
of the temporal pattern of locomotor activity describe different aspects of the fly's central pattern generator for locomotion
and its motivational control.
Accepted: 10 October 1998 相似文献
139.
María A. Rodrigo Carmen Rojo Miguel lvarez‐Cobelas 《International Review of Hydrobiology》2003,88(5):464-481
This study describes the occurrence, importance and seasonal patterns of picoplankton in two wetlands (TDNP and La Safor), and compares them to a system of fifteen interconnected lakes (Ruidera). In TDNP we performed a six‐year monthly study in three sites of the wetland. Bacterial abundance increased throughout time and the autotrophic picoplankton (APP) range was wide (up to 33 × 106 cells/ml). The annual averaged APP contribution to total picoplankton and phytoplankton biovolumes was 0.5–22% and 0.03–6% respectively. There were large differences among sites in terms of APP absolute and relative abundance and seasonal patterns. In La Safor, the APP relative contribution to picoplankton and phytoplankton biovolumes was 0–25% and 0–40%, respectively, while in the Ruidera lakes was 0–47% and 0–5%, respectively. In the three systems there was a significant correlation between bacterial abundance and chlorophyll a but the slopes of the linear regressions were different. No significant relationships were found of APP abundance and trophic status in the wetlands, but were noted in the lake system. There was no clear relationship of APP contribution to total phytoplankton biomass to the trophic gradient in wetlands. In the lakes, the higher contribution of APP was found in those with higher trophic levels. 相似文献
140.