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Long-term Patterns (long-term + pattern)
Selected AbstractsExtracting long-term patterns of population changes from sporadic counts of migrant birdsENVIRONMETRICS, Issue 5 2010Joanna Mills Flemming Abstract Declines of many North American birds are of conservation concern. For almost 40 years, experienced birders have kept daily counts of migrant landbirds during visits to Seal and Brier Islands, both of which are off Nova Scotia's southern tip. Here we assess the utility of Generalized Additive Models (GAMs) to extract patterns of population change of a common migrant to Seal Island, the Ruby-crowned Kinglet, while controlling for other influences including season, weather and effort. We also demonstrate, using counts of the Kinglet from Brier Island as well as counts of another common migrant, the Yellow-rumped Warbler, how our GAM methods can combine data from different geographic areas or distinct species. Most existing analyses of similar long-term data sets have used linear models to estimate trends. Our results and comparisons suggest that GAMs are a powerful way of extracting more information from such data. Copyright © 2009 John Wiley & Sons, Ltd. [source] Soil arthropods as indicators of water stress in Antarctic terrestrial habitats?GLOBAL CHANGE BIOLOGY, Issue 12 2003Peter Convey Abstract Abiotic features of Antarctic terrestrial habitats, particularly low temperatures and limited availability of liquid water, strongly influence the ecophysiology and life histories of resident biota. However, while temperature regimes of a range of land microhabitats are reasonably well characterized, much less is known of patterns of soil water stress, as current technology does not allow measurement at the required scale. An alternative approach is to use the water status of individual organisms as a proxy for habitat water status and to sample over several years from a population to identify seasonal or long-term patterns. This broad generalization for terrestrial invertebrates was tested on arthropods in the maritime Antarctic. We present analyses of a long-term data set of body water content generated by monthly sampling for 8,11 years of seven species of soil arthropods (four species of Acari, two Collembola and one Diptera) on maritime Antarctic Signy Island, South Orkney Islands. In all species, there was considerable within- and between-sample variability. Despite this, clear seasonal patterns were present in five species, particularly the two collembolans and a prostigmatid mite. Analyses of monthly water content trends across the entire study period identified several statistically significant trends of either increase or decrease in body water content, which we interpret in the context of regional climate change. The data further support the separation of the species into two groups as follows: firstly, the soft-bodied Collembola and Prostigmata, with limited cuticular sclerotization, which are sensitive to changes in soil moisture and are potentially rapid sensors of microhabitat water status, secondly, more heavily sclerotized forms such as Cryptostigmata (=Oribatida) and Mesostigmata mites, which are much less sensitive and responsive to short-term fluctuations in soil water availability. The significance of these findings is discussed and it is concluded that annual cycles of water content were driven by temperature, mediated via radiation and precipitation, and constituted reliable indicators of habitat moisture regimes. However, detailed ecophysiological studies are required on particular species before such information can be used to predict over long timescales. [source] A quarter century of declining suspended sediment fluxes in the Mississippi River and the effect of the 1993 flood,HYDROLOGICAL PROCESSES, Issue 1 2010Arthur J. Horowitz Abstract Annual fluxes, flow-weighted concentrations and linear least squares trendline calculations for a number of long-term Mississippi River Basin (MRB) sampling sites covering 1981 through 2007, whilst somewhat ,noisy', display long-term patterns of decline. Annual flow-weighted concentration plots display the same long-term patterns of decline, but are less noisy because they reduce/eliminate variations due to interannual discharge differences. The declines appear greatest in the middle MRB, but also are evident elsewhere. The pattern for the lower Ohio River differs and may reflect ongoing construction at the Olmsted lock and dam that began in 1993 and currently is ongoing. The ,Great Flood of 1993' appears to have superimposed a step function (a sharp drop) on the long-term rate of decline in suspended sediment concentrations (SSC), annual fluxes and flow-weighted concentrations in the middle MRB at St Louis and Thebes, Missouri and Vicksburg, Mississippi, and in the lower MRB at St Francisville, Louisiana. Evidence for a step function at other sites is less substantial, but may have occurred. The step function appears to have resulted from losses in available (erodible) sediment, rather than to a reduction in discharge; hence, the MRB appears to be supply limited rather than discharge limited. These evaluations support the need for daily discharge and SSC data collections in the MRB to better address questions regarding long-term trends in sediment-related issues. This is apparent when the results for the Mississippi River at Thebes and St Louis sites are compared with those from other MRB sites where intensive (daily) data collections are lacking. Published in 2009 by John Wiley & Sons, Ltd. [source] 100 years of change: examining agricultural trends, habitat change and stakeholder perceptions through the 20th centuryJOURNAL OF APPLIED ECOLOGY, Issue 2 2009Martin Dallimer Summary 1The 20th century has witnessed substantial increases in the intensity of agricultural land management, much of which has been driven by policies to enhance food security and production. The knock-on effects in agriculturally dominated landscapes include habitat degradation and biodiversity loss. We examine long-term patterns of agricultural and habitat change at a regional scale, using the Peak District of northern England as a case study. As stakeholders are central to the implementation of successful land-use policy, we also assess their perceptions of historical changes. 2In the period 1900 to 2000, there was a fivefold rise in sheep density, along with higher cattle density. We found a reduction in the number of farms, evidence of a shift in land ownership patterns, and increased agricultural specialization, including the virtual disappearance of upland arable production. 3Despite previous studies showing a substantial loss in heather cover, we found that there had been no overall change in the proportion of land covered by dwarf shrub moor. Nonetheless, turnover rates were high, with only 55% of sampled sites maintaining dwarf shrub moor coverage between 1913 and 2000. 4Stakeholders identified many of the changes revealed by the historical data, such as increased sheep numbers, fewer farms and greater specialization. However, other land-use changes were not properly described. For instance, although there had been no overall change in the proportion of dwarf shrub moor and the size of the rural labour force had not fallen, stakeholders reported a decline in both. Spatial heterogeneity of the changes, shifting baselines and problems with historical data sources might account for some of these discrepancies. 5Synthesis and applications. A marked increase in sheep numbers, combined with general agricultural intensification, have been the dominant land-use processes in the Peak District during the 20th century. Stakeholders only correctly perceived some land-use changes. Policy and management objectives should therefore be based primarily on actual historical evidence. However, understanding stakeholder perceptions and how they differ from, or agree with, the available evidence will contribute to the successful uptake of land management policies and partly determine the costs of policy implementation. [source] The importance of biological inertia in plant community resistance to invasionJOURNAL OF VEGETATION SCIENCE, Issue 3 2003Betsy Von Holle Abstract. Insights into the ecology of historic invasions by introduced species can be gained by studying long-term patterns of invasions by native species. In this paper, we review literature in palaeo-ecology, forest-stand simulation modelling, and historical studies of plant species invasions to illustrate the relevance of biological inertia in plant communities to invasion ecology. Resistance to invasion occurs in part because of environmental, demographic, and biotic factors influencing the arrival and establishment of invading species. We propose that biological inertia within the resident community is a fourth component of resistance to invasion, because of the lag time inherent in eliminating resident species and perhaps their traces after environmental conditions become suitable for invasion by immigrating species. Whether or not an introduced species invades can be conditioned by the presence of the pre-existing community (and/or its legacy) in addition to the other biotic and abiotic factors. [source] Willingness to Communicate in the Second Language: Understanding the Decision to Speak as a Volitional ProcessMODERN LANGUAGE JOURNAL, Issue 4 2007PETER D. MACINTYRE Previous research has devoted a great deal of attention to describing the long-term patterns and relationships among trait-level or situation-specific variables. The present discussion extracts kernels of wisdom, based on the literatures on language anxiety and language learning motivation, that are used to frame the argument that choosing to initiate communication at a particular moment in time can be conceptualized as a volitional (freely chosen) process. The result is a degree of willingness to communicate (WTC) with the potential to rise and fall rapidly as the situation changes. Previous research based on both qualitative and quantitative methodologies is described that demonstrates the complexity of the processes involved in creating WTC. It is argued that methodologies must be adapted to focus upon the dynamic process of choosing to initiate or avoid second language communication when the opportunity arises. [source] HOW DID LIFE BECOME SO DIVERSE?PALAEONTOLOGY, Issue 1 2007THE DYNAMICS OF DIVERSIFICATION ACCORDING TO THE FOSSIL RECORD AND MOLECULAR PHYLOGENETICS Abstract:, The long-term diversification of life probably cannot be modelled as a simple equilibrial process: the time scales are too long, the potential for exploring new ecospace is too large and it is unlikely that ecological controls can act at global scales. The sum of many clade expansions and reductions, each of which happens according to its own dynamic, probably approximates more a damped exponential curve when translated into a global-scale species diversification curve. Unfortunately, it is not possible to plot such a meaningful global-scale species diversification curve through time, but curves at higher taxonomic levels have been produced. These curves are subject to the vagaries of the fossil record, but it is unlikely that the sources of error entirely overwhelm the biological signal. Clades radiate when the external and internal conditions are right: a new territory or ecospace becomes available, and the lineage has acquired a number of characters that open up a new diet or mode of life. Modern high levels of diversity in certain speciose clades may depend on such ancient opportunities taken. Dramatic climatic changes through the Quaternary must have driven extinctions and originations, but many species responded simply by moving to more favourable locations. Ecological communities appear to be no more than merely chance associations of species, but there may be real interactions among species. Ironically, high species diversity may lead to more speciation, not, as had been assumed, less: more species create more opportunities and selective pressures for other species to respond to, rather than capping diversity at a fixed equilibrium level. Studies from the scale of modern ecosystems to global long-term patterns in the fossil record support a model for the exponential diversification of life, and one explanation for a pattern of exponential diversification is that as diversity increases, new forms become ever more refinements of existing forms. In a sense the world becomes increasingly divided into finer niche space. Organisms have a propensity to speciate freely, species richness within ecosystems appears to generate opportunities for more speciation, clades show all kinds of patterns from sluggish speciation rates and constant diversity through time to apparently explosive speciation, and there is no evidence that rapidly speciating clades have reached a limit, nor that they are driving other clades to extinction. A corollary of this view is that current biodiversity must be higher than it has ever been. Limits to infinite growth are clearly local, regional, and global turnover and extinction events, when climate change and physical catastrophes knock out species and whole clades, and push the rising exponential curve down a notch or two. [source] Testing long-term patterns of basin sedimentation by detrital zircon geochronology, Centralian Superbasin, AustraliaBASIN RESEARCH, Issue 3 2007D. W. Maidment ABSTRACT Detrital zircon geochronology of Neoproterozoic to Devonian sedimentary rocks from the Georgina and Amadeus basins has been used to track changes in provenance that reflect the development and inversion of the former Australian Superbasin. Through much of the Neoproterozoic, sediments appear to have been predominantly derived from local sources in the Arunta and Musgrave inliers. Close similarities between the detrital age signatures of late Neoproterozoic sedimentary rocks in the two basins suggests that they were contiguous at this time. A dominant population of 1.2,1.0 Ga zircon in Early Cambrian sediments of the Amadeus Basin reflects the uplift of the Musgrave Inlier during the Petermann Orogeny between 560 and 520 Ma, which shed a large volume of detritus northwards into the Amadeus Basin. Early Cambrian sedimentary rocks in the Georgina Basin have a much smaller proportion of 1.2,1.0 Ga detritus, possibly due to the formation of sub-basins along the northern margin of the Amadeus Basin which might have acted as a barrier to sediment transfer. An influx of 0.6,0.5 Ga zircon towards the end of the Cambrian coincides with the transgression of the Larapintine Sea across central Australia, possibly as a result of intracratonic rifting. Detrital zircon age spectra of sedimentary rocks deposited within this epicontinental sea are very similar to those of coeval sedimentary rocks from the Pacific Gondwana margin, implying that sediment was transported into central Australia from the eastern continental margin. The remarkably consistent ,Pacific Gondwana' signature of Cambro-Ordovician sediments in central and eastern Australia reflects a distal source, possibly from east Antarctica or the East African Orogen. The peak of the marine incursion into central Australia in the early to mid Ordovician coincides with granulite-facies metamorphism at mid-crustal depths between the Amadeus and Georgina basins (the Larapinta Event). The presence of the epicontinental sea, the relative lack of a local basement zircon component in Cambro-Ordovician sedimentary rocks and their maturity suggest that metamorphism was not accompanied by mountain building, consistent with an extensional or transtensional setting for this tectonism. Sediments deposited at ,435,405 and ,365 Ma during the Alice Springs Orogeny have detrital age signatures similar to those of Cambro-Ordovician sedimentary rocks, reflecting uplift and reworking of the older succession into narrow foreland basins adjacent to the orogen. [source] | |||||||||||||