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Latitude
Kinds of Latitude Selected AbstractsEnvironmental and spatial effects on the distribution of blue marlin (Makaira nigricans) as inferred from data for longline fisheries in the Pacific OceanFISHERIES OCEANOGRAPHY, Issue 6 2008NAN-JAY SU Abstract Blue marlin is distributed throughout tropical and temperate waters in the Pacific Ocean. However, the preference of this species for particular habitats may impact its vulnerability to being caught. The relationship between spatio-temporal patterns of blue marlin abundance and environmental factors is examined using generalized additive models fitted to catch and effort data from longline fisheries. The presence of blue marlin, and the catch rate given presence, are modeled separately. Latitude, longitude, and sea-surface temperature explain the greatest proportion of the deviance. Spatial distributions of relative density of blue marlin, based on combining the probability of presence and relative density given presence, indicate that there is seasonal variation in the distribution of blue marlin, and that the highest densities occur in the tropics. Seasonal patterns in the relative density of blue marlin appear to be related to shifts in SST. The distribution and relative abundance of blue marlin are sufficiently heterogeneous in space and time that the results of analyses of catch and effort data to identify ,hotspots' could be used as the basis for time-area management to reduce the amount of blue marlin bycaught in longline fisheries. [source] Annual performance analysis and thermal modelling of passive solar still for different inclinations of condensing coverINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 14 2007Anil Kr. Abstract This paper reports the annual as well as seasonal performance analysis of single-slope passive solar stills having three different inclinations of condensing cover, namely 15, 30 and 45°. The analysis is based on the experiments conducted throughout the year from June 2004 to May 2005 on one clear day every month. Each experiment has been carried over for 24 h for the New Delhi (Latitude: 28°37, North and Longitude: 77°13, East) climatic conditions. It was observed that the 15° inclination of condensing cover gives maximum annual yield and distillation efficiency. The concept of solar fraction has been used for the validation of thermal modelling. The fair agreement has been noted between the values observed experimentally and calculated theoretically for temperatures and yield in all seasons. Copyright © 2007 John Wiley & Sons, Ltd. [source] Composition, geographical affinities and endemism of the Iberian Peninsula orchid floraNORDIC JOURNAL OF BOTANY, Issue 3-4 2007Sonia Bernardos The orchid flora of the Iberian Peninsula is relatively well known, but its biogeographical and diversity patterns have until now remained unanalysed. This work compares the richness of this flora with that of 27 other territories in different continents and at different latitudes, with the aim of establishing whether it is richer or poorer than might be expected. Latitude was found to be an excellent predictor of regional orchid species richness. With 122 taxa, the orchid flora of the Iberian Peninsula is more or less as diverse as that of other Mediterranean areas of similar latitude (e.g. France, Greece or Italy), but more diverse than other European or indeed North African orchid floras. In this study, the Iberian orchid species were assigned to eight monophyletic clades and the global distribution of these are mapped to establish continental affinities between the floras. A recent floristic account on the Iberian orchids was also used to assign the orchid taxa to habitats, and the relationship between the number of endemisms and their habitats was analysed. The patterns of endemism differed in different habitats. Very high levels of endemism were found in habitats peculiar to the Mediterranean Basin, indicating the relict status of its orchid flora. [source] Latitude and Incidence of Ocular MelanomaPHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 4 2007Claire M. Vajdic No abstract is available for this article. [source] Latitude and Incidence of Ocular MelanomaPHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 6 2006Guo-Pei Yu We investigated the associations between latitude and the incidence of two different types of ocular melanoma, external ocular melanoma (exposed to sunlight) and internal melanoma (not exposed to sunlight), separately. Using 1992,2002 data from the Surveillance, Epidemiology, and End Results (SEER) Program of National Cancer Institute, we identified 2142 ocular melanoma cases in non-Hispanic whites, and then regressed the incidences of various types of ocular melanomas with latitude. Our analysis indicated that the higher the latitude (away from the equator, the less sun exposure), the lower the risk of external ocular melanoma (eyelid and conjunctival melanomas) among non-Hispanic whites (P for trend = 0.018). The incidence increased 2.48 fold from 47,48° to 20,22°. This trend is very similar to that of skin melanoma. The incidence of internal ocular melanoma (uveal melanoma) increased significantly with increasing latitudes (the less sun exposure, P for trend < 0.0001), it increased 4.91 fold from 20,22° to 47,48°. The latitudinal patterns of ocular melanomas may reflect the dual effects of sunlight exposure, i.e. a mutagenic effect of direct solar radiation on external ocular melanomas and a protective effect for internal uveal melanoma, which is similar to the sun radiation protective effects for various internal malignant tumors that are not exposed to the sunlight. [source] The Electronic Cultural Atlas InitiativePROCEEDINGS OF THE AMERICAN SOCIETY FOR INFORMATION SCIENCE & TECHNOLOGY (ELECTRONIC), Issue 1 2003Michael Buckland The Electronic Cultural Atlas Initiative (ECAI, ecai.org) is an international collaborative effort based administratively at Berkeley. Its mission is to improve education and scholarship through greater attention to time and place. Latitude, longitude, and time provide a useful basis for bringing together diverse network accessible resources that are related in time and place. [source] ,Latitude' and geographic patterns in species richnessECOGRAPHY, Issue 2 2004Bradford A. Hawkins First page of article [source] Enhanced terrestrial carbon uptake in the Northern High Latitudes in the 21st century from the Coupled Carbon Cycle Climate Model Intercomparison Project model projectionsGLOBAL CHANGE BIOLOGY, Issue 2 2010HAIFENG QIAN Abstract The ongoing and projected warming in the northern high latitudes (NHL; poleward of 60 °N) may lead to dramatic changes in the terrestrial carbon cycle. On the one hand, warming and increasing atmospheric CO2 concentration stimulate vegetation productivity, taking up CO2. On the other hand, warming accelerates the decomposition of soil organic matter (SOM), releasing carbon into the atmosphere. Here, the NHL terrestrial carbon storage is investigated based on 10 models from the Coupled Carbon Cycle Climate Model Intercomparison Project. Our analysis suggests that the NHL will be a carbon sink of 0.3 ± 0.3 Pg C yr,1 by 2100. The cumulative land organic carbon storage is modeled to increase by 38 ± 20 Pg C over 1901 levels, of which 17 ± 8 Pg C comes from vegetation (43%) and 21 ± 16 Pg C from the soil (8%). Both CO2 fertilization and warming enhance vegetation growth in the NHL. Although the intense warming there enhances SOM decomposition, soil organic carbon (SOC) storage continues to increase in the 21st century. This is because higher vegetation productivity leads to more turnover (litterfall) into the soil, a process that has received relatively little attention. However, the projected growth rate of SOC begins to level off after 2060 when SOM decomposition accelerates at high temperature and then catches up with the increasing input from vegetation turnover. Such competing mechanisms may lead to a switch of the NHL SOC pool from a sink to a source after 2100 under more intense warming, but large uncertainty exists due to our incomplete understanding of processes such as the strength of the CO2 fertilization effect, permafrost, and the role of soil moisture. Unlike the CO2 fertilization effect that enhances vegetation productivity across the world, global warming increases the productivity at high latitudes but tends to reduce it in the tropics and mid-latitudes. These effects are further enhanced as a result of positive carbon cycle,climate feedbacks due to additional CO2 and warming. [source] The Ultraviolet Radiation Environment of High Southern Latitudes: Springtime Behavior over a Decadal Timescale,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 2 2005Yixiang Liao ABSTRACT Four spectroradiometers located at latitudes from 55° to 90°S conducted near-continuous measurements of ground-level solar ultraviolet irradiance from 1990 through 2001. The behavior during months from October through December is of special interest because this period includes the springtime loss in column ozone and the naturally large irradiances of early summer. Monthly integrated irradiances using biological weightings for erythema and damage to DNA show a distortion of the normal annual cycle in irradiance, with enhanced values occurring in October and November. In some cases, these irradiances exceed those near summer solstice in December. Changes in local cloudiness and column ozone both contribute significantly to interannual variability in erythemal irradiance. This is particularly the case at Palmer Station, near 65°S, where the monthly integrated erythemal irradiance in November 1997 was more than double that observed 5 years earlier. In general, at sites on the Antarctic continent, interannual variability in monthly integrated erythemal irradiance is greatest in November, when the observation for any given year can fall 40% above or below the multiyear mean. Near the tip of South America, interannual variability is approximately half that seen in Antarctica. [source] The Role of Amoeboid Protists and the Microbial Community in Moss-Rich Terrestrial Ecosystems: Biogeochemical Implications for the Carbon Budget and Carbon Cycle, Especially at Higher Latitudes,THE JOURNAL OF EUKARYOTIC MICROBIOLOGY, Issue 3 2008O. ROGER ANDERSON ABSTRACT. Moss-rich terrestrial communities are widely distributed in low- and high-latitude environments, covering vast surface areas in the boreal forests and tundra. The microbial biota in these organic-rich communities may contribute substantially to the carbon budget of terrestrial communities and the carbon cycle on a global scale. Recent research is reported on the carbon content of microbial communities in some temperate and high-latitude moss communities. The total carbon content and potential respiratory carbon dioxide (CO2) efflux is reported for bacteria, microflagellates, naked amoebae, and testate amoebae within sampling sites at a northeastern forest and the tundra at Toolik, Alaska. Quantitative models of the predicted total CO2 efflux from the microbes, based on microscopic observations and enumeration of the microbiota in samples from the research sites, are described and predictions are compared with published field-based data of CO2 efflux. The significance of the predictions for climate change and global warming are discussed. [source] Evaluation of Uncertainties Associated with Geocoding TechniquesCOMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 3 2004Hassan A. Karimi Geocoded data play a major role in numerous engineering applications such as transportation and environmental studies where geospatial information systems (GIS) are used for spatial modeling and analysis as they contain spatial information (e.g., latitude and longitude) about objects. The information that a GIS produces is impacted by the quality of the geocoded data (e.g., coordinates) stored in its database. To make appropriate and reasonable decisions using geocoded data, it is important to understand the sources of uncertainty in geocoding. There are two major sources of uncertainty in geocoding, one related to the database that is used as a reference data set to geocode objects and one related to the interpolation technique used. Factors such as completeness, correctness, consistency, currency, and accuracy of the data in the reference database contribute to the uncertainty of the former whereas the specific logic and assumptions used in an interpolation technique contribute to the latter. The primary purpose of this article is to understand uncertainties associated with interpolation techniques used for geocoding. In doing so, three geocoding algorithms were used and tested and the results were compared with the data collected by the Global Positioning System (GPS). The result of the overall comparison indicated no significant differences between the three algorithms. [source] MAY ISSUE VERSUS SHALL ISSUE: EXPLAINING THE PATTERN OF CONCEALED-CARRY HANDGUN LAWS, 1960,2001CONTEMPORARY ECONOMIC POLICY, Issue 2 2008RICHARD S. GROSSMAN We analyze the timing and pattern of adoption of "shall issue" concealed-carry handgun laws. "Shall issue" laws require the authorities to issue permits to qualified applicants; "may issue" laws give the authorities more latitude to reject applications. We find three factors influence the shift from "may issue" to "shall issue." First, more urban states are less likely to shift to "shall issue," although the size of this effect is quantitatively small. Second, the switch is influenced by the decisions taken by neighboring states. Third, we find evidence that increases in the crime rate accelerated the switch to "shall issue."(JEL K40) [source] Seasonal variation of diagnosis of Type 1 diabetes mellitus in children worldwideDIABETIC MEDICINE, Issue 7 2009E. V. Moltchanova Abstract Aims, To determine if there is a worldwide seasonal pattern in the clinical onset of Type 1 diabetes. Methods, Analysis of the seasonality in diagnosis of Type 1 diabetes was based on the incidence data in 0- to 14-year-old children collected by the World Health Organization Diabetes Mondiale (WHO DiaMond) Project over the period 1990,1999. One hundred and five centres from 53 countries worldwide provided enough data for the seasonality analysis. The incidence seasonality patterns were also determined for age- and sex-specific groups. Results, Forty-two out of 105 centres exhibited significant seasonality in the incidence of Type 1 diabetes (P < 0.05). The existence of significant seasonal patterns correlated with higher level of incidence and of the average yearly counts. The correlation disappeared after adjustment for latitude. Twenty-eight of those centres had peaks in October to January and 33 had troughs in June to August. Two out of the four centres with significant seasonality in the southern hemisphere demonstrated a different pattern with a peak in July to September and a trough in January to March. Conclusions, The seasonality of the incidence of Type 1 diabetes mellitus in children under 15 years of age is a real phenomenon, as was reported previously and as is now demonstrated by this large standardized study. The seasonality pattern appears to be dependent on the geographical position, at least as far as the northern/southern hemisphere dichotomy is concerned. However, more data are needed on the populations living below the 30th parallel north in order to complete the picture. [source] A latitudinal gradient of beta diversity for exotic vascular plant species in North AmericaDIVERSITY AND DISTRIBUTIONS, Issue 3 2008Hong Qian ABSTRACT Determining relationships between the ranges of introduced species and geographical and environmental factors is an important step in understanding the mechanisms and processes of the spread of introduced species. In this study, I examined the beta diversity and latitude relationship for all naturalized exotic species of vascular plants in North America at a continental scale. Beta diversity was calculated as the absolute value of the slope of the relationship between the natural logarithm of the Simpson index of similarity (lnS) and spatial distance between pairs of state-level exotic floras within four latitudinal zones examined. Relative contributions of spatial distance and environmental difference to species turnover between exotic floras were examined. I found that beta diversity decreased monotonically from low to high latitudes: beta diversity for the southernmost zone was shallower than that for the northernmost zone by a factor of 2.6. Regression models of lnS in relation to spatial distance and environmental (climatic and topographical) difference for each latitudinal zone demonstrated that the explanatory power of these variables diminishes monotonically with latitude: the explained variance in lnS is 70.4%, 62.1%, 53.9%, and 33.9%, respectively, for the four latitudinal zones from south to north. For the southernmost zone, 58.3% of the variance in lnS is explained by climate variables and topography, and spatial distance explains only 2.3% of the variance. In contrast, for the northernmost zone, more than half the amount (22.5%) of the explained variance in lnS is attributable to spatial distance, and the remaining (18.9%) of the explained variance is attributable to climate variables and topography. [source] Determinants for the successful establishment of exotic ants in New ZealandDIVERSITY AND DISTRIBUTIONS, Issue 4 2005Philip J. Lester ABSTRACT Biological invasions can dramatically alter ecosystems. An ability to predict the establishment success for exotic species is important for biosecurity and conservation purposes. I examine the exotic New Zealand ant fauna for characteristics that predict or determine an exotic species' ability to establish. Quarantine records show interceptions of 66 ant species: 17 of which have established, 43 have failed to establish, whereas nests of another six are periodically observed but have failed to establish permanently (called ,ephemeral' establishment). Mean temperature at the highest latitude and interception variables were the only factors significantly different between established, failed or ephemeral groups. Aspects of life history, such as competitive behaviour and morphology, were not different between groups. However, in a stepwise discriminant analysis, small size was a key factor influencing establishment success. Interception rate and climate were also secondarily important. The resulting classification table predicted establishment success with 71% accuracy. Because not all exotic species are represented in quarantine records, a further discriminant model is described without interception data. Though with less accuracy (65%) than the full model, it still correctly predicted the success or failure of four species not used in the previous analysis. Techniques for improving the prediction accuracy are discussed. Predicting which species will establish in a new area appears an achievable goal, which will be a valuable tool for conservation biology. [source] Profiling invasive fish species: the importance of phylogeny and human useDIVERSITY AND DISTRIBUTIONS, Issue 4 2005Carles Alcaraz ABSTRACT Understanding the ecological differences between native and invasive species is of considerable scientific and practical interest. We examined such differences between native and invasive inland fish species from the Iberian Peninsula in order to analyse the importance of phylogenetic correction and variability (in addition to central tendency). We collected 26 quantitative and qualitative variables on the ecology, life-history traits and human use of the 69 inland fish species of the Iberian Peninsula, including native, invasive and migratory species. The taxonomic distribution of invasive fish species deviated significantly from world freshwater richness and in contrast to native species, invasive fish belongs to only five taxonomic orders but to a wide spectrum of families not native to the Iberian Peninsula. Because the life-history traits were highly dependent on taxonomy, the results, with or without applying phylogenetic methods, differed and after accounting for phylogeny, invasive species displayed higher and wider latitude in general and a different reproductive season mainly among salmonids and cyprinids. Human use was also significantly different between native and invasive fish species and produced more variability in life-history traits of invasive species and uneven taxonomic distribution because of the high diversity of species introduced. We show that accounting for taxonomy and studying variability in addition to central tendency is important in the comparison of life-history traits between native and invasive species. [source] Introduced plants of the invasive Solidago gigantea (Asteraceae) are larger and grow denser than conspecifics in the native rangeDIVERSITY AND DISTRIBUTIONS, Issue 1 2004Gabi Jakobs ABSTRACT Introduced plant species that became successful invaders appear often more vigorous and taller than their conspecifics in the native range. Reasons postulated to explain this better performance in the introduced range include more favourable environmental conditions and release from natural enemies and pathogens. According to the Evolution of Increased Competitive Ability hypothesis (EICA hypothesis) there is a trade-off between investment into defence against herbivores and pathogens, and investment into a stronger competitive ability. In this study, we conducted field surveys to investigate whether populations of the invasive perennial Solidago gigantea Ait (Asteraceae) differ with respect to growth and size in the native and introduced range, respectively. We assessed size and morphological variation of 46 populations in the native North American range and 45 populations in the introduced European range. Despite considerable variation between populations within continents, there were pronounced differences between continents. The average population size, density and total plant biomass were larger in European than in American populations. Climatic differences and latitude explained only a small proportion of the total variation between the two continents. The results show that introduced plants can be very distinct in their growth form and size from conspecifics in the native range. The apparently better performance of this invasive species in Europe may be the result of changed selection pressures, as implied by the EICA hypothesis. [source] Patterns of isozyme variation as indicators of biogeographic history in Pilgerodendron uviferum (D. Don) FlorínDIVERSITY AND DISTRIBUTIONS, Issue 2 2002A. C. Premoli Abstract. The effects of Pleistocene glaciations on the genetic characteristics of the most austral conifer in the world, Pilgerodendron uviferum, were analysed with specific reference to the hypothesis that the species persisted locally in ice-free areas in temperate South America. It was expected that genetic variation would decrease with latitude, given that ice fields were larger in southern Patagonia and thus refugia were probably located towards the northern distributional limit of the species as suggested by the fossil record. In addition, an increase in among-population genetic divergence was expected with increasing distance to putative glacial refugia. We examined the relationship between location and within-population variability indices of 20 Pilgerodendron populations derived from isozyme analyses. We analysed possible refugia hypotheses by the distribution of allele frequencies using multivariate discriminant analysis. The degree of genetic differentiation with geographical distance between all population pairs was investigated by Mantel tests. Results indicated that Pilgerodendron populations are highly monomorphic, probably reflecting past population bottlenecks and reduced gene flow. Southernmost populations tend to be the least genetically variable and were therefore probably more affected by glacial activity than northern ones. Populations located outside ice limits seem to have been isolated during the glacial period. The presence of centres of genetic diversity, together with the lack of a significant correlation between genetic and geographical distances and the absence of geographical patterns of allelic frequencies at most analysed alleles, may indicate that Pilgerodendron did not advance southward after the last glaciation from a unique northern refugium, but spread from several surviving populations in ice-free areas in Patagonia instead. [source] Effects of terrain smoothing on topographic shielding correction factors for cosmogenic nuclide-derived estimates of basin-averaged denudation ratesEARTH SURFACE PROCESSES AND LANDFORMS, Issue 1 2009Kevin P. Norton Abstract Estimation of spatially averaged denudation rates from cosmogenic nuclide concentrations in sediments depends on the surface production rates, the scaling methods of cosmic ray intensities, and the correction algorithms for skyline, snow and vegetation shielding used to calculate terrestrial cosmogenic nuclide production. While the calculation of surface nuclide production and application of latitude, altitude and palaeointensity scaling algorithms are subjects of active research, the importance of additional correction for shielding by topographic obstructions, snow and vegetation is the subject of ongoing debate. The derivation of an additional correction factor for skyline shielding for large areas is still problematic. One important issue that has yet to be addressed is the effect of the accuracy and resolution of terrain representation by a digital elevation model (DEM) on topographic shielding correction factors. Topographic metrics scale with the resolution of the elevation data, and terrain smoothing has a potentially large effect on the correction of terrestrial cosmogenic nuclide production rates for skyline shielding. For rough, high-relief landscapes, the effect of terrain smoothing can easily exceed analytical errors, and should be taken into account. Here we demonstrate the effect of terrain smoothing on topographic shielding correction factors for various topographic settings, and introduce an empirical model for the estimation of topographic shielding factors based on landscape metrics. Copyright © 2008 John Wiley and Sons, Ltd. [source] Coastal conglomerates around the Hadjer el Khamis inselbergs (western Chad, central Africa): new evidence for Lake Mega-Chad episodesEARTH SURFACE PROCESSES AND LANDFORMS, Issue 10 2003Mathieu Schuster Abstract This paper reports on a study dealing with the rhyolitic inselbergs of Hadjer el Khamis that formed palaeoislands during Lake Mega-Chad events. Field observations have shown that: (1) conglomeratic patches of immature to mature clasts are preserved at the feet of the Hadjer el Khamis inselbergs; (2) in cross-section, their pro,le reveals a well de,ned cliff,platform junction at a constant elevation (325 m). The monolithological clasts show all degrees of roundness, from angular cobbles to well rounded pebbles. This wide range of maturity suggests a coastal origin for these cobbles. The system was permanently fed with angular clasts, which were progressively worn by waves. Cobbles that were wave-worked for the longest time are the best rounded. The cliff,platform junction is the result of erosion by waves, which attacked and undercut the inselberg cliffs during Lake Mega-Chad events. Asymmetrical erosion pro,les moreover suggest a wind regime dominated by SW to NE oriented winds. These interpretations have two implications. The elevation of the cliff,platform junction is an indication of the highest water level of Lake Mega-Chad at 320,325 m, which is in agreement with other observations elsewhere in the basin. The SW to NE oriented winds show that monsoon-related winds were prevalent during Lake Mega-Chad events, suggesting the Inter-Tropical Convergence Zone was located higher in latitude than today. Copyright © 2003 John Wiley & Sons, Ltd. [source] Sexual patterns of prebreeding energy reserves in the common frog Rana temporaria along a latitudinal gradientECOGRAPHY, Issue 5 2009K. Ingemar Jönsson The ability to store energy is an important life history trait for organisms facing long periods without energy income, and in particular for capital breeders such as temperate zone amphibians, which rely on stored energy during reproduction. However, large scale comparative studies of energy stores in populations with different environmental constraints on energy allocation are scarce. We investigated energy storage patterns in spring (after hibernation and before reproduction) in eight common frog Rana temporaria populations exposed to different environmental conditions along a 1600,km latitudinal gradient across Scandinavia (range of annual activity period is 3,7,months). Analyses of lean body weight (eviscerated body mass), weight of fat bodies, liver weight, and liver fat content, showed that 1) post-hibernation/pre-breeding energy stores increased with increasing latitude in both sexes, 2) males generally had larger energy reserves than females and 3) the difference in energy stores between sexes decreased towards the north. Larger energy reserves towards the north can serve as a buffer against less predictable and/or less benign weather conditions during the short activity period, and may also represent a risk-averse tactic connected with a more pronounced iteroparous life history. In females, the continuous and overlapping vitellogenic activity in the north may also demand more reserves in early spring. The general sexual difference could be a consequence of the fact that, at the time of our sampling, females had already invested their energy into reproduction in the given year (i.e. their eggs were already ovulated), while the males' main reproductive activities (e.g. calling, mate searching, sexual competition) occurred later in the season. [source] Parasite loads are higher in the tropics: temperate to tropical variation in a single host-parasite systemECOGRAPHY, Issue 4 2008Daniel J. Salkeld Parasites are important selective forces upon the evolutionary ecology of their hosts. At least one hypothesis suggests that high species diversity in the tropics is associated with higher parasite abundance in tropical climates. Few studies, however, have directly assessed whether parasite abundance is higher in the tropics. To address this question, it is ideal, although seldom achievable, to compare parasite abundance in a single species that occurs over a geographical area including both temperate and tropical regions. We examined variation in blood parasite abundance in seven populations of a single lizard host species (Eulamprus quoyii) using a transect that spans temperate and tropical climates. Parasite prevalence (proportion of the host population infected) showed no geographical pattern. Interestingly though, parasite load was higher in lizard populations in the tropics, and was related to mean annual temperature, but not to rainfall. We speculate that in this system the relationship between latitude and parasite load is most likely due to variation in host life history over their geographic range. [source] Energy input and zooplankton species richnessECOGRAPHY, Issue 6 2007Dag O. Hessen What are the relative contribution of temperature and solar irradiance as types of energy deliveries for species richness at the ecosystem level? In order to reveal this question in lake ecosystems, we assessed zooplankton species richness in 1891 Norwegian lakes covering a wide range in latitude, altitude, and lake area. Geographical variables could largely be replaced by temperature-related variables, e.g. annual monthly maximum temperature or growth season. Multivariate analysis (PCA) revealed that not only maximum monthly temperature, but also energy input in terms of solar radiation were closely associated with species richness. This was confirmed by stepwise, linear regression analysis in which lake area was also found to be significant. We tested the predictive power of the "metabolic scaling laws" for species richness by regressing Ln of species richness over the inverse of the air temperature (in Kelvin), corrected for the activation energy (eV) as predicted by the Boltzmann constant. A significant, negative slope of 0.78 for ln richness over temperature, given as 1/kT, was found, thus slightly higher than the range of slopes predicted from the scaling law (0.60,0.70). Temperature basically constrained the upper bound of species number, but it was only a modest predictor of actual richness. Both PCA-analysis and linear regression models left a large unexplained variance probably due to lake-specific properties such as catchment influence, lake productivity, food-web structure, immigration constraints or more stochastic effects. [source] Spatial variation in population density across the geographical range in helminth parasites of yellow perch Perca flavescensECOGRAPHY, Issue 5 2007Robert Poulin The abundance of a species is not constant across its geographical range; it has often been assumed to decrease from the centre of a species' range toward its margins. The central assumption of this "favourable centre" model is tested for the first time with parasites, using different species of helminth parasites exploiting fish as definitive hosts. Data on prevalence (percentage of hosts that are infected) and abundance (mean no. parasites per host) were compiled for 8 helminth species occurring in 23 populations of yellow perch Perca flavescens, from continental North America. For each parasite species, correlations were computed between latitude and both local prevalence and abundance values. In addition, the relationships between the relative prevalence or abundance in one locality and the distance between that locality and the one where the maximum value was reported, were assessed separately for each species to determine whether abundance tends to decrease away from the presumed centre of the range, where it peaks. For both the cestode Proteocephalus pearsei and the acanthocephalan Leptorhynchoides thecatus, there was a positive relationship between prevalence or abundance and the latitude of the sampled population. There was also a significant negative relationship between relative prevalence and the distance from the locality showing the maximum value in P. pearsei, but no such pattern was observed for the other 7 parasite species. Since this single significant decrease in prevalence with increasing distance from the peak value may be confounded by a latitudinal gradient, it appears that the distribution of abundance in parasites of perch does not follow the favourable centre model. This means that the environmental variables affecting the density of parasites (host availability, abiotic conditions) do not show pronounced spatial autocorrelation, with nearby sites not necessarily providing more similar conditions for the growth of parasite populations than distant sites. [source] The relative importance of latitude matching and propagule pressure in the colonization success of an invasive forbECOGRAPHY, Issue 6 2006John L. Maron Factors that influence the early stages of invasion can be critical to invasion success, yet are seldom studied. In particular, broad pre-adaptation to recipient climate may importantly influence early colonization success, yet few studies have explicitly examined this. I performed an experiment to determine how similarity between seed source and transplant site latitude, as a general indicator of pre-adaptation to climate, interacts with propagule pressure (100, 200 and 400 seeds/pot) to influence early colonization success of the widespread North American weed, St. John's wort Hypericum perforatum. Seeds originating from seven native European source populations were sown in pots buried in the ground in a field in western Montana. Seed source populations were either similar or divergent in latitude to the recipient transplant site. Across seed density treatments, the match between seed source and recipient latitude did not affect the proportion of pots colonized or the number of individual colonists per pot. In contrast, propagule pressure had a significant and positive effect on colonization. These results suggest that propagules from many climatically divergent source populations can be viable invaders. [source] Beta diversity and latitude in North American mammals: testing the hypothesis of covariationECOGRAPHY, Issue 5 2004Pilar Rodríguez Several hypotheses attempt to explain the latitudinal gradient of species diversity, but some basic aspects of the pattern remain insufficiently explored, including the effect of scales and the role of beta diversity. To explore such components of the latitudinal gradient, we tested the hypothesis of covariation, which states that the gradient of species diversity should show the same pattern regardless of the scale of analysis. The hypothesis implies that there should be no gradients of beta diversity, of regional range size within regions, and of the slope of the species-area curve. For the fauna of North American mammals, we found contrasting results for bats and non-volant species. We could reject the hypothesis of covariation for non-volant mammals, for which the number of species increases towards lower latitudes, but at different rates depending on the scale. Also, for this group, beta diversity is higher at lower latitudes, the regional range size within regions is smaller at lower latitudes, and z, the slope of the species-area relationship is higher at lower latitudes. Contrarily bats did not show significant deviations from the predictions of the hypothesis of covariation: at two different scales, species richness shows similar trends of increase at lower latitudes, and no gradient can be demonstrated for beta diversity, for regional range size, or for the slopes of the species-area curve. Our results show that the higher diversity of non-volant mammals in tropical areas of North America is a consequence of the increase in beta diversity and not of higher diversity at smaller scales. In contrast, the diversity of bats at both scales is higher at lower latitudes. These contrasting patterns suggest different causes for the latitudinal gradient of species diversity in the two groups that are ultimately determined by differences in the patterns of geographic distribution of the species. [source] Benthic macroinvertebrates in Swedish streams: community structure, taxon richness, and environmental relationsECOGRAPHY, Issue 3 2003Leonard Sandin Spatial scale, e.g. from the stream channel, riparian zone, and catchment to the regional and global scale is currently an important topic in running water management and bioassessment. An increased knowledge of how the biota is affected by human alterations and management measures taken at different spatial scales is critical for improving the ecological quality of running waters. However, more knowledge is needed to better understand the relationship between environmental factors at different spatial scales, assemblage structure and taxon richness of running water organisms. In this study, benthic macroinvertebrate data from 628 randomly selected streams were analysed for geographical and environmental relationships. The dataset also included 100 environmental variables, from local measures such as in-stream substratum and vegetation type, catchment vegetation and land-use, and regional variables such as latitude and longitude. Cluster analysis of the macroinvertebrate data showed a continuous gradient in taxonomic composition among the cluster groups from north to south. Both locally measured variables (e.g. water chemistry, substratum composition) and regional factors (e.g. latitude, longitude, and an ecoregional delineation) were important for explaining the variation in assemblage structure and taxon richness for stream benthic macroinvertebrates. This result is of importance when planning conservation and management measurements, implementing large-scale biomonitoring programs, and predicting how human alterations (e.g. global warming) will affect running water ecosystems. [source] Does habitat use explain large scale species richness patterns of aquatic beetles in Europe?ECOGRAPHY, Issue 2 2003Ignacio Ribera Regularities in species richness are widely observed but controversy continues over its mechanistic explanation. Because richness patterns are usually a compound measure derived from taxonomically diverse species with different ecological requirements, these analyses may confound diverse causes of species numbers. Here we investigate species richness in the aquatic beetle fauna of Europe, separating major taxonomic groups and two major ecological types, species occurring in standing and running water bodies. We collated species distributions for 800+ species of water beetles in 15 regions across western Europe. Species number in any of these regions was related to three variables: total area size, geographic connectedness of the area, and latitude. Pooled species numbers were accurately predicted, but correlations were different for species associated with either running or standing water. The former were mostly correlated with latitude, while the latter were only correlated with the measure of connectedness or with area size. These differences were generally also observed in each of the four phylogenetically independent lineages of aquatic Coleoptera when analysed separately. We propose that effects of habitat, in this case possibly mediated by different long term persistence of running and standing water bodies, impose constraints at the population or local level which, if effective over larger temporal and spatial scales, determine global patterns of species richness. [source] Body size determines the strength of the latitudinal diversity gradientECOGRAPHY, Issue 3 2001Helmut Hillebrand In most groups of organisms, the species richness decreases from the tropics to the poles. The mechanisms causing this latitudinal diversity gradient are still controversial. We present data from a comprehensive weighted meta-analysis on the strength of the latitudinal gradient in relation to body size. We sampled literature data on the correlation between species richness and latitude for a variety of organisms, ranging from trees to protozoa. In addition, own data on the presence of large-scale diversity patterns for diatoms were included, both for local and regional species richness. The strength of the latitudinal gradient was positively correlated to the size of the organisms. Strongest decreases of species richness to the poles was found for large organisms like trees and vertebrates, whereas meiofauna, protozoa and diatoms showed weak or no correlations between species richness and latitude. These results imply that latitudinal gradients are shaped by non-equilibrium (regional) processes and are persistent under conditions of dispersal limitation. [source] Selection for discontinuous life-history traits along a continuous thermal gradient in the butterfly Aricia agestisECOLOGICAL ENTOMOLOGY, Issue 6 2005Steve Burke Abstract., 1.,Voltinism may be conceptualised as the product of development rate and the timing of diapause , two components that together translate gradual environmental variation, through periods of growth and development, into ,generational units'. This may result in very different selection pressures on diapause induction and development time in populations with different numbers of generations per year. 2.,Developmental data from univoltine and bivoltine populations of the butterfly Aricia agestis (Lepidoptera: Lycaenidae) in North Wales were used to examine larval development time and the timing of diapause, and their contribution towards voltinism in populations that occur at the same latitude and in geographic proximity to one another along a thermal gradient. 3.,The critical photoperiod for diapause induction in univoltines and bivoltines from the same latitude differed by more than 1.5 h. 4.,Development time also differed significantly between these populations, in line with predictions that bivoltines would need to exhibit shorter development times in order to achieve two complete generations per year. Shorter development times for bivoltines result in lower pupal weights, suggesting a trade-off exists between generation number and body size that may dictate the position of the transition zone between the two life-history strategies. Analysis of development times in a third population, from southern England, with greater thermal availability than those from North Wales, further supports this hypothesised trade-off. 5.,To achieve the conversion of a continuous thermal gradient into the binary biological response from univoltism to bivoltism, bivoltines speed up development, reduce adult body size and shift their diapause induction response. [source] | ||||||||||||||||||||||||||||||||||||||||||||||||||||