Search results for "570 Life Sciences"
showing 10 items of 313 documents
The 1430s: a cold period of extraordinary internal climate variability during the early Spörer Minimum with social and economic impacts in north-west…
2016
Changes in climate affected human societies throughout the last millennium. While European cold periods in the 17th and 18th century have been assessed in detail, earlier cold periods received much less attention due to sparse information available. New evidence from proxy archives, historical documentary sources and climate model simulations permit us to provide an interdisciplinary, systematic assessment of an exceptionally cold period in the 15th century. Our assessment includes the role of internal, unforced climate variability and external forcing in shaping extreme climatic conditions and the impacts on and responses of the medieval society in north-western and central Europe. Climate…
Land Use Affects Carbon Sources to the Pelagic Food Web in a Small Boreal Lake
2016
Small humic forest lakes often have high contributions of methane-derived carbon in their food webs but little is known about the temporal stability of this carbon pathway and how it responds to environmental changes on longer time scales. We reconstructed past variations in the contribution of methanogenic carbon in the pelagic food web of a small boreal lake in Finland by analyzing the stable carbon isotopic composition (δ13C values) of chitinous fossils of planktivorous invertebrates in sediments from the lake. The δ13C values of zooplankton remains show several marked shifts (approx. 10 ‰), consistent with changes in the proportional contribution of carbon from methane-oxidizing bacteri…
Sun-Induced Chlorophyll Fluorescence I: Instrumental Considerations for Proximal Spectroradiometers
2019
Growing interest in the proximal sensing of sun-induced chlorophyll fluorescence (SIF) has been boosted by space-based retrievals and up-coming missions such as the FLuorescence EXplorer (FLEX). The European COST Action ES1309 “Innovative optical tools for proximal sensing of ecophysiological processes” (OPTIMISE, ES1309; https://optimise.dcs.aber.ac.uk/) has produced three manuscripts addressing the main current challenges in this field. This article provides a framework to model the impact of different instrument noise and bias on the retrieval of SIF; and to assess uncertainty requirements for the calibration and characterization of state-of-the-art SIF-oriented spectroradiom…
Dental wear at macro- and microscopic scale in rabbits fed diets of different abrasiveness: A pilot investigation
2020
To differentiate the effects of internal and external abrasives on tooth wear, we performed a controlled feeding experiment in rabbits fed diets of varying phytolith content as an internal abrasive and with addition of sand as an external abrasive. 13 rabbits were each fed one of the following four pelleted diets with different abrasive characteristics (no phytoliths: lucerne L; phytoliths: grass G; more phytoliths: grass and rice hulls GR; phytoliths plus external abrasives: grass, rice hulls and sand GRS) for two weeks. At the end the feeding period, three tooth wear proxies were applied to quantify wear on the cheek teeth at macroscopic and microscopic wear scales: CT scans were obtained…
Holocene vegetation and fire history of the mountains of Northern Sicily (Italy)
2016
Knowledge about vegetation and fire history of the mountains of Northern Sicily is scanty. We analysed five sites to fill this gap and used terrestrial plant macrofossils to establish robust radiocarbon chronologies. Palynological records from Gorgo Tondo, Gorgo Lungo, Marcato Cixé, Urgo Pietra Giordano and Gorgo Pollicino show that under natural or near natural conditions, deciduous forests (Quercus pubescens, Q. cerris, Fraxinus ornus, Ulmus), that included a substantial portion of evergreen broadleaved species (Q. suber, Q. ilex, Hedera helix), prevailed in the upper meso- mediterranean belt. Mesophilous deciduous and evergreen broadleaved trees (Fagus sylvatica, Ilex aquifolium) dominat…
Continental-scale temperature variability during the past two millennia
2013
Past global climate changes had strong regional expression. To elucidate their spatio-temporal pattern, we reconstructed past temperatures for seven continental-scale regions during the past one to two millennia. The most coherent feature in nearly all of the regional temperature reconstructions is a long-term cooling trend, which ended late in the nineteenth century. At multi-decadal to centennial scales, temperature variability shows distinctly different regional patterns, with more similarity within each hemisphere than between them. There were no globally synchronous multi-decadal warm or cold intervals that define a worldwide Medieval Warm Period or Little Ice Age, but all reconstructi…
Controlled feeding experiments with diets of different abrasiveness reveal slow development of mesowear signal in goats ( Capra aegagrus hircus )
2018
ABSTRACT Dental mesowear is applied as a proxy to determine the general diet of mammalian herbivores based on tooth-cusp shape and occlusal relief. Low, blunt cusps are considered typical of grazers and high, sharp cusps typical of browsers. However, how internal or external abrasives impact mesowear, and the time frame the wear signature takes to develop, still need to be explored. Four different pelleted diets of increasing abrasiveness (lucerne, grass, grass and rice husks, and grass, rice husks and sand) were fed to four groups of a total of 28 adult goats in a controlled feeding experiment over a 6-month period. Tooth morphology was captured by medical CT scans at the beginning and end…
Within trophic level shifts in collagen-carbonate stable carbon isotope spacing are propagated by diet and digestive physiology in large mammal herbi…
2018
Stable carbon isotope analyses of vertebrate hard tissues such as bones, teeth, and tusks provide information about animal diets in ecological, archeological, and paleontological contexts. There is debate about how carbon isotope compositions of collagen and apatite carbonate differ in terms of their relationship to diet, and to each other. We evaluated relationships between δ13Ccollagen and δ13Ccarbonate among free-ranging southern African mammals to test predictions about the influences of dietary and physiological differences between species. Whereas the slopes of δ13Ccollagen–δ13Ccarbonate relationships among carnivores are ≤1, herbivore δ13Ccollag…
Daphnia invest in sexual reproduction when its relative costs are reduced
2018
The timing of sex in facultatively sexual organisms is critical to fitness, due to the differing demographic consequences of sexual versus asexual reproduction. In addition to the costs of sex itself, an association of sex with the production of dormant life stages also influences the optimal use of sex, especially in environments where resting eggs are essential to survive unfavourable conditions. Here we document population dynamics and the occurrence of sexual reproduction in natural populations of Daphnia magna across their growing season. The frequency of sexually reproducing females and males increased with population density and with decreasing asexual clutch sizes. The frequency of…
Social transmission of avoidance among predators facilitates the spread of novel prey.
2018
Warning signals are an effective defence strategy for aposematic prey, but only if they are recognized by potential predators. If predators must eat prey to associate novel warning signals with unpalatability, how can aposematic prey ever evolve? Using experiments with great tits (Parus major) as predators, we show that social transmission enhances the acquisition of avoidance by a predator population. Observing another predator’s disgust towards tasting one novel conspicuous prey item led to fewer aposematic than cryptic prey being eaten for the predator population to learn. Despite reduced personal encounters with unpalatable prey, avoidance persisted and increased over subsequent trials.…