Showing papers by "University of Maine published in 2002"

Kelp forest ecosystems: biodiversity, stability, resilience and future

Abstract: Kelp forests are phyletically diverse, structurally complex and highly productive components of coldwater rocky marine coastlines. This paper reviews the conditions in which kelp forests develop globally and where, why and at what rate they become deforested. The ecology and long archaeological history of kelp forests are examined through case studies from southern California, the Aleutian Islands and the western North Atlantic, well-studied locations that represent the widest possible range in kelp forest biodiversity. Global distribution of kelp forests is physiologically constrained by light at high latitudes and by nutrients, warm temperatures and other macrophytes at low latitudes. Within mid-latitude belts (roughly 40–60° latitude in both hemispheres) well-developed kelp forests are most threatened by herbivory, usually from sea urchins. Overfishing and extirpation of highly valued vertebrate apex predators often triggered herbivore population increases, leading to widespread kelp deforestation. Such deforestations have the most profound and lasting impacts on species-depauperate systems, such as those in Alaska and the western North Atlantic. Globally urchin-induced deforestation has been increasing over the past 2–3 decades. Continued fishing down of coastal food webs has resulted in shifting harvesting targets from apex predators to their invertebrate prey, including kelp-grazing herbivores. The recent global expansion of sea urchin harvesting has led to the widespread extirpation of this herbivore, and kelp forests have returned in some locations but, for the first time, these forests are devoid of vertebrate apex predators. In the western North Atlantic, large predatory crabs have recently filled this void and they have become the new apex predator in this system. Similar shifts from fish- to crab-dominance may have occurred in coastal zones of the United Kingdom and Japan, where large predatory finfish were extirpated long ago. Three North American case studies of kelp forests were examined to determine their long history with humans and project the status of future kelp forests to the year 2025. Fishing impacts on kelp forest systems have been both profound and much longer in duration than previously thought. Archaeological data suggest that coastal peoples exploited kelp forest organisms for thousands of years, occasionally resulting in localized losses of apex predators, outbreaks of sea urchin populations and probably small-scale deforestation. Over the past two centuries, commercial exploitation for export led to the extirpation of sea urchin predators, such as the sea otter in the North Pacific and predatory fishes like the cod in the North Atlantic. The large-scale removal of predators for export markets increased sea urchin abundances and promoted the decline of kelp forests over vast areas. Despite southern California having one of the longest known associations with coastal kelp forests, widespread deforestation is rare. It is possible that functional redundancies among predators and herbivores make this most diverse system most stable. Such biodiverse kelp forests may also resist invasion from non-native species. In the species-depauperate western North Atlantic, introduced algal competitors carpet the benthos and threaten future kelp dominance. There, other non-native herbivores and predators have become established and dominant components of this system. Climate changes have had measurable impacts on kelp forest ecosystems and efforts to control the emission of greenhouse gasses should be a global priority. However, overfishing appears to be the greatest manageable threat to kelp forest ecosystems over the 2025 time horizon. Management should focus on minimizing fishing impacts and restoring populations of functionally important species in these systems.

Fluorescence Inner-Filtering Correction for Determining the Humification Index of Dissolved Organic Matter

Abstract: The use of fluorescence spectrometry has been suggested as a simple method to determine the extent of natural organic matter humification by quantifying the red-shifting of fluorescence emission that occurs with increasing humification. Humification indices are calculated by dividing fluorescence intensity at longer wavelengths by intensity at shorter wavelengths. These indices calculated without any specific efforts to standardize dissolved organic matter (DOM) concentration will result in index values thatvary with DOM concentration due to fluorescence innerfiltering effects. This study critically evaluated the effect of DOM concentration on humification index determination using organic matter isolated from field corn extract, soil: water extract, and soil fulvic acid. The results show that humification index values are sensitive to DOM concentration of the solution and are linear with respect to transmittance of the solution at the 254 nm used as the excitation wavelength. An approximate correction for DOM is to exploit the linear nature of the regression fit and to determine index values at the extrapolated 100% transmittance value. An exact correction using explicit correction factors for both primary and secondary innerfiltration effects was shown to give humification index values that are concentration invariant when absorbance of the solution at 254 nm was less than approximately 0.3 unit. Defining the humification index as the fluorescence intensity in the 300-345 nm region divided by the sum of intensity in the 300-345 nm and 435-480 nm regions was statistically advantageous. This study suggests that for quantitative results which can be used to compare humification of natural organic matter across different studies, correction of the fluorescence emission spectra for innerfiltration effects is needed.

Mycosporine-Like Amino Acids and Related Gadusols: Biosynthesis, Accumulation, and UV-Protective Functions in Aquatic Organisms

Abstract: Organisms living in clear, shallow water are exposed to the damaging wavelengths of solar ultraviolet radiation (UVR) coincident with the longer wavelengths of photosynthetically available radiation (PAR) also necessary for vision. With the general exception of bacteria, taxonomically diverse marine and freshwater organisms have evolved the capacity to synthesize or accumulate UV-absorbing mycosporine-like amino acids (MAAs), presumably for protection against environmental UVR. This review highlights the evidence for this UV-protective role while also considering other attributed functions, including reproductive and osmotic regulation and vision. Probing the regulation and biosynthesis of MAAs provides insight to the physiological evolution and utility of UV protection and of biochemically associated antioxidant defenses.

Racial and Ethnic Achievement Gap Trends: Reversing the Progress Toward Equity?

Abstract: Racial and ethnic achievement gaps narrowed substantially in the 1970s and 1980s. As some of the gaps widened in the 1990s, there were some setbacks in the progress the nation made toward racial and ethnic equity. This article offers a look below the surface at Black-White and Hispanic-White achievement gap trends over the past 30 years. The literature review and data analysis identify the key factors that seem to have contributed to bifurcated patterns in achievement gaps. The conventional measures of socioeconomic and family conditions, youth culture and student behavior, and schooling conditions and practices might account for some of the achievement gap trends for a limited time period or for a particular racial and ethnic group. However, they do not fully capture the variations. This preliminary analysis of covariations in racial and ethnic gap patterns across several large data sets has implications for future research on the achievement of minority groups.

Resolution of Prochlorococcus and Synechococcus Ecotypes by Using 16S-23S Ribosomal DNA Internal Transcribed Spacer Sequences

Abstract: Cultured isolates of the marine cyanobacteria Prochlorococcus and Synechococcus vary widely in their pigment compositions and growth responses to light and nutrients, yet show greater than 96% identity in their 16S ribosomal DNA (rDNA) sequences. In order to better define the genetic variation that accompanies their physiological diversity, sequences for the 16S-23S rDNA internal transcribed spacer (ITS) region were determined in 32 Prochlorococcus isolates and 25 Synechococcus isolates from around the globe. Each strain examined yielded one ITS sequence that contained two tRNA genes. Dramatic variations in the length and G+C content of the spacer were observed among the strains, particularly among Prochlorococcus strains. Secondary-structure models of the ITS were predicted in order to facilitate alignment of the sequences for phylogenetic analyses. The previously observed division of Prochlorococcus into two ecotypes (called high and low-B/A after their differences in chlorophyll content) were supported, as was the subdivision of the high-B/A ecotype into four genetically distinct clades. ITS-based phylogenies partitioned marine cluster A Synechococcus into six clades, three of which can be associated with a particular phenotype (motility, chromatic adaptation, and lack of phycourobilin). The pattern of sequence divergence within and between clades is suggestive of a mode of evolution driven by adaptive sweeps and implies that each clade represents an ecologically distinct population. Furthermore, many of the clades consist of strains isolated from disparate regions of the world's oceans, implying that they are geographically widely distributed. These results provide further evidence that natural populations of Prochlorococcus and Synechococcus consist of multiple coexisting ecotypes, genetically closely related but physiologically distinct, which may vary in relative abundance with changing environmental conditions.

Amenities Drive Urban Growth

Abstract: Studies of the city traditionally posit a division between a city’s economy and its culture, with culture subordinate in explanatory power to work. However, post–industrial and globalizing trends are dramatically elevating the importance of culture. Cultural activities are increasingly crucial to urban economic vitality. Models to explain the growth of cities from the era of industrial manufacturing are outmoded. Citizens in the postindustrial city increasingly make quality of life demands, treating their own urban location as if tourists, emphasizing aesthetic concerns. These practices impact considerations about the proper nature of amenities that post–industrial cities can sustain.

Exact Solution for Thermoelastic Deformations of Functionally Graded Thick Rectangular Plates

Abstract: An exact solution is obtained for three-dimensional deformations of a simply supported functionally graded rectangular plate subjected to mechanical and thermal loads on its top and/or bottom surfaces. Suitable temperature and displacement functions that identically satisfy boundary conditions at the edges are used to reduce the partial differential equations governing the thermomechanical deformations to a set of coupled ordinary differential equations in the thickness coordinate, which are then solved by employing the power series method. The exact solution is applicable to both thick and thin plates. Results are presented for two-constituent metal‐ceramic functionally graded rectangular plates that have a power law through-the-thickness variation of the volume fractions of the constituents. The effective material properties at a point are estimated by either the Mori‐Tanaka or the self-consistentschemes. Exact displacementsand stressesatseveral locations for mechanical and thermal loads are used toassess theaccuracyof the classical plate theory, thee rst-ordershear deformation theory, and athird-order shear deformation theory for functionally graded plates. Results are alsocomputed for a functionally graded plate with material properties derived by the Mori‐Tanaka method, the self-consistent scheme, and a combination of these two methods.

Anger and Sadness Regulation: Predictions to Internalizing and Externalizing Symptoms in Children

Abstract: Examined the relation between children's self-reported anger and sadness regulation and the presence of internalizing and externalizing symptoms. Participants were 121 boys and 106 girls in the fourth and fifth grades who completed the Children's Depression Inventory (CDI), State-Trait Anxiety Inventory for Children (STAIC), Emotion Expression Scale for Children (EESC), and Children's Emotion Management Scales (CSMS, CAMS) and rated each other on aggressive behavior. Results of multiple regression analyses indicated that the inability to identify emotional states, the inhibition of anger, the dysregulation of anger and sadness, and the constructive coping with anger predicted internalizing symptoms. The dysregulated expression of sadness and constructive coping with anger were inversely related to externalizing symptoms.

Toward the semantic geospatial web

Abstract: With the growth of the World Wide Web has come the insight that currently available methods for finding and using information on the web are often insufficient. In order to move the Web from a data repository to an information resource, a totally new way of organizing information is needed. The advent of the Semantic Web promises better retrieval methods by incorporating the data's semantics and exploiting the semantics during the search process. Such a development needs special attention from the geospatial perspective so that the particularities of geospatial meaning are captured appropriately. The creation the Semantic Geospatial Web needs the development multiple spatial and terminological ontologies, each with a formal semantics; the representation of those semantics such that they are available both to machines for processing and to people for understanding; and the processing of geospatial queries against these ontologies and the evaluation of the retrieval results based on the match between the semantics of the expressed information need and the available semantics of the information resources and search systems. This will lead to a new framework for geospatial information retrieval based on the semantics of spatial and terminological ontologies. By explicitly representing the role of semantics in different components of the information retrieval process (people, interfaces, search systems, and information resources), the Semantic Geospatial Web will enable users to retrieve more precisely the data they need, based on the semantics associated with these data.

Knowledge warehouse: an architectural integration of knowledge management, decision support, artificial intelligence and data warehousing

Abstract: Decision support systems (DSS) are becoming increasingly more critical to the daily operation of organizations. Data warehousing, an integral part of this, provides an infrastructure that enables businesses to extract, cleanse, and store vast amounts of data. The basic purpose of a data warehouse is to empower the knowledge workers with information that allows them to make decisions based on a solid foundation of fact. However, only a fraction of the needed information exists on computers; the vast majority of a firm's intellectual assets exist as knowledge in the minds of its employees. What is needed is a new generation of knowledge-enabled systems that provides the infrastructure needed to capture, cleanse, store, organize, leverage, and disseminate not only data and information but also the knowledge of the firm. The purpose of this paper is to propose, as an extension to the data warehouse model, a knowledge warehouse (KW) architecture that will not only facilitate the capturing and coding of knowledge but also enhance the retrieval and sharing of knowledge across the organization. The knowledge warehouse proposed here suggests a different direction for DSS in the next decade. This new direction is based on an expanded purpose of DSS. That is, the purpose of DSS in knowledge improvement. This expanded purpose of DSS also suggests that the effectiveness of a DSS will, in the future, be measured based on how well it promotes and enhances knowledge, how well it improves the mental model(s) and understanding of the decision maker(s) and thereby how well it improves his/her decision making.

Signal analysis of behavioral and molecular cycles

Abstract: Circadian clocks are biological oscillators that regulate molecular, physiological, and behavioral rhythms in a wide variety of organisms. While behavioral rhythms are typically monitored over many cycles, a similar approach to molecular rhythms was not possible until recently; the advent of real-time analysis using transgenic reporters now permits the observations of molecular rhythms over many cycles as well. This development suggests that new details about the relationship between molecular and behavioral rhythms may be revealed. Even so, behavioral and molecular rhythmicity have been analyzed using different methods, making such comparisons difficult to achieve. To address this shortcoming, among others, we developed a set of integrated analytical tools to unify the analysis of biological rhythms across modalities. We demonstrate an adaptation of digital signal analysis that allows similar treatment of both behavioral and molecular data from our studies of Drosophila. For both types of data, we apply digital filters to extract and clarify details of interest; we employ methods of autocorrelation and spectral analysis to assess rhythmicity and estimate the period; we evaluate phase shifts using crosscorrelation; and we use circular statistics to extract information about phase. Using data generated by our investigation of rhythms in Drosophila we demonstrate how a unique aggregation of analytical tools may be used to analyze and compare behavioral and molecular rhythms. These methods are shown to be versatile and will also be adaptable to further experiments, owing in part to the non-proprietary nature of the code we have developed.

Corporate Reputation: A Research Agenda Using Strategy and Stakeholder Literature

Abstract: This article explores three literature bases in some depth: strategy, stakeholder/social issues, and the newly emerging works in reputation. The focus is on the potential research and practical overlaps that exist in these literatures. A model of reputation is developed that highlights these research opportunities for scholars in all three endeavors.A model of reputation formation is developed that can be used for further study and action. Throughout the analysis, various research avenues are suggested for active consideration.

Corporate reputation: a research agenda using strategy and stakeholder literature

Abstract: This article explores three literature bases in some depth: strategy, stakeholder/ social issues, and the newly emergingworks in reputation. The focus is on the potential research and practical ove...

Amphibian Distributions in a Landscape of Forests and Agriculture: an Examination of Landscape Composition and Conf iguration

Abstract: Landscapes can be described by two essential features: the composition and spatial arrangement of patches. We considered the roles of these basic landscape descriptors by examining how the occurrence of nine amphibian species in breeding ponds was associated with the area of forested habitat and the proximity of ponds to forested habitat. We used visual and call surveys to compare the composition of amphibian assemblages in 116 ponds adjacent to or separated from forest and surrounded by different amounts of forested land. The area of forest and pond adjacency to forest were not associated ( t = −0.13, nisolated = 64, nconnected = 52, p = 0.21), which means these factors can manifest their effects separately. We used logistic regression to test predictions about associations between each species and forest area and to test for associations with pond-forest adjacency. Seven of nine species were associated with forest area. Wood frogs ( Rana sylvatica), green frogs ( Rana clamitans), eastern newts ( Notopthalmus viridescens), spotted salamanders (Ambystoma maculatum), and salamanders of the blue-spotted/Jefferson's complex (Ambystoma laterale/A. jeffersonianum) were more likely to occupy ponds in more forested areas, whereas leopard frogs ( Rana pipiens) and American toads ( Bufo americanus) were negatively associated with forest area. Three species were associated with pond-forest adjacency. Spotted salamanders and salamanders of the blue-spotted/Jefferson's complex were more likely to occupy ponds that were adjacent to forest. In areas with little forest, leopard frogs were more likely to occur in adjacent ponds, but the reverse was true for areas with extensive forests. Our results suggest that the composition of the landscape surrounding breeding ponds is associated with the likelihood of occurrence of most of the species examined and that landscape configuration is also important for a smaller subset of species. Resumen: Los paisajes pueden ser descritos por dos caracteristicas esenciales: la composicion y la disposicion de fragmentos. Consideramos la funcion de estos descriptores basicos de paisaje analizando como se asocio la presencia de nueve especies de anfibios en estanques de reproduccion con el area de habitat boscoso y la cercania de estanques a habitat boscoso. Utilizamos registros visuales y auditivos para comparar la composicion de comunidades de anfibios en 116 estanques adyacentes a un bosque o separados del mismo y rodeados de diferentes cantidades de terreno boscoso. El area de bosque y la distancia de los estanques del al bosque no estuvieron asociados ( t = −0.13, naislado= 64, nconectado = 52, p = 0.21) lo que significa que estos factores pueden manifestar sus efectos por separado. Utilizamos regresion logistica para probar predicciones referentes a asociaciones entre cada especie y el area de bosque y para comprobar si las asociaciones si relacionaban con la adyacencia de los estanques al bosque. asociaciones con la adyacencia de estanques - bosque. Siete de nueve especies se asociaron con el area de bosque. Ranas de bosque ( Rana sylvatica), ranas verdes ( Rana clamitans), tritones del este ( Notopthalmus viridescens), salamandras manchadas (Ambystoma maculatum) y salamandras del complejo manchas azules/Jefferson (Ambystoma laterale/A. jeffersonianum) ocuparon mas estanques en areas mas boscosas, mientras que ranas leopardo ( Rana pipiens) y sapos americanos ( Bufo americanus) se asociaron negativamente con el area de bosque. Tres especies se asociaron con la adyacencia al bosque. Salamandras manchadas y salamandras del complejo manchas azules/Jefferson tenian mayor probabilidad de ocupar estanques adyacentes a bosque. En areas con poco bosque, ranas leopardo ocurrieron en estanques adyacentes, pero lo contrario sucedio en areas con bosques extensos. Nuestros resultados sugieren que la composicion del paisaje que rodea a los estanques de reproduccion se asocia con la probabilidad de ocurrencia de la mayoria de las especies analizadas y que la configuracion del paisaje tambien es importante para un subconjunto de especies mas pequeno.

Holocene atmosphere-ocean interactions: records from Greenland and the Aegean Sea

Abstract: We compare paleoclimate proxy records from central Greenland and the Aegean Sea to offer new insights into the causes, timing, and mechanisms of Holocene atmosphere-ocean interactions. A direct atmospheric link is revealed between Aegean sea surface temperature (SST) and high-latitude climate. The major Holocene events in our proxies of Aegean SST and winter/spring intensity of the Siberian High (GISP2 K+ record) follow an 2300 year spacing, recognised also in the D14C record and in worldwide Holocene glacier advance phases, suggesting a solar modulation of climate. We argue that the primary atmospheric response involved decadal-centennial fluctuations in the meridional pressure gradient, driving Aegean SST events via changes in the strength, duration, and/or frequency of northerly polar/continental air outbreaks over the basin. The observed natural variability should be accounted for in predictions of future climate change, and our timeframe for the Aegean climate events in addition provides an independent chronostratigraphic argument to Middle Eastern archaeological studies.

Habitat selection by wood turtles (clemmys insculpta): an application of paired logistic regression

Abstract: Models of habitat selection have been developed primarily for mobile animals with well-defined home ranges. The assumptions made by traditional techniques about habitat availability are inappropriate for species with low mobility and large home ranges, such as the wood turtle. We used paired logistic regression, typically used in medical case - control studies, to model selection of habitat within activity areas in a population of wood turtles in a watershed in western Maine. We also modeled selection of activity areas within the watershed, using nonpaired logistic regression. Within activity areas, wood turtles selected nonforested locations close to water with low canopy cover. Within the watershed, they selected activity areas close to streams and rivers with moderate forest cover and little open water. The difference between selection at these two scales suggests that wood turtles select forest edges to balance thermoregulatory and feeding needs. The model of selection of activity areas within the watershed correctly classified 84% of activity areas and random areas. This model may be useful for identifying wood turtle habitat across the landscape as part of regional conservation efforts. We suggest that paired logistic regression shows promise for analysis of habitat selection of species with movement patterns that violate the assumptions of traditional habitat selection models.

One-dimensional ecosystem model of the equatorial Pacific upwelling system. Part I: model development and silicon and nitrogen cycle

Abstract: A one-dimensional ecosystem model was developed for the equatorial Pacific upwelling system, and the model was used to study nitrogen and silicon cycle in the equatorial Pacific. The ecosystem model consisted of 10 components (nitrate, silicate, ammonium, small phytoplankton, diatom, micro- and meso-zooplankton, detrital nitrogen and silicon, and total CO2). The ecosystem model was forced by the area-averaged (5°S–5°N, 90°W–180°, the Wyrtki Box) annual mean upwelling velocity and vertical diffusivity obtained from a three-dimensional circulation model. The model was capable of reproducing the low-silicate, high-nitrate, and low-chlorophyll (LSHNLC) conditions in the equatorial Pacific. The linkage to carbon cycle was through the consumption of assimilated nitrate and silicate (i.e. new productions). Model simulations demonstrated that low-silicate concentration in the equatorial Pacific limits production of diatoms, and it resulted in low percentage of diatoms, 16%, in the total phytoplankton biomass. In the area of 5°S–5°N and 90°W–180°, the model produced an estimated sea-to-air CO2 flux of 4.3 mol m−2 yr−1, which is consistent with the observed results ranging of 1.0–4.5 mol m−2 yr−1. The ammonium inhibition played an important role in determining the nitrogen cycle in the model. The modeled surface nitrate concentration could increase by a factor of 10 (from 0.8 to 8.0 mmol m−3) when the strength of the ammonium inhibition increased from ψ=1.0 to 10.0 (mmol m−3)–1. The effects of both micro- and meso-zooplankton grazing were tested by varying the micro- and meso-zooplankton maximum grazing rates, G1max and G2max. The modeled results were quite sensitive to the zooplankton grazing parameters. The current model considered the role of iron implicitly through the parameters that determine the growth rate of diatoms. Several iron-enrichment experiments were conducted by changing the parameter α (the initial slope of the photosynthetic rate over irradiance at low irradiance), KSi(OH)4 (half-saturation concentration of silicate uptake by diatom), and μ2max (the potential maximum specific diatom growth rate) in the regulation terms of silicate uptake by diatom. Within the first 5 days in the modeled iron-enrichment experiment, the diatom biomass increased from 0.08 to 2.5 mmol m−3, more than a factor of 30 increase. But the diatom populations crashed 2 weeks after the experiment started, due to exhaustion of available silicate and increased mesozooplankton population. The modeled iron-enrichment experiments produced several ecological behaviors similar to these observed during the IronEx-2.

Formation of patterned ground and sublimation till over Miocene glacier ice in Beacon Valley, southern Victoria Land, Antarctica

Abstract: A thin glacial diamicton, informally termed Granite drift, occupies the floor of central Beacon Valley in southern Victoria Land, Antarctica. This drift is 40 Ar/ 39 Ar analyses of presumed in situ ash-fall deposits that occur within Granite drift. At odds with the great age of this ice are high-centered polygons that cut Granite drift. If polygon development has reworked and retransported ash-fall deposits, then they are untenable as chronostratigraphic markers and cannot be used to place a minimum age on the underlying glacier ice. Our results show that the surface of Granite drift is stable at polygon centers and that enclosed ash-fall deposits can be used to define the age of underlying glacier ice. In our model for patterned-ground development, active regions lie only above polygon troughs, where enhanced sublimation of underlying ice outlines high-centered polygons. The rate of sublimation is influenced by the development of porous gravel-and-cobble lag deposits that form above thermal-contraction cracks in the underlying ice. A negative feedback associated with the development of secondary-ice lenses at the base of polygon troughs prevents runaway ice loss. Secondary-ice lenses contrast markedly with glacial ice by lying on a δD versus δ 18 O slope of 5 rather than a precipitation slope of 8 and by possessing a strongly negative deuterium excess. The latter indicates that secondary-ice lenses likely formed by melting, downward percolation, and subsequent refreezing of snow trapped preferentially in deep polygon troughs. The internal stratigraphy of Granite drift is related to the formation of surface polygons and surrounding troughs. The drift is composed of two facies: A nonweathered, matrix-supported diamicton that contains >25% striated clasts in the >16 mm fraction and a weathered, clast-supported diamicton with varnished and wind-faceted gravels and cobbles. The weathered facies is a coarse-grained lag of Granite drift that occurs at the base of polygon troughs and in lenses within the nonweathered facies. The concentration of cosmogenic 3 He in dolerite cobbles from two profiles through the nonweathered drift facies exhibits steadily decreasing values and shows the drift to have formed by sublimation of underlying ice. These profile patterns and the 3 He surface-exposure ages of 1.18 ± 0.08 Ma and 0.18 ± 0.01 Ma atop these profiles indicate that churning of clasts by cryoturbation has not occurred at these sites in at least the past 10 5 and 10 6 yr. Although Granite drift is stable at polygon centers, low-frequency slump events occur at the margin of active polygons. Slumping, together with weathering of surface clasts, creates the large range of cosmogenic-nuclide surface-exposure ages observed for Granite drift. Maximum rates of sublimation near active thermal-contraction cracks, calculated by using the two 3 He depth profiles, range from 5 m/m.y. to 90 m/m.y. Sublimation rates are likely highest immediately following major slump events and decrease thereafter to values well below our maximum estimates. Nevertheless, these rates are orders of magnitude lower than those computed on theoretical grounds. During eruptions of the nearby McMurdo Group volcanic centers, ash-fall debris collects at the surface of Granite drift, either in open thermal-contraction cracks or in deep troughs that lie above contraction cracks; these deposits subsequently lower passively as the underlying glacier ice sublimes. The fact that some regions of Granite drift have escaped modification by patterned ground for at least 8.1 Ma indicates long-term geomorphic stability of individual polygons. Once established, polygon toughs likely persist for as long as 10 5 –10 6 yr. Our model of patterned-ground formation, which applies to the hyperarid, cold-desert, polar climate of Antarctica, may also apply to similar-sized polygons on Mars that occur over buried ice in Utopia Planitia.

Resetting the Circadian Clock by Social Experience in Drosophila melanogaster

Abstract: Circadian clocks are influenced by social interactions in a variety of species, but little is known about the sensory mechanisms underlying these effects. We investigated whether social cues could reset circadian rhythms in Drosophila melanogaster by addressing two questions: Is there a social influence on circadian timing? If so, then how is that influence communicated? The experiments show that in a social context Drosophila transmit and receive cues that influence circadian time and that these cues are likely olfactory.

Chestnut: history and ecology of a transformed species

Abstract: Aim The character and distribution of American chestnut (Castanea dentata) populations in New England are analysed to identify the extent to which the introduced chestnut blight and historic land use practices have affected chestnut distribution and life history Location The study focuses on chestnut in Connecticut and Massachusetts but includes analysis of data related to other Castanea species in North America and Europe Methods The ecology and palaeoecology of chestnut is investigated using a range of techniques, including examination of the growth form of chestnut trees in plantations located away from blight, mapping of chestnut sprouts and blight-killed trees at various locations, anatomical examination of chestnut stems, analysis of early forestry practices, identification of changes in the relative abundance of chestnut pollen in Holocene lake sediments and comparison of American chestnut with other Castanea species Results Examination of chestnut sprouts surviving in the former range of that species shows that most sprouts originated from suppressed seedlings and that environmental factors severely limited the survival of sprouts from large blight-killed trees Palynological data show that chestnut was either present in very low populations or entirely absent from New England and only became abundant after about 2500 years ago All factors suggest that chestnut abundance is related to the natural disturbance cycle, while human-induced transformations of the landscape and the introduction of chestnut blight have further transformed the character of chestnut in New England Main conclusions Most surviving chestnut sprouts in New England forests represent old seedlings that have continued to re-sprout since establishment before the introduction of blight nearly 100 years ago The growth form of these sprouts ensures a minimal substrate of bark tissue for blight establishment so that blight has a relatively minor effect on seedling–sprout survival The identification of modern chestnut sprouts as old seedlings indicates that the observed distribution of sprouts in New England woodlands is strongly influenced by land use conditions and especially field abandonment at the time when chestnut blight arrived from its point of introduction