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Environmental Constraints (environmental + constraint)
Selected AbstractsEnvironmental constraints on life histories in Antarctic ecosystems: tempos, timings and predictabilityBIOLOGICAL REVIEWS, Issue 1 2006Lloyd S. Peck ABSTRACT Knowledge of Antarctic biotas and environments has increased dramatically in recent years. There has also been a rapid increase in the use of novel technologies. Despite this, some fundamental aspects of environmental control that structure physiological, ecological and life-history traits in Antarctic organisms have received little attention. Possibly the most important of these is the timing and availability of resources, and the way in which this dictates the tempo or pace of life. The clearest view of this effect comes from comparisons of species living in different habitats. Here, we (i) show that the timing and extent of resource availability, from nutrients to colonisable space, differ across Antarctic marine, intertidal and terrestrial habitats, and (ii) illustrate that these differences affect the rate at which organisms function. Consequently, there are many dramatic biological differences between organisms that live as little as 10 m apart, but have gaping voids between them ecologically. Identifying the effects of environmental timing and predictability requires detailed analysis in a wide context, where Antarctic terrestrial and marine ecosystems are at one extreme of the continuum of available environments for many characteristics including temperature, ice cover and seasonality. Anthropocentrically, Antarctica is harsh and as might be expected terrestrial animal and plant diversity and biomass are restricted. By contrast, Antarctic marine biotas are rich and diverse, and several phyla are represented at levels greater than global averages. There has been much debate on the relative importance of various physical factors that structure the characteristics of Antarctic biotas. This is especially so for temperature and seasonality, and their effects on physiology, life history and biodiversity. More recently, habitat age and persistence through previous ice maxima have been identified as key factors dictating biodiversity and endemism. Modern molecular methods have also recently been incorporated into many traditional areas of polar biology. Environmental predictability dictates many of the biological characters seen in all of these areas of Antarctic research. [source] Teaching: An Interplay of Aims, Constraints, Conflicts, and CompromisesMODERN LANGUAGE JOURNAL, Issue 3 2000Larbi Oukada is essentially a contentious interplay of curricular and instructional aims and a host of regressive constraints, 4 of which are discussed in the present article. They are: (a) the endless and fallible nature of fully understanding knowledge and of representing it in an ontologically congruous manner (epistemological constraint); (b) the problems inherent in mediating knowledge through language (semiotic constraint); (c) the tenuous validity of the psychological assumptions on which the presentation of knowledge is conducted in the classroom (learning constraint); and (d) the local and potentially regressive variables, such as instructional time, language aptitude, attitude, personality, and motivation (environmental constraint). The thrust of the present article is to show that these 4 constraints exert inevitable and pedagogically fruitful tension on classroom teaching. [source] Environmental performance and equilibriumCANADIAN JOURNAL OF ECONOMICS, Issue 4 2007Thierry Bréchet Abstract., In this paper we show why firms' or industries' rankings in terms of environmental performance depend not only on the technology but also on market equilibrium. Between two industries committed to the same environmental constraint, the more eco-efficient is the one with the higher output level. By comparing industries and firms, we show that the rankings are not robust, for they are affected by market outcome. The role of eco-efficiency in firms' profitability in equilibrium is also scrutinized. All this shows that the usual eco-efficiency indicators are inadequate. To tackle this problem, we propose a sound indicator. Dans cet article nous montrons pourquoi les classements de firmes ou d'industries en terme d'éco-efficacité dépendent non seulement de la technologie, mais aussi de l'équilibre des marchés. Entre deux industries soumises à la même contrainte environnementale, la plus éco-efficace est celle ayant le niveau de production le plus élevé. En comparant des industries et des firmes, nous montrons que les classements ne sont pas robustes, car ils sont affectés par l'équilibre du marché. Le rôle de l'éco-efficacité dans la profitabilité de la firme est également analysé. Tout ceci révèle que les indicateurs habituels d'éco-efficacité sont inadaptés. Pour faire face à ce problème, nous proposons un indicateur robuste. [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] Sensory Systems and Spatial Memory in the Fruit Bat Rousettus aegyptiacusETHOLOGY, Issue 8 2005Richard A. Holland The megachiropteran fruit bat Rousettus aegyptiacus is able to orient and navigate using both vision and echolocation. These two sensory systems have different environmental constraints however, echolocation being relatively short range when compared with vision. Despite this difference, an experiment testing their memory of a perch location demonstrates that once the location of a perch is learned R. aegyptiacus is not influenced by the movement of local landmark cues in the vicinity of the perch under either light or dark conditions. Thus despite the differing constraints of vision and echolocation, this suggests a place is remembered as a location in space and not by associations with landmarks in the vicinity. A decrease in initial performance when the task was repeated in the dark suggested the possibility that a memory of a location learned using vision does not generalize to echolocation. [source] Theoretical and conceptual issues in time,place discriminationEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 9 2009Jonathon D. Crystal Abstract The need to discover resources that are available under specific environmental constraints represents a fundamental environmental pressure on the evolution of behavior. Time,place discrimination refers to the ability to secure resources when they are available under specific temporal and spatial contingencies. This article reviews a number of examples of time,place discrimination. The review highlights theoretical and conceptual issues that are needed to behaviorally identify the mechanisms responsible for time,place performance. Next, limitations on time,place performance that may be imposed by a circadian system are described. Finally, a number of lines of research that broaden these limitations are discussed. These lines of research include studies that suggest that (i) a broad range of long intervals (outside the limited range of circadian entrainment) are timed, (ii) at least some long intervals (16,21 h) are timed with an endogenous self-sustaining oscillator, (iii) short intervals (in the range of 1,3 min) are timed with an endogenous self-sustaining oscillator, and (iv) memory for specific unique events (including when and where they occurred) is based on a circadian representation of time. It is concluded that a unified theory of timing that can retain the times of occurrence of individual events is needed. The time of occurrence of an event may be encoded not only with respect to a circadian oscillator but also with respect to other oscillators in the long-interval and short-interval ranges. [source] Working Women's Selection of Care for Their Infants: A Prospective Study,FAMILY RELATIONS, Issue 3 2000Elizabeth Puhn Pungello We interviewed 102 employed women before and after the birth of their first child to examine: (1) the influences of environmental constraints and maternal beliefs on mothers' care decisions, and (2) change in environmental constraints and beliefs. Both employment-related constraints and maternal beliefs were related to infant care decisions, and mothers who chose nonparental versus parent-only care differed in how their constraints and beliefs changed over time. Implications for practitioners are discussed. [source] Recruitment variability of resident brown trout in peripheral populations from southern EuropeFRESHWATER BIOLOGY, Issue 12 2008GRACIELA G. NICOLA Summary 1. Population regulation was studied for seven consecutive years (1992,98) in five rivers at the periphery of the distribution of Salmo trutta, where the fish were living under environmental constraints quite different from those of the main distribution area. 2. Recruitment is naturally highly variable and the populations had been earlier classified as overexploited. Thus we expected that densities of young trout in most populations would be too low for density-dependent mortality to operate. We tested this by fitting the abundance of recruits to egg densities over seven consecutive years (stock,recruitment relationship), and used the results to judge whether exploitation should be restricted in the interests of conserving the populations. 3. The density of 0+ trout in early September, as well as the initial density of eggs and parents, varied greatly among localities and years. The data for all populations fitted the Ricker stock,recruitment model. The proportion of variance explained by the population curves varied between 32% and 51%. However, in most cases the observations were in the density-independent part of the stock,recruitment curve, where densities of the recruits increased proportionally with egg densities. 4. Our findings suggest that recruitment densities in most rivers and years were below the carrying capacity of the habitats. Although density-dependent mechanisms seemed to regulate fish abundance in some cases, environmental factors and harvesting appeared generally to preclude populations from reaching densities high enough for negative feedbacks to operate. The findings thus lend support to Haldane's (1956) second hypothesis that changes in population density are primarily due to density-independent factors in unfavourable areas and areas with low density due to exploitation. Exploitation should be reduced to allow natural selection to operate more effectively. [source] Linking ecological theory with stream restorationFRESHWATER BIOLOGY, Issue 4 2007P. S. LAKE Summary 1. Faced with widespread degradation of riverine ecosystems, stream restoration has greatly increased. Such restoration is rarely planned and executed with inputs from ecological theory. In this paper, we seek to identify principles from ecological theory that have been, or could be, used to guide stream restoration. 2. In attempts to re-establish populations, knowledge of the species' life history, habitat template and spatio-temporal scope is critical. In many cases dispersal will be a critical process in maintaining viable populations at the landscape scale, and special attention should be given to the unique geometry of stream systems 3. One way by which organisms survive natural disturbances is by the use of refugia, many forms of which may have been lost with degradation. Restoring refugia may therefore be critical to survival of target populations, particularly in facilitating resilience to ongoing anthropogenic disturbance regimes. 4. Restoring connectivity, especially longitudinal connectivity, has been a major restoration goal. In restoring lateral connectivity there has been an increasing awareness of the riparian zone as a critical transition zone between streams and their catchments. 5. Increased knowledge of food web structure , bottom-up versus top-down control, trophic cascades and subsidies , are yet to be applied to stream restoration efforts. 6. In restoration, species are drawn from the regional species pool. Having overcome dispersal and environmental constraints (filters), species persistence may be governed by local internal dynamics, which are referred to as assembly rules. 7. While restoration projects often define goals and endpoints, the succession pathways and mechanisms (e.g. facilitation) by which these may be achieved are rarely considered. This occurs in spite of a large of body of general theory on which to draw. 8. Stream restoration has neglected ecosystem processes. The concept that increasing biodiversity increases ecosystem functioning is very relevant to stream restoration. Whether biodiversity affects ecosystem processes, such as decomposition, in streams is equivocal. 9. Considering the spatial scale of restoration projects is critical to success. Success is more likely with large-scale projects, but they will often be infeasible in terms of the available resources and conflicts of interest. Small-scale restoration may remedy specific problems. In general, restoration should occur at the appropriate spatial scale such that restoration is not reversed by the prevailing disturbance regime. 10. The effectiveness and predictability of stream ecosystem restoration will improve with an increased understanding of the processes by which ecosystems develop and are maintained. Ideas from general ecological theory can clearly be better incorporated into stream restoration projects. This will provide a twofold benefit in providing an opportunity both to improve restoration outcomes and to test ecological theory. [source] Organizational failure: a critique of recent research and a proposed integrative frameworkINTERNATIONAL JOURNAL OF MANAGEMENT REVIEWS, Issue 1 2004Kamel Mellahi There is a long-running debate in the business literature on the causes of organizational failure. On the one hand, classical industrial organization (IO) and organization ecology (OE) scholars have typically assumed a deterministic role of the environment and argued that managers are constrained by exogenous industrial and environmental constraints leaving them with little real strategic choice, and hence managers' role should be ignored. On the other hand, the organization studies (OS) and organizational psychology (OP) literature takes a more voluntaristic perspective and argues that managers are the principal decision makers of the firm and, consequently, their actions and perceptions are the fundamental cause of organizational failure. This paper addresses the major deficiencies observed in the diverse body of literature covering this field, suggests an integrative framework and identifies the specific theoretical and methodological challenges ahead for researchers seeking to advance knowledge in the field of organizational failure. [source] Barriers to reducing the use of restraints in residential elder care facilitiesJOURNAL OF ADVANCED NURSING, Issue 6 2007Kirsten Moore Abstract Title.,Barriers to reducing the use of restraints in residential elder care facilities Aim., This paper is a report of a study to compare perspectives of staff in residential elder care facilities with those of residents and family members from the same facilities about barriers to reducing the use of physical, chemical and environmental restraints. Background., There is growing research evidence of the potential risk of physical and emotional harm of restraining residents in residential elder care facilities. Despite the potential harms, restraints continue to be a common practice in facilities across Australia. Little research has been undertaken to explore the barriers to reducing the use of restraints. Method., Eighteen individual interviews were conducted with staff, general practitioners and a pharmacist and three focus groups were conducted with a total of 12 residents and 17 family members associated with three residential elder care facilities in Melbourne, Australia in 2004. Findings., The three participating facilities were committed to reducing the use of restraints, although physical, chemical and environmental restraints were used in all three facilities. Barriers to reducing restraint use included fear of resident injury, staff and resource limitations, lack of education and information about alternatives to restraints, environmental constraints, policy and management issues, beliefs and expectations (of staff, family and residents), inadequate review practices and communication barriers. Conclusion., Further education and support for staff and family members in evidence-based practice in relation to resident care and restraint use is needed in at least some residential elder care facilities. [source] Dendritic network structure constrains metacommunity properties in riverine ecosystemsJOURNAL OF ANIMAL ECOLOGY, Issue 3 2010B. L. Brown Summary 1.,Increasingly, ecologists conceptualize local communities as connected to a regional species pool rather than as isolated entities. By this paradigm, community structure is determined through the relative strengths of dispersal-driven regional effects and local environmental factors. However, despite explicit incorporation of dispersal, metacommunity models and frameworks often fail to capture the realities of natural systems by not accounting for the configuration of space within which organisms disperse. This shortcoming may be of particular consequence in riverine networks which consist of linearly -arranged, hierarchical, branching habitat elements. Our goal was to understand how constraints of network connectivity in riverine systems change the relative importance of local vs. regional factors in structuring communities. 2.,We hypothesized that communities in more isolated headwaters of riverine networks would be structured by local forces, while mainstem sections would be structured by both local and regional processes. We examined these hypotheses using a spatially explicit regional analysis of riverine macroinvertebrate communities, focusing on change in community similarity with distance between local communities [i.e., distance-decay relationships; (DDRs)], and the change in environmental similarity with distance. Strong DDRs frequently indicate dispersal-driven dynamics. 3.,There was no evidence of a DDR in headwater communities, supporting our hypothesis that dispersal is a weak structuring force. Furthermore, a positive relationship between community similarity and environmental similarity supported dynamics driven by local environmental factors (i.e., species sorting). In mainstem habitats, significant DDRs and community × environment similarity relationships suggested both dispersal-driven and environmental constraints on local community structure (i.e., mass effects). 4.,We used species traits to compare communities characterized by low vs. high dispersal taxa. In headwaters, neither strength nor mode (in-network vs. out of network) of dispersal changed our results. However, outcomes in mainstems changed substantially with both dispersal mode and strength, further supporting the hypothesis that regional forces drive community dynamics in mainstems. 5.,Our findings demonstrate that the balance of local and regional effects changes depending on location within riverine network with local (environmental) factors dictating community structure in headwaters, and regional (dispersal driven) forces dominating in mainstems. [source] Floristic patterns and plant traits of Mediterranean communities in fragmented habitatsJOURNAL OF BIOGEOGRAPHY, Issue 7 2006Guillem Chust Abstract Aim, To contrast floristic spatial patterns and the importance of habitat fragmentation in two plant communities (grassland and scrubland) in the context of ecological succession. We ask whether plant assemblages are affected by habitat fragmentation and, if so, at what spatial scale? Does the relative importance of the niche differentiation and dispersal-limitation mechanisms change throughout secondary succession? Is the dispersal-limitation mechanism related to plant functional traits? Location, A Mediterranean region, the massif of Albera (Spain). Methods, Using a SPOT satellite image to describe the landscape, we tested the effect of habitat fragmentation on species composition, determining the spatial scale of the assemblage response. We then assessed the relative importance of dispersal-related factors (habitat fragmentation and geographical distance) and environmental constraints (climate-related variables) influencing species similarity. We tested the association between dispersal-related factors and plant traits (dispersal mode and life form). Results, In both community types, plant composition was partially affected by the surrounding vegetation. In scrublands, animal-dispersed and woody plants were abundant in landscapes dominated by closed forests, whereas wind-dispersed annual herbs were poorly represented in those landscapes. Scrubby assemblages were more dependent on geographical distance, habitat fragmentation and climate conditions (temperature, rainfall and solar radiation); grasslands were described only by habitat fragmentation and rainfall. Plant traits did not explain variation in spatial structuring of assemblages. Main conclusions, Plant establishment in early Mediterranean communities may be driven primarily by migration from neighbouring established communities, whereas the importance of habitat specialization and community drift increases over time. Plant life forms and dispersal modes did not explain the spatial variation of species distribution, but species richness within the community with differing plant traits was affected by habitat patchiness. [source] A regional impact assessment of climate and land-use change on alpine vegetationJOURNAL OF BIOGEOGRAPHY, Issue 3 2003Thomas Dirnböck Abstract Aim, Assessing potential response of alpine plant species distribution to different future climatic and land-use scenarios. Location, Four mountain ranges totalling 150 km2 in the north-eastern Calcareous Alps of Austria. Methods, Ordinal regression models of eighty-five alpine plant species based on environmental constraints and land use determining their abundance. Site conditions are simulated spatially using a GIS, a Digital Terrain Model, meteorological station data and existing maps. Additionally, historical records were investigated to derive data on time spans since pastures were abandoned. This was then used to assess land-use impacts on vegetation patterns in combination with climatic changes. Results, A regionalized GCM scenario for 2050 (+ 0.65 °C, ,30 mm August precipitation) will only lead to local loss of potential habitat for alpine plant species. More profound changes (+ 2 °C, ,30 mm August precipitation; + 2 °C, ,60 mm August precipitation) however, will bring about a severe contraction of the alpine, non-forest zone, because of range expansion of the treeline conifer Pinus mugo Turra and many alpine species will loose major parts of their habitat. Precipitation change significantly influences predicted future habitat patterns, mostly by enhancing the general trend. Maintenance of summer pastures facilitates the persistence of alpine plant species by providing refuges, but existing pastures are too small in the area to effectively prevent the regional extinction risk of alpine plant species. Main conclusions, The results support earlier hypotheses that alpine plant species on mountain ranges with restricted habitat availability above the treeline will experience severe fragmentation and habitat loss, but only if the mean annual temperature increases by 2 °C or more. Even in temperate alpine regions it is important to consider precipitation in addition to temperature when climate impacts are to be assessed. The maintenance of large summer farms may contribute to preventing the expected loss of non-forest habitats for alpine plant species. Conceptual and technical shortcomings of static equilibrium modelling limit the mechanistic understanding of the processes involved. [source] An explanatory model of medical practice variation: a physician resource demand perspectiveJOURNAL OF EVALUATION IN CLINICAL PRACTICE, Issue 2 2002Michael J. Long MA PhD Abstract Practice style variation, or variation in the manner in which physicians treat patients with a similar disease condition, has been the focus of attention for many years. The research agenda is further intensified by the unrealistic assumption that by reducing variation, quality will be improved, costs will be reduced, or both. There is a wealth of literature that identifies differences in health care use of many kinds, in apparently similar communities. Attempts have been made by many scholars to identify the determinants of variation in terms of differences in the population characteristics (e.g. age, sex, insurance, etc.) and geographical characteristics (e.g. distance to provider, number of physicians, number of hospital beds, etc.). When significant differences in use rates prevail after controlling for differences in population characteristics, it is often attributed to ,uncertainty', or the fact that there is no consensus on what constitutes the optimum treatment process. It is suggested by this literature that the greatest variation can be found in the circumstances where there is the most ,uncertainty'. In this work, a physician resource demand model is proposed in which it is suggested that, during the diagnosis and treatment process, physicians demand resources consistent with the clinical needs of the patients, modified by the intervening forces under which they practice. These intervening forces, or constraints, are categorized as patient agency constraints, organizational constraints and environmental constraints, which are characterized as ,induced variation'. It is suggested that when all of the variables that constitute these constraints are identified, the remaining variance represents ,innate variance', or practice style differences. It is further suggested that the more completely this model is specified, the more likely area differences will be attenuated and the smaller will be the residual variance. [source] Stable genetic polymorphism in heterogeneous environments: balance between asymmetrical dispersal and selection in the acorn barnacleJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 2 2006D. VÉLIZ Abstract Elucidating the processes responsible for maintaining polymorphism at ecologically relevant genes is intimately related to understanding the interplay between selection imposed by habitat heterogeneity and a species' capacity for dispersal in the face of environmental constraints. In this paper, we used a model-based approach to solve equilibria of balanced polymorphism, given values of fitness and larval dispersal among different habitats in the acorn barnacle Semibalanus balanoides from the Gulf of St Lawrence. Our results showed that allele frequencies observed at both MPI* and GPI* loci represented stable equilibria, given empirical estimates of fitness values, and that considerably more larvae dispersed from one region (north) to the other (south) than vice versa. Dispersal conditions were predicted to be similar for the maintenance of polymorphism at both loci. Moreover, the values of asymmetrical dispersal required by the model to reach stable equilibria were compatible with empirical estimates of larval dispersal and oceanic circulation documented in this system. Overall, this study illustrated the usefulness of a modified and computable version of Bulmer's model (1972) in order to test hypotheses of balanced polymorphism resulting from interactions between spatial selection and asymmetrical dispersal. [source] State space sampling of feasible motions for high-performance mobile robot navigation in complex environmentsJOURNAL OF FIELD ROBOTICS (FORMERLY JOURNAL OF ROBOTIC SYSTEMS), Issue 6-7 2008Thomas M. Howard Sampling in the space of controls or actions is a well-established method for ensuring feasible local motion plans. However, as mobile robots advance in performance and competence in complex environments, this classical motion-planning technique ceases to be effective. When environmental constraints severely limit the space of acceptable motions or when global motion planning expresses strong preferences, a state space sampling strategy is more effective. Although this has been evident for some time, the practical question is how to achieve it while also satisfying the severe constraints of vehicle dynamic feasibility. The paper presents an effective algorithm for state space sampling utilizing a model-based trajectory generation approach. This method enables high-speed navigation in highly constrained and/or partially known environments such as trails, roadways, and dense off-road obstacle fields. © 2008 Wiley Periodicals, Inc. [source] Introduction: is it possible to create pro-poor agriculture-related biotechnology?JOURNAL OF INTERNATIONAL DEVELOPMENT, Issue 5 2005Joanna Chataway Biotechnology represents hope for those who believe that new technology can contribute to overcoming a range of pressing productivity and environmental constraints facing poor farmers. Pouring money into the science and technology however without recognizing institutional and systemic complexities associated with creating ,pro-poor' technologies is unlikely to deliver much for those farmers. Moreover, there are a range of economic and political contextual factors which further complicate efforts to put the technology to use for poorer farmers. This article outlines some of the issues and possible new approaches which are discussed in more detail in later articles in this special issue. Copyright © 2005 John Wiley & Sons, Ltd. [source] Water, Adaptation, and Property Rights on the Snake and Klamath Rivers,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 2 2007Richard A. Slaughter Abstract:, Water demand in a viable economy tends to be dynamic: it changes over time in response to growth, drought, and social policy. Institutional capacity to re-allocate water between users and uses under stress from multiple sources is a key concern. Climate change threatens to add to those stresses in snowmelt systems by changing the timing of runoff and possibly increasing the severity and duration of drought. This article examines Snake and Klamath River institutions for their ability to resolve conflict induced by demand growth, drought, and environmental constraints on water use. The study finds that private ownership of water rights has been a major positive factor in successful adaptation, by providing the basis for water marketing and by promoting the use of negotiation and markets rather than politics to resolve water conflict. [source] EFFECTS OF INCREASED DELTA EXPORTS ON SACRAMENTO VALLEY'S ECONOMY AND WATER MANAGEMENT,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 6 2003Stacy K. Tanaka ABSTRACT: Exports from the Sacramento-San Joaquin Delta are an important source of water for Central Valley and Southern California users. The purpose of this paper is to estimate and analyze the effects increased exports to south of Delta users would have on the Sacramento Valley economy and water management if water were managed and reallocated for purely economic benefits, as if there were an ideal Sacramento Valley water market. Current Delta exports of 6,190 thousand acre-feet per year were increased incrementally to maximum export pumping plant capacities. Initial increases in Delta exports did not increase regional water scarcity, but decreased surplus Delta flows. Further export increases raised agricultural scarcity. Urban users suffer increased scarcity only for exports exceeding 10,393 taf/yr. Expanding exports raises the economic value of expanding key facilities (such as Engle bright Lake and South Folsom Canal) and the opportunity costs of environmental requirements. The study illustrates the physical and economic capacity of the Sacramento Valley to further increase exports of water to drier parts of the state, even within significant environmental flow restrictions. More generally, the results illustrate the physical capacity for greater economic benefits and flexibility in water management within environmental constraints, given institutional capability to reoperate or reallocate water resources, as implied by water markets. [source] Rainfall, dispersal and reproductive inhibition in eusocial Damaraland mole-rats (Cryptomys damarensis)JOURNAL OF ZOOLOGY, Issue 4 2002A. J. Molteno Abstract Non-reproductive female Damaraland mole-rats Cryptomys damarensis that were caught before a period of good rainfall (during which 90% of the average annual fell) (Group 1), exhibited a significantly lower pituitary sensitivity to gonadotrophin-releasing hormone compared to non-reproductive females (Group 2) caught in the same area, close to the end of the wet period. Group 2 were also significantly heavier than Group 1. Pituitary sensitivity was not significantly correlated to body mass within either group of females, nor within groups of reproductive males and non-reproductive males from a laboratory held colony. This suggests that rainfall may have resulted in the simultaneous, but unrelated, increase in pituitary sensitivity and body mass. Larger size and reduced sexual inhibition assist dispersal and the probability of successful independent reproduction, during periods when environmental constraints on dispersal are relaxed. These findings support the hypothesis that low rainfall may be an important constraint on dispersal and an important factor promoting the evolution of reproductive inhibition, and consequently eusociality, in this species. [source] Fish Assemblages in Shallow Marine Caves of the Salento Peninsula (Southern Apulia, SE Italy)MARINE ECOLOGY, Issue 2002Simona Bussotti Abstract. Fish assemblages of three shallow marine caves from the Salento Peninsula (Apulia, SE Italy) were investigated in July 2000. Data were collected in situ by using visual census. A total of nineteen fish species were recorded inside the caves. The species richness generally displayed a similar pattern in all three caves, decreasing from the entrance towards the innermost sections, whereas the patterns of total fish abundance differed among caves. Apogon imberbis (mainly represented by juveniles) was the most important species in terms of number of individuals (accounting for more than 85% of the censused fish) and showed a fairly even distribution inside the investigated caves. Without the numerical contribution of A. imberbis, fish abundance decreased from the entrance to the inner sections and this pattern was common to all three caves. Juvenile fishes of economic interest (e. g., Diplodus vulgaris and Epinephelus marginatus) were also recorded inside. The present study suggests that: (1) environmental constraints could affect distribution patterns in fish species richness and in the abundance of several fish along the axis of "blind caves" (with a single entrance), as already observed for sessile benthos and plankton assemblages; (2) shallow marine caves of the Salento Peninsula could exert the role of refuge and/or nursery for some littoral fish species during the adult and/or juvenile stages of their life histories. [source] Genomic pattern of adaptive divergence in Arabidopsis halleri, a model species for tolerance to heavy metalMOLECULAR ECOLOGY, Issue 9 2009CLAIRE-LISE MEYER Abstract Pollution by heavy metals is one of the strongest environmental constraints in human-altered environments that only a handful of species can cope with. Identifying the genes conferring to those species the ability to grow in polluted areas is a first step towards a global understanding of the evolutionary processes involved and will eventually improve phytoremediation practices. We used a genome-scan approach to detect loci under divergent selection among four populations of Arabidopsis halleri growing on either polluted or nonpolluted habitats. Based on a high density of amplified fragment length polymorphism (AFLP) markers (820 AFLP markers, i.e. ~1 marker per 0.3 Mb), evidence for selection was found for some markers in every sampled population. Four loci departed from neutrality in both metallicolous populations and thus constitute high-quality candidates for general adaptation to pollution. Interestingly, some candidates differed between the two metallicolous populations, suggesting the possibility that different loci may be involved in adaptation in the different metallicolous populations. [source] Phenotypic plasticity , contrasting species-specific traits induced by identical environmental constraintsNEW PHYTOLOGIST, Issue 3 2004John A. Strand No abstract is available for this article. [source] The Flask model: emergence of nutrient-recycling microbial ecosystems and their disruption by environment-altering ,rebel' organismsOIKOS, Issue 7 2007Hywel T. P. Williams Here we introduce a new model of life,environment interaction, which simulates an evolving microbial community in a ,Fask' of liquid with prescribed inputs of nutrients. The flask is seeded with a clonal population of ,microbes' that are subject to mutation on genetic loci that determine their nutrient uptake patterns, release patterns, and their effects on, and response to, other environmental variables. In contrast to existing models of life-environment interaction, notably Daisyworld, what benefits the individual organisms is decoupled from their ,global' (system-level) effects. A robust property of the model is the emergence of ecosystems that tend toward a state where nutrients are efficiently utilised and differentially recycled, with a correlated increase in total population. Organisms alter the environment as a free ,by-product' of their growth, and their growth is constrained by adverse environmental effects. This introduces environmental feedback, which can disrupt the model ecosystems, even though there are no constraints on the conditions to which the organisms can theoretically adapt. ,Rebel' organisms can appear that grow rapidly by exploiting an under-utilised resource, but in doing so shift the environment away from the state to which the majority of the community are adapted. The result can be a population crash with lossof recycling, followed by later recovery, or in extreme cases, a total extinction of the system. Numerous runs of these ,flask' ecosystems show that tighter environmental constraints on growth make the system more vulnerable to internally generated ecosystem extinction. [source] High divorce rates in Corsican blue tits: how to choose a better option in a harsh environmentOIKOS, Issue 3 2000Jacques Blondel We investigate which hypothesis, the "better mate hypothesis" or the "better territory hypothesis" best explains the unusually high divorce rate (59%) in a population of blue tits (Parus caeruleus) living in a sclerophyllous habitat characterised by severe environmental constraints (trophic, parasitic, climatic) on the island of Corsica, France. Using data from the breeding seasons 1985,1998 and from a brood size experiment (1990,1993) we examined the causes of divorce and their consequences on breeding performance, mate assortment and territory choice. Breeding performance had no significant effect on whether birds re-united or divorced in the next breeding season. Re-uniting pairs did better than divorced females and the latter improved their breeding performance compared to prior to divorce, but this was mainly due to age and territory effects. There were no differences in male performance depending on whether they re-united or divorced. The age combination of pairs did not differ between re-uniting and divorcing pairs, but mate assortment changed after divorce with males re-mating more often with older partners than females. Manipulation of brood size showed a trend for birds with enlarged broods to divorce more. Pairs responded significantly to territory quality by divorcing more often in poor than in good breeding sites. Both faithful pairs and male divorcees had shorter breeding dispersal distances than female divorcees. Divorce rates were determined by the large differences in quality among breeding sites. Males, whatever their status, usually retained their previous territory whereas divorced females moved significantly longer distances and improved their breeding site. Moving to a better territory after divorce benefits only females which appear to be the choosing sex in the decision to divorce. This study strongly supports the "habitat mediated hypothesis" and we suggest that the large observed intraspecific variation in the magnitude of divorce rates in many species of birds is mostly determined by habitat characteristics. [source] Growth rates and life histories in twenty-two small-scale societies,AMERICAN JOURNAL OF HUMAN BIOLOGY, Issue 3 2006Robert Walker This study investigates variation in body growth (cross-sectional height and weight velocity) among a sample of 22 small-scale societies. Considerable variation in growth exists among hunter-gatherers that overlaps heavily with growth trajectories present in groups focusing more on horticulture. Intergroup variation tends to track environmental conditions, with societies under more favorable conditions displaying faster growth and earlier puberty. In addition, faster/earlier development in females is correlated with higher mortality. For example, African "Pygmies," Philippine "Negritos," and the Hiwi of Venezuela are characterized by relatively fast child-juvenile growth for their adult body size (used as a proxy for energetic availability). In these societies, subadult survival is low, and puberty, menarche, and first reproduction are relatively early (given their adult body size), suggesting selective pressure for accelerated development in the face of higher mortality. In sum, the origin and maintenance of different human ontogenies may require explanations invoking both environmental constraints and selective pressures. Am. J. Hum. Biol. 18:295,311, 2006. © 2006 Wiley-Liss, Inc. [source] The response of photosynthesis and stomatal conductance to rising [CO2]: mechanisms and environmental interactionsPLANT CELL & ENVIRONMENT, Issue 3 2007ELIZABETH A. AINSWORTH ABSTRACT This review summarizes current understanding of the mechanisms that underlie the response of photosynthesis and stomatal conductance to elevated carbon dioxide concentration ([CO2]), and examines how downstream processes and environmental constraints modulate these two fundamental responses. The results from free-air CO2 enrichment (FACE) experiments were summarized via meta-analysis to quantify the mean responses of stomatal and photosynthetic parameters to elevated [CO2]. Elevation of [CO2] in FACE experiments reduced stomatal conductance by 22%, yet, this reduction was not associated with a similar change in stomatal density. Elevated [CO2] stimulated light-saturated photosynthesis (Asat) in C3 plants grown in FACE by an average of 31%. However, the magnitude of the increase in Asat varied with functional group and environment. Functional groups with ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco)-limited photosynthesis at elevated [CO2] had greater potential for increases in Asat than those where photosynthesis became ribulose-1,5-bisphosphate (RubP)-limited at elevated [CO2]. Both nitrogen supply and sink capacity modulated the response of photosynthesis to elevated [CO2] through their impact on the acclimation of carboxylation capacity. Increased understanding of the molecular and biochemical mechanisms by which plants respond to elevated [CO2], and the feedback of environmental factors upon them, will improve our ability to predict ecosystem responses to rising [CO2] and increase our potential to adapt crops and managed ecosystems to future atmospheric [CO2]. [source] Searching for a Role for Citizens in the Budget ProcessPUBLIC BUDGETING AND FINANCE, Issue 1 2004Carol Ebdon Citizen participation in the local budget process is not prevalent, despite encouragement from scholars and professional organizations. This case study of two Kansas cities that have used a variety of input mechanisms in the budget process analyzes the effectiveness of citizen budget participation. Limited effectiveness was found, which may largely be due to the timing of the input, unstated or unclear goals, implementation difficulties, and political and environmental constraints. Citizen input appears to have had little effect on budget decisions, and neither city has institutionalized participation in the process. However, the input mechanisms serve other purposes, such as education and support for specific proposals. Describing the benefits as well as the difficulty of involving citizens in a meaningful way is beneficial to other governments as they wrestle with the issue of defining the citizens' role in the budget process. [source] Rare Earth Deposits of North AmericaRESOURCE GEOLOGY, Issue 4 2008Stephen B. Castor Abstract Rare earth elements (REE) have been mined in North America since 1885, when placer monazite was produced in the southeast USA. Since the 1960s, however, most North American REE have come from a carbonatite deposit at Mountain Pass, California, and most of the world's REE came from this source between 1965 and 1995. After 1998, Mountain Pass REE sales declined substantially due to competition from China and to environmental constraints. REE are presently not mined at Mountain Pass, and shipments were made from stockpiles in recent years. Chevron Mining, however, restarted extraction of selected REE at Mountain Pass in 2007. In 1987, Mountain Pass reserves were calculated at 29 Mt of ore with 8.9% rare earth oxide based on a 5% cut-off grade. Current reserves are in excess of 20 Mt at similar grade. The ore mineral is bastnasite, and the ore has high light REE/heavy REE (LREE/HREE). The carbonatite is a moderately dipping, tabular 1.4-Ga intrusive body associated with ultrapotassic alkaline plutons of similar age. The chemistry and ultrapotassic alkaline association of the Mountain Pass deposit suggest a different source than that of most other carbonatites. Elsewhere in the western USA, carbonatites have been proposed as possible REE sources. Large but low-grade LREE resources are in carbonatite in Colorado and Wyoming. Carbonatite complexes in Canada contain only minor REE resources. Other types of hard-rock REE deposits in the USA include small iron-REE deposits in Missouri and New York, and vein deposits in Idaho. Phosphorite and fluorite deposits in the USA also contain minor REE resources. The most recently discovered REE deposit in North America is the Hoidas Lake vein deposit, Saskatchewan, a small but incompletely evaluated resource. Neogene North American placer monazite resources, both marine and continental, are small or in environmentally sensitive areas, and thus unlikely to be mined. Paleoplacer deposits also contain minor resources. Possible future uranium mining of Precambrian conglomerates in the Elliott Lake,Blind River district, Canada, could yield by-product HREE and Y. REE deposits occur in peralkaline syenitic and granitic rocks in several places in North America. These deposits are typically enriched in HREE, Y, and Zr. Some also have associated Be, Nb, and Ta. The largest such deposits are at Thor Lake and Strange Lake in Canada. A eudialyte syenite deposit at Pajarito Mountain in New Mexico is also probably large, but of lower grade. Similar deposits occur at Kipawa Lake and Lackner Lake in Canada. Future uses of some REE commodities are expected to increase, and growth is likely for REE in new technologies. World reserves, however, are probably sufficient to meet international demand for most REE commodities well into the 21st century. Recent experience shows that Chinese producers are capable of large amounts of REE production, keeping prices low. Most refined REE prices are now at approximately 50% of the 1980s price levels, but there has been recent upward price movement for some REE compounds following Chinese restriction of exports. Because of its grade, size, and relatively simple metallurgy, the Mountain Pass deposit remains North America's best source of LREE. The future of REE production at Mountain Pass is mostly dependent on REE price levels and on domestic REE marketing potential. The development of new REE deposits in North America is unlikely in the near future. Undeveloped deposits with the most potential are probably large, low-grade deposits in peralkaline igneous rocks. Competition with established Chinese HREE and Y sources and a developing Australian deposit will be a factor. [source] | |||||||||||||||||||||||||||||||||||||||||||