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561.
562.
The effects of learning versus outcome distal goals in conjunction with proximal goals were investigated in a laboratory setting using a class‐scheduling task. The participants (n = 96) needed to acquire knowledge in order to perform the task correctly. A ‘do your best’ outcome goal led to higher performance than the assignment of a specific, difficult outcome goal. However, the assignment of a specific, difficult learning goal led to higher performance than urging people to ‘do their best.’ Goal commitment was higher in the learning goal than in the outcome goal condition. The correlation between task‐relevant strategies discovered and performance was positive and significant. The number of task‐relevant strategies implemented by participants assigned a distal learning goal in conjunction with proximal goals was higher than in any other goal condition. Setting a distal outcome or learning goal that included proximal outcome goals, however, did not lead to higher performance than the setting of a distal outcome or learning goal alone. Self‐efficacy correlated significantly with performance, and this effect was mediated through strategy development. Furthermore, the discovery of task‐relevant strategies affected self‐efficacy through an increase in performance. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
563.
564.
Avian sibling aggression plays an important role in controlling food distribution among nest mates. The food-amount hypothesis
predicts that the amount of food obtained by siblings acts as a proximate cue controlling their level of aggression. The importance
of this cue to cattle egrets (Bubulcus ibis) in Oklahoma was evaluated by studying parental feeding rates, food distribution among nestlings, and nestling aggression
in three-chick broods [A-(oldest), B-, and C-chicks]. We compared nests in which siblicide occurred to nests where all three
chicks survived (nonsiblicide nests). Relative to nonsiblicide nests, siblicide nests received decreasing amounts of food
as the day of siblicide approached. Similarly, aggression levels of all three chicks in siblicide nests increased significantly
compared with nonsiblicide nests, with most of the aggressive behavior involving B- and C-chicks. As a result, on a per-day
basis, food amount and aggression exhibited a strong, negative correlation, thus providing support for the food-amount hypothesis.
Though the total amount of food delivered to siblicide nests declined on the days prior to siblicide, the amount of food received
by A-chicks in these nests did not. Relative to nonsiblicide nests, A-chicks in siblicide nests received an increased share
(percent of volume) of the food delivered at the expense of C-chicks, with the percent remaining the same for B-chicks. The
percentage of food B-chicks received the day after siblicide increased significantly from that received the day before siblicide,
with no change occurring in either the amount or percentage of food received by A-chicks; clearly, B-chicks were the beneficiary
of their aggressive actions that resulted in the death of C-chicks. We provide evidence supporting the hypothesis that aggression
is proximately linked to food amount, possibly by a relatively simple cue such as hunger.
Received: 25 November 1994/Accepted after revision: 10 February 1996 相似文献
565.
Recent evidence indicates that acid rain is a growing environmental phenomenon of potentially far reaching consequences and increasing geographical extent in North America. Acid rain is but one aspect of the broader problem of atmospheric deposition which includes snow, fog, and dry deposition of material. First noticed and studied in the Scandinavian countries, acid precipitation has now been well documented in the United States, first in the northeast and more recently throughout much of the United States east of the Mississippi River. Numerous streams and lakes in regions with poorly buffered soils have become devoid of fish, have an impoverished aquatic flora and fauna, and are changing toward conditions of low aquatic productivity. Evidence also indicates that acid precipitation may cause damage to forest growth, crop production, wildlife, and man-made materials such as buildings, metals, paints, and statuary. 相似文献
566.
A simplistic aggregate model of global economic activity supports a 50-year visioning exercise with targets defined in terms of aggregate measures of global equity (convergence) and sustainability (contraction). Some ambitious combinations of these targets turn out to be infeasible even under the most favorable modeling assumptions. No contraction target (no reduction in fossil fuel consumption relative to the present) was possible, for example, if international capital transfers pushed per capita incomes in low-income countries above 33% of levels achieved in high-income countries. Lower prices for renewable alternatives to exhaustible resources generally made sustainability targets easier to achieve, but lower prices for renewable resources also made equity targets more difficult to achieve. Improved substitution between capital and labor made equity targets easier to achieve in relative terms, but improved substitution between capital and labor could make any given sustainability target more or less difficult to achieve. All the results suggest that it is possible to overstate the purported conflict between achieving sustainability and equity targets. The very transfers of international capital that would promote relative equity between high-income and low-income countries could also work to spread the incidence of achieving any sustainability target more evenly across their boundaries. 相似文献
567.
Gary D. Lynne 《Journal of the American Water Resources Association》1977,13(1):93-107
ABSTRACT: Society has many objectives, many of which are not commensurable. This incommensurability problem is generally referred to as the multiple objective problem and leads to the notion of tradeoffs. Various approaches to calculating tradeoffs in water resource development have been advocated by several authors. Many have made errors in the context of the conceptural model presented in this paper. It is argued the correct framework for tradeoff analysis is the neoclassical economic model. The relevant tradeoffs, then, are really price ratios. These, in turn, must be calculated in such a manner as to allow comparison of product mixes where the expenditure on resources is the same. This is where several authors have erred. An empirical example which illustrates the correct application of the model is presented. 相似文献
568.
Gary A. Campbell 《Resources Policy》1990,16(4)
The purpose of this article is to analyse the use of diversification and market specialization as corporate strategies by non-ferrous metal company managements as responses to adverse financial conditions. The analytical framework is provided by the financial theory of risk. Managements must deal with both company specific risk and market risk as they attempt to improve the profitability of their companies. Companies from the US copper industry are used as empirical examples. Deversification is a flexible but risky strategy. Specialization is a more restrictive strategy but it is less risky. The appropriate strategy to use depends on the particular situation of a company. 相似文献
569.
Translocations and the Preservation of Allelic Diversity 总被引:3,自引:0,他引:3
Translocation is a tool commonly used for the conservation of threatened and endangered fish species. Despite extensive use, the biological implications of translocation remain poorly understood. Of particular interest is the effect of translocation on genetic variability. Maintenance of genetic variability in these "refuge" populations is assumed to be important for both short- and long-term success. We examined allozyme variability at 16 loci for western mosquitofish ( Gambusia affinis ) populations with known histories of introduction. Refuge populations had significantly lower levels of heterozygosity. Refuge populations also had considerably lower levels of allelic diversity than parental populations. All losses were of relatively rare alleles (frequency less than 0.1 in parental population). These losses were probably due to an undocumented bottleneck early in the introduction history. These results were surprising because the initial transplant involved 900 fish and because mosquitofish have numerous reproductive traits that should minimize the effects of bottlenecks on genetic diversity. A literature review revealed that genetic variability is often reduced in refuge populations and that such reductions typically involve the loss of alleles. We suggest that translocated populations be examined periodically for losses of genetic variability. 相似文献
570.
A Decision-Support System for Prioritizing Restoration Sites on the Mississippi River Alluvial Plain 总被引:4,自引:0,他引:4
Daniel W. Llewellyn Gary P. Shaffer Nancy Jo Craig Lisa Creasman David Pashley Mark Swan Cindy Brown 《Conservation biology》1996,10(5):1446-1455
Conversion of forested wetlands to agricultural use and the resulting fragmentation of the landscape has led to concerns for the functional integrity of the Mississippi River Alluvial Plain ecosystem. We describe an effort spearheaded by The Nature Conservancy to initiate a multi-decade partnership dedicated to creating and implementing a viable, cooperative, landscape-level restoration project in the Mississippi River Alluvial Plain. Important phases of the process during the first 5 years were (1) initiation of the development of an extensive network of partners, including state and federal agencies, private land owners, conservation groups, academicians, and other interested citizens; (2) development of a geographic information system (GIS) for the entire extent of the ecosystem; and (3) for one watershed, the Tensas basin in northeastern Louisiana, refinement of a high resolution GIS to generate more detailed land-use conversion statistics to demonstrate the feasibility of a semi-objective, landscape-scale restoration planning procedure, including methodology for prioritization of existing wetland forest patches and areas most suitable for reforestation and connection via corridors. 相似文献