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251.
252.
Pierre Michel Forget Pedro Jordano Joanna E. Lambert Anna Traveset S. Joseph Wright Katrin Böhning‐Gaese 《Conservation biology》2012,26(6):1072-1081
Animal‐mediated seed dispersal is important for sustaining biological diversity in forest ecosystems, particularly in the tropics. Forest fragmentation, hunting, and selective logging modify forests in myriad ways and their effects on animal‐mediated seed dispersal have been examined in many case studies. However, the overall effects of different types of human disturbance on animal‐mediated seed dispersal are still unknown. We identified 35 articles that provided 83 comparisons of animal‐mediated seed dispersal between disturbed and undisturbed forests; all comparisons except one were conducted in tropical or subtropical ecosystems. We assessed the effects of forest fragmentation, hunting, and selective logging on seed dispersal of fleshy‐fruited tree species. We carried out a meta‐analysis to test whether forest fragmentation, hunting, and selective logging affected 3 components of animal‐mediated seed dispersal: frugivore visitation rate, number of seeds removed, and distance of seed dispersal. Forest fragmentation, hunting, and selective logging did not affect visitation rate and were marginally associated with a reduction in seed‐dispersal distance. Hunting and selective logging, but not fragmentation, were associated with a large reduction in the number of seeds removed. Fewer seeds of large‐seeded than of small‐seeded tree species were removed in hunted or selectively logged forests. A plausible explanation for the consistently negative effects of hunting and selective logging on large‐seeded plant species is that large frugivores, as the predominant seed dispersers for large‐seeded plant species, are the first animals to be extirpated from hunted or logged forests. The reduction in forest area after fragmentation appeared to have weaker effects on frugivore communities and animal‐mediated seed dispersal than hunting and selective logging. The differential effects of hunting and selective logging on large‐ and small‐seeded tree species underpinned case studies that showed disrupted plant‐frugivore interactions could trigger a homogenization of seed traits in tree communities in hunted or logged tropical forests. Meta Análisis de los Efectos de la Perturbación Humana sobre la Dispersión de Semillas por Animales 相似文献
253.
Assessment of zerovalent iron for stabilization of chromium, copper, and arsenic in soil 总被引:6,自引:0,他引:6
Kumpiene J Ore S Renella G Mench M Lagerkvist A Maurice C 《Environmental pollution (Barking, Essex : 1987)》2006,144(1):62-69
Stabilization of soil contaminated with trace elements is a remediation practice that does not reduce the total content of contaminants, but lowers the amounts of mobile and bioavailable fractions. This study evaluated the efficiency of Fe(0) to reduce the mobility and bioavailability of Cr, Cu, As and Zn in a chromated copper arsenate (CCA)-contaminated soil using chemical, biochemical and biotoxicity tests. Contaminated soil was stabilized with 1% iron grit. This treatment decreased As and Cr concentrations in leachates (by 98% and 45%, respectively), in soil pore water (by 99% and 94%, respectively) and in plant shoots (by 84% and 95%, respectively). The stabilization technique also restored most of analyzed soil enzyme activities and reduced microbial toxicity, as evaluated by the BioTox test. After stabilization, exchangeable and bioaccessible fractions of Cu remained high, causing some residual toxicity in the treated soil. 相似文献
254.
Habitat fragmentation is expected to impose strong selective pressures on dispersal rates. However, evolutionary responses of dispersal are not self-evident, since various selection pressures act in opposite directions. Here we disentangled the components of dispersal behavior in a metapopulation context using the Virtual Migration model, and we linked their variation to habitat fragmentation in the specialist butterfly Proclossiana eunomia. Our study provided a nearly unique opportunity to study how habitat fragmentation modifies dispersal at the landscape scale, as opposed to microlandscapes or simulation studies. Indeed, we studied the same species in four landscapes with various habitat fragmentation levels, in which large amounts of field data were collected and analyzed using similar methodologies. We showed the existence of quantitative variations in dispersal behavior correlated with increased fragmentation. Dispersal propensity from habitat patches (for a given patch size), and mortality during dispersal (for a given patch connectivity) were lower in more fragmented landscapes. We suggest that these were the consequences of two different evolutionary responses of dispersal behavior at the individual level: (1) when fragmentation increased, the reluctance of individuals to cross habitat patch boundaries also increased; (2) when individuals dispersed, they flew straighter in the matrix, which is the best strategy to improve dispersal success. Such evolutionary responses could generate complex nonlinear patterns of dispersal changes at the metapopulation level according to habitat fragmentation. Due to the small size and increased isolation of habitat patches in fragmented landscapes, overall emigration rate and mortality during dispersal remained high. As a consequence, successful dispersal at the metapopulation scale remained limited. Therefore, to what extent the selection of individuals with a lower dispersal propensity and a higher survival during dispersal is able to limit detrimental effects of habitat fragmentation on dispersal success is unknown, and any conclusion that metapopulations would compensate for them is flawed. 相似文献
255.
Neutral community models embody the idea that individuals are ecologically equivalent, having equal fitness over all environmental conditions, and describe how the spatial dynamics and speciation of such individuals can produce a wide range of patterns of distribution, diversity, and abundance. Neutral models have been controversial, provoking a rush of tests and comments. The debate has been spurred by the suggestion that we should test mechanisms. However, the mechanisms and the spatial scales of interest have never clearly been described, and consequently, the tests have often been only peripherally relevant. At least two mechanisms are present in spatially structured neutral models. Dispersal limitation causes clumping of a species, which increases the strength of intraspecific competition and reduces the strength of interspecific competition. This may prolong coexistence and enhance local and regional diversity. Speciation is present in some neutral models and gives a donor-controlled input of new species, many of which remain rare or are short lived, but which directly add to species diversity. Spatial scale is an important consideration in neutral models. Ecological equivalence and equal fitness have implicit spatial scales because dispersal limitation and its emergent effects operate at population levels, and populations and communities are defined at a chosen spatial scale in recent neutral models; equality is measured relative to a metacommunity, and this necessitates defining the spatial scale of that metacommunity. Furthermore, dispersal has its own scales. Thorough empirical tests of neutral models will require both tests of mechanisms and pattern-producing ability, and will involve coupling theoretical models and experiments. 相似文献
256.
Threshold-Based Resource Management: A Framework for Comprehensive Ecosystem Management 总被引:5,自引:0,他引:5
The problems posed by adaptive management for improved ecosystem health are reviewed. Other kinds of science-informed ecosystem
management are needed for those regions of conflict between rapid human population growth, increased resource extraction,
and the rising demand for better environmental amenities, where large-scale experiments are not feasible. One new framework
is threshold-based resource management. Threshold-based resource management guides management choices among four major science
and engineering approaches to achieve healthier ecosystems: self-sustaining ecosystem management, adaptive management, case-by-case
resource management, and high-reliability management. As resource conflicts increase over a landscape (i.e., as the ecosystems
in the landscape move through different thresholds), management options change for the environmental decision-maker in terms
of what can and cannot be attained by way of ecosystem health. The major policy and management implication of the framework
is that the exclusive use or recommendation of any one management regime, be it self-sustaining, adaptive, case-by-case, or
high-reliability management, across all categories of ecosystems within a heterogeneous landscape that is variably populated
and extractively used is not only inappropriate, it is fatal to the goals of improved ecosystem health. The article concludes
with detailed proposals for environmental decision-makers to undertake “bandwidth management” in ways that blend the best
of adaptive management and high-reliability management for improved ecosystem health while at the same time maintaining highly
reliable flows of ecosystem services, such as water. 相似文献
257.
258.
Deflector Designs for Fish Habitat Restoration 总被引:1,自引:0,他引:1
Paired current deflectors are structures that are installed on each bank of a river to locally reduce the width of the channel, thereby creating flow acceleration and promoting scouring. These instream habitat structures have been used extensively in restoration projects to create pool habitat for fish, but there are many discrepancies in deflector design recommendations in terms of orientation, height, and length. Our objectives were to (1) examine how the angle, height, and length of paired deflectors affect scour hole dimensions and potential for bank erosion; and (2) test the applicability to paired deflectors of existing equations for scour hole depth and volume. Three deflector angles (45°, 90°, and 135°), two deflector heights (with flow under and over the deflector height), and two lengths (reducing the width by 25% and 50%) were investigated using uniform sand in a laboratory flume. Results showed a 26–30% smaller scour depth resulting from 45° deflectors than from 90° deflectors and a 5–10% smaller scour depth for 135° deflectors compared to 90° deflectors. The volume of scour and the potential for bank erosion were greater when flow was under the height of the deflectors rather than overtopping and when the length of deflector was increased. When flow was under the deflector height, 135° deflectors had the highest amount of bank erosion; whereas during overtopping flow conditions, 90° deflectors had the greatest bank erosion potential. Values predicted by the model of Kuhnle and others were closest to observed scour depth and volume measurements. The assumption that upstream-oriented deflectors always generate the largest scour should be revised. 相似文献
259.
After satisfying their quantitative and qualitative needs as regards nutrition, consumers in developed countries are becoming
more involved in the ethical aspects of food production, especially when it relates to animal products. Social demands for
respecting animal welfare in housing systems are increasing rapidly, as is social awareness of human responsibility towards
farm animals. Many studies have been conducted on animal welfare measurement in different production systems, but the available
information for small ruminants remains insufficient. In this study, a 75 criteria-evaluation tool has been set up on the
basis of the five freedoms concept. Animal welfare considerations have been analyzed in 25 documents, including labeling schemes,
regulations, and recommendations from different European countries. The results show many differences between regular and
organic small ruminant farming standards. Emergency measures are generally lacking. A weak representation of psychological
aspects of animal welfare, especially by the current European legislation, is highlighted. 相似文献
260.
Fran?ois Cail Michel Aptel 《International journal of occupational safety and ergonomics》2005,11(2):119-130
A comparative study concerning the incidence of psychosocial factors and stress on musculoskeletal disorders (MSD) was conducted on 30 males carrying out a computer-aided design (CAD) task and on 26 females carrying out a data entry task. Both populations completed a questionnaire concerning complaints of MSD, stress symptoms, psychosocial factors and working life. This study showed that the work context was more favourable to the data entry task operators than to the CAD task operators. In addition, there were relationships in CAD and in data entry between complaints of MSD and stress variables as well as between anguish and psychosocial factors. This field study has shown the importance of stress and of the work context in the occurrence of MSD in computer work. 相似文献