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101.
Attila?HettyeyEmail author J.?Dale?Roberts 《Behavioral ecology and sociobiology》2007,61(8):1303-1310
In species where males use alternative reproductive tactics and male phenotypes are confronted with different risks of sperm
competition, theory predicts that between-male-type differences in sperm expenditure may evolve. In the frog Crinia georgiana big males can monopolize females, whereas small males often engage in polyandrous matings. Consequently, big males may experience
a lower risk of sperm competition than do small males. We tested if the predictions from theoretical models can be applied
to the mating system of C. georgiana. Our results showed that small males do not have larger testes relative to their body size compared to their larger counterparts
and that the efficiency with which sperm number, size, motility, and longevity are produced by the testes does not differ
between small and large males in the predicted way. These results are not in alignment with predictions from a loaded raffle
model of sperm competition on sperm expenditure in males with alternative phenotypes. The plasticity in mating tactics used
by C. georgiana males and a high intraseasonal variation in male densities may have prevented the evolution of enhanced sperm performance
in smaller males. A fair raffle in the sperm competition game played by C. georgiana males could also explain the observed patterns in sperm traits. Future investigations determining the parameters responsible
for the deviation from theoretical predictions in this system will test the degree to which current theoretical models can
indeed be applied to species with plastic reproductive tactics. 相似文献
102.
103.
Frederick Amon-Armah Emmanuel K. Yiridoe Nafees H. M. Ahmad Dale Hebb Rob Jamieson David Burton Ali Madani 《Environmental management》2013,52(5):1177-1191
Government priorities on provincial Nutrient Management Planning (NMP) programs include improving the program effectiveness for environmental quality protection, and promoting more widespread adoption. Understanding the effect of NMP on both crop yield and key water-quality parameters in agricultural watersheds requires a comprehensive evaluation that takes into consideration important NMP attributes and location-specific farming conditions. This study applied the Soil and Water Assessment Tool (SWAT) to investigate the effects of crop and rotation sequence, tillage type, and nutrient N application rate on crop yield and the associated groundwater ${\text{NO}_{3}}^{ - } {\text{-N }}$ leaching and sediment loss. The SWAT model was applied to the Thomas Brook Watershed, located in the most intensively managed agricultural region of Nova Scotia, Canada. Cropping systems evaluated included seven fertilizer application rates and two tillage systems (i.e., conventional tillage and no-till). The analysis reflected cropping systems commonly managed by farmers in the Annapolis Valley region, including grain corn-based and potato-based cropping systems, and a vegetable-horticulture system. ANOVA models were developed and used to assess the effects of crop management choices on crop yield and two water-quality parameters (i.e., ${\text{NO}_{3}}^{ - } {\text{-N }}$ leaching and sediment loading). Results suggest that existing recommended N-fertilizer rate can be reduced by 10–25 %, for grain crop production, to significantly lower ${\text{NO}_{3}}^{ - } {\text{-N }}$ leaching (P > 0.05) while optimizing the crop yield. The analysis identified the nutrient N rates in combination with specific crops and rotation systems that can be used to manage ${\text{NO}_{3}}^{ - } {\text{-N }}$ leaching while balancing impacts on crop yields within the watershed. 相似文献
104.
Lyman K. Thorsteinson Dale L. Taylor 《Journal of the American Water Resources Association》1997,33(4):795-810
ABSTRACT: The National Park Service and the National Biological Service initiated research in Denali National Park and Preserve, a 2.4 million-hectare park in southcentral Alaska, to develop ecological monitoring protocols for national parks in the Arctic/Subarctic biogeographic area. We are focusing pilot studies on design questions, on scaling issues and regionalization, ecosystem structure and function, indicator selection and evaluation, and monitoring technologies. Rock Creek, a headwater stream near Denali headquarters, is the ecological scale for initial testing of a watershed ecosystem approach. Our conceptual model embraces principles of the hydrological cycle, hypotheses of global climate change, and biological interactions of organisms occupying intermediate, but poorly studied, positions in Alaskan food webs. The field approach includes hydrological and depositional considerations and a suite of integrated measures linking key aquatic and terrestrial biota, environmental variables, or defined ecological processes, in order to establish ecological conditions and detect, track, and understand mechanisms of environmental change. Our sampling activities include corresponding measures of physical, chemical, and biological attributes in four Rock Creek habitats believed characteristic of the greater system diversity of Denali. This paper gives examples of data sets, program integration and scaling, and research needs. 相似文献
105.
Rebecca Efroymson Henriette Jager Virginia Dale James Westervelt 《Environmental management》2009,44(6):1163-1179
A decision framework for setting management goals for species at risk is presented. Species at risk are those whose potential
future rarity is of concern. Listing these species as threatened or endangered could potentially result in significant restrictions
to activities in resource management areas in order to maintain those species. The decision framework, designed to foster
proactive management, has nine steps: identify species at risk on and near the management area, describe available information
and potential information gaps for each species, determine the potential distribution of species and their habitat, select
metrics for describing species status, assess the status of local population or metapopulation, conduct threat assessment,
set and prioritize management goals, develop species management plans, and develop criteria for ending special species management
where possible. This framework will aid resource managers in setting management goals that minimally impact human activities
while reducing the likelihood that species at risk will become rare in the near future. The management areas in many of the
examples are United States (US) military installations, which are concerned about potential restrictions to military training
capacity if species at risk become regulated under the US Endangered Species Act. The benefits of the proactive management
set forth in this formal decision framework are that it is impartial, provides a clear procedure, calls for identification
of causal relationships that may not be obvious, provides a way to target the most urgent needs, reduces costs, enhances public
confidence, and, most importantly, decreases the chance of species becoming more rare. 相似文献
106.
Abstract A local sustainable development initiative to establish a temporary pedestrian zone within a Canadian urban community served as a research study into the efficacy of social capital in the development of a network for community action. This community-based initiative used social capital to overcome campaign obstacles and the campaign itself generated new social capital within the neighbourhood through the creation of adaptive networks of participants. The campaign succeeded in creating a part-time pedestrian-only space that serves as an educational example of change for sustainable community development that is replicable in other communities, and provides an example of alternative occupation of community space. Contrary to other literature, little evidence of “core burnout” was found although the network does continue to expend a large amount of effort and time on fundraising. While social capital is a powerful tool for local grassroots action, the availability of a critical source of economic capital may prove vital to the long-term success and sustainability of the network. 相似文献
107.
A commercially available thermal-infrared scanning system was used to survey populations of several wildlife species. The
system's ability to detect species of different sizes in varying habitats relative to conventional survey methods, to differentiate
between species in the same habitat, and the influence of environtmental factors on operational aspects of employing this
technology in the field were evaluated. Total costs for the surveys were approximately $0.36/ha. There were marked discrepancies
in the counts of untrained observers and those from trained analysis. Computer-assisted analysis of infrared imagery recorded
52% fewer deer than were estimated from drive counts, and densities of moose were five times those estimated from conventional
aerial methods. By flying concentric circles and using telephoto, detailed counts of turkeys and deer were possible. With
the aid of computer-assisted analysis, infrared thermography may become a useful wildlife population survey tool. More research
is needed to verify the actual efficiency of detection by combining aerial scans with ground truthing for a variely of species
and habitals. 相似文献
108.
Landscape Planning for Agricultural Nonpoint Source Pollution Reduction III: Assessing Phosphorus and Sediment Reduction Potential 总被引:2,自引:0,他引:2
Riparian buffers have the potential to improve stream water quality in agricultural landscapes. This potential may vary in
response to landscape characteristics such as soils, topography, land use, and human activities, including legacies of historical
land management. We built a predictive model to estimate the sediment and phosphorus load reduction that should be achievable
following the implementation of riparian buffers; then we estimated load reduction potential for a set of 1598 watersheds
(average 54 km2) in Wisconsin. Our results indicate that land cover is generally the most important driver of constituent loads in Wisconsin
streams, but its influence varies among pollutants and according to the scale at which it is measured. Physiographic (drainage
density) variation also influenced sediment and phosphorus loads. The effect of historical land use on present-day channel
erosion and variation in soil texture are the most important sources of phosphorus and sediment that riparian buffers cannot
attenuate. However, in most watersheds, a large proportion (approximately 70%) of these pollutants can be eliminated from
streams with buffers. Cumulative frequency distributions of load reduction potential indicate that targeting pollution reduction
in the highest 10% of Wisconsin watersheds would reduce total phosphorus and sediment loads in the entire state by approximately
20%. These results support our approach of geographically targeting nonpoint source pollution reduction at multiple scales,
including the watershed scale. 相似文献
109.
110.