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1.
Kung-Jong Lui Duane Steffey Jamie K. Pugh 《Biometrical journal. Biometrische Zeitschrift》1993,35(6):677-688
Calculating the required sample size for a desired power at a given type I error level, we often assume that we know the exact time of all subject responses whenever they occur during our study period. It is very common, however, in practice that we only monitor subjects periodically and, therefore, we know only whether responses occur or not during an interval. This paper includes a quantitative discussion of the effect resulting from data grouping or interval censoring on the required sample size when we have two treatment groups. Furthermore, with the goal of exploring the optimum in the number of subjects, the number of examinations per subject for test responses, and the total length of a study time period, this paper also provides a general guideline about how to determine these to minimize the total cost of a study for a desired power at a given α-level. A specified linear cost function that incorporates the costs of obtaining subjects, periodic examinations for test responses of subjects, and the total length of a study period, is assumed, primarily for illustrative purpose. 相似文献
2.
3.
The potential for and constraints on the evolution of compensatory ability in Asclepias syriaca 总被引:2,自引:0,他引:2
To investigate the potential for and constraints on the evolution of compensatory ability, we performed a greenhouse experiment
using Asclepias syriaca in which foliar damage and soil nutrient concentration were manipulated. Under low nutrient conditions, significant genetic
variation was detected for allocation patterns and for compensatory ability. Furthermore, resource allocation to storage was
positively, genetically correlated both with compensatory ability and biomass when damaged, the last two being positively,
genetically correlated with each other. Thus, in the low nutrient environment, compensatory ability via resource allocation
to storage provided greater biomass when damaged. A negative genetic correlation between compensatory ability and plant biomass
when undamaged suggests that this mechanism entailed an allocation cost, which would constrain the evolution of greater compensatory
ability when nutrients are limited. Under high nutrient conditions, neither compensatory ability nor allocation patterns predicted
biomass when damaged, even though genetic variation in compensatory ability existed. Instead, plant biomass when undamaged
predicted biomass when damaged. The differences in outcomes between the two nutrient treatments highlight the importance of
considering the possible range of environmental conditions that a genotype may experience. Furthermore, traits that conferred
compensatory ability did not necessarily contribute to biomass when damaged, demonstrating that it is critical to examine
both compensatory ability and biomass when damaged to determine whether selection by herbivores can favor the evolution of
increased compensation.
Received: 2 April 1999 / Accepted: 21 September 1999 相似文献
4.
5.
《Journal of biological dynamics》2013,7(4):318-334
In this paper, we study a two-species competitive system where both the species produce toxin against each other at some cost to their growth rates. A much wider set of outcomes is possible for our system. These outcomes are important contrasts to competitive exclusion or bistable attractors that are often the outcomes for competitive systems. We show that toxin helps to gain an advantage in competition for toxic species whenever the cost of toxin production remains within some moderate value; otherwise it may result in the extinction of the species itself. 相似文献
6.
The cost of interspecific competition in two gerbil species 总被引:5,自引:1,他引:4
7.
We carried out an ecosystem service (ES) assessment at Soto de Pajares, a 400 ha active gravel quarry site located close to protected areas in the southeast of the Community of Madrid, Spain. The currently approved restoration plan is for quarry‐made excavations to be restored back to agricultural land. However, the site has been identified as being important for nature, so different restoration strategies should be considered. To better understand how these compare in terms of ES provision, which had not previously been done at mineral extraction sites in Spain, we used an established toolkit: the Toolkit for Ecosystem Service Site‐based Assessments (TESSA). We compared the agriculture‐focused restoration plan and two nature‐focused alternative scenarios, one without public access (conservation scenario) and the other with public access (compromise scenario). Monetary estimations of the value of agricultural production, climate change mitigation, and recreation were calculated in three scenarios. Results indicated that the compromise scenario provided the greatest annual value (€91,409), mainly due to its potential visitors, surpassing both agricultural (€68,504) and conservation (€48,556) scenarios. Considering the higher costs associated with restoring sites to agricultural production, nature conservation may be an attractive option for extraction companies. The use of TESSA at this site has provided valuable information to quarry managers to help guide their decision‐making. 相似文献
8.
NICOLAS RAY 《Molecular ecology resources》2005,5(1):177-180
pathmatrix is a tool used to compute matrices of effective geographical distances among samples using a least‐cost path algorithm. This program is dedicated to the study of the role of the environment on the spatial genetic structure of populations. Punctual locations (e.g. individuals) or zones encompassing sample data points (e.g. demes) are used in conjunction with a species‐specific friction map representing the cost of movement through the landscape. Matrices of effective distances can then be exported to population genetic software to test, for example, for isolation by distance. pathmatrix is an extension to the geographical information system (GIS) software arcview 3.x. 相似文献
9.
Reproductive success and the energetic cost of parental care in male smallmouth bass 总被引:4,自引:0,他引:4
Direct field measurements of the energetic expenditure on parental care and within-nest reproductive success of individual male smallmouth bass Micropterus dolomieui were determined by measuring the change in total body mass as well as by total body electroconductivity analysis (TOBEC™). With TOBEC, the change in total body lean mass of the same live individual was measured non-destructively at the beginning and end of the parental care period. Lean mass was the primary source of energy utilized during parental care indicating starvation and potential loss of future reproduction. Individual loss in lean mass was related positively to reproductive success suggesting that the energy expended during parental care does affect individual fitness. 相似文献
10.
The energetics of middle-distance running 总被引:2,自引:0,他引:2
J. R. Lacour S. Padilla-Magunacelaya J. C. Barthélémy D. Dormois 《European journal of applied physiology and occupational physiology》1990,60(1):38-43
In order to assess the relative contribution of aerobic processes to running velocity (v), 27 male athletes were selected on the basis of their middle-distance performances over 800, 1500, 3000 or 5000 m, during the 1987 track season. To be selected for study, the average running velocity (v) corresponding to their performances had to be superior to 90% of the best French v of the season. Maximum O2 consumption (VO2max) and energy cost of running (C) had been measured within the 2 months preceding the track season, which, together with oxygen consumption at rest (VO2rest) allowed us to calculate the maximal v that could be sustained under aerobic conditions: vamax = (VO2max - VO2rest) x C-1. The treadmill running v corresponding to a blood lactate of 4 mmol.l-1 (vla4), was also calculated. In the whole group, C was significantly related to height (r = -0.43; P less than 0.03). Neither C nor VO2max (with, in this case, the exception of the 3000 m athletes) were correlated to v. On the other hand, vamax was significantly correlated to v over distances longer than 800 m. These v were also correlated to vla4. However vla4 occurred at 87.5% SD 3.3% of vamax, this relationship was interpreted as being an expression of the correlation between vamax and v. Calculation of vamax provided a useful means of analysing the performances. At the level of achievement studied, v sustained over 3000 m corresponded to vamax.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献