Use of prior information in simple random sampling

Is is assumed that the population mean, to be estimated, is less than or equal to a known constant. An estimator is suggested which takes into account this information to advantage. It is also suggested that stratification coupled with the modified estimator can be best suited in such situations.     

不同采样设计评估鱼类群落效果比较

鱼类群落生态学研究结果的准确性很大程度上依赖于采样设计的合理性和准确性,正确的采样调查设计不仅可以降低调查成本,其结果也对渔业资源的评估或者管理起到相当重要的作用.本文利用计算机模拟定点采样、简单随机采样和分层采样,比较了3种采样设计的采样效果、相对误差及相对偏差.结果表明： 定点采样设计的采样效果 (采样效果平均值为3.37)要弱于简单随机采样和分层随机采样 (采样效果平均值为0.961).3种采样设计中,分层采样设计在鱼类群落丰富度评估时表现最好,其采样效果、相对误差和相对偏差表现最佳.随着采样数的增加,分层采样设计的采样效果有所下降,但其采样精度提高.     

When does it pay to invest in a patch? The evolution of intentional niche construction

Humans modify their environments in ways that significantly transform the earth's ecosystems. 1 - 3 Recent research suggests that such niche‐constructing behaviors are not passive human responses to environmental variation, but instead should be seen as active and intentional management of the environment. 4 - 10 Although such research is useful in highlighting the interactive dynamics between humans and their natural world, the niche‐construction framework, as currently applied, fails to explain why people would decide to modify their environments in the first place. 11 - 13 To help resolve this problem, we use a model of technological intensification 14 , 15 to analyze the cost‐benefit trade‐offs associated with niche construction as a form of patch investment. We use this model to assess the costs and benefits of three paradigmatic cases of intentional niche construction in Western North America: the application of fire in acorn groves, the manufacture of fishing weirs, and the adoption of maize agriculture. Intensification models predict that investing in patch modification (niche construction) only provides a net benefit when the amount of resources needed crosses a critical threshold that makes the initial investment worthwhile. From this, it follows that low‐cost investments, such as burning in oak groves, should be quite common, while more costly investments, such as maize agriculture, should be less common and depend on the alternatives available in the local environment. We examine how patterns of mobility, 16 risk management, 17 territoriality, 12 and private property 18 also co‐evolve with the costs and benefits of niche construction. This approach illustrates that explaining niche‐constructing behavior requires understanding the economic trade‐offs involved in patch investment. Integrating concepts from niche construction and technological intensification models within a behavioral ecological framework provides insights into the coevolution and active feedback between adaptive behaviors and environmental change across human history.     

Does a long‐term shift in Wood Stork diet foreshadow adaptability to human‐induced rapid environmental change?

To preserve biodiversity, identifying at‐risk populations and developing conservation plans to mitigate the effects of human‐induced rapid environmental change (HIREC) are essential. Changes in diet, especially for food‐limited species, can aid in detecting populations being impacted by HIREC, and characterizing the quality, abundance, and temporal and spatial consistency of newly consumed food items may provide insight concerning the likelihood of a species persisting in a changing environment. We used Wood Storks (Mycteria americana) nesting in the Florida Everglades as a model system to study the possible effects of HIREC on a food‐limited population. We compared the diets of Wood Storks in 2013 and 2014 with those reported during the 1970s before major anthropogenic activities affected the Everglades system and prey availability. Wood Storks in our study consumed more large‐bodied sunfish species (Lepomis spp.), fewer native marsh fishes, and more non‐native fish species than during the 1970s. Large sunfish and non‐native fish are relatively rare in the drying pools of Everglades marshes where storks traditionally forage, suggesting that Wood Storks may be using novel foraging habitats such as created wetlands (i.e., canals and stormwater ponds). Although created wetlands have long hydroperiods conducive to maintaining large‐bodied fishes and could provide alternative foraging habitat when prey availability is reduced in natural marshes, additional studies are needed to determine the extent to which these wetlands are used by Wood Storks and, importantly, the quality of prey items potentially available to foraging Wood Storks in created wetlands.     

Epidemiologic assessment of reproductive success and infant mortality in ruffed lemurs (Varecia variegata)

Retrospective epidemiologic evaluation of 27 years of colony data (1966–1993) from a large breeding center for ruffed lemurs (Varecia variegata) was used to quantitatively assess the risk imposed by different management variables on reproductive success (littering) and infant viability (litter death). Logistic regression analysis was used, both with and without a term to account for extra-binomial variation in the data (random effects) associated with repeated assessments of individual lemur dams during the study period. Population-based littering rates are defined and shown not to fluctuate substantially over time, although the proportion of females given the opportunity to breed was drastically reduced in 1986 due to changes in the species management strategy and limited breeding center space resources. No management-related factors were found to be associated with littering success. However, young age of dam (odds ratio = 4.3, P = 0.016) and housing in natural habitat enclosures (odds ratio = 6.5, P = 0.003) significantly predicted complete litter mortality by 48 hr post-partum. Varecia females >15 years of age (8 dams, 42 observation-years) produced 18 litters and 37 infants, 31 of which survived at least 48 hr. Use of established epidemiologic methods to analyze data from existing colony records should be used to help direct the management of this endangered species toward maximally efficient goals, especially in light of current conservation resource limitations. © 1994 Wiley-Liss, Inc.     

The effect of prey density on foraging mode selection in juvenile lumpfish: balancing food intake with the metabolic cost of foraging

1. In many species, individuals will alter their foraging strategy in response to changes in prey density. However, previous work has shown that prey density has differing effects on the foraging mode decisions of ectotherms as compared with endotherms. This is likely due to differences in metabolic demand; however, the relationship between metabolism and foraging mode choice in ectotherms has not been thoroughly studied. 2. Juvenile lumpfish Cyclopterus lumpus forage using one of two modes: they can actively search for prey while swimming, or they can 'sit-and-wait' for prey while clinging to the substrate using a ventral adhesive disk. The presence of these easily distinguishable foraging modes makes juvenile lumpfish ideal for the study of foraging mode choice in ectotherms. 3. Behavioural observations conducted during laboratory experiments showed that juvenile lumpfish predominantly use the 'cling' foraging mode when prey is abundant, but resort to the more costly 'swim' mode to seek out food when prey is scarce. The metabolic cost of active foraging was also quantified for juvenile lumpfish using swim-tunnel respirometry, and a model was devised to predict the prey density at which lumpfish should switch between the swim and cling foraging modes to maximize energy intake. 4. The results of this model do not agree with previous observations of lumpfish behaviour, and thus it appears that juvenile lumpfish do not try to maximize their net energetic gain. Instead, our data suggest that juvenile lumpfish forage in a manner that reduces activity and conserves space in their limited aerobic scope. This behavioural flexibility is of great benefit to this species, as it allows young individuals to divert energy towards growth as opposed to activity. In a broader context, our results support previous speculation that ectotherms often forage in a manner that maintains a minimum prey encounter rate, but does not necessarily maximize net energy gain.     

Human adaptation and energetic efficiency

A lack of consensus on the general adaptive significance of energetic efficiency can be shown to exist in ecology and anthropology. After briefly reviewing key studies in optimal foraging theory and ecological anthropology, a model is presented which includes the following elements: (1) an equation of adaptive success with reproductive fitness, within an optimality framework; (2) a definition of energy limitation consistent with this framework; (3) a distinction between efficiency of energy capture and efficiency of energy use in achieving other goals; (4) a multiple definition of energetic efficiency that distinguishes purely energetic measures (output/input) from rate measures (energy captured per unit time); (5) the inclusion of time budgeting as a primary adaptive constraint; (6) a quantitative demonstration that increased output/input ratios do not consistently predict an increase in net energy captured, and are poor measures where time is a constraint. The general conclusion is that where energy is limiting, increased efficiency in the rate of energy capture will be adaptive because more net energy will be made available; where energy is not limiting, an increased net capture rate may still confer increased adaptive success, since time and labor energy are freed from energy-capture activities and can be devoted to achieving other adaptive goals. But while energetic efficiency, properly defined, is shown to have general adaptive significance in all cases where time or energy are constraints, considerations of adaptive optimality preclude the general equation of energetic efficiency and adaptive success.     

A Combined Product Estimator in Sample Survey

For the estimation of the population mean in stratified random sampling a ‘Combined Product Estimator’ is proposed which is more efficient than the ‘Combined Ratio’ and ‘Separate Ratio’ estimators. Also, the proposed estimator have exact expressions for bias and mean square error. An empirical illustration is given to compare the efficiencies of different estimators.     

Can honey bees change foraging patterns?

Abstract. 1. Foraging patterns were studied using honey bees on artificial flower patches to determine if given individuals could change behaviours under differing conditions.
2. Two types of flower patches were used; those simulating a population of flowers, dimorphic for colour, and grids simulating a single colour-dimorphic inflorescence.
3. In the simulated population of flowers bees were individually constant to colour over a range of reward volumes and flower patch sizes.
4. Each bee remained individually constant to a flower morph when visiting a population-type grid but changed to random visitation on the simulated inflorescence.
5. On the simulated inflorescence, with morphs providing unequal qualities of reward, most bees foraged on the higher molarity morph.
6. Most, but not all bees, failed to minimize uncertainty on the simulated inflorescence.
7. On the simulated inflorescence, bees failed to optimize when one morph provided a greater reward volume than did the other.
8. In the population of flowers bees flew from flower to flower, whereas, they walked on the simulated inflorescence.     

Inverse sampling of controls in a matched case control study

A method of inverse sampling of controls in a matched case-control study is described in which, for each case, controls are sampled until a discordant set is achieved. For a binary exposure, inverse sampling is used to determine the number of controls for each case. When most individuals in a population have the same exposure, standard case-control sampling may result in many case-control sets being concordant with respect to exposure and thus uninformative in the conditional logistic analysis. The method using inverse control sampling is proposed as a solution to this problem in situations when it is practically feasible. In many circumstances, inverse control sampling is found to offer improved statistical efficiency relative to a comparable study with a fixed number of controls per case.