公众对黑河流域生态系统服务消费偏好及支付意愿研究——基于选择实验法的实证分析

运用选择实验法研究了黑河流域居民对流域生态系统服务的消费偏好及其支付意愿,并结合Mixed logit模型和潜类别模型分别从连续和离散的视角对消费者偏好的异质性进行了检验和实证研究。研究发现：① 黑河流域居民对流域生态系统服务的改善存在显著的异质性偏好,且流域居民从流域水质改善中能获得最大的效用,生态导向型消费者对平均扬沙天气情况改善存在显著偏好,娱乐享受型消费者对流域休闲娱乐条件改善存在显著的偏好。② 黑河流域居民对河流水质、东居延海水面面积和休闲娱乐条件改善3个属性指标具有显著的支付意愿,且对河流水质改善的支付意愿最大,为133.91元/（a·户）。③ 黑河流域居民愿意为流域生态系统服务改善的整体支付意愿为473.16元/（a·户）。     

武汉市蜜月旅游者行为特征与开发对策研究

蜜月旅游作为一种新兴的旅游产品,自进入中国市场以来发展迅速,引起了人们的广泛关注。在旅游经营中,了解客源市场旅游者的行为特征,对市场开发具有重要的意义。在综合分析国内外蜜月旅游研究现状的基础上,通过问卷调查的方式,对武汉市蜜月旅游市场进行了实证研究,揭示了武汉市蜜月旅游者具有出游时间长、消费能力强、偏好海滨型目的地等行为特征,并根据这些特征提出设计多样化产品、完善产业链、品牌化经营及加大宣传营销力度等具体开发对策。     

Bottom-up and top-down control of seagrass overgrazing by the sea urchin Tripneustes gratilla

The lack of top-down control on Tripneustes gratilla, a sea urchin commonly known to graze on seagrass, and the bottom-up control of its feeding preference, led to the overgrazing of seagrass meadows of the species Thalassodendron ciliatum in Changuu Island (Zanzibar Archipelago). The impact of overgrazing on seagrasses was assessed by mapping the presence of grazed versus non-grazed seagrass patches in the study site, while the top-down control on T. gratilla was assessed by measuring the abundance of its fish predators. The feeding preference and distribution of T. gratilla were characterized by calculating the electivity indexes for each seagrass species and measuring sea urchin density, respectively. Approximately half of the patches of T. ciliatum were overgrazed, while predatory fishes of T. gratilla were absent from the site. The Vanderploeg and Scavia's Relativized Electivity Index indicated that T. gratilla had a feeding preference for T. ciliatum, which was also supported by higher urchin densities within T. ciliatum dominated patches. Bottom-up control of grazing activity was observed by quantifying and analyzing morphological, nutritional, and the chemical defense traits of the seagrass in relation to feeding preference and urchin density. Feeding was positively correlated to the seagrass tissue C:P ratio (ρ = 0.9), whereas urchin density showed no correlations. The bottom-up control of the feeding preference and agglomeration of T. gratilla in T. ciliatum meadows, together with the lack of evidence of substantial top-down control and the long recovery time of T. ciliatum led to the overgrazing of this species at this site. Overgrazing, therefore, was shown to be the result of multiple factors ranging from the traits of the seagrass and feeding preference of T. gratilla, to the abundance of predators in this area.     

基于偏好融合的群组推荐研究

传统的推荐系统主要针对单个用户,但随着社会和电子商务的快速发展,人们越来越多地以多个用户的形式一起参与活动,而群组推荐旨在为多个用户组成的群组提供服务,已成为当前研究的热点之一.针对目前群组推荐准确率低,群组成员之间偏好冲突难以融合的问题,本文提出了一种新的共识模型策略,融合了群组领袖影响因子和项目热度影响因子,基于K近邻为目标群组寻找邻居群组,借鉴邻居群组的偏好,设计了基于偏好融合的群组推荐算法.在MovieLens数据集上的实验结果表明,本文所提的融合策略较传统的偏好融合策略有着更优越的表现,推荐准确率（nDCG）的总体平均性能约提高13%,推荐列表多样性指标的总体平均性能约提高10%.     

Size Selective Predation by the Asteroid Pisaster ochraceus on the Bivalve Mytilus calif ornianus: A Cost-Benefit Analysis

Abstract. When simultaneously presented with equal numbers of four sizes of clumped Mytilus californianus (20, 35, 55 and 85 mm shell length), Pisaster ochraceus (arm length of 70-110mm R) showed a preference for the medium sizes (35 and 55mm length). Prey-size preference was positively correlated with predator size. Mean prey-digestion times (insertion of the stomach, opening of the valves and digestive period) decreased significantly following fiiing of an artificial gape between the valves of mussels. When presented with different sizes of clumped filed mussels, starfish still chose medium mussels, indicating that stomach insertion, valve opening, and digestion rate may not be important constraints determining size selective predation. Measurements of the force required to dislodge mussels from the substratum and conspecifics showed an increasing exponential relationship with mussel size. Size selective feeding may be an energy maximizing and time minimizing strategy, where energy gained from choosing larger mussels is balanced against disproportionately increased costs in energy and time of removing large mussels from the substratum.     

Diel Activity Patterns and Foraging Dynamics of the Sea Urchin Tripneustes ventricosus in a Tropical Seagrass Community and a Reef Environment (Virgin Islands)

Abstract. Feeding and movement activity patterns and the foraging behavior of the sea urchin Tripneustes ventricosus were investigated in a Thalassia testudinum seagrass bed and on a patch reef at St. Croix, U.S. Virgin Islands.
Most of T. ventricosus in the seagrass bed fed during both the day and night. Consumption of seagrass blades amounted to 1.4 g dw · individual^-1· d^-1 (mean sea urchin size 12.1 cm ambitus diameter). The population consumed approximately 3.6% of the daily seagrass production.
The movement of T. ventricosus was diel with high nocturnal activity levels and rates of locomotion, and little activity during daylight hours. Foraging activity was reduced under turbulent conditions. Movement rates were not governed by food availability. T. ventricosus travelled 3.7 m · d^-1 on the patch reef. Individuals in the seagrass bed moved 8.8 m · d^-1, most of which was accomplished during the night. The area traversed contained more than one hundred times the amount of food consumed daily. It is assumed that this behavior requires high energy expenditures for locomotion, thus yielding a low net energy profit from feeding.
The high rate of movement in seagrass beds may represent an innate behavioral adaptation to predation by night-active helmet conchs ( Cassis spp.). Fitness optimization by T. ventricosus may have been achieved by minimizing the predation risk during night hours. In an evolutionary context, survival by means of an increased energy expenditure for locomotion may compensate for the lower net energy gain from foraging.     

Dietary Preferences and Carbon Absorption by two Grazing Gastropods, G/bbula umbilicaris (LINNÉ) and Jujubinus striatus (LINNÉ)

Abstract. Ingestion rates and absorption efficiencies in Gibbula umbilicaris and Jujubinus striatus feeding on green algal films, diatoms, macro-epiphytes, and dead Posidonia ocean/'ca-Ieaves have been investigated in laboratory experiments.
For both gastropod species, ingestion rates were highest in diatoms and thin green algal films as food source. G. umbilicaris exhibited significant lower consumption rates when feeding on seagrass debris or macro-epiphytes, J. striatus consumed neither Posidonia-debris nor macro-epiphytes.
Highest carbon absorption efficiencies were found in both gastropod species when feeding on diatoms and green algal films. Significantly lower efficiencies were found in G. umbilicaris when consuming seagrass debris or macro-epiphytes.
Analyses of fecal material confirmed these findings. Highest organic carbon contents were measured in fecal pellets produced after consumption of seagrass debris or macro-epiphytes reflecting the presence of structural carbohydrates. SEM examinations of feces revealed mainly diatom frustules, refractory parts of macroalgal and other plant material. Analyses of gut contents gave similar results suggesting a basically microphagous herbivory for both gastropod species.
Since seagrass debris and macro-epiphytes are not used very effectively, the high absorption efficiencies when animals feed on the microfloral component of the periphyton are discussed as possible adaptation to limited food availability.     

Understanding the association between the non-geniculate coralline red alga Spongites discoidea and the mollusc Oxystele sinensis

Nearly all adult winkles Oxystele sinensis encountered in the Kalk Bay (Western Cape province, South Africa) shallow subtidal zone were observed to bear a thick, convoluted form of the non-geniculate coralline red alga Spongites discoidea. To understand this association, various data were collected. The results show that O. sinensis is for the most part restricted to the shallow subtidal zone and rockpools, whereas the morphologically similar O. tigrina is largely restricted to the intertidal zone. Fleshy macroalgae were absent from all habitats sampled, with much of the primary substratum being occupied by encrusting algae. Spongites discoidea was restricted to intertidal rockpools and the shallow subtidal zone where O. sinensis was the most abundant winkle. Subtidal specimens of S. discoidea were generally thicker (7.24?mm [SE 0.55] on shells, 6.02?mm [SE 0.67] on boulders) than intertidal specimens (2.39?mm [SE 0.21] on boulders, 1.02?mm [SE 0.09] on bedrock), were more heavily burrowed into (44% [SE 3.32] for subtidal shells, 36% [SE 3.94] for subtidal boulders), and were more weakly attached (2.2?kg [SE 0.58] for subtidal shells, 8.4?kg [SE 0.77] for subtidal boulders). Experimental evidence showed that the coralline has no preference for shells of O. sinensis and that, contrary to our assumption, there is no apparent advantage to the winkle bearing the coralline, other than perhaps for camouflage to avoid predation. The high frequency of the association is more likely due to the substantial overlap in the niches of the coralline and the winkle.