对我国食物结构的测算与建议

本文从我国国情出发,论证了几种食物结构方案,提出2000年我国的食物结构方案,并同农业部、营养学会的两个方案相比较。认为选择我国食物结构,要立足国情,不能照搬西方的模式;要根据经济状况、消费水平的差异,分成四个档次。指出要按确定的食物结构来调整农业结构。种植业要增加大豆、玉米,饲养业要增加禽类与水产。建议发展食品工业与饲料工业。

Status and historical changes in the fish community in Erhai Lake

Erhai Lake is the second largest freshwater lake on the Yunnan Plateau, Southwest China. In recent decades, a number of exotic fish species have been introduced into the lake and the fish community has changed considerably. We evaluated the status of the fish community based on surveys with multimesh gillnet, trap net, and benthic fyke-net between May 2009 and April 2012. In addition, we evaluated the change in the community using historical data （1952-2010） describing the fish community and fishery harvest. The current fish community is dominated by small-sized fishes, including Pseudorasbora parva, Rhinogobius giurinus, Micropercops swinhonis, Hemiculter leucisculus, and Rhinogobius cliffordpopei. These accounted for 87.7% of the 22 546 total specimens collected. Omnivorous and carnivorous species dominated the community. A canonical correspondence analysis （CCA） plot revealed that the distribution of fishes in the lake is influenced by aquatic plants, water temperature, pH, and season. The abundance of indigenous species has declined sharply, and a majority of endemic species have been extirpated from the lake （a decrease from seven to two species）. In contrast, the number of exotic species has increased since the 1960s to a total of 22 at present. The fishery harvest decreased initially following the 1960s, but has since increased due to the introduction of non-native fish and stocking of native fish. The fishery harvest was significantly correlated with total nitrogen, not total phosphorus, during the past 20 years. Based on our results, we discuss recommendations for the restoration and conservation of the fish resources in Erhai Lake.

Analysis of a harvested tritrophic food chain model in the presence of additional food for top predator

In this paper, we propose and analyze a three-species predator prey system in the presence of additional food for top predator. It is assumed that the middle predator is acting as a prey as well as a predator and the top predator consumes both prey as well as middle predator. It is also considered that a constant amount of additional food for top predator exists in the ecosystem. The effects of harvesting of top predator are investigated. The existence and stability conditions of the equilibria have been discussed analytically. The Hopf bifurcation analysis of the system with respect to predation rate of prey to the top predator and the harvesting effort have been analyzed both analytically and numerically. Pontryagin＇s maximum principle is used to determine the optimal harvesting of top predator population to maximize the discounted net revenue. From our analysis, it is seen that the additional food has a significant impact to prevent the extinction risk of top predator population and also to increase revenue collection. Finally, some numerical results have been given in support of our analytical findings.

A high-fat diet increases body fat mass and up-regulates expression of genes related to adipogenesis and inflammation in a genetically lean pig

Because of their physiological similarity to humans, pigs provide an excellent model for the study of obesity. This study evaluated diet-induced adiposity in genetically lean pigs and found that body weight and energy intake did not differ between controls and pigs fed the high-fat （HF） diet for three months. However, fat mass percentage, adi- pocyte size, concentrations of total cholesterol （TC）, triglyceride （TG）, high-density lipoprotein cholesterol （HDL-C） and low-density lipoprotein cholesterol （LDL-C）, insulin, and leptin in plasma were significantly higher in HF pigs than in controls. The HF diet increased the expression in backfat tissue of genes responsible for cholesterol synthesis such as Insig-1 and Insig-2. Lipid metabolism-related genes including sterol regulatory element binding protein lc （SREBP-lc）, fatty acid synthase 1 （FASN1）, diacylglycerol O-acyltransferase 2 （DGAT2）, and fatty acid binding protein 4 （FABP4） were significantly up-regulated in backfat tissue, while the expression of proliferator-activated receptor-α（PPAR-α） and carnitine palmitoyl transferase 2 （CPT2）, both involved in fatty acid oxidation, was reduced. In liver tissue, HF feeding significantly elevated the expression of SREBP-lc, FASN1, DGAT2, and hepatocyte nuclear factor-4α （HNF-4α） mRNAs. Microarray analysis further showed that the HF diet had a significant effect on the expression of 576 genes. Among these, 108 genes were related to 21 pathways, with 20 genes involved in adiposity deposition and 26 related to immune response. Our results suggest that an HF diet can induce genetically lean pigs into obesity with body fat mass expansion and adipose-related inflammation.

SPECIAL ISSUE： DISTRIBUTION OF NATIONAL INCOME IN A TRANSITIONAL ECONOMY Who is the predator, who the prey？ --an analysis of changes in the state of China＇s national income distribution

This paper investigates how national income distribution among the corporate, government, and household sectors has changed from 1992 to 2005 using the Flow of Funds Accounts adjusted after the National Economic Census 2004. We analyze the changes in institutional distribution of national income from the primary and secondary distribution of national income, with a focus on explaining the fall in the household sector＇s share of the national income pie since 1996. To analyze the primary distribution of national income among institutional sectors, we formulate the share of each sector in primary national income as the weighted average of the product of factor income share using each sector＇s proportion of the different types of factor income as weights. With this formula, we adjust factor income shares in the Flow of Funds Account, re-compute the distribution of disposable income by institutional sector from 1993 to 2005, and extrapolate the distribution to 2006 and 2007. Our findings are： the share of the household sector in national disposable income reached its peak in 1996, and declined by over twelve percentage points between 1996 and 2005, of which 10.71 and 2.01 percentage points were due to primary distribution and secondary distribution respectively. In contrast, the share of the corporate and government sectors in primary distribution increased by 7.49 and 3.21 percentage points respectively. In secondary distribution, the share of the government sector further increased by 3.17 percentage points, at the expense of the other two sectors. We also find that the decline in the share of labor income and property income in factor income distribution are the two main sources for the decline in the household share of primary distribution. In the period 2005-2007, the household share of national income fell further by over three percentage points, mostly resulting from the increase in the share of net production tax.

Facing different predators： adaptiveness of behavioral and morphological traits under predation

Predation is thought to be one of the main structuring forces in animal communities. However, se- lective predation is often measured on isolated traits in response to a single predatory species, but only rarely are selective forces on several traits quantified or even compared between different predators naturally occurring in the same system. In the present study, we therefore measured be- havioral and morphological traits in young-of-the-year Eurasian perch Perca fluviatilis and com- pared their selective values in response to the 2 most common predators, adult perch and pike Esox lucius. Using mixed effects models and model averaging to analyze our data, we quantified and compared the selectivity of the 2 predators on the different morphological and behavioral traits. We found that selection on the behavioral traits was higher than on morphological traits and perch predators preyed overall more selectively than pike predators. Pike tended to positively se- lect shallow bodied and nonvigilant individuals （i.e. individuals not performing predator inspec- tion）. In contrast, perch predators selected mainly for bolder juvenile perch （i.e. individuals spend- ing more time in the open, more active）, which was most important. Our results are to the best of our knowledge the first that analyzed behavioral and morphological adaptations of juvenile perch facing 2 different predation strategies. We found that relative specific predation intensity for the di- vergent traits differed between the predators, providing some additional ideas why juvenile perch display such a high degree of phenotypic plasticity.

Exploring the dynamics of a Holling-Tanner model with cannibalism in both predator and prey population

Cannibalism is an intriguing life history trait, that has been considered primarily in the predator, in predator-prey population models. Recent experimental evidence shows that prey cannibalism can have a significant impact on predator-prey population dyna- mics in natural communities. Motivated by these experimental results, we investigate a ratio-dependent Holling-Tanner model, where cannibalism occurs simultaneously in both the predator and prey species. We show that depending on parameters, whilst prey or predator cannibalism acting alone leads to instability, their joint effect can actually stabilize the unstable interior equilibrium. Furthermore, in the spatially explicit model, we find that depending on parameters, prey and predator cannibalism acting jointly can cause spatial patterns to form, while not so acting individually. We discuss ecologicalconsequences of these findings in light of food chain dynamics, invasive species control and climate change.

Size and shape information serve as labels in the alarm calls of Gunnison＇s prairie dogs Cynomys gunnisoni

Some animals have the capacity to produce different alarm calls for terrestrial and aerial predators. However, it is not clear what cognitive processes are involved in generating these calls. One possibility is the position of the predator： Anything on the ground receives a terrestrial predator call, and anything in the air receives an aerial predator call. Another possibility is that animals are able to recognize the physical features of predators and incorporate those into their calls. As a way of elucidating which of these mechanisms plays a primary role in generating the structure of different calls, we performed two field experiments with Gunnison＇s prairie dogs. First, we presented the prairie dogs with a circle, a triangle, and a square, each moving across the colony at the same height and speed. Second, we presented the prairie dogs with two squares of differing sizes. DFA statistics showed that 82.6 percent of calls for the circle and 79.2 percent of the calls for the triangle were correctly classified, and 73.3 percent of the calls for the square were classified as either square or circle. Also, 100 percent of the calls for the larger square and 90 percent of the calls for the smaller square were correctly classified. Because both squares and circles are features of terrestrial predators and triangles are features of aerial predators, our results suggest that prairie dogs might have a cognitive mechanism that labels the abstract shape and size of different predators, rather than the position of the predator [Current Zoology 58 （5）： 741-748, 2012].

Locomotor adaptations in Plio-Pleistocene large carnivores from the Italian Peninsula： Palaeoecological implications

Mammalian carnivores are rarely considered for environmental reconstructions because they are extremely adaptable and their geographic range is usually large. However, the functional morphology of carnivore long bones can be indicative of locomotor behaviour as well as adaptation to specific kind of habitats. Here, different long bone ratios belonging to a subsample of extant large carnivores are used to infer palaeoecology of a comparative sample of Plio-Pleistocene fossils belonging to Italian paleo-communities. A multivariate long bone shape space reveals similarities between extant and fossil carnivores and multiple logistic regression models suggest that specific indices （the brachial and the Mt/F） can be applied to predict adaptations to grassland and tropical biomes. These functional indices exhibit also a phylogenetic signal to different degree. The brachial index is a significant predictor of adaptations to tropical biomes when phylogeny is taken into account, while Mt/F is not correlated anymore to habitat adaptations. However, the proportion of grassland-adapted carnivores in Italian paleo-communities exhibits a negative relationship with mean oxygen isotopic values, which are indicative of past climatic oscillations. As climate became more unstable during the Ice Ages, large carnivore guilds from the Italian peninsula were invaded by tropical/closed-adapted species. These species take advantage of the temperate forest cover that was more spread after 1.0 Ma than in the initial phase of the Quaternary （2.0 Ma） when the climate was more arid [Current Zoology 57 （3）： 269-283, 2011].

Modeling and analysis of a predator-prey model with state-dependent delay

We propose and study a predator prey model with state-dependent delay where the prey population is assumed to have an age structure. The state-dependent delay appears due to the mature condition that the prey must spend an amount of time in the immature stage sufficient to accumulate a threshold amount of food. We perform a qualitative analysis of the solutions, which includes studying positivity and boundedness, existence and local stability of equilibria. For the global dynamics of the system, we discuss an attracting region which is determined by solutions, and the region collapses to the interior equilibrium in the constant delay case.

A diffusive Holling-Tanner prey-predator model with free boundary

This paper is concerned with a diffusive Holling-Tanner prey-predator model in a bounded domain with Dirichlet boundary condition and a free boundary. The global existence of the unique solution is proved. Moreover, the criteria governing spreading- vanishing are derived by mainly using the comparison principle. The results show that if the length of the occupying line is bigger than a threshold value （spreading barrier）, then the spreading of predators will make an achievement, and, if the length of the occupying line is smaller than this spreading barrier and the spreading coefficient is relatively small depending on initial size of predators, then the predators will fail in establishing themselves and eventually die out.

Study of the interactive effect of prey toxin and optimal foraging strategy on a predator-prey model

The optimal foraging theory predicts that predators choose prey with more net rate of energy intake and less energy costs if there are multiple food sources available. Toxins are found in many species in nature. Those toxins may be produced by prey as self- protection from predatory animals, or come from other sources such as pesticide residue. Therefore, it requires a balance between energy intake and toxicity damage. In order to study the interactive effect of prey toxin and optimal foraging strategy, we construct a predator-prey model with toxin-induced functional response and optimal foraging property. Dynamical analysis shows that the optimal strategy system presents more complex dynamical behavior than the fixed preference system. We conclude that optimal foraging strategy might play a key role in stabilizing or destabilizing the coexistence states of the species in the system, depending on the level of prey toxins.