中国正在取代美国成为世界最大消费国

尽管美国长期以来消耗了大部分的世界资源，但是，随着中国经济的崛起。这种状况正在迅速改变。在资源消耗方面，中国正在多方面——超过美国。     

The occurrence of aristolochic acids in neotropical troidine swallowtails (Lepidoptera: Papilionidae)

Summary. Analysis of individuals of 17 troidine species demonstrated the presence of aristolochic acids in these butterflies in varying concentrations. Although aristolochic acids do not occur in Aristolochia galeata leaves, they were present in Battus polydamas larvae reared on these leaves, and thus may be synthesized by the larvae from chemical precursors in the plant. Received 17 August 1999; accepted 20 January 2000     

FOREST PRACTICES AS NONPOINT SOURCES OF POLLUTION IN NORTH AMERICA1

ABSTRACT: Forest management activities may substantially alter the quality of water draining forests, and are regulated as nonpoint sources of pollution. Important impacts have been documented, in some cases, for undesirable changes in stream temperature and concentrations of dissolved oxygen, nitrate-N, and suspended sediments. We present a comprehensive summary of North American studies that have examined the impacts of forest practices on each of these parameters of water quality. In most cases, retention of forested buffer strips along streams prevents unacceptable increases in stream temperatures. Current practices do not typically involve addition of large quantities of fine organic material to streams, and depletion of streamwater oxygen is not a problem; however, sedimentation of gravel streambeds may reduce oxygen diffusion into spawning beds in some cases. Concentrations of nitrate-N typically increase substantially after forest harvesting and fertilization, but only a few cases have resulted in concentrations approaching the drinking-water standard of 10 mg of nitrate-NIL. Road construction and harvesting increase suspended sediment concentrations in streamwater, with highly variable results among regions in North America. The use of best management practices usually prevents unacceptable increases in sediment concentrations, but exceptionally large responses (especially in relation to intense storms) are not unusual.     

Colony choice in birds: models based on temporally invariant site quality

We propose two stochastic models to explain how birds choose colonies. In the resource choice model, birds settle at each site at a rate proportional to the total resources the site contains. In the reduced resource choice model, a smaller cohort of birds enters sites at a rate determined by the total resources at each, and the remaining individuals enter sites at a rate that is linearly proportional to the total number of birds already nesting at each site. Thus, a fraction of birds chooses sites based on the resources present, and the remainder are attracted to a site by the presence of other birds. Colony site quality is assumed not to vary between years. Both models result, on average, in an ideal free distribution of colony sizes if the birds' settlement rate is linearly related to the resources in a site, if resources are distributed equally among individuals within sites, and if individuals with equal resources have equal fitness. We applied these models to long-term data on colony sizes and site usage of cliff swallows in south-western Nebraska. A test of the resource choice model suggested that the swallow population as a whole did not choose sites based strictly on site quality or the total resources contained at each site. However, a test of the reduced resource choice model suggested that a smaller fraction of the individuals in each colony may have based their choice of site on local resource availability, with the remaining birds aggregating at those sites based on the number of birds already settled there. Tests of these models may provide insight into how individuals choose colony sites and why colonies vary in size.     

Fish Assemblage Response to a Small Dam Removal in the Eightmile River System,Connecticut, USA

We examined the effects of the Zemko Dam removal on the Eightmile River system in Salem, Connecticut, USA. The objective of this research was to quantify spatiotemporal variation in fish community composition in response to small dam removal. We sampled fish abundance over a 6-year period (2005–2010) to quantify changes in fish assemblages prior to dam removal, during drawdown, and for three years following dam removal. Fish population dynamics were examined above the dam, below the dam, and at two reference sites by indicator species analysis, mixed models, non-metric multidimensional scaling, and analysis of similarity. We observed significant shifts in fish relative abundance over time in response to dam removal. Changes in fish species composition were variable, and they occurred within 1 year of drawdown. A complete shift from lentic to lotic fishes failed to occur within 3 years after the dam was removed. However, we did observe increases in fluvial and transition (i.e., pool head, pool tail, or run) specialist fishes both upstream and downstream from the former dam site. Our results demonstrate the importance of dam removal for restoring river connectivity for fish movement. While the long-term effects of dam removal remain uncertain, we conclude that dam removals can have positive benefits on fish assemblages by enhancing river connectivity and fluvial habitat availability.     

Thermal reaction norms for growth vary among cohorts of Pacific cod (Gadus macrocephalus)

While much effort has been directed at determining the spatial scales of adaptation in thermal reaction norms for growth, it is widely assumed that these reaction norms have high temporal stability. Water temperatures in the Gulf of Alaska in 2007 were the coldest on record since the mid-1970s and we present evidence that the thermal reaction norm for growth of age-0 Pacific cod (Gadus macrocephalus) in this cohort differed significantly from two adjacent cohorts. In addition to exhibiting higher growth potential at low temperatures, the 2007 cohort had a higher mean vertebral count, consistent with the widespread thermal effect known as “Jordan’s Rule.” Variation among cohorts in these physiological and morphological traits suggests a persistent response to environmental history (epigenetic effect). Temperature-induced phenotypic plasticity in the reaction norm for growth has significant implications for using growth rates to evaluate habitat quality and illustrates the complex responses of fishes to climate variability.