Migration and Agricultural Change: The Case of Smallholder Agriculture in Highland Ecuador

A large and growing number of agricultural households in less developed countries are also engaged in international migration. Thousands of farmers from the highland provinces of Cañar and Azuay, Ecuador, have immigrated to metropolitan New York, where they work in menial jobs and remit, as a group, millions of dollars annually. This paper examines the effects of international migration on agricultural production and land-use in two regions of Cañar Province. An agricultural survey was administered in two communities to determine land-use and agricultural production of migrant and nonmigrant households. Contrary to most reports on the subject, migration has neither led to agricultural abandonment nor have remittances been dedicated to agricultural improvements. Semisubsistence agriculture remains an important riskaverse economic and cultural activity, but cultivation is a poor investment. A large investment in housing and land has converted much of the region into a peri-urban landscape of cultivated real estate.     

The Effect of Visual Features on Jumping Spider Movements Across Gaps

Our objective was to determine whether an animal’s decisions to cross inhospitable open space are influenced by the visual characteristics of targets it can see across the space. We studied jumping spiders (Salticidae) in the genus Phidippus. We considered the effect of target size (short vs. tall) and distance (close vs. distant) in no-choice experiments. How often spiders approached close targets, regardless of target size, was not significantly different from how often they approached tall, distant targets, but they approached close targets of either size significantly more often than short, distant targets. When presented simultaneously with short, close and tall, distant targets the spiders’ choices did not differ significantly from random. We also tested for the effects of the contrast of targets with their background and found that the spiders crossed open space to reach green, but not white, targets, regardless of background. Finally, spiders were more likely to approach a green grass-like target rather than a target composed of geometric shapes. We conclude that target size, distance and appearance all influence the spiders’ willingness to cross open space.     

Quantifying Change Through Time in Spider Assemblages: Sampling Methods, Indices and Sources of Error

Using a sample dataset from six sites in the Southern Appalachian mountains in the United States, I evaluate the usefulness of diversity indices and similarity/difference indices for monitoring the changes in spider (Order Araneae) assemblages through time. The Shannon index, Brillouin index, Simpson's index and Margalef's index were correlated with each other and were able to detect successional changes in two old clear-cuts as well as disturbance to a Beech gap forest possibly due to Beech Bark Disease. Turnover, Bray-Curtis similarity, and Morisita-Horn similarity also detected successional differences between the forest types and indicated the short-term and long-term changes in a mature forest stand. Seasonal changes (early to late summer) in spider communities were consistently higher than yearly changes. I identify and discuss the implications of various sources of error that will adversely affect the accuracy and efficiency of a monitoring protocol: sensitivity of indices to sample size, sampler bias, inclusion of juveniles, taxonomic uncertainty and stochastic sampling effects. Although gross trends are still apparent in the sample data regardless of these errors, more subtle changes may be obscured. It is these subtle trends which may be more useful to managers attempting to identify disturbance before irreversible damage occurs.     

小麦,玉米轮作田蜘蛛群落结构及多样性研究

一、研究方法本项工作于1988—1990年在青州市南郊农田进行。位于东经118°17′,北纬36°27′,年平均气温9℃,年降雨量860mm以上,无霜期180天左右。调查了不同作物类型的地块,包括玉米间作(大豆)田、净玉米田、有水浇条件的麦田、旱麦田和田埂杂草五种生境。其中小麦、玉米轮作田各3块,每块面积0.2ha以     

Spider predators of lepidopteran eggs in south Texas field crops

Observations were made of spiders attacking lepidopteran eggs in south Texas field crops (cotton, corn, and soybean) from 2001 to 2004. Twelve species of spider from seven families were observed feeding on the eggs during the 4 years. These spiders were primarily cursorial hunting spiders, and they were observed feeding on eggs most frequently in cotton, representing 26.6% of all observations in cotton over the 4 years. Spider predation on eggs was proportionally less frequent in corn and soybean with 6.3% and 15.4% of observed predation in those crops, respectively. Four species of spider were responsible for 86.1% of the predation by spiders. The anyphaenid Hibana futilis (Banks) was the spider most frequently observed feeding on lepidopteran eggs during the 4 years of this study, constituting 45.1% of all spiders observed. Grammonota texana Banks (Linyphiidae), Hibana arunda Platnick (Anyphaenidae), and Cheiracanthium inclusum (Hentz) (Miturgidae) were the 2nd, 3rd, and 4th most frequently observed spiders constituting 15.6%, 12.8%, and 11.7% of all spiders observed, respectively. Most spiders represented taxa that are known to forage without a web. However, G. texana was observed feeding on eggs independent of a web, which is uncharacteristic of linyphiids. Other cursorial hunting spiders feeding on eggs included members of the Clubionidae, Corrinnidae, and Salticidae. Ninety-eight percent of all observations of egg predation by spiders were nocturnal; only the Salticidae were diurnal. It is likely that previous studies of predation in crops have vastly underestimated the importance of spiders as predators of lepidopteran eggs due to inadequate evaluation of nocturnal predation.     

人为活动对地表节肢动物多样性的影响——以沈阳市北陵公园地表蜘蛛为例

为了解人为活动对地表节肢动物多样性的影响,2010年9月至10月,采用陷阱法对沈阳市北陵公园地表蜘蛛多样性进行了调查.共采集蜘蛛标本737头,经鉴定隶属于9科15属23种.调查发现,沈阳市北陵公园地表蜘蛛物种多样性较低,狼蛛和密蛛是该地区的优势类群,其中类奇异獾蛛Trochosa ruricoloides和拟吉小密蛛Mysmenella pseudojobi为优势种.从公园的边缘到内部,蜘蛛群落组成及多样性相似,各多样性指数间均无统计学差异.研究结果表明,由于北陵公园开放程度较高,公园内锻炼、游憩的人数众多,频繁的人为干扰对地表蜘蛛造成较大影响,地表蜘蛛物种组成单一、群落结构简单以及物种多样性从边缘到内部无明显差异,这说明人为活动是影响市区开放式公园内节肢动物多样性的重要因素.     

The Appearance of a Different DNA Sequence May Decrease Nucleotide Diversity

Nucleotide diversity may be decreased when a different DNA sequence type appears in a population. This undesirable property in a genetic diversity index is demonstrated by mathematical examples. The possibility of this phenomenon in natural populations is briefly discussed. Received: 21 June 1999 / Accepted: 27 July 1999     

缙云山自然保护区蜘蛛物种多样性初步研究

总结了自2007年10月以来对缙云山蜘蛛物种多样性研究的初步成果。到目前为止,共采集成熟蜘蛛标本超过1万头,鉴定出27科112属219种蜘蛛,其中包括73种中国特有物种。填补了重庆市蜘蛛多样性研究的空白。     

The effect of afforestation on fresh waters in Tayside,Scotland. Zooplankton and other microfauna

This paper reports the findings of one section of a freshwater synoptic survey in the Tayside Region of Scotland and deals with the distribution and abundance of the crustacean zooplankton and other microfauna of 25 standing waters of small to medium size and 24 small running waters. The objectives were to assess the possible effects of land-use, especially afforestation, and of catchment area sub-surface geology, on such fauna. Various methods, statistical and non-statistical, have been used to assess the influence of these parameters on the presence, absence and relative abundance of the dominant taxonomic groups. The main findings indicate that the nature of the water-body is of prime importance in determining the abundance and composition of the fauna and little effect can be associated with land-use or sub-surface geology.     

Reconsidering the green revolution: Diversity and stability in cradle areas of crop domestication

This paper reconsiders two widely held hypotheses about the effects of the green revolution, that it led to biological simplification and instability. The hypothesis of biological simplification (genetic erosion) is tested with evidence from Andean agriculture, where farmers maintain a significant degree of crop diversity even as they adopt modern crop varieties. The hypothesis of increased instability is tested with evidence from Asia where wheat and rice yields show no general pattern of increased instability. Neither of these hypotheses is confirmed. The conventional wisdom about the green revolution should be reconsidered with emphasis on resilience and variation in modernizing farming systems.     

大茂山国家森林公园蜘蛛群落结构及多样性研究

2007年5月对河北唐县大茂山国家森林公园蜘蛛的物种多样性和群落结构进行了调查,采用样方与随机扫网相结合的方法,共采集标本728头,隶属25科63种(属)。运用群落多样性指数对其进行分析,研究结果显示:大茂山地区蜘蛛物种多样性丰富,不同生境中蜘蛛群落的种类和结构差别较大。落叶层的蜘蛛种类最多,个体密度最高,群落结构稳定;灌木丛的蜘蛛均匀度最高,结构比较稳定;而草丛中的蜘蛛种类少,个体密度较低,优势种明显。     

Determinants of Mating Frequency in the Spiny Orbweaving Spider,Micrathena gracilis (Araneae: Araneidae)

Male Micrathena gracilis require two copulations, separated by a dismount, in order to inseminate both reproductive tracts of the female. We examined several factors that might influence a male's copulatory success. Web structure influenced male courtship and dismount tactics, but not copulatory frequency. The presence of another male reduced the likelihood of a given male copulating with both tracts, a limitation mediated by sexual responsiveness of the female. Mating status of the female did influence copulatory frequency; males were less likely to copulate a second time with nonvirgin females. In summary, males modify mating activities to reduce predation by females, to reduce intermale competition, and to avoid expending gametes when there is little chance of fertilization. Females influence males by predatory activities, mediated through web structure, and enhancing sperm competition among males.     

长沙望城县早稻田蜘蛛群落结构及动态研究

长沙望城县早稻田蜘蛛群落有9科20种,以微蛛科中的食虫沟瘤蛛所占比例最大,为第一优势种,其次是拟水狼蛛、锥腹肖蛸、八斑鞘蛛。八斑鞘蛛在早稻生长中后期发生量上升。综防田与化防田的优势种一致,施用化学农药对蜘蛛群落的丰富度、多样性有明显降低作用。稻田蜘蛛数量变动与白背飞虱及黑尾叶蝉的消长基本一致,稻田蜘蛛具有明显的控虫效应。综防田与化防田对照试验证明：现有化学农药用量减少是可行的。     

不同秋眠性苜蓿的遗传多样性研究

苜蓿的秋眠性是苜蓿引种,栽培的依据。采用RAPD技术对32份不同秋眠性苜蓿进行遗传多样性和系统发育研究。结果表明,13条引物共扩增出217个标记,有214个多态位点,多态频率达到98．6％,说明这些苜蓿品种具有很高的遗传多样性。聚类分析表明,安徽野生南苜蓿和其它栽培品种苜蓿有大的遗传差异,单独聚为一类。其余31个品种在相似系数为0．815的地方聚为4类,并且,相对秋眠性强的苜蓿品种的遗传基础更为丰富,而秋眠级数低的苜蓿品种相对遗传基础较狭窄。本研究同时表明,安徽野生苜蓿将能够为南方苜蓿育种丰富遗传基础,应加大保护和研究。     

The rivers of North East Scotland: physicochemical characteristics

Multivariate analysis of spatial variation in 15 physicochemical characteristics grouped the seven major north-east rivers into two sets — highland and lowland rivers. The highland rivers formed a continuum that could be further divided into rivers with low concentrations of dissolved materials including the Spey and Dee (full highland rivers), and a more variable group with higher concentrations of dissolved materials including the Don, Deveron and Lossie (intermediate highland rivers) emphasising the diversity of river types classically described as highland. The Lossie was differentiated from the other intermediate highland rivers by lower oxygen concentration and pH. The major differences in physicochemistry between rivers were consistent with differences in catchment geology, soil type, climate, and land use. The large amounts of dissolved material and high nutrient status of the lowland Ythan and Ugie rivers reflected the high proportion of their catchments under agriculture, and the acidity of the Lossie reflected the high proportion of its catchment under forest. The small amounts of dissolved material in the Spey and Dee were attributable to the high proportion of slow weathering acidic rocks and acid soils in their catchments, and to the high volume flows of these rivers relative to the others. The amounts of dissolved material were greater in summer during low base flows and were accomparied by an increase in phosphate concentration in the lowland rivers. Oxygen saturation increased in summer in the Ythan and the Don, presumably as a result of greater photosynthetic activity. Marked declines in silica were thought to result from significant diatom growth in the highland and intermediate highland rivers, particularly the Don, during summer.     

Coordination of Behavioral Sequences Between Individuals During Prey Capture in a Social Spider, Anelosimus eximius

The analysis of collaborative predation sequences performed by groups of 10 individuals (females) in a nonterritorial permanent-social spider, A. eximius, shows that prey-captures are organized in successive steps. Spiders begin by throwing sticky silk, which hinders the prey in the web; they then throw dry silk, which completes the immobilization of the prey. The third step is characterized by bites that paralyze the prey that will be then carried. A concordance test reveals a coordination of the individual's acts that explains the collaborative prey-capture efficiency. No individual specialization in one type of act has been shown. On the contrary, by using living preys or artificially dead vibrated preys, we show that all individuals have equipotential behaviors. Furthermore, each spider is able to adjust its behavior to the state of the prey. Individuals already involved in prey transportation can again display bites or sticky silk throwing if the prey is artificially vibrated. This mechanism, which corresponds to stimergic processes responsible for self-organized phenomena, already described in social insects, permits a coordination of individual acts without the recourse of direct communication. These results permit us to understand better how individuals coordinate their acts and lead us to support the hypothesis that the transition between solitary species and social species in spiders could have been sudden.     

Diversity of canopy and understorey spiders in north-temperate hardwood forests

1 We characterized and compared diversity patterns of canopy and understorey spiders (Arachnida: Araneae) on sugar maple ( Acer saccharum Marsh.) and American beech ( Fagus grandifolia Ehrh.) in hardwood forests of southern Québec, Canada.
2 We sampled canopies of 45 sugar maple and 45 American beech trees and associated understorey saplings in mature protected forests near Montréal. Samples were obtained by beating the crown foliage at various heights and by beating saplings around each tree.
3 Eighty-two species were identified from 13 669 individuals. Forty-eight species and 3860 individuals and 72 species and 9809 individuals were collected from the canopy and the understorey, respectively.
4 Multivariate analyses (NMDS ordination and NPMANOVA) showed the composition of canopy and understorey assemblages differed significantly, and canopy assemblages differed between tree species. Rank-abundance distribution models fitted to the canopy and understorey data indicated that different mechanisms structure the assemblages in both habitats. Three abundant spider species were significantly more common in the canopy; ten species were collected significantly more often in the understorey.
5 The forest canopy was shown to be an important reservoir for spider diversity in north-temperate forests.     

The distribution and status of the adder (Vipera berus L) in Scotland determined from questionnaire surveys

Abstract. During 1992 two questionnaire surveys, aimed at farmers and sections of the general public, were conducted to determine the distribution and status of the adder ( Vipera berus L.) in Scotland. In total, 94% of the Scottish mainland and inner isles were covered by the two surveys. The adder appears to be widespread throughout Scotland, although it is absent from much of the Central Valley, the Outer Hebrides and Northern Isles, and from much of the mountainous region between Inverness and Glasgow.
The distribution of the adder in Scotland was compared with the distributions of different habitat types defined in the ITE Land Class survey. Adders were strongly associated with areas of heterogeneous land use and negatively associated with intensively arable areas and rugged mountainous areas. Strong evidence was found to suggest that perceived adder abundance had declined during the last 10 years. Although the evidence suggesting that the distribution of adders in Scotland had changed was less strong, the results of the Farm Survey did indicate that it had contracted. The perceived change in status of the adder in Scotland during the last 10 years was compared with the observed changes in land use over the same period.