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921.
922.
The "Moynihan controversy" concerning the existence of a subculture of poverty among the Negro poor has been marked by polar positions. There are those who feel that much of the "deviant behavior" of this group is actually normative and transmitted in the socialization process. Others maintain that such behavior is not normative and represents merely situational responses to extreme poverty and other forms of deprivation. The data in this paper, derived from interviews with a sample of the Negro population of Philadelphia, indicate that Negroes living in poverty hold attitudes that can be characterized as a "subculture of poverty." On the other hand, the data also suggest that such attitudes represent but one segment of the total range of attitudes and reference values held by this population, many of which are shared by the larger society. Furthermore, the evidence indicates that these attitudes serve to maintain the mental health of those living in a severely disadvantaged social situation. [deviant behavior, Negro, poverty] 相似文献
923.
Individual plants of Chenopodium rubrum were given differentnumbers of inductive cycles in a 12 h photoperiod and the patternof reproductive development was analysed after 40 d of growth.At least 2 inductive cycles are required to form any determinatereproductive organs and at least 12 cycles are required fornormal reproductive development. Individuals given a singleinductive cycle display a loss of apical dominance at thosenodes formed immediately after the treatment without the subsequentformation of any floral structures. Plants given between 2 and12 mductive cycles display both determinate reproductive organsand indeter minate vegetative shoots. The pattern of reproductivedevelopment on such plants depends upon the number of cyclesrelative to the developmental age of newly initiated primordia.It is suggested that the early events of floral induction mayinvolve a radical decrease in the ratio of auxin to cytokinin. 相似文献
924.
925.
LAURA NAGEL ROBERT MONTGOMERIE STEPHEN C. LOUGHEED 《Biological journal of the Linnean Society. Linnean Society of London》2008,94(3):569-587
The blood‐feeding juvenile stages of gnathiid isopods are important ectoparasites of marine fishes on the Great Barrier Reef (GBR), and are a major component of the diet of cleaner fishes. We report here that these gnathiids have undergone evolutionary diversification, both geographically and temporally (into diurnally and nocturnally active taxa), which has been accompanied by changes in their morphology and behaviour. To perform this analysis, we sequenced a portion of the nuclear ribosomal ITS2 for 47 gnathiids collected from 29 host fishes of 11 species at three locales spanning 2000 km on the GBR. Maximum parsimony and Bayesian phylogenetic analyses both revealed four major clades. There was some degree of geographical structuring in these clades, but there was no evidence supporting host fish specialization, as gnathiids collected from the skin of different teleost taxa did not resolve into distinct clades. The topology of the phylogeny also implied some structuring that was dependent upon collection time (day or night), so we investigated whether there were also behavioural and morphological differences between taxa active at these different times. Nocturnal gnathiids had significantly longer antennules and larger eyes than diurnal gnathiids – two traits presumably adaptive for nocturnal activity. Behavioural tests showed that both nocturnal and diurnal gnathiids use olfaction and vision while foraging, but that nocturnal gnathiids used olfaction more often in dark conditions, and that they were able to perceive movement under extremely low levels of light. Diurnal gnathiids used vision more effectively when there was some ambient light. Our results thus suggest that both phenotypic and genotypic divergence in gnathiids may be influenced by natural selection acting on ecological traits, such as predator avoidance and host detection. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 94 , 569–587. 相似文献
926.
Observations of these strands are consistent with the idea of trans-cellular strands of cytoplasm in sieve tubes. 相似文献
927.
928.
ROBERT B. PAYNE 《Ibis》1998,140(3):369-381
A firefinch of the Jos Plateau, northern Nigeria, is described as a new species, Rock Fire-finch Lagonosticta sanguinodorsalis. This firefinch has distinctive songs and a distinctive habitat—bushy and grassy rocky outcrops on the plateau and inselbergs to the north and east. It has a blue-grey bill, red back in the male and reddish brown back in the female and juvenile and broad primaries in both the adult and juvenile. It appears most closely related to the Mali Firefinch Lagonosticta virata and the Chad Firefinch Lagonosticta umbrinodorsalis. Its songs are mimicked by the brood-parasitic Jos Plateau Indigobird Vidua maryae , which occurs within the range of the firefinch and whose songs led to the discovery of the firefinch. The songs of the firefinch, the song mimicry of the indigobird and the apparent continuity of song mimicry across 27 years indicate a unique association of this distinct pair of species. 相似文献
929.
930.
The Damara Tern Sterna balaenarum is a rare, near-endemic breeder along the southwestern coast of Africa. Found predominantly in Namibia, its world population was once believed to be 4000 birds. Population surveys in the northern Namib Desert have recently estimated that 12,000 adults exist. The aims of this study were to (1) determine the population status along the southern coast, thereby completing Namibian surveys, (2) assess latitudinal trends (over 10̀) in relation to ocean upwellings for the entire coast and (3) determine breeding habitat preferences. This was completed in 1994 and 1996 using random sampling techniques. Survey squares of 1 km2 , randomly plotted on 1:50,000 maps, were located in the desert with a Global Positioning System (GPS) unit and searched for breeding terns. A total of 1780 km2 was sampled in the southern desert and extrapolations indicated that about 1450 adult terns occur in this region. This gives a global population estimate of 13,500 adult Damara Terns. Significant habitat preferences were apparent with terns nesting most often on gravel plains in the north but switching to salt pans in the south. Lower salt pan temperatures in the south may account for these trends. The peak density was in central areas (23|dGS) with a decreasing density north and south along Namibia's 1470 km-coast. This is parallel to recent findings for linear shorebird densities and macro-invertebrate density. This suggests that primary productivity of the Benguela is highest in the central regions and not where the upwellings occur 400 km south. We propose a delayed blooming effect to account for these trends and conclude that this diminutive tern is influenced in many aspects of its life history by Namibia's cold offshore upwellings. 相似文献