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European beachgrass ( Ammophila arenaria [L] Link), introduced to stabilize sand, is fully naturalized in central and northern California and has supplanted populations of native dune plants in many areas, including the North Spit of Humboldt Bay. We interpreted air photos of the North Spit for the presence of Ammophila arenaria at three points in time: 1939/1942, 1962, and 1989. To quantify the spread and to detect invasion patterns of Ammophila , we then compiled maps using a geographic information system. We documented introduction dates and locations to improve the accuracy of our photo interpretation. Interpretation of the three photo series revealed invasion and expansion of Ammophila in both foredunes and inland dunes. The most dramatic increase in cover was found in the foredunes, whereas documented and presumed plantings were found mostly on inland dunes. Adjusting for intentional eradication, Ammophila cover on the North Spit was found to have increased between 1939 and 1989 by 574%. The square root of the area occupied by Ammophila on the North Spit increased linearly with time, conforming to biological invasion theory. 相似文献
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John P Dwyer Douglas Wallace David R. Larsen 《Journal of the American Water Resources Association》1997,33(2):481-489
ABSTRACT: Following the Midwest flood of 1993, a study was initiated along a 39-mile segment of the Missouri River to determine if there was an association between woody corridors and levee stability. A systematic sample of levee failures revealed that primary levees which did not fail had a significantly wider woody corridor than failed levees. Analysis of the total inventory of failed levees revealed that as the width of the woody corridor decreased, the length of the levee failure increased. Number of levee failures and their severity of damage could be reduced if woody corridors were at least 300 feet wide. 相似文献
567.
In order to keep subscribers up-to-date with the latest developments in their field, John Wiley & Sons are providing a current awareness service in each issue of the journal. The bibliography contains newly published material in the field of prenatal diagnosis. Each bibliography is divided into 17 sections: 1 Books, Reviews & Symposia; 2 General Interest; 3 Normal Fetal Development; 4 Gametogenesis and Pre-implantation Diagnosis; 5 First Trimester Diagnosis; 6 Second Trimester Diagnosis; 7 Fetal Diagnosis by Ultrasound and Other Imaging; 8 Maternal Screening; 9 Screening for Carriers of Genetic Abnormality; 10 Technological Developments; 11 Confined Placental Mosaicism and Uniparental Disomy; 12 Molecular Cytogenetics; 13 Fetal Cells in Maternal Circulation; 14 Fetal Therapy; 15 Psychosocial Aspects; 16 Epidemiology and Environmental Factors; 17 Developmental Pathology. Within each section, articles are listed in alphabetical order with respect to author. If, in the preceding period, no publications are located relevant to any one of these headings, that section will be omitted 相似文献
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Studies of the otariids (fur seals and sea lions), a highly sexually dimorphic group, have provided conflicting evidence of
differential maternal expenditure in male and female offspring and, thus, suggestions that they conform to predictions of
investment theory are equivocal. Since the mid-1970s, a diversity of research on Antarctic fur seals (Arctocephalus gazella) including studies of their reproductive ecology, lactation energetics, and foraging behaviour have been conducted at Bird
Island, South Georgia that have resulted in one of the more complete and diverse data sets for any species of otariid. These
long-term data were reviewed to determine whether there was any evidence to support that differential maternal expenditure
occurred in Antarctic fur seals. Most of the data examined were collected during five consecutive austral summers from 1988
through 1992 and included years in which local food resources were abundant and scarce. We were unable to detect differences
in the sex ratios of pups at birth or sex-biased differences in growth rates estimated from serial data, the number of foraging
trips made, the duration of attendance ashore, diving behaviour, suckling behaviour, or milk consumption in any year and in
the duration of foraging trips or age at weaning in 2 of 3 years. In addition, we found no evidence of greater reproductive
costs between mothers with sons or daughters relative to their reproductive performance the following year. In contrast, sex-biased
differences were only found in the duration of foraging trips in 1990, the age at weaning in 1988, and consistently in growth
rates estimated from cross-sectional data. We suggest that differential maternal expenditure does not occur in Antarctic fur
seals because male pups probably do not gain greater benefit from additional maternal expenditure than female pups. After
weaning, males experience a period of rapid juvenile growth over 3–4 years during which time body mass nearly trebles. This
growth will almost certainly be dependent upon available food resources then rather than on any maternal expenditure received
over the first 4 months of life and, thus, the assumptions of the Trivers and Willard hypothesis are probably invalid for
Antarctic fur seals.
Received: 10 July 1996 / Accepted after revision: 3 March 1997 相似文献