bluuebunny/crossref_metadata_2025_split huggingface dataset:
The ecology of the climbing fern Dicranopteris linearis on windward Mauna Loa, Hawaii
Authors: Russell Ann E. , Raich James W. , Vitousek Peter M. 
Published: May 2003

Summary

Dicranopteris linearis (Gleicheniaceae), a native fern common throughout the Old World tropics and Polynesia, forms dense thickets > 3m deep over large areas of open‐canopy, oligotrophic, wet Hawaiian rainforests. Our objectives were to identify leaf‐ and whole plant‐level traits that are key to its success and to determine its community‐and ecosystem‐level consequences in primary successional sites.
Along an elevational gradient from 90 to 1660m, mean maximum net assimilation rates of Dicranopteris ranged from 2.9 to 5.0 μmol m−2 s−1, compared with 3.6–9.5 μmol m−1 s−1 in the codominant tree Metrosideros polymorpha. Gas‐exchange characteristics did not explain Dicranopteris' success, nor its trends in production.
However, indeterminate, clonal growth form, shallow rhizomes, marcescent leaves with low decomposability, and a mat‐forming capacity enabled Dicranopteris to colonize sites and to maintain dominance via high effective leaf area, despte its low biomass. Phosphorus use efficiency, which reached 24 kg g−1, was exceptionally high, allowing colonization of phosphorus‐poor sites.
Dicranopteris contributed up to 74% of above‐ground net primary productivity in a site where it contained only 14% of live biomass. It accounted for up to 57% and 47% of total nitrogen and phosphorus uptake by plants, respectively, where it contained only 24% and 30% of plant nitrogen and phosphorus. Dicranopteris leaves are short‐lived and slow to decompose; thus, fixed carbon is transferred quickly to soil detrital pools where it contributes to aggrading soil organic matter pools and may exacerbate oligotrophic conditions, thereby strongly influencing soil genesis and ecosystem development.
The fern therefore influences forest‐floor light regimes and directs later community development. An exclusion experiment demonstrated that Dicranopteris competed with Metrosideros, but lack of revegetation in 40% of the exclusion area after 39 months showed that Dicranopteris also colonized microenvironments unavailable to its endemic codominants. Dicranopteris may play an important role in resisting invasions of exotic species into Hawaiian rainforests.
Colonization by annual plants of an experimentally altered desert landscape: source—sink relationships
Authors: Boeken Bertrand , Shachak Moshe 
Published: May 2003

Summary

We studied how annual plant species colonize a set of patches (natural and humanmade) in a shrubland landscape in the Negev desert. We asked what patch properties and species' attributes affect colonization during 4 years after experimental formation of eight sets of pits and mounds.
The ‘sink function’ of patches was measured as the numbers of colonizing species, the proportion of patches colonized during each year, and the abundance of the colonizers. The effects of species' dispersal mode and propagule size were examined.
In the first growing season, pits and mounds were colonized by large numbers of species. The total number of colonizing species was similar for the two patch types, but incidence was higher in pits than in mounds.
The early colonizers were mainly wind‐dispersed and showed both high abundance and incidence. Dispersal mode did not affect colonization in the second year and later, nor did propagule size througout the experiment.
Most early colonizers became resident in the patches, but pits and mounds showed some further colonization during the second year. In the third and fourth year both the numbers of colonizing species and their incidence decreased.
Pits were mainly colonized from outside the experimental units to which they belonged, whereas mounds received species mostly from the adjacent pits within the same units.
From the second year on, patches of undisturbed crusted soil were also colonized, mainly from the adjacent pits and mounds. The number of colonizing species in undisturbed patches increased during the last, high‐rainfall, year both per patch and for the whole set of patches.
We conclude that the sink function of patches for colonization increases with removal of vegetation, soil crust and seed bank, with patch capacity to capture resource and plant propagules, and with amount of rainfall. Sink function decreased with time due to decreasing availability of new species, but increased with the presence of stronger sink patches in the vicinity.
We suggest that the concept of sink function, in terms of the numbers, incidence and abundance of species of colonizing sets of patches, can be a powerful tool for linking community and landscape processes.
Phenotypic selection and population differentiation in relation to habitat heterogeneity in Arrhenatherum elatius (Poaceae)
Authors: Petit Christophe , Thompson John D. 
Published: May 2003

Summary

Population differentiation in variable environments is often related to the different local selection pressures that plants may experience. We examine the relation between reproductive success and morphological and phenological traits in woodland and open habitat populations of the tetraploid grass Arrhenatherum elatius.
The reproductive correlates of morphological and phenological variation were estimated in woodland and open habitats, and on plants from each of three populations from woodland and three from open habitats grown in a garden environment at two light intensity levels. Genetic variation in these populations was estimated in uniform conditions.
Temporal and spatial differences in phenotypic selection on morphology and phenology were observed within and between the two sites. Plants from the two sites showed significant phenotypic and genetic differences, and there is a dramatic reduction in reproductive success in the woodland habitat and in plants from this habitat grown in the two garden environments.
In controlled conditions, selection patterns were similar to those observed in natural habitats, suggesting that light availability may be an important ecological factor involved in population differentiation in A. elatius. The presence of significant genetic variability for the studied traits indicates the presence of a genetic potential to respond to the detected selection pressures.
We argue that a clear understanding of patterns of local adaptation and phenotypic selection in this species requires that they are examined in the light of regional processes related to seed dispersal and relative abundance in open and woodland habitats.
Selection of micro‐organisms in a spatially explicit environment and implications for plant access to nitrogen
Authors: Kinzig Ann P. , Harte John 
Published: May 2003

Summary

Evolution of a microbial nitrogen‐uptake strategy that removes nitrogen at less than the maximum potential rate creates soil environments favourable for increased plant access to nitrogen. Plant productivity is thus increased, and achievement of maximum microbial biomass is facilitated through increased microbial access to plant‐derived carbon.
Simulations show that micro‐organisms exhibiting such a ‘strategic’ nitrogen uptake will be competitively excluded by more voracious micro‐organisms in a homogeneous system, but can persist in a spatially explicit system. This persistence of less voracious micro‐organisms contrasts with the frequently held view that micro‐organisms in soil systems take up nitrogen at the maximum possible rate.
The selection of strategic or voracious microbial types in a spatially explicit environment is sensitive to the frequency of plant and microbial disturbance, and to the rate of diffusion of inorganic nitrogen in the soil system. In particular, the strategic (less voracious) microbial types are favoured under conditions of low plant disturbance, low to moderate diffusion of inorganic nitrogen, and moderate microbial disturbance.
When selection favours strategic microbial types, plant access to nitrogen is increased. Plants may also evolve strategies in a spatially explicit environment that will increase population densities of favourable, strategic microbial types.
Shrikes, lizards and Lycium intricatum (Solanaceae) fruits: a case of indirect seed dispersal on an oceanic island (Alegranza, Canary Islands)
Authors: Nogales M. , Delgado J. D. , Medina F. M. 
Published: May 2003

Summary

Indirect seed dispersal in the system Lycium intricatum (Solanaceae)–lizards (Gallotia atlantica)–shrikes (Lanius excubitor) was studied in Alegranza, a xerophytic small island of the Canarian archipelago.
A total of 835 seeds (224 obtained from lizard droppings and 611 from shrike pellets) was found by analysing 123 droppings and 146 pellets. Lycium fruit remains (including seeds) were observed in 31.7% of the lizard droppings and 50% of the shrike pellets.
As would be expected for legitimate seed dispersers, external seed damage produced by each species was negligible. Lycium seeds were significantly matched with the presence of lizard remains in shrike pellets. Seeds in shrike pellets have come from fruit consumed by lizards that have been predated by the shrikes, and not directly from bird frugivory.
Seeds from shrike pellets showed significantly higher germination rates than those from uneaten fruits and lizard droppings.
It seems probable that different treatments in the guts of each species and retention time are two main factors influencing the germination process. While gut pass time in G. atlantica has been estimated to be 2.42 days on average, the retention time of a seed inside a shrike gizzard is much shorter (45–55 min).
This is a new case of the scarcely known phenomenon of indirect seed dispersal, which seems to acquire a relatively important role in small islands where the animal–plant interaction is very intense and all the elements of the system are native.
Evaluation of an intervention system for parents of children with intellectual disability and challenging behaviour
Authors: Hudson A. M. , Matthews J. M. , Gavidia‐Payne S. T. , Cameron C. A. , Mildon R. L. , Radler G. A. , Nankervis K. L. 
Published: May 2003

AbstractBackground  Signposts is a flexible intervention system for families of children who have intellectual disability and challenging behaviour. The Signposts materials include eight information booklets, a workbook and videotape for parents, and a series of instructional manuals for therapists. The system was designed so that it can be delivered in several different ways, i.e. group support, telephone support and self‐directed modes.Methods  The present study was an evaluation of these three modes of delivery and involved 115 families.Results  Following the use of the Signposts materials in parent training programmes, the subjects reported that they were less stressed, felt more efficacious about managing their children's behaviour, were less hassled about meeting their own needs and that their children's behaviour had improved. Additionally, families generally reported high levels of satisfaction with the content and delivery of the materials.Conclusions  Finally, there were minimal differences among the three modes of delivery on the measures used, although families who used the self‐directed mode were less likely to complete the materials. Implications of these results for service delivery are discussed.
Explaining the parental stress of fathers and mothers caring for a child with intellectual disability: a Double ABCX Model
Authors: Saloviita T. , Itälinna M. , Leinonen E. 
Published: May 2003

AbstractBackground  Twenty variables based on the Double ABCX Model of adaptation and selected on the basis of previous research were chosen to explain the parental stress of the mothers (n = 116) and fathers (n = 120) of children with an intellectual disability (age range = 1– 10 years).Methods  Principal component analysis, rotated into varimax‐criterion, was done separately for mothers and fathers. The solution containing eight factors was considered best for both groups. They accounted for more than 70% of the total variance of the original variables. These eight orthogonal components were then entered into a stepwise regression analysis that was done separately for mothers and fathers.Results  The multiple regression equations obtained explained 72% of the variance in maternal stress and 78% of the variance in paternal stress. The equations for mothers and fathers contained six and seven components, respectively.Conclusions  The variables used in the present study were highly successful in accounting for parental stress. The results confirm the importance of intervening factors in explaining the stress. The single most important predictor of parental stress was the negative definition of the situation. In mothers, the negative definition was associated with the behavioural problems of the child while, in fathers it was connected with the experienced social acceptance of the child.
Influence of macrostructure of society on the life situation of families with a child with intellectual disability: Sweden as an example
Authors: Olsson M. B. , Hwang P. C. 
Published: May 2003

AbstractBackground Most studies on families with children with intellectual disability (ID) have been carried out in the UK or the USA, and are influenced by the societal organization, and political and economic climate of those countries. In the USA and the UK, the care and well‐being of children, with or without ID, are seen almost exclusively as the individual family's responsibility. In Sweden, the care and well‐being of children are seen more as a joint responsibility. Swedish society has developed many privileges for all parents in order to help them care for their children, and the support for parents of children with disabilities is provided exclusively by the Government and the community. The overall question explored in this descriptive, quantitative and qualitative study was: Are families in Sweden experiencing the stressors and life situations described in the studies of parents in more individualistic societies?Methods Two hundred and twenty‐six families with children with ID and 234 control families with children ranging from 0 to 16 years of age answered mail surveys.Results Taken together, parents in Sweden describe most of the stressors proposed in the international literature with the exception of financial strain. Restricted social life and time restrictions seem to be the two most evident and bothersome stressors for Swedish families with children who have ID.Conclusions As in previous research, the parents of children with ID and autism experienced more stressors and restrictions in their lives than the parents of children with DS and control families.
Management of respite and personal assistance services in a consumer‐directed family support programme
Authors: Caldwell J. , Heller T. 
Published: May 2003

AbstractBackground  The present study explores the management of respite and personal assistance services by families with relatives with developmental disability (DD). It focuses on the control of families over recruiting, hiring, training, scheduling, directing and negotiating wages of the staff they hire to provide services.Methods  Surveys from 97 families using paid respite or personal assistance services were used to test associations between: 1) level of control of services and outcome variables; 2) hiring relatives to provide services and outcome variables.Results  More control by families in the management of their respite/personal assistance services was associated with increased service satisfaction, increased community involvement of individuals with DD and increased employment of mothers. Families tended to hire friends, neighbours, and to a great extent, other family members. Hiring of other relatives to provide services was associated with the increased community involvement of individuals with DD.Conclusions  The present study supports the idea that there are benefits for both caregivers and individuals with DD with increased control of respite and personal assistance services. The study also supports benefits associated with hiring relatives and recommends additional research in this area to guide policies.
Are the native giant tortoises from the Seychelles really extinct? A genetic perspective based on mtDNA and microsatellite data
Authors: Palkovacs Eric P. , Marschner Monique , Ciofi Claudio , Gerlach Justin , Caccone Adalgisa 
Published: May 2003

AbstractThe extinction of the giant tortoises of the Seychelles Archipelago has long been suspected but is not beyond doubt. A recent morphological study of the giant tortoises of the western Indian Ocean concluded that specimens of two native Seychelles species survive in captivity today alongside giant tortoises of Aldabra, which are numerous in zoos as well as in the wild. This claim has been controversial because some of the morphological characters used to identify these species, several measures of carapace morphology, are reputed to be quite sensitive to captive conditions. Nonetheless, the potential survival of giant tortoise species previously thought extinct presents an exciting scenario for conservation. We used mitochondrial DNA sequences and nuclear microsatellites to examine the validity of the rediscovered species of Seychelles giant tortoises. Our results indicate that the morphotypes suspected to represent Seychelles species do not show levels of variation and genetic structuring consistent with long periods of reproductive isolation. We found no variation in the mitochondrial control region among 55 individuals examined and no genetic structuring in eight microsatellite loci, pointing to the survival of just a single lineage of Indian Ocean tortoises.
The novel protein phosphatase PphA fromSynechocystisPCC 6803 controls dephosphorylation of the signalling protein PII
Authors: Ruppert Ulrike , Irmler Angelika , Kloft Nicole , Forchhammer Karl 
Published: May 2003

SummaryThe family of PIIsignal transduction proteins consists of one of the most highly conserved signalling proteins in nature. The cyanobacterial PIIhomologue transmits signals on the nitrogen and carbon status of the cells through phosphorylation of a seryl residue. Recently, we identified a protein phospha‐tase 2C (PP2C) homologue from the cyanobacteriumSynechocystisPCC 6803, termed PphA, to be the cellular phospho‐PII(PII‐P) phosphatase. In this investigation, we characterized the enzymatic properties of PphA and investigated the regulation of its catalytic activity towards PII‐P. PphA dephosphorylates phosphocasein and PII‐P with similar efficiency in a strictly Mg2+‐ or Mn2+‐dependent reaction. Low‐molecular‐weight phosphorylated molecules are poor substrates for PphA. Its reactivity towards PII‐P, but not towards phosphocasein, is inhibited by various nucleotides, suggesting that this effect is based on specific properties of the PIIprotein. The inhibitory effect of ATP can be strongly enhanced by the addition of 2‐oxoglutarate or oxaloacetate. At low concentrations of 2‐oxoglutarate, changes in the ATP levels within the physiological range affect the degree of PII‐Pase inhibition, whereas at 2‐oxoglutarate levels beyond 0.1 mM, inhibition is almost complete at very low ATP levels. This suggests that PIIdephosphorylation is not only sensitive to 2‐oxoglutarate and oxaloacetate levels, it also integrates signals from the energy charge of the cells under specific cellular conditions.
Sperm cells of Zea mays have a complex complement of mRNAs
Authors: Engel Michele L. , Chaboud Annie , Dumas Christian , McCormick Sheila 
Published: May 2003

SummaryAlthough double fertilization in angiosperm was discovered in 1898, we still know nothing about the proteins that mediate gamete recognition and fusion in plants. Because sperm are small and embedded within the large vegetative cell of the pollen grain, mRNAs from sperm are poorly represented in EST databases. We optimized fluorescence‐activated cell sorting (FACS) in order to isolate Zea mays sperm free of contaminating vegetative cell cytoplasm, and constructed a cDNA library. Sequencing of over 1100 cDNAs from the unamplified library revealed that sperm have a diverse complement of mRNAs. Most transcripts were singletons; the most abundant was sequenced only 17 times. About 8% of the sequences are predicted to encode secreted or plasma membrane‐localized proteins and are therefore candidates that might mediate gamete interactions. About 8% of the sequences correspond to retroposons. Plant sperm have condensed chromatin and are thought to be transcriptionally inactive. We used RT‐PCR and in situ hybridization to determine when selected sperm mRNAs were transcribed. Sperm transcripts encoding proteins involved in general cell functions were present throughout pollen development and were more abundant in tricellular pollen than in sperm cells, suggesting that these transcripts were also present in the larger vegetative cell. However, several transcripts, which encode proteins that are most similar to hypothetical Arabidopsis proteins, appeared to be present exclusively in the sperm cells inside mature pollen, but were already present in unicellular microspores. This suggests that certain transcripts might be transcribed early during pollen development and later partitioned into the sperm cells.
Remuneration for blood donation and attitudes towards blood donation and receipt in Leeds
Authors: Jones R. P. O. , Prasad V. , Kuruvatti J. , Tahir N. , Whitaker P. , Dawson A. S. J. , Williams R. 
Published: May 2003

Summary. In a survey of attitudes towards remuneration for blood donation in Leeds, the following questions were completed by 489 adults (N), of whom 89 were regular donors, 105 were lapsed donors and 295 had never donated:‘If you needed blood, would you be content if the donor had been paid: yes/no’.‘If I were paid enough I would be less/equally/more likely to donate blood ’.The majority (67·7%) of potential recipients would be content if the donor had been paid. The prospect of remuneration made 16·4% of respondents more likely and 14·5% less likely to donate. As the difference is less than 2% of N, offering remuneration may not lead to a significant increase in the number of donations. A statistical comparison (χ2 = 45, d.f. = 2, P << 0·001) showed associations between the responses ‘more likely to donate if paid’ and ‘content to receive blood from a paid donor’, and between the responses ‘less likely to donate if paid’ and ‘not content to receive blood from a paid donor’. Age distributions are presented for the donor status categories and the responses to the main questions. Of 129 people who stated a minimum, nonzero payment that would persuade them to donate, 103 (80%) suggested £10 or less.