bluuebunny/crossref_metadata_2025_split huggingface dataset:
Comparing biological productivity in cropping systems: a competition approach
Authors: Park Sarah E. , Benjamin Laurence R. , Watkinson Andrew R. 
Published: March 2003

Summary

Intercropping, the practice of growing two or more crops in close association, is attracting increasing interest in developed countries, primarily due to claims that it can provide increased yields in an environmentally sustainable manner.
The land equivalent ratio (LER) is frequently used to attest the claim that intercropping produces a greater total biological productivity per unit area of land than monocropping. However, similar to other indices, the value of the LER is dependent on the relative densities of the two crops and fails to provide an indication of the optimal crop density combination required to produce maximum biological productivity. We used an alternative methodology to predict the optimum density for planting two crops in a mixed stand.
Maize and beans were grown both in monoculture and in intercropped stands at a range of densities. Monocrop stands of both maize and bean displayed an asymptotic yield–density relationship. When a second crop was introduced into the stand there was no effect on the yield of maize, but there was a large reduction in the yield of bean.
The LER did not demonstrate an unequivocal advantage to intercropping. Less than a third of the LER values, over the range of densities considered, were greater than one, although none was significantly different to unity. The highest values were obtained from those plots sown with a high density of maize.
An alternative method of analysing the biological productivity of an intercrop system is proposed. This approach requires a combination of (i) an additive experimental design, (ii) the use of a regression model to measure the competitive effect of two species, and (iii) the presentation of the net competitive effect on individual and total yields using a response surface. The reciprocal model was used to dissociate and quantify intra‐ and interspecific competition, estimate a competitive equivalence coefficient and predict the individual yields of the full complement of density combinations included in the maize and bean experiment.
The model explained up to 90% of the variation in the observed yields of maize and bean in an intercrop. An inspection of the response surface for the LER indicated that the minimum density combination required to produce the maximum yield advantage within the density range considered comprised maize being planted at a density of 11 plants m−2 and bean being planted at a density of 39 plants m−2. Although this combination would provide the maximum biological productivity, it is considered unlikely to provide the maximum gross economic margin.
The above methodology may provide a useful tool for managing competition, either between two or more crops in an intercrop, or within a crop–weed interaction.
Red deer management and vegetation on the Isle of Rum
Authors: Virtanen R. , Edwards G. R. , Crawley M. J. 
Published: March 2003

Summary

Understanding the effects of red deer Cervus elaphus grazing on a range of plant communities is important for formulating guidelines for the management of forestry plantations, nature reserves and deer hunting enterprises.
The effects of red deer on the species composition of plant communities varying in productivity were examined on the Isle of Rum, Inner Hebrides, north‐west Scotland.
The study compared vegetation inside and outside fences erected to exclude deer for more than 20 years, and between areas of the island where different deer culling policies were instigated in 1991.
The effect of the exclusion of deer was directly proportional to vegetation type. Long‐term deer exclusion (20–40 years) had negligible effects on the species composition of the most unproductive plant communities, but caused a marked decline in the species richness of productive grassland. The decline was due to the loss of prostrate herb species inside exclosures where Festuca rubra had assumed a high dominance.
Changes in the size and sex ratio of the deer populations were not associated with major changes in plant species richness or relative abundance. The most notable change occurred in productive grassland. Here, Festuca rubra had greater cover and several low‐growing herbs such as Polygala serpyllifolia and Thymus polytrichus had lower cover in areas where hind numbers had been reduced than in areas where there was no culling.
High deer densities within an unculled food‐limited population were associated with negligible effects on plants in Molinia caerulea flush and Calluna–Molinia wet heath vegetation.
Tree regeneration inside the exclosures or in areas where deer were culled was minor; only two solitary rowan Sorbus aucuparia saplings were found.
Flowerhead densities of herbaceous plant species and grasses showed trends that could be associated with cattle grazing. It is suggested that this may lead to changed recruitment, although seed sowing experiments are required to test this.
The results suggest that red deer grazing sustains the plant species diversity of productive grasslands, with reduced deer grazing leading to the loss of plant species in these communities. In contrast, the effects of reduced deer densities and altered culling policies on unproductive vegetation types are negligible.
Effects of nutrient addition and acidification on plant species diversity and seed germination in heathland
Authors: Roem W. J. , Klees H. , Berendse F. 
Published: March 2003

Summary

The atmospheric deposition of sulphur and nitrogen compounds in the Netherlands has been responsible for decreasing plant species diversity in heathland. To unravel the relative importance of nitrogen compounds on soil acidification and eutrophication, and hence on the vegetation, we carried out a factorial addition experiment and a germination experiment in heathland on nutrient‐poor sandy soil.
We changed nutrient availability and acidity independently in eight different treatments that, respectively, added nutrients or carbon in various combinations (N, P, glucose) or added acidifying or neutralizing compounds. One treatment also involved adding Al. Additions occurred five times per year during 5 years, in an area from which sods had been removed before the experiment began. The same design was used for the germination experiment, but the treatments were applied for 2 years.
Our results showed that acidification was the most important factor in reducing species diversity. In addition, the germination of several heathland species was significantly reduced in plots with a pH below 5, and germination was very poor in plots where Al had been added.
The number of plant species declined particularly with increasing Al in the upper soil horizons. We conclude that this relationship is responsible for the influence of acidification on plant species richness in heathland.
The influence of nutrient availability on species composition in heathland was subsidiary to acidity, but nutrient availability influenced species composition in an independent way. The growth of the three dominant species (Molinia caerulea, Calluna vulgaris and Erica tetralix) was limited by different nutrients. Erica tetralix was limited by N, Calluna vulgaris by P and Molinia caerulea by both N and P. We argue that increased N availability will change the relative availability of N and P, which can decrease species diversity.
Together these results show how factorial experiments can elucidate the complex ecological effects arising from sulphur and nitrogen deposition, revealing different mechanisms that change species richness and community composition.
Role of peptidase and cyclooxygenase inhibitors in the guinea‐pig bronchial response to the synthetic endothelin ETB agonist IRL 1620 and antagonist BQ‐788
Authors: Lazzeri N. , Nieri P. , Lenzi P. , Ratti C. , Breschi M. C. 
Published: March 2003

1ŸIn isolated guinea‐pig bronchial preparations the selective endothelin ETB agonist, IRL 1620 caused a concentration‐dependent contraction. The pD2 value (7.16_±0.09, n_=6) was significantly increased in the presence of peptidase inhibitors (thiorfan 1_μm, captopril 1_μm, bestatin 1_μm) (pD2_=7.75_±0.09, n_=6). Indomethacin (5_μm) did not appear to influence the ETB‐agonist pD2 value (6.92_+0.11, n_=6) but potentiated its maximal response significantly (67.23_±4.81% vs. 53.37_±4.80%). 2ŸThe concentration‐response curve for the contractile response to IRL 1620 (pD2=7.83__0.01, n=16); was reproducible, although not completely, since the second curve to this selective ETB agonist was shifted significantly to the right (pD2_=7.34_±0.09, n_=_16) and a decrease in the maximal response was observed (20.0_±2.0%). 3ŸBQ 788, a selective antagonist for ETB receptors, employed in concentrations ranging from 1.5 to 150_n
m, caused a dose‐dependent shift to the right of the concentration‐response curve to IRL 1620, with a pIC50 value of 8.11_±0.03; this action was not influenced by adding enzyme inhibitors (pIC50_=8.17_±0.29). 4ŸOur data show that IRL 1620 undergoes a hydrolytic metabolism in guinea‐pig bronchial preparations, which could influence the calculation of the pD2. Pretreatment of the tissue with peptidase inhibitors and indomethacin is consequently significant in the evaluation of IRL 1620 activity, while it does not influence the action of the antagonist, BQ 788.
The comparison of vitamin C and vitamin E on the protein oxidation of diabetic rats
Authors: Je H. D. , Shin C. Y. , Park H. S. , Huh I. H. , Sohn U. D. 
Published: March 2003

Summary 1 We measured the plasma glucose and the glycosylated haemoglobin at the time of sacrifice in streptozotocin‐induced diabetic mellitus (DM) rats. 2 In diabetic rats, plasma glucose and glycosylated haemoglobin was increased as compared with normal rats, and vitamin E inhibited the increase of glycosylated haemoglobin level but vitamin C had no effect. 3 The peroxidized proteins and lipids from the diabetic organs such as liver or kidney were measured to assess the oxidative damage. The 2,4‐dinitrophenyl‐hydrazine (DNPH) incorporation method was used to measure the peroxidized protein. In diabetic rats, DNPH incorporation was increased as compared with normal rats and vitamin E also inhibited the increase of DNPH incorporation but vitamin C had no effect. It suggests that the protein oxidation occurred on the liver in diabetic rats and the oxidative stress is general in the diabetic condition. 4 We measured the systolic arterial pressure and mean arterial pressure in normal rats, nephrectomy (NEPH)‐rats, diabetic rats (DM), and NEPH‐diabetic rats (NEPH‐DM). Blood pressure was significantly increased in DM and NEPH‐DM as compared with normal rats. 5 In conclusion, plasma glucose, glycosylated haemoglobin, and the oxidation of proteins or lipid were increased in diabetic rats. Vitamin E decreased the plasma glucose, glycosylated haemoglobin and the oxidation of proteins and lipid, but vitamin C had no effects.
Evidence for the recent dispersal of Sophora (Leguminosae) around the Southern Oceans: molecular data
Authors: Hurr Kathryn A , Lockhart Peter J , Heenan Peter B , Penny David 
Published: March 2003

Summary Aim The aim is to use DNA sequence data to test between vicariance and long range dispersal (by floating seed‐pods) explanations for the origin and range of the Edwardsia species of Sophora (Sophoreae: Papilionoideae: Leguminosae). Location This group is widely distributed around the South Pacific and into the South Atlantic on both continental fragments and oceanic islands. Methods DNA sequences from an intergene region (atpB‐rbcL) of the chloroplast were determined for twelve taxa (including outgroups) and used to test these hypotheses. Sophora fossils were used to calibrate the evolutionary tree. Results The Edwardsia group of Sophora appears monophyletic and is well differentiated from other Sophora. However, the genetic difference between species within the South Pacific and to the South Atlantic is very low. Main conclusionsThe results eliminate vicariance explanations for this section of Sophora and strongly support an origin from other (non‐Edwardsia) Sophora in the north‐west Pacific. Dispersal appears initially to be to Tuvalu, Lord Howe Island, New Zealand, and subsequently across the South Pacific, probably within the last 2–5 million years. Dispersal of buoyant Sophora seeds to oceanic islands is the most likely explanation of its distributions. Fossil pollen dates in New Zealand are consistent with the conclusion.
Regional tectonics, disturbance, and population size of isolated stands of Nothofagus fusca (Nothofagaceae) in a forest ecotone in south‐western New Zealand
Authors: Haase P. 
Published: March 2003

Summary AimNew Zealand's cool temperate forests are usually dominated by one or more of the five native taxa of Nothofagus (Nothofagaceae; southern beech), but in certain regions there are sharp boundaries against podocarp–broadleaved forest where Nothofagus is rare or completely absent, either for historical (Pleistocene Glaciation) or climatic/biological (mild superhumid climate and competition) reasons. The dynamics of a Nothofagus boundary was investigated by monitoring disturbance‐initiated establishment of isolated stands of N. fusca at the extreme limits of its regional distribution. LocationThe research was carried out in a regional forest ecotone between Nothofagus forest and podocarp–broadleaved forest in the upper Taramakau Valley, South Island, New Zealand. The survey region straddles a major, active fault system and associated tectonic movements and earthquakes with more distant epicentres have contributed to intermittent canopy disturbance of the local forests. MethodsIsolated stands of Nothofagus fusca beyond the limits of continuous Nothofagus forest were investigated during two field surveys, separated by 7–10 years. Changes in population size, stem diameter of individual trees, stand basal area and mean annual diameter increment were calculated for each of fifty‐four isolated stands. Types of past and recent disturbance and the probable cause of mortality of trees were noted. ResultsThe total population of fifty‐four sample stands, ranging in size from one to > 400 stems, increased by 37.4%, and compound basal area increased by 4.7% between the two surveys. Mean stem diameter growth of isolated stands was lower than expected by empirical data for N. fusca, suggesting reduced wood increment at the limits of its distribution. Tree mortality was 0.8% per year. Fifty‐one per cent of the dead stems had died as a consequence of various types of natural disturbance, uproots being more common than snaps and crown breakage. Main conclusionsThe isolated N. fusca stands preferentially occupy sites likely to experience intermittent disturbance, mostly including disturbance of the soil cover, which facilitates their initial establishment and persistence. Because of causal relationships between mass movement on steep slopes and erosion/deposition of talus fans and river terraces, disturbance‐initiated changes in forest composition are observed across a range of different landforms.
Abundance distribution, morphological variation and juvenile condition of robins, Erithacus rubecula (L.), in their Mediterranean range boundary
Authors: Pérez‐Tris Javier , Carbonell Roberto , Tellería José Luis 
Published: March 2003

AbstractAimIt has been suggested that populations nearing the border of a species’ range should be maladapted because they occupy progressively less suitable environments. In some instances, however, peripheral populations might acclimate or even be adapted to local conditions. We studied Iberian robins to evaluate whether southern, peripheral populations become more restrictive in selecting their habitats, are locally differentiated or show evidence of maladaptation.LocationWe divided the Iberian Peninsula into three regions (the Eurosiberian and Supra‐Mediterranean regions in northern Iberia, and the Mediterranean Lowlands in southern Iberia), which define a gradient of increasing dryness southwards. In each region, we selected one representative locality, where we captured individuals during three study years.MethodsWe reviewed 72 community studies to test whether Iberian robins occupy fewer forests and decrease in abundance southwards. Because robins are sedentary in the southernmost region, but largely abandon both northern areas in winter, we analysed the variation in migration‐related morphology to test for population differentiation in the range boundary. To examine how populations cope with environmental variation, we studied four indices of juvenile condition (fluctuating asymmetry, fledgling size, ptilochronology and size‐corrected body mass), each related to nutritional conditions in a particular stage of growth, from early development to independence.ResultsAlthough robins restricted their range southwards, there was no change in local abundance between regions. Southernmost robins, consistent with their sedentary behaviour, had shorter and more rounded wings than northern robins, although the populations did not differ in terms of body size. Fluctuating asymmetry and fledgling size did not evidence a higher developmental stress in peripheral populations, although southernmost robins had a lower juvenile condition during their independence (as shown by ptilochronology and residual body mass).Main conclusionsThe distribution of abundance found in this study supports the idea that Iberian robins could select habitats above a somehow restrictive threshold of quality. In addition, morphological correlates of migratory behaviour provided evidence of population differentiation at the range edge. This introduces the possibility that among‐region variations in juvenile condition actually reflect reproductive benefits for migrants, related to the occupation of seasonally productive habitats, rather than the maladaptation of sedentary, peripheral populations. From this perspective, and in view of the patterns of distribution and morphology that we found, southern Iberian robins might be independent populations locally adapted in the range boundary.
Shiitake mushrooms and molecular clocks: historical biogeography of Lentinula
Authors: Hibbett David S. 
Published: March 2003

AimFungi make up a large, ecologically important group of eukaryotes that has been neglected in historical biogeography. In this study, molecular phylogenies and molecular clock dating were used to infer historical biogeography of the shiitake genus, Lentinula Earle, which occurs in both the Old World and New World. The major goals of this study were to determine if the Old World and New World groups are monophyletic, and whether the Old World/New World disjunction is the result of vicariance or long distance dispersal.LocationCollections studied are from Asia, Australasia, the Gulf Coast region of North America, the Caribbean, Central America, and northern South America.MethodsPhylogenetic trees were inferred with nuclear large subunit (nuc‐Isu) ribosomal DNA (rDNA) and internal transcribed spacer (ITS) sequences. Molecular clock dating was performed using trees derived from nuc‐Isu rDNA and mitochondrial small‐subunit (mt‐ssu) rDNA sequences. Rate constancy was tested with maximum likelihood, and clocks were calibrated using evidence from fossils or other molecular clock studies, or according to expected ages under different historical biogeographic scenarios.ResultsAnalyses of ITS and nuc‐Isu rDNA sequences suggest that there are seven species of Lentinula worldwide, which occur in two main clades, one in the New World the other in the Old World. Rate constancy cannot be rejected in nuc‐Isu rDNA, but can be rejected in mt‐ssu rDNA. Both genes suggest that the Old World/New World disjunction could be due to fragmentation of an ancient Laurasian range. An alternative Gondwanan hypothesis is not supported by the molecular clock age estimates.Main conclusionsOnly one long distance dispersal event must be invoked in Lentinula, that being between Australia and New Zealand. Despite having airborne spores, it appears that long distance dispersal is rare in Lentinula. This may also be true in other fungi, which are therefore excellent candidates for historical biogeographic studies using molecular characters.
Vicariance or dispersal: the use of natural historical data to test competing hypotheses of disjunction on the Tyrrhenian coast
Authors: Estabrook George F. 
Published: March 2003

AimTo illustrate the use of natural historical data to evaluate vicariance and dispersal as hypotheses competing to explain disjunct populations.LocationNine disjunct areas on the margin of the Tyrrhenian basin of the Mediterranean Sea.MethodsFirst describe how each hypothesized mechanism might explain the observed morphological variation in the model species complex, Genista ephedroides (Fabaceae); then confront the hypotheses with natural historical data including geology, oxygen isotopes, palynology, macro‐, micro‐ and nano‐fossils, and sea level changes, and with the ecological tolerances of the model species complex.ResultsDispersal seems the more credible explanation.Main conclusionPatterns of morphological (or other) variation among related disjunct taxa can fit both vicariance and dispersal hypotheses. However they can possibly be distinguished by considering natural historical data.
Distribution of forest birds in the Andaman islands: importance of key habitats
Authors: Davidar Priya , Yoganand K. , Ganesh T. 
Published: March 2003

AimThe aim of this study was to assess the influence of island area, distance to source pool, latitude, habitat diversity and habitat type on species richness of forest birds in the Andaman islands.LocationThe Andaman islands (India) in the Bay of Bengal.MethodsThe distributions of 47 species of forest birds were surveyed on 45 islands in the Andaman islands across a latitudinal gradient. The size of the island and distance to the nearest large island were assessed on a satellite image of 1 : 250,000 scale. The number and types of habitats and the species richness of birds on each island were recorded during a field survey. The effects of the variables measured on the species richness of forest birds were assessed using regression analyses. The best fit models were selected for interpretation of the results. Separate analyses were conducted with selected islands to eliminate the effects of latitude and to control the effects of area and habitat diversity.ResultsThe number of species of forest birds was strongly influenced by island area and habitat diversity. However the key determinant of species richness was habitat type, particularly the presence of wet forests. Wet forests, either semi‐evergreen or evergreen tropical forests are more common towards the southern islands and are usually restricted to larger islands.Main conclusionsArea, habitat diversity and the presence of wet forests on islands significantly influenced species richness of forest birds. The wet forests maintain the biodiversity of the Andamans and should be regarded as a ‘keystone habitat’. This is probably because wet forests are species rich and also because the Andaman biota has affinities with that of the Malay peninsula where wet forests predominate. Therefore biogeographical history probably plays an important role in influencing biodiversity at a regional scale.