bluuebunny/crossref_metadata_2025_split huggingface dataset:
Pollination of Coffea canephora in relation to local and regional agroforestry management
Authors: Klein A.‐M. , Steffan‐Dewenter I. , Tscharntke T. 
Published: September 2003

Summary

Pollination of crops depends on local agricultural management and the quality of adjacent habitats. Lowland coffee Coffea canephora, is an important tropical cash crop. Fruit set depends on cross‐pollination by bees, so inadequate pollination leads to reduced yield. In this study we analyse the relationship between bee pollinators, fruit set in coffee, and the local and regional agroforestry systems to identify the optimal conditions for pollinators.
We analysed the abundance and species composition of coffee flower‐visiting bees in 15 agroforestry systems differing in distance to forest (important for wood‐nesting species), light intensity (important for ground‐nesting species), blossom cover of coffee and noncoffee‐flowering plants, and species richness of flowering plants (as pollen and nectar resources) in Central Sulawesi (Indonesia). We examined which factors were most important for optimal pollination success. We carried out bagged and open pollination experiments in each agroforestry system, to measure the pollination efficiency of 15 bee species.
The number of social bee species decreased with distance to forest, whereas the number of solitary bee species increased with light intensity (less shade) and greater quantities of blossoms.
Fruit set of open pollinated flowers (as opposed to manually cross‐pollinated flowers) increased with the diversity and abundance of flower‐visiting bees. In the agroforestry systems studied, a bee community of 20 species or more led to a higher fruit set (95%) than a species‐poor bee community of six species (70% fruit set).
Pollination activity by members of the species‐rich solitary bee assemblage led to higher levels of fruit set than that arising from pollination activity by members of the more abundant social bee assemblage.
Synthesis and applications. A species‐rich and abundant bee assemblage will facilitate high pollination success in lowland coffee. This will increase fruit set and coffee yield. Farmers can encourage different species of bees through simple management measures such as growing coffee in shade beneath a variety of trees; by pruning trees to increase levels of sunlight and numbers of flowering herbs; and by increasing the availability of nesting sites for solitary bees. Weed control and the use of herbicides should be kept to a minimum so that a diverse nectar and pollen resource is available to bees throughout the year. Natural forests and forest fragments should be preserved in the vicinity of coffee agroforestry systems (< 500 m) so that forest‐nesting social bees can travel easily to the coffee fields to pollinate the flowers.
Annual losses of weed seeds due to predation in organic cereal fields
Authors: Westerman P. R. , Wes J. S. , Kropff M. J. , Van Der Werf W. 
Published: September 2003

Summary

Post‐dispersal seed losses in annual arable weed species are poorly quantified, but may be of significance for natural population control, especially if they can be manipulated. We hypothesized that weed seed predation on the soil surface was significant, so we measured rates in the field to estimate annual seed losses due to predation.
Temporal patterns of weed seed losses due to predation (‘demand’) as well as weed seed production (‘supply’) were measured from May to June until harvest in August 1999 and 2000 during 2‐week exposure periods in four organic cereal fields in the Netherlands. The proportion of weed seeds lost to predators Mi (number of seeds consumed per number of seeds exposed per 14 days) was measured, using cards containing seeds of Stellaria media, Chenopodium album or Avena fatua. Seed production, Yi (number of seeds per m2 per 14 days), was measured in 2000, using seed traps.
Annual seed loss due to predation, &#x004d;̄ (number of seeds consumed per number of seeds produced per year), was calculated based on Mi and the exposure period of seeds to predators, starting with seed shed and ending with seed burial. The importance of the length of the exposure period on total seed loss was explored using a model.
The temporal trend in Mi was consistent among farms and years: high in June and early July, lower in the second half of July and negligible in August and after harvest. Total seed production varied considerably among fields, i.e. 800–16 000 seeds per m2 per year. The timing of peak seed production also varied substantially.
Calculated &#x004d;̄ ranged from 32% to 70%, when assuming continuous exposure of seeds to predators from seed shed till crop harvest. When exposure was limited to 2 or 4 weeks after seed shed, &#x004d;̄ decreased to 18–57% or 28–67%, respectively. Differences between fields and weed species were mainly due to differences in the timing of seed shed.
Synthesis and applications. Our results suggest that seed predation in organic cereal fields is an important factor shaping the population dynamics of arable weeds. A combination of environmental conditions (hot and dry weather) and agricultural practices (an early crop sowing) can advance weed phenology and postpone seed burial, resulting in higher proportions of weed seed loss to predation in cereals.
The marine survival and growth of wild and hatchery‐reared Atlantic salmon
Authors: Jonsson Nina , Jonsson Bror , Hansen Lars Petter 
Published: September 2003

Summary

Catches of Atlantic salmon Salmo salar L. decreased in the 1980s and 1990s over its entire area in the North Atlantic and smolts were often released for stock enhancement. However, there are questions about their survival and performance relative to fully wild fish. This paper reports on the survival and sea growth of River Imsa salmon released from 1981 to 1999 as 1‐ and 2‐year‐old hatchery and wild smolts.
Survival was significantly higher for wild than hatchery fish. Hatchery salmon released as 2‐year‐old smolts had lower survival, were captured more in coastal than freshwaters, grew more slowly and attained maturity younger than corresponding 1‐year‐old smolts.
The survival rate of hatchery fish released as 2‐year‐old smolts, but not 1‐year‐olds and wild smolts, decreased during the 1980s and 1990s. Growth rates at sea, adult size and the proportion of multi‐sea‐winter fish of all three groups also decreased over time.
Catches in coastal relative to freshwaters were higher for two‐ than one‐sea‐winter fish. Salmon captured in coastal water were greater in length than those captured in rivers. Mean specific growth rate at sea was similar for wild and hatchery salmon released as 1‐year‐old smolts, and higher than in hatchery fish released as 2‐year‐olds.
The proportion of two‐sea‐winter salmon correlated positively with the specific growth rate in the first year at sea. Total capture of wild adult salmon in rivers and Norwegian home waters each year correlated positively with the specific growth rate in the first year at sea. The same correlation held for hatchery fish released as 2‐ but not 1‐year‐old smolts.
Synthesis and applications. The coastal fishery was size‐selective in reducing the size and age of salmon. Releases of 1‐year‐old smolts were financially more profitable than those of 2‐year‐olds. Decreasing production of River Imsa salmon since 1981 was chiefly caused by reduced sea‐age at maturity and growth rate at sea of both hatchery and wild fish. A counteracting measure would be to reduce the size selectivity of the salmon fisheries.
Evidence for indigenous selection and distribution of the shea tree, Vitellaria paradoxa, and its potential significance to prevailing parkland savanna tree patterns in sub‐Saharan Africa north of the equator
Authors: Maranz S. , Wiesman Z. 
Published: September 2003

AbstractAim  Woody vegetation patterns in African savannas north of the equator are closely connected to human presence, but the distinctions between natural and anthropogenic landscapes have not been clear to many observers. Criteria for identifying savanna landscapes on a continuum of intensity of anthropic impact are explored.Methods  A key savanna tree species, Vitellaria paradoxa (Sapotaceae), was used as model for evaluating anthropic impact. Fruits harvested from tree populations across the species range were analysed for variation in traits valued by indigenous peoples. A simple selection index was used to scale tree populations from a hypothetical wild state to a hypothetical domesticated state. Index values were compared with trait values along climate zone gradients and evaluated in the context of indigenous savanna management practices and historical species distribution reports.Results  Trait values such as fruit size and shape, pulp sweetness, and kernel fat content show a significant influence of temperature and rainfall. At the same time, the mean values of groups of traits vary perpendicular to the general climatic zone gradient. Selection index values between Vitellaria populations vary up to sixfold, with highest values in central Burkina Faso. Comparison of present day Vitellaria distribution with historical range limits show range expansion by human migration.Main conclusions  The prevalence of major economic tree species in the savannas of Africa north of the equator is a strong indicator of human involvement in tree dispersal. This conclusion is supported by paleobotanical evidence and by recent Vitellaria range expansion as a result of human migration. The presence of high mean values of several Vitellaria fruit traits in central Burkina Faso suggests that selection for desired characteristics has occurred. The impact of indigenous savanna peoples on woody species composition and spatial distribution is probably much greater than usually thought and is the result of a deliberate strategy of altering the landscape to provide needed human resources.
The trans‐Pacific zipper effect: disjunct sister taxa and matching geological outlines that link the Pacific margins
Authors: McCarthy Dennis 
Published: September 2003

AbstractAimTo combine analyses of trans‐Pacific sister taxa with geological evidence in order to test the hypothesis of the existence of a Panthalassa superocean.LocationThe study is concerned with taxa, both fossil and extant, from East Asia, Australia, New Zealand, South America and North America.MethodsPhylogenetic and distributional analyses of trans‐Pacific biota were integrated with geological evidence from the Pacific and circum‐Pacific regions.ResultsA series of recent biogeographical analyses delineates a zipper‐like system of sister areas running up both margins of the Pacific, with each section of western North and South America corresponding to a particular section from East Asia/Australia/New Zealand. These sister areas coincide neatly with a jigsaw‐like fit provided by the matching Mesozoic coastlines that bracket the Pacific.Main conclusionsThe young age (<200 Myr) of oceanic crust, the matching Mesozoic circum‐Pacific outlines, and a corresponding system of interlocking biogeographical sister areas provide three independent avenues of support for a closed Pacific in the Upper Triassic–Lower Jurassic. The hypothesis of the existence and subsequent subduction of the pre‐Pacific superocean Panthalassa is not only unnecessary, it conflicts with this evidence. Panthalassa‐based paleomaps necessitate the invention of dozens of additional hypotheses of species‐dependent, trans‐oceanic dispersal events, often involving narrow‐range taxa of notoriously limited vagility, in order to explain repeated examples of the same biogeographical pattern. Removing the vanished‐superocean hypothesis reunites both the matching geological outlines and all the disjunct sister taxa. In brief, what appears to be a multi‐era tangle of convoluted, trans‐oceanic distributions on Panthalassa‐based paleomaps is actually a relatively simple biogeographical pattern that is explainable by a single vicariant event: the opening and expansion of the Pacific.
Adaptive latitudinal trends in the mandible shape of Apodemus wood mice
Authors: Renaud Sabrina , Michaux Johan R. 
Published: September 2003

AbstractAim Size and shape of the mandible are investigated across the latitudinal range of the European wood mouse (Apodemus sylvaticus), in order to address the relative importance of genetic structure, insularity, and geographical gradient in patterning morphological variation. Results are compared with those on two Asiatic species of wood mice, A. argenteus and A. speciosus.Location The European wood mouse is sampled by a set of trapping localities including both, islands and mainland populations, as well as the four genetic groups identified in previous studies. The localities cover a latitudinal gradient from 55° N to 36° N.Methods Different Fourier methods are applied to the outlines of mandibles and their results compared in the case of A. sylvaticus. All provide similar results and allow a quantification of the size and shape variations across the geographical range of the European wood mouse. Using the method allowing for the best reduction of the informative data set, a comparison of the European wood mouse with the two Asiatic species was performed.Results Within the European wood mouse A. sylvaticus, a strong latitudinal gradient in mandible shape overrides the influence of insularity and genetic structure. Yet, random morphological divergence in insular conditions can be identified as a secondary process of shape differentiation. Size displays no obvious pattern of variation, neither with insularity or latitude. A comparison with two other species of wood mice suggests that a similar latitudinal gradient in mandible shape exists in different species, mandibles being flatter in the north and wider in the south.Main conclusion The latitudinal gradient in mandible shape observed in the three species of wood mice is interpreted as an intraspecific adaptive response to gradual changes in feeding behaviour.
A method using indicator plants to map local climatic variation in the Kangerlussuaq/Scoresby Sund area, East Greenland
Authors: Karlsen Stein R. , Elvebakk Arve 
Published: September 2003

AbstractAimTo describe a method for mapping local climatic variation using plants as temperature indicators.LocationThe study area is situated on the northern side near the mouth of the fiord Kangerlussuaq/Scoresby Sund, East Greenland (70–71°N). The study area consists of three subareas, divided into 136 1 × 1 km study units. It was selected because of its very strong climatic gradient as shown by data from four meteorological stations in the area, with mean July temperatures ranging from 2.7 to 9.3 °C.MethodsThe method is based on the fact that most vascular plant species occurring in the Arctic have circumpolar distribution patterns obviously limited by temperatures to a varying extent. By comparing the circumpolar distribution maps with summer temperatures, species are grouped according to minimum temperature demands and assigned indicator values. In the field, frequency and abundance of all indicator species and the occurrence of habitats are recorded in all study units. Indicator values and abundance data are entered into a formula of Index of Thermophily, and the resulting values are modified according to deviating habitat diversity and cover of unproductive areas. Index values are supposed to reflect local climatic conditions, and the results are tested by comparing with temperatures measured in the field.ResultsA total of 147 taxa, 139 of these being vascular plants, were defined in six categories of temperature indicators. The Index of Thermophily values calculated for the 136 study units show a complex pattern and a strong positive relationship with the temperatures measured during 1991 and 1993, withr2values of 0.82 and 0.92, respectively. The unmodified Index version gave slightly lower correlations. A very strong gradient is demonstrated from the extremely cold coastal community of Uunarteq/Kap Tobin to more protected sites only 20 km inland, where a similar climate is found at 1100 m altitude. Favourable slopes also produce a favourable climate at altitudes of 700 m. The warmest sites are the south‐facing slopes of five deep river gorges, all with similar Index values and the occurrence ofSalixshrubs. The results are used to make a local bioclimatic map, including allowances for topographic features and detailed knowledge on the occurrence of concentrations of thermophilous plants. Here fourteen climate classes are mapped in detail, and these mapping units can be correlated to four of five subzones present in the Arctic on a circumpolar scale. The correlation with these subzones shows that the study area has the strongest horizontal climate gradient recorded from the Arctic.Main conclusionsThe strong positive correlation between the calculated Index of Thermophily values and measured temperatures indicate that the present method is successful in mapping local bioclimatic heterogeneity in the Arctic.
The decay of similarity with geographical distance in parasite communities of vertebrate hosts
Authors: Poulin Robert 
Published: September 2003

AbstractAim The rate at which similarity in species composition decays with increasing distance was investigated among communities of parasitic helminths in different populations of the same host species. Rates of distance decay in similarity of parasite communities were compared between populations of fish and mammal hosts, which differ with respect to their vagility and potential to disperse parasite species over large distances.Location Data on helminth communities were compiled for several populations of three mammalian host species (Ondatra zibethicus, Procyon lotor and Canis latrans) and three fish host species (Perca flavescens, Catostomus commersoni and Esox lucius) from continental North America.Methods Distances between localities and similarity in the composition of helminth communities, the latter computed using the Jaccard index, were calculated for all possible pairs of host populations within each host species. Similarity values were then regressed against distance to see if they decayed at exponential rates, as reported for plant communities; the significance of the regressions was assessed using randomization tests.Results The number of hosts examined per population did not correlate with the number of helminth species found per population, and thus sampling effort is unlikely to have confounded the results. In four (two mammals and two fish) of the six host species, similarity in helminth communities decayed exponentially with distance. When the log of similarity is plotted against untransformed distance, the slopes obtained for the two fish species are lower than those obtained for the two mammalian host species.Main conclusions Similarity in the composition of parasite communities appears to decay exponentially with increasing distance in some host species, but not in all host species. The rate of decay is not necessarily associated with the vagility of the host. Although distance decay of similarity is generally occurring, it seems that other ecological processes, related either to the host or its habitat, can obscure it.
The range expansion of the great‐tailed grackle (Quiscalus mexicanus Gmelin) in North America since 1880
Authors: Wehtje Walter 
Published: September 2003

AbstractAims  This study aimed to document and describe the current range expansion of the great‐tailed grackle (Quiscalus mexicanus Gmelin) into the USA. By examining the habitat associations and pattern of spread of this species, I intended to determine the factors responsible for this remarkable expansion by a tropical species into a temperate environment.Location  This study focused on the spread of the great‐tailed grackle in the continental USA, Canada and Baja California.Methods  I used published records, museum specimens, and egg collections to document this range expansion from 1880 through 2002. In addition I surveyed large portions of Arizona, Nevada, southern Utah and southern California for great‐tailed grackles during 2000 and 2001. The data gathered was used to create maps in order to quantify the rate of spread of this species.Results  Between 1880 and 2000 the great‐tailed grackle expanded its breeding range in the USA from c. 64,000 km2 to more than 3,561,000 km2, an increase of 5530%. The average annual rate of increase is 3.4%, but has lessened during the past 20 years. Northward movement in the eastern portion of the range has slowed down, reflecting this decrease. However, in the central and western portion of the species range, the rate of northward movement is still accelerating. During this expansion, the average time between first sighting in a state and first breeding was 5.8 years. The species has become less migratory during its range expansion, wintering in 17 of the 20 states where it breeds.Main conclusions  This range expansion has been marked by great‐tailed grackles preferring human‐modified environments as breeding grounds, especially in the western states. This association appears to benefit the species in two ways; nest predation is lessened in such areas compared with natural conditions, whereas human activities tend to generate an abundant and consistent food supply for feeding offspring. Wintering birds are often associated with cattle feed lots and large‐scale dairies, where abundant waste grain provides them with a reliable food supply. Given the continued human population increase throughout large areas of the western USA, the great‐tailed grackle will continue its range expansion.
Signalling mechanism coupled to 5‐hydroxytryptamine4 receptor‐mediated facilitation of fast synaptic transmission in the guinea‐pig ileum myenteric plexus
Authors: Galligan J. J. , Pan H. , Messori E. 
Published: September 2003

Abstract5‐hydroxytryptamine (HT)4 receptor agonists stimulate gastrointestinal motility partly by facilitating acetylcholine release from myenteric neurones. However, the signalling mechanisms that couple 5‐HT4 receptor activation to increased transmitter release in the myenteric plexus are unknown. We used conventional intracellular electrophysiological methods to record fast excitatory postsynaptic potentials (fEPSPs) from neurones in the guinea‐pig ileum myenteric plexus preparation. The substituted benzamide, renzapride, acted at 5‐HT4 receptors to facilitate fEPSPs. This response was mimicked by forskolin, an activator of adenylate cyclase. Facilitation of fEPSPs by renzapride and forskolin was not blocked by treating tissues with pertussis toxin (PTX) (2 h, 2 μg mL−1). Facilitation of fEPSPs caused by renzapride was blocked by the non‐selective protein kinase inhibitors, staurosporine (1 μmol L−1) and H‐8 (30 μmol L−1) and by the selective protein kinase A (PKA) inhibitor, H‐89 (10 μmol L−1). These data indicate that 5‐HT4 receptors act via a PTX‐resistant mechanism to activate PKA. Protein kinase A activation leads to an increase in transmitter release from myenteric nerve terminals and a facilitation of fast excitatory synaptic transmission.