bluuebunny/crossref_metadata_2025_split huggingface dataset:
The population dynamics of Anisantha sterilis in winter wheat: comparative demography and the role of management
Authors: Lintell Smith G. , Freckleton R.P. , Firbank L.G. , Watkinson A.R. 
Published: March 2003

Summary 1. We report on a 3‐year field study designed to monitor the detailed population dynamics of Anisantha sterilis in winter wheat, as well as to explore the consequences of changing broad‐scale patterns of management, in the form of reduced fertilizer inputs. 2. In the absence of herbicides, population dynamics were dominated by density‐dependent population growth. Unusually, this occurred mainly through density‐dependent recruitment. This was estimated to reduce population growth rates by 50‐fold, compared with the effects of density‐dependent competition between plants for resources. Density‐dependent recruitment also tended to buffer populations against year‐to‐year variations in emergence levels. 3. Little evidence for temporal variations in allometric seed production, the strength of competition between plants for resources or maximal mean plant performance was found in this study, or in comparison with previously published data. 4. No aspect of the life cycle was significantly affected by variation in the level of applied nitrogen fertilizer. In the case of competitive interactions we postulate that this lack of effect results from reduced intraspecific competitive effects as a consequence of decreased maximal plant size under low nitrogen conditions. The highly competitive nature of the environment in which A. sterilis occurs means that such changes tend to mask the effects of changing nitrogen levels. 5. Estimates of the effects of cultivation, on the other hand, indicated that seed germination, and hence population growth, was reduced by up to 90% when ploughing was employed rather than minimum tillage. While to some extent the effects of variation in the form of cultivation on population numbers may be buffered by density‐dependent recruitment, this effect outweighs any effects of nutrients or spatial or temporal variability in population dynamics. 6. Using previously published models for the dynamics of Alopecurus myosuroides, Avena sterilis and Avena fatua, we show that the response of populations of Anisantha sterilis to cultivation is very different from that of other grass weeds. In addition we show how single species models for population dynamics may be used to predict the responses of weed assemblages to changes in forms of management.
Butterfly spatial distribution and habitat requirements in a tropical forest: impacts of selective logging
Authors: Hill Jane K. 
Published: March 2003

Summary 1. Spatial distribution, abundance and habitat requirements of Ragadia makuta (Satyrinae) were studied in Sabah (Borneo) in 1997, in unlogged forest and forest that had been selectively logged 8–9 years ago. 2. Measurement of vegetation structure showed that unlogged forest had significantly larger trees and greater canopy cover than logged forest. A principal components analysis extracted two factors related to forest density and tree size that were also significantly higher in unlogged forest. However, there was significant spatial heterogeneity in vegetation structure within logged forest. 3. In undisturbed forest, a logistic regression model identified suitable habitat for R. makuta as areas of less dense forest close to streams. There were no differences between logged and unlogged habitats in spatial distribution and abundance of R. makuta. Availability of suitable habitat and habitat requirements of butterflies also did not differ between habitats. There was, however, significant heterogeneity in butterfly abundance within logged forest, corresponding with availability of suitable habitat. 4. Fieldwork in 1997 coincided with a severe drought on Borneo, and butterfly spatial distribution and abundance were significantly reduced compared with a year of more normal rainfall (1996); populations in 1997 contracted to areas around streams and to areas with high cover of host‐plant. 5. Selectively logged areas can be highly heterogeneous in relation to levels of disturbance. Quantifying the effects of selective logging on forest structure and the availability of suitable habitat was crucial to understanding the responses of R. makuta to habitat disturbance.
A landscape‐scale study of bumble bee foraging range and constancy, using harmonic radar
Authors: Osborne J.L. , Clark S.J. , Morris R.J. , Williams I.H. , Riley J.R. , Smith A.D. , Reynolds D.R. , Edwards A.S. 
Published: March 2003

Summary 1. Bumble bees play a vital role in the pollination of many crops and wild flowers, and plans for their conservation require a knowledge of the dynamics and spatial scale of their foraging flights, which are, at present, poorly understood. 2. We investigated the foraging range and constancy of two colonies of bumble bees Bombus terrestris L. on a mixed arable farm using harmonic radar, which has a unique capability to record the trajectories of insects flying at low altitude in the field. 3. Foraging bees were fitted with lightweight radar transponders and tracked as they flew to and from the nest to forage. The resulting tracks gave information on length, direction and straightness of foraging routes. Superimposition onto a map of the foraging landscape allowed interpretation of the bees’ destinations in relation to the spatial distribution of forage. 4. Outward tracks had a mean length of 275·3 ± 18·5 m (n = 65) and a range of 70–631 m, and were often to forage destinations beyond the nearest available forage. Most bees were constant to compass bearing and destination over successive trips, although one bee was tracked apparently switching between forage patches. Both outward and return tracks had a mean straightness ratio of 0·93 ± 0·01 (n = 99). The bees’ ground speeds ranged from 3·0 m s–1 to 15·7 m s–1 (n = 100) in a variety of wind conditions. 5. The results support the hypothesis that bumble bees do not necessarily forage close to their nest, and illustrate that studies on a landscape scale are required if we are to evaluate bee foraging ranges fully with respect to resource availability. Such evaluations are required to underpin assessments of gene flow in bee‐pollinated crops and wild flowers. They are also required when making decisions about the management of bees as pollinators and the conservation of bee and plant biodiversity.
Predation by introduced foxes on native bush rats in Australia: do foxes take the doomed surplus?
Authors: Banks Peter B. 
Published: March 2003

Summary 1. Introduced vertebrate predators are one of the most important threats to endemic mammal species. Prey naivety can lead to heavy losses to alien predators, which may be additive to ‘natural’ sources of mortality that limit prey populations. Alternatively, predators may take only individuals that are surplus to the population, and hence predator control may have little benefit for susceptible native prey populations. 2. A field‐based predator removal experiment was used to test the predator limitation and doomed surplus hypotheses on the impact of introduced red foxes Vulpes vulpes on populations of native bush rats Rattus fuscipes in south‐eastern Australia. 3. Poison baiting was used in July 1993 to reduce fox numbers in two fox‐removal sites from 2·8–3·4 km–1 (spotlight counts) to less than 0·5 km–1 within 6 months. Fox density in two non‐removal sites remained typically five times higher than that in removal sites. 4. Bush rat numbers on replicated trapping plots showed no response to fox removal, and rodent numbers fluctuated seasonally in all sites over 22 months of fox control, which represented two breeding seasons for rats. 5. Fox removal also had no effect on rat persistence time, adult body weight, captures of juveniles or immature animals during the breeding season, nor captures of immigrant or transient animals. 6. The general lack of response by rat populations to fox removal supported the doomed surplus hypothesis, that fox predation operated as a compensatory source of mortality rather than an additive one. Consequently, there was no measured benefit to native rat populations of intensive short‐term fox control. 7. The results suggest that where predation pressure is low, not all predation mortality will be additive to prey populations even if it results from a predator introduced to the ecosystem. Hence, indiscriminate control of introduced predators is unlikely to produce uniform benefits for all the species they prey upon. Feral predator control should therefore be targeted for native species known to be predation limited or for species where any mortality threatens persistence.
Predicting the spatial distribution of non‐indigenous riparian weeds: issues of spatial scale and extent
Authors: Collingham Yvonne C. , Wadsworth Richard A. , Huntley Brian , Hulme Philip E. 
Published: March 2003

1. The existence of a hierarchical scheme of environmental controls on the spatial distribution of plant species was explored for three non‐indigenous weeds, Fallopia japonica, Heracleum mantegazzianum and Impatiens glandulifera, in the British Isles. 2. Logistic regression analyses of the presence/absence of the three weed species examined the relative importance of 60 environmental variables, encompassing land cover, geology and climate. Analyses were undertaken using variables assessed at a hectad (10 × 10 km) or tetrad (2 × 2 km) resolution at national (England and Wales) and regional (County Durham, UK) spatial extents. 3. The ranges of all three species in the British Isles are currently increasing, and the non‐equilibrium nature of their distribution limited the goodness‐of‐fit of logistic models. Interpretation of whether a species has expanded to occupy entirely its potential spatial range was scale‐dependent, and species' distributions, when viewed at coarser spatial scales, may be more likely to be interpreted as having reached stasis. 4. Spatial autocorrelation was more evident at the finer tetrad spatial resolution for both F. japonica and I. glandulifera, but not evident at all for H. mantegazzianum. Only the distribution of I. glandulifera revealed significant spatial autocorrelation among hectads at the national scale. These patterns appear related to the different dispersal mechanisms of the three species. 5. The majority of the environmental variables identified as important at the tetrad resolution for County Durham were also important at the hectad resolution for England and Wales for both F. japonica and I. glandulifera, but not for H. mantegazzianum. However, for all three species the environmental variables identified as significant were consistent with qualitative descriptions of the species' habitat characteristics. There was no evidence of a hierarchy of environmental controls. 6. At the regional extent, scaling‐up species' distributions from tetrads to hectads was relatively successful, but scaling‐down was not. The coarser resolution models were too unrefined to model fine‐scale distributions successfully. Similarly, at a coarse hectad resolution, regional models were poor predictors of national species' distributions. It therefore appears that scaling‐up from fine to coarse resolution is appropriate when spatial extent is held constant, and focusing‐down from large to small spatial extents is appropriate when data resolution is held constant.
Enhancing insect diversity in agricultural grasslands: the roles of management and landscape structure
Authors: Di Giulio Manuela , Edwards Peter J. , Meister Erhard 
Published: March 2003

Summary

During the last few years a variety of methods have been applied in Switzerland to preserve and enhance biological diversity in agricultural systems. The purpose of this study was to evaluate grassland management techniques in respect of their effectiveness within a managed area and to examine how these areas contribute to species diversity at a landscape scale.
We examined insect diversity in grasslands subject to different management in a heterogeneous landscape in part of the Swiss Jura. Four study areas with varying landscape structure were selected and, in each area, meadows of two grassland management types were investigated.
The true bugs (Heteroptera) were chosen as an indicator group for insect diversity on the basis of previous work that had shown that the richness of the bug fauna correlates strongly with total insect diversity.
The variance of the heteropteran species data was partitioned into spatial (area) and management components. Area accounted for 35·4%, management for 29·7% and the interaction management × area for 7·2% of the species variance. The species diversity was greater in extensively managed meadows than in intensive ones; extensive sites had more individuals and showed a more even rank abundance distribution.
Individual species differed in their responses to management. Two species benefited from intensification whereas six species were affected negatively by intensive management. Two main groups of species did not appear to respond to management; these were mostly widespread species occurring in a variety of habitats, and polyphagous species which live in a wide range of grasslands but which show a certain affinity to managed meadows.
Our study indicates that extensive management of grasslands can enhance both local and regional insect diversity in agricultural landscapes. Extensively managed meadows were species‐rich habitats that supported some rare and specialized species. In contrast, the bug community of intensive meadows was dominated by more widespread and less specialist species.
Habitat manipulation in lucerne Medicago sativa: arthropod population dynamics in harvested and ‘refuge’ crop strips
Authors: Hossain Zamir , Gurr Geoff M. , Wratten Steve D. , Raman Anantanarayanan 
Published: March 2003

Summary

In order to realize the full potential of natural enemies in integrated pest management, it is necessary to understand their population dynamics, particularly in relation to the role of refuges. Harvested and unharvested plots were established in a commercial hay lucerne Medicago sativa crop and the potential for the unharvested vegetation to constitute a refuge for natural enemies of Helicoverpa spp., one of the key pests, was evaluated.
The temporal and spatial dynamics of arthropod populations were evaluated using sequential samples from directional traps (pitfall and Malaise) and vacuum sampling in both crop treatments.
The spatial dynamics of predation were measured using ‘sentinel’ cards baited with Helicoverpa spp. eggs.
There was no significant directional movement of arthropods captured in pitfall traps, except for a 3‐day period immediately after harvest when there was a net movement of the natural enemies Dicranolaius bellulus, Carabidae adults, spiders and the phytophagous mite Halotydeus destructor from harvested to unharvested plots.
There was net movement of adult Netelia producta, D. bellulus, Coccinella transversalis and Syrphidae as well as the pest Helicoverpa spp. from harvested to unharvested plots for 24 h following a harvest.
Densities of D. bellulus and C. transversalis within unharvested plots decreased with increasing distance from the borders with harvested plots.
Predation rates of Helicoverpa eggs placed in unharvested plots were broadly consistent with predator densities and decreased with distance from the harvested plots.
Predation rates of Helicoverpa eggs placed in harvested plots declined with increasing distance from unharvested plots, suggesting that natural enemies from the latter dispersed into regrowing lucerne.
Strips narrower than the plot width used (30 m) may be adequate to accommodate natural enemies displaced by harvesting. Unharvested refuge strips should ideally be spaced less than 30 m apart so that the natural enemies can contribute to biological control of pests over the entire width of harvested strips.
Nitrergic and purinergic mechanisms and their interactions for relaxation of the rat internal anal sphincter
Authors: De Luca A. , Li C. G. , Rand M. J. 
Published: March 2003

1 The NANC neuronal mechanisms for relaxations of the rat internal anal sphincter in response to electrical field stimulation (EFS) were studied in isolated preparations in the presence of atropine (1 μm), propranolol (3 μm) and phentolamine (3 μm). 2 EFS‐induced relaxations were abolished by tetrodotoxin (1 μm) and reduced to 64% of control by the guanylate cyclase inhibitor ODQ (1 μm), but were not significantly reduced by the nitric oxide synthase inhibitor L‐NAME (100 μm) or oxyhaemoglobin (10 μm). However, in the presence of tubocurarine (10 μm) or apamin (0.1 μm), L‐NAME or oxyhaemoglobin greatly reduced or abolished EFS‐induced relaxations. 3 The EFS‐induced relaxations were mimicked by NO (10–100 μm) and by ATP (3–10 m
m). The relaxations elicited by these agents were not affected by tetrodotoxin, L‐NAME, tubocurarine or apamin. However, ATP‐induced relaxations were reduced by the combination of L‐NAME with tubocurarine or apamin. 4 Nicotine (10–100 μm) produced concentration‐dependent relaxations that were abolished by tubocurarine (10 μm) or hexamethonium (200 μm). After desensitisation to nicotine (100 μm) and in its continued presence, the addition of L‐NAME (100 μm) resulted in almost complete abolition of EFS‐induced relaxations. 5 It is suggested that tubocurarine, hexamethonium and desensitisation to nicotine have an apamin‐like action in the rat internal anal sphincter, the main effect being blockade of a purinergic component of the relaxant transmission process. 6 The findings suggest that both nitrergic and purinergic transmissions are involved in EFS‐induced NANC relaxations of the rat internal anal sphincter, and there appears to be a complex interaction between these two pathways of transmission.
The autonomic and sensory innervation of the smooth muscle of the prostate gland: a review of pharmacological and histological studies
Authors: Pennefather J. N. , Lau W. A. K. , Mitchelson F. , Ventura S. 
Published: March 2003

1 We review literature demonstrating (a) the presence and (b) the actions of substances that mediate or modify neuroeffector transmission to the smooth muscle of the prostrate stroma of a number of species including man. 2 In all species studied prostatic stroma, but not secretory acini, receives rich noradrenergic innervation. Stimulation of these nerves causes contractions of prostate smooth muscle that are inhibited by guanethidine and by α1‐adrenoceptor antagonists that probably act at the α1L‐adrenoceptor. Such actions underlie the clinical use of α1‐adrenoceptor antagonists in benign prostatic hyperplasia (BPH). 3 Acetylcholinesterase‐positive nerves innervate prostatic stroma as well as epithelium. Atropine reduces nerve‐mediated contractions of stromal muscle in the rat, guinea‐pig and rabbit. M1, M2 and M3 muscarinic receptors have been implicated in eliciting or facilitating contraction in the prostate from guinea‐pig, dog and rat, respectively. 4 Adenine nucleotides and nucleosides, nitric oxide (NO), opioids, neuropeptide Y (NPY) and vasoactive intestinal peptide (VIP) may act as co‐transmitters or modulators in autonomic effector nerves supplying prostate stroma. Adenosine inhibits neurotransmission to the rat prostate, and NO is inhibitory in prostate from human, rat, rabbit, pig and dog. The activity of peptides present in the relatively sparse sensory innervation of the prostate exhibits species variation, but, when effective, calcitonin gene‐related peptide is inhibitory while tachykinins are stimulant. The roles of NPY and VIP in modulating stromal contractility remain unclear. 5 Taken together the current literature indicates that, in addition to noradrenaline, other neurotransmitters and neuromodulators may regulate the tone of prostatic smooth muscle. Whether drugs that mimic or modify their actions might be useful in providing symptomatic relief of the urinary symptoms associated with BPH remains to be established.
Woody plant phenology in the West Africa savanna
Authors: De Bie Steven , Ketner Pieter , Paasse Martine , Geerling Chris 
Published: March 2003

In the savanna of West Africa the seasonality of rainfall, with a drought period of at least four months, strongly influences the vegetation. Rainfall is a very critical abiotic variable and therefore plant species must be well adapted to survive in this habitat.In our research, phenological patterns of 120 woody plant species have been examined based on the presence of green leaves. According to the patterns found, these species can be classified in phenological groups, which represent different strategies for survival. Two extreme strategies are found to resist drought: (1) by using the waterstorage in the deeper soil layers and river beds and by restricting drought‐damage through scleromorphic features, and (2) by avoiding the drought through foliage shedding in the dry period.The first strategy is represented by the riparian and upland evergreens, and the semi‐evergreens. The evergreens bear leaves the whole year, gradually replacing old leaves by new ones. The riparian evergreens are strictly bound to riverbeds and grow in or immediately adjacent to them. The semi‐evergreens shed their leaves and start sprouting during a short period (one‐two weeks) once a year. Because the evergreens and the semi‐evergreens are in leaf in the dry period they have to protect themselves to drought damage by scleromorphic features.Contrary to these species are the deciduous species which are bare for at least some months per year. When the dry season starts their leaves dry out and are subsequently shed. They start sprouting before or at the beginning of the first rains. Although much less in number, some deciduous trees also have scleromorphic features to resist drought‐damage. The strategy of sprouting just before the rainy season begins indicates that certain water resources remain available to these deep‐rooting woody plants throughout the year, providing them with a fully operating photosynthetic apparatus when favourable conditions arrive.
Effects of stream size on bird community structure in coastal temperate forests of the Pacific Northwest, U.S.A.
Authors: Lock Patricia A. , Naiman Robert J. 
Published: March 2003

Abstract. Vegetation and spring breeding bird populations associated with riparian forests on high and low order rivers of the Olympic peninsula, Washington (USA), were censussed in 1990 and 1991. The objectives were to (1) provide a baseline description of bird communities associated with unmanaged riparian forests, (2) determine whether there is a difference between bird communities along large and small rivers, and (3) identify what biophysical aspects of the fluvial corridor are most important in determining bird community structure. The approach was to link riparian bird community structure to river order and discuss relationships to vegetation, geomorphology and associated hydrologic disturbance regimes.Large rivers tended to have more deciduous vegetation than small rivers (P = 0.07). Deciduous vegetation and patch types appeared to be linked to river size through stream valley shape and disturbance history. Bird species richness and abundance were significantly higher (P<0.05) on larger rivers (67–140 m width) than on small rivers (12–21 m width) and were positively correlated with the percentage of deciduous trees present at a site. The data suggest that migrant birds, such as the black‐throated grey warbler (Dendroica nigrescens) and warbling vireo (Vireo gilvus), require large tracts of contiguous hardwoods for successful breeding. Additionally, birds such as the Hammond's flycatcher (Empidonax hammondii) and hairy woodpecker (Picoides villosus) appear to depend on the juxtaposition of hardwoods and conifers during the breeding season. We conclude that bird communities on large rivers differ from those on small rivers and that these differences occur predictably with stream order.