bluuebunny/crossref_metadata_2025 huggingface dataset:
Chronic fishing disturbance has changed shelf sea benthic community structure
Authors: Kaiser M. J. , Ramsay K. , Richardson C. A. , Spence F. E. , Brand A. R.
Published: March 2003

1. Bottom fishing using towed nets and dredges is one of the most widespread sources of physical disturbance to the continental shelf seas throughout the world. Previous studies suggest that degradation and ecosystem changes have occurred in intensively fished areas. Nevertheless, to date it has been difficult to attribute habitat and benthic community changes to fishing effort at a spatial scale that is truly representative of commercial fishing activities.

2. In this study we present convincing evidence that chronic bottom‐fishing disturbance has caused significant and widespread changes in the structure of two distinct soft‐sediment benthic assemblages and habitats.

3. Our study compared the benthic fauna found in areas that have been exposed to either high or low levels of bottom‐fishing disturbance over the past 10 years. We were able to validate the fishing effort data in some areas using scars in the shells of a long‐lived bivalve mollusc (Glycymeris glycymeris) which result from fishing disturbance. Shell scars occurred most frequently in bivalves collected from the area of highest fishing effort.

4. Multivariate analyses and the response of abundance/biomass curves indicated that chronic fishing has caused a shift from communities dominated by relatively sessile, emergent, high biomass species to communities dominated by infaunal, smaller‐bodied fauna. Removal of emergent fauna has thus degraded the topographic complexity of seabed habitats in areas of high fishing effort. The communities within these areas currently may be in an alternative stable state.
Bird diversity and environmental gradients in Britain: a test of the species–energy hypothesis
Authors: Lennon J. J. , Greenwood J. J. D. , Turner J. R. G.
Published: March 2003

1. We tested the species diversity–energy hypothesis using the British bird fauna. This predicts that temperature patterns should match diversity patterns. We also tested the hypothesis that the mechanism operates directly through effects of temperature on thermoregulatory loads; this further predicts that seasonal changes in temperature cause matching changes in patterns of diversity, and that species’ body mass is influential.

2. We defined four assemblages using migration status (residents or visitors) and season (summer or winter distribution). Records of species’ presence/absence in a total of 2362, 10 × 10‐km, quadrats covering most of Britain were used, together with a wide selection of habitat, topographic and seasonal climatic data.

3. We fitted a logistic regression model to each species’ distribution using the environmental data. We then combined these individual species models mathematically to form a diversity model. Analysis of this composite model revealed that summer temperature was the factor most strongly associated with diversity.

4. Although the species–energy hypothesis was supported, the direct mechanism, predicting an important role for body mass and matching seasonal patterns of change between diversity and temperature, was not supported.

5. However, summer temperature is the best overall explanation for bird diversity patterns in Britain. It is a better predictor of winter diversity than winter temperature. Winter diversity is predicted more precisely from environmental factors than summer diversity.

6. Climate change is likely to influence the diversity of different areas to different extents; for resident species, low diversity areas may respond more strongly as climate change progresses. For winter visitors, higher diversity areas may respond more strongly, while summer visitors are approximately neutral.
Species richness of insects and mites on trees: expanding Southwood
Authors: Brändle Martin , Brandl Roland
Published: March 2003

Data on the species richness of phytophagous insects and mites associated with 25 tree genera occurring as natives in Germany were compiled and compared to data for British trees published byKennedy & Southwood (1984). For tree genera occurring in Germany and Britain patterns of species richness and composition of phytophage faunas were similar.

 Present abundance of trees, their distributional history during the Holocene, morphological traits and taxonomic isolation were used to explain the variance of species richness and proportion of specialists across tree genera occurring as natives in Germany. Tree genera were either used as independent data points or to calculate phylogenetically independent contrasts. For the latter approach, a phylogeny for the tree genera was generated from publishedrbcL gene sequences. In general, the conclusions from the two types of analyses were similar.

 The species richness of phytophages on German tree genera were positively related to present tree abundance, tree height and tree abundance derived from pollen samples. For phylogenetically independent contrasts the length of time a genus was present since the end of the last glaciation also became significant.

 The proportions of specialists showed a negative relationship with present abundance of trees, a positive relationship with taxonomic isolation as well as the length of time of genus was present since the end of the last glaciation. For phylogenetically independent contrasts only the latter two variables remained significant.

 Overall the results support the species–area and the coevolutionary hypotheses.
High predictability in introduction outcomes and the geographical range size of introduced Australian birds: a role for climate
Authors: Duncan Richard P. , Bomford Mary , Forsyth David M. , Conibear Louise
Published: March 2003

We investigated factors hypothesized to influence introduction success and subsequent geographical range size in 52 species of bird that have been introduced to mainland Australia.

The 19 successful species had been introduced more times, at more sites and in greater overall numbers. Relative to failed species, successfully introduced species also had a greater area of climatically suitable habitat available in Australia, a larger overseas range size and were more likely to have been introduced successfully outside Australia. After controlling for phylogeny these relationships held, except that with overseas range size and, in addition, larger‐bodied species had a higher probability of introduction success. There was also a marked taxonomic bias: gamebirds had a much lower probability of success than other species. A model including five of these variables explained perfectly the patterns in introduction success across‐species.

Of the successful species, those with larger geographical ranges in Australia had a greater area of climatically suitable habitat, traits associated with a faster population growth rate (small body size, short incubation period and more broods per season) and a larger overseas range size. The relationships between range size in Australia, the extent of climatically suitable habitat and overseas range size held after controlling for phylogeny.

We discuss the probable causes underlying these relationships and why, in retrospect, the outcome of bird introductions to Australia are highly predictable.
Intraguild predation in larval parasitoids: implications for coexistence
Authors: Borer Elizabeth T.
Published: March 2003

Many coexisting parasitoids interact via intraguild predation (IGP); however, in IGP theory without stage structure the intraguild predator and intraguild prey coexist via this mechanism over only a relatively narrow region of parameter space. A recent formulation of IGP theory with a stage of the intraguild prey species that is invulnerable to attack by the intraguild predator shows that coexistence between guild members can occur across a much broader range of resource productivity than is predicted by IGP theory without stage structure. These general theoretical predictions are used to explore the implications for coexistence ofAphytis melinus(DeBach) andEncarsia perniciosi(Tower), a pair of parasitoids that coexist on California red scale.

Reanalysis of a published laboratory competition experiment between two parasitoid species suggests thatAphytis, an ectoparasitoid, survives at a lower rate when the reparasitized host contains a more developed juvenile endoparasitoid (Encarsia). This pattern is contrary to a common assumption that ectoparasitoids always consume endoparasitoids in a shared host, and may affect coexistence. The experiment covered only the first ∼30% of theEncarsiadevelopment period and did not describe the outcome forEncarsia, so the dynamic effects of this interaction in the context of IGP remain unclear. In addition,Encarsiais capable of parasitizing much younger hosts than isAphytis, which the experiment did not examine.

The experiment was repeated, and extended to cover the full developmental duration ofEncarsia. An additional experiment was performed to explore whetherEncarsiacould pre‐emptAphytisby attacking younger hosts.Aphytisjuvenile survival was found to decrease as a function of the age of the juvenileEncarsiaonto which it was laid. WhenEncarsiaparasitized very young hosts, it was increasingly invulnerable to attack byAphytisand increasingly more likely to survive to emergence. However, until the formation of an invulnerable pseudomoult,Encarsiawas always killed in larger hosts, regardless of its age at the time ofAphytisattack.

According to stage‐structured IGP theory, the decline inAphytissuccess combined with an invulnerableEncarsiastage may promote coexistence in this system.
Factors affecting the establishment of Cytisus scoparius in southern France: implications for managing both native and exotic populations
Authors: PAYNTER QUENTIN , FOWLER SIMON V. , MEMMOTT JANE , SHEPPARD ANDREW W.
Published: March 2003

The ecology of the woody shrub Cytisus scoparius was studied for 4 years in its native range in southern France to investigate how it can become an invasive weed.

The proportion of the seed bank that germinated each year was highest in disturbed plots and was correlated with the March rainfall. The seed bank declined at a rate of c. 50% per year when fresh seed rain was excluded.

The fate of 2863 seedlings was followed for a variety of treatments.

Seedling survival depended on disturbance: none survived their first summer in undisturbed plots; more than 40% survived their first summer and c. 14% survived to flowering age in plots that were initially cultivated.

Seedlings flowered first in their fourth year, although only c. 10% set seed.

Neither inter‐ nor intraspecific competition was found to affect significantly seedling survival on cultivated plots. However, some seedlings grown in the absence of interspecific competitors flowered and set seed in their third year.

Applications of insecticide, molluscicide or fungicide did not affect significantly seedling survival, growth or minimum age of reproduction on cultivated plots.

It is concluded that management strategies should minimize disturbance to competing vegetation, which can inhibit germination and smother emerging seedlings. In many circumstances strategies that target the seed bank, such as burning, are not expected to work.

Herbivores and pathogens may prevent stand re‐establishment indirectly, by reducing the size, vigour and density of broom plants so that competing vegetation can persist and smother emergent seedlings following the death of the parent stand.
Host‐plant affinities of two biotypes of Dactylopius opuntiae (Homoptera: Dactylopiidae): enhanced prospects for biological control of Opuntia stricta (Cactaceae) in South Africa
Authors: Volchansky C. R. , Hoffmann J. H. , Zimmermann H. G.
Published: March 2003

1. Until recently, neither the phycitid moth Cactoblastis cactorum nor the cochineal insect Dactylopius opuntiae have been satisfactory biological control agents of Opuntia stricta in South Africa.

2. In marked contrast, both of these agents have kept O. stricta under biological control for many decades in Australia.

3. In an attempt to improve the situation in South Africa, a stock of D. opuntiae was obtained from O. stricta in Australia during 1996.

4. Host‐specificity tests confirmed that the newly imported D. opuntiae from Australia is a different biotype to the one already established in South Africa.

5. The Australian (‘stricta’) biotype thrives on O. stricta but is unable to develop satisfactorily on O. ficus‐indica, while the converse is true for the South African (‘ficus’) biotype, which thrives on O. ficus‐indica but fares poorly on O. stricta.

6. The integrity of the host‐plant specificity of the two biotypes of D. opuntiae has important implications for biological control of Cactaceae in South Africa, and has greatly enhanced prospects that O. stricta can be brought under biological control successfully.
Variation in the effectiveness of symbiotic associations between native rhizobia and temperate Australian Acacia: within‐species interactions
Authors: Burdon J. J. , Gibson A. H. , Searle Suzette D. , Woods M. J. , Brockwell J.
Published: March 2003

1. The ability of different rhizobial isolates collected from any one site to establish effective nitrogen‐fixing associations with host‐plants from that site showed significant variation in 22 host Acacia species and nearly all of 67 populations. The average Acacia host–Rhizobium strain combination was only about 70% effective. Many combinations were far poorer; in a few cases the worst combination resulted in plants less than one‐tenth the size of the best combinations.

2. The ability of rhizobial isolates to form effective symbiotic interactions showed marked host population and rhizobial‐isolate effects in a study of eight, four and nine populations of A. dealbata, A. implexa and A. mearnsii. A more complete trial involved three populations of each of A. dealbata, A. implexa, A. irrorata, A. mearnsii and A. melanoxylon. These were inoculated with a range of rhizobial isolates previously shown to be highly, moderately or weakly successful in forming an effective association. Evidence of marked host population and rhizobial origin effects was found but there was very little evidence of isolate–host population interaction effects.

3. The general lack of host population–rhizobial origin interaction effects suggests that rhizobial strains selected as highly effective for an Acacia species growing in a particular population will generally perform well symbiotically with that species in other populations. This will make their practical application as inoculants in revegetation and forestry situations much easier.

4. Significant host‐based variability in the ability to form effective symbiotic interactions was detected in comparisons of half‐sib families of A. dealbata, A. mearnsii and A. melanoxylon. In the case of A. dealbata, the interaction between half‐sib family lines and rhizobial isolates was complex, with ‘locally’ derived isolates performing better than ‘foreign’ ones. There were also significant interaction effects. In A. mearnsii, on the other hand, the only significant differences were detected between the response of different half‐sib families to the same rhizobial isolate. The occurrence of host‐based variability indicates that in Acacia breeding programmes attention should be given to the possibility of inadvertent selection affecting these relationships.
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

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

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

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

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

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

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.
Lack of Ca2+‐ and ATP‐dependent priming stage in caffeine‐induced exocytosis in bovine adrenal chromaffin cells: comparison with Ca2+
Authors: Matsumura C. , Kuwashima H. , Kimura T.
Published: March 2003

1 Caffeine (20–40 m
m) secreted catecholamines from β‐escin‐permeabilized bovine adrenal chromaffin cells in the presence or absence of 2 m
m MgATP. The caffeine‐induced catecholamine secretion in the presence of MgATP was to the same extent as that in the absence of MgATP.  2 Ca2+ (0.1–10 μm) induced a significantly greater secretion of catecholamines in the presence of MgATP than in the absence of MgATP.  3 ML‐9 (100 μm) and ML‐7 (100 μm), myosin light chain kinase inhibitors, and W‐7 (100 μm) and trifluoperazine (TFP; 30 μm), calmodulin antagonists, inhibited the Ca2+‐induced catecholamine secretion in the presence of MgATP but not in the absence of MgATP. They did not inhibit the caffeine‐induced catecholamine secretion in the presence of MgATP.  4 The ATP‐independent phase in Ca2+‐dependent exocytosis is thought to be associated with the final step that ultimately leads to fusion, while the ATP‐dependent phase is thought to be associated with a vesicle priming reaction. Therefore, these results suggest that the ATP‐requiring priming stage is lacking in the process of caffeine‐induced exocytosis in bovine adrenal chromaffin cells.
Neurotransmitters adenosine triphosphate and noradrenaline induce nitric oxide release in rat vas deferens
Authors: Vetri T. , Di Maio R. , Bonafede G. , Passafiume L. , Postorino A.
Published: March 2003

1 In rat vas deferens, electrical field stimulation (EFS) evoked a muscular biphasic tetrodotoxin (TTX)‐sensitive contractile response.  2 The amplitude of this response increased with the frequency of stimulation.  3 After each stimulation, nitric oxide (NO) release was assayed and found to be released in a frequency‐dependent manner.  4 NO release also occurred after treatment with exogenous neurotransmitters, adenosine 5′‐triphosphate (ATP) and noradrenaline (NA).  5 Prazosin and pyridoxalphosphate‐6‐azophenyl‐2′,4′‐disulphonic acid (PPADS), respective antagonists of α1‐adrenoceptors and P2x purinoceptors, inhibited NO release induced by NA and ATP. Both prazosin and PPADS inhibited NO release by EFS.  6 TTX failed to modify the NO release induced by exogenous neurotransmitters but abolished the release of NO and contractile response by EFS.  7 EFS and released noradrenaline and ATP induce the release of NO through postjunctional α1‐adrenoceptors and P2x‐purinoceptors, respectively.
Functional innervation of the biliary sphincter of the guinea‐pig revealed by anti‐autonomic drugs
Authors: Vogalis F. , Smith T. K.
Published: March 2003

1 The roles of excitatory and inhibitory intrinsic motor nerves on contractions reflexly evoked by wall distension were investigated in the isolated sphincter of Oddi of the guinea‐pig (SO‐GP).  2 Distension of the terminal bile duct for 30–60 s time periods increased the frequency of contractions from about 2 to 12 min−1 (n=16).  3 Hexamethonium (HEX; 300 μm) largely prevented the distension‐evoked increase in contraction frequency (4.5 min−1, n=8) as did atropine (ATR; 1 μm) (0.8 min−1, n=6), while tetrodotoxin (TTX; 1 μm) blocked the contractions triggered during distension.  4 L‐nitroarginine (L‐NA; 100 μm) significantly increased the frequency of contractions during and in the absence distension while apamin (APAM; 0.5 μm) significantly increased their frequency and doubled their mean amplitude during distension.  5 These results suggest that distension activates excitatory cholinergic motor nerves to increase the frequency of contractions in the SO‐GP. These actions are modulated by the concomitant activation of intrinsic nitrergic and non‐nitrergic inhibitory motor nerves.
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.
The supply of regeneration micro‐sites and segregation of tree species in a hardwood/boreal forest transition zone
Authors: Barras Nathalie , Kellman Martin
Published: March 2003

We examine the role that demand for, and supply of, micro‐sites for seedling regeneration plays in preserving segregation of species into boreal and hardwood communities in the Lake Superior region of northern Ontario. The sensitivity of tree seedlings of the two dominant species in each community to micro‐environmental variations was measured in transitional zones, where all species were present, and these responses compared to the availability of micro‐sites in adjacent ‘pure’ communities. Acer saccharum Marsh seedlings exhibited the largest ecological amplitude, and were found growing on the deepest litter layers and where the greatest mass of hardwood litter had accumulated. Abies balsamea (L.) Mill., Picea glauca (Moench) Voss, and Betula alleghaniensis Britton seedlings were found growing where hardwood litter layers were thinnest, more moss was present, and light levels were higher, all conditions most frequent in the boreal community. The results imply that Acer should regenerate well in both community types, while the other three species should regenerate well only in boreal communities. The abruptness of the hardwood/boreal community boundary in this area is explained by the abrupt population boundary of Acer saccharum, the potential regional dominant; this is tentatively attributed to temperature limitation on this species at its northern range limit.
Bill and body size in the peregrine falcon, north versus south: is size adaptive?
Authors: Johansson Carl , Linder Eric , Hardin Perry , White Clayton
Published: March 2003

Visually, the bill size on southern hemisphere peregrine falcons (Falco peregrinus), especially from Australasia and the Philippines, appears appreciably larger for their body size than in other peregrine populations. Accordingly, we measured the bill ‘size’ or ‘volume’ (length, width, depth) as a function of body mass on a sample of peregrines. We used both wing and tarsal length as indicators of body mass. We compared bill volume between two northern hemisphere groups, a medium‐sized tundra breeding group and the largest of all peregrines (F.p. pealei) from the Aleutian Islands of North America, and also among three southern hemisphere groups, South American, Australian and Melanesian/Philippine. Finally, we com‐ pared northern hemisphere and southern hemisphere birds. Southern hemisphere peregrines have a more massive bill relative to body mass than those of the northern group, and can be distinguished from the northern hemisphere birds using ratios of bill volume to wing or tarsus length. Absolute bill volume generally shows a stabilizing selection and, except for tundra birds which are smaller, all bills are statistically the same by sex while body size or mass changes geographically showing directional selection. It is not clear why body mass is consistently smaller in the southern hemisphere than in north temperate regions nor why the convergence in bill volume to body mass among southern groups should be so evident for such isolated geographical locations, especially since there is apparently no gene flow. Further, habitats and thus foods that might alter bill structure differ among locations.
Myrmecochorous dispersal distances: a world survey
Authors: Gómez C. , Espadaler X.
Published: March 2003

Abstract. Myrmecochorous dispersal distances are reviewed; the seed dispersal curve generated by ants shows a characteristic peak at short distances and a long tail, a shape suited to small densities of safe sites. Mean global distance is of 0.96 m (n= 2524) with a range of 0.01–77 m. Data have been broken down by geography (Northern hemisphere v. Southern hemisphere), taxonomy (ant subfamilies) and ecology (vegetation: sclerophyllous v. mesophyllous). Although a statistical difference exists between dispersal curves from the Northern hemisphere and the Southern hemisphere, this may be an artefact of lack of data from mesophyllous myrmecochores from this hemisphere. The four ant subfamilies do show also numerical differences but could not be subjected to statistical analysis. A difference between the shape of dispersal curve for sclerophyllous myrmecochores and mesophyllous myrmecochores has also been detected. We hypothesize that this difference is related to the myrmecological communities from both types of vegetation: dispersing ants from sclerophyllous vegetation would have smaller nest densities and/or bigger foraging areas than dispersing ants from mesic environments.
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.