bluuebunny/crossref_metadata_2025 huggingface dataset:
Diurnal and seasonal mass variation in blackbirds Turdus merula: consequences for mass‐dependent predation risk
Authors: Cresswell Will
Published: March 2003

1.  A bird’s mass in winter should reflect the trade‐off between the benefits of an increased energy store to reduce starvation risk, and its costs in terms of increasing mass‐dependent predation risk. State‐dependent models of this trade‐off predict that as starvation risk increases then energy reserves should (i), increase, and (ii) be acquired earlier in the day.

2.  Blackbirds increased their minimum weight by 25. ±. 1·5% in midwinter; adults weighed significantly more than juveniles in midwinter, but weighed less in late winter. Weight for both sexes, and particularly adults, decreased with increasing daylength, but weight increases with respect to temperature decreases were most pronounced in males. Female blackbirds showed relatively small seasonal weight changes so that their midwinter mass‐dependent predation risk relative to males was independent of diurnal weight changes.

3.  Blackbirds lost at least 1–9% of their body weight overnight depending on temperature. Over 60% of the weight lost was then regained in the first 3 hours after dawn, with only 5% being regained after 12.00 h. The pattern of early morning weight gain was maintained throughout the winter, with the ratio of weight gain rates in the first 4. h of dawn compared to the rest of the day being c.. 3:1 in midwinter (when individuals maintained high weights) and in early spring (when individuals were losing weight seasonally).

4.  The results agree with the theoretical prediction that energy reserves should increase as risk of starvation increased (as measured by seasonal factors such as cold, short midwinter days). There was, however, little change in the seasonal pattern of diurnal weight gain, with weight always being gained early in the day. In the likely absence of foraging constraints within the study system, this result fits the predictions of state‐dependent foraging models where animals can escape from predation after achieving weight gains, by either using refuges or adopting low‐risk foraging options.
Further perspectives on the breeding distribution of migratory birds: South American austral migrant flycatchers
Authors: Chesser R. Terry
Published: March 2003

1.  Patterns of distribution of breeding austral migrant tyrant‐flycatchers in temperate South America were quantified and analysed in conjunction with a variety of ecological, biogeographical and climatic variables.

2.  The pattern of proportion of migratory to total breeding tyrannids was most strongly associated with latitude and two temperature variables, mean temperature of the coldest month and relative annual range of temperature.

3.  The strong associations of latitude and temperature with percentage of migrants are consistent with the results of most similar investigations of the breeding distributions of migratory birds, both for migrants breeding in North America and in Europe, but contradict the hypothesis that habitat complexity plays a major role in structuring the proportion of migrants in communities of breeding birds.

4.  The consistency of results among studies of migrants on different continents suggests that temperature and latitude, presumably a surrogate for one or more climatic variables, are globally significant factors in the breeding distributions of migratory birds.

5.  The results for austral migrant flycatchers are consistent with the hypothesis that the prevalence of migration at any particular locality is ultimately dependent on the abundance of resources in the breeding season and the severity of the winter season, or on the difference in resource levels between summer and winter.
Effects of habitat fragmentation on carabid beetles: experimental evidence
Authors: DAVIES KENDI F. , MARGULES CHRIS R.
Published: March 2003

1.  We tested for effects of habitat fragmentation in a controlled, replicated, field experiment, in south‐eastern Australia. Our experimental subjects were eight carabid beetle species, and the carabid assemblage (45 species). Monitoring was by pitfall trapping in forest remnants and in adjacent continuous‐forest controls. Remnants were of three sizes (0·25, 0·875, 3·062 ha.). Monitoring commenced 2 years prior to habitat fragmentation. Here we present results for 6 years after habitat fragmentation (4 years for species richness).

2.  We tested four hypotheses. Hypothesis one: habitat fragmentation reduces species richness in the remaining remnants. Carabid species richness was not different in habitat remnants compared to continuous forest, neither was carabid richness different for remnants of different sizes, or at monitoring sites close to remnant edges compared to sites in remnant interiors.

3.  Hypothesis two: populations decline as a result of habitat fragmentation. Two species of eight were completely isolated on remnants and both declined in abundance on remnants compared to control plots in continuous forest. The other six species responded in various ways, which included relative increases and decreases in abundance and no change, but as they were not completely isolated on remnants, their responses could not be explained by isolation.

4.  Hypothesis three: remaining subpopulations decline further on smaller habitat remnants than on larger remnants. Three species responded to remnant size; one was most abundant in small remnants, the second was most abundant in large remnants, and the third was equally abundant in small and large remnants and less abundant in medium‐sized remnants.

5.  Hypothesis four: populations near to remnant edges decline further than populations in remnant interiors. Two species were more likely to occur in remnant interiors than at edges, whereas three species were equally likely to occur in remnant interiors and at edges.

6.  The effects of habitat fragmentation may be the consequence of: (i) isolation; and (ii) habitat modification. In this study, we were able to consider effects of isolation for two carabid species. We tested only one aspect of the habitat modification hypothesis, edge effects. We discuss the possibility that other aspects of habitat modification in remnants may explain some of our results and suggest that this is where future research be directed.
Survival costs of chick rearing in black‐legged kittiwakes
Authors: Golet Gregory H. , Irons David B. , Estes James A.
Published: March 2003

1. We tested for costs of chick rearing in the black‐legged kittiwake Rissa tridactyla (Linnaeus) by removing entire clutches from 149 of 405 randomly selected nests, in which one or both mates was colour‐banded. After the manipulation, we monitored adult nest attendance and body condition at unmanipulated and manipulated nests, and measured the survival and fecundity of these adults the following year.

2. Late in the chick‐rearing period, adults from unmanipulated nests (i.e. with chicks) went on significantly longer foraging trips, and were significantly lighter for their size, than adults from manipulated nests (i.e. without chicks).

3. Adults from unmanipulated nests also survived to the following nesting season at a significantly lower rate than those from the manipulated nests (0·898 vs. 0·953), suggesting that attempting to raise chicks can reduce life expectancy by 55%.

4. There was a tendency for adults from nests that were unmanipulated in year one to have lower reproductive success in year two, primarily because of reduced fledging success, and a higher incidence of non‐breeding.

5. These findings suggest that mass loss in kittiwakes during chick rearing may not be adaptive. Raising chicks can lead to reproductive costs, and the causal mechanism appears to be a reduction in body condition.

6. We compare our results with previous brood (or clutch) size manipulation experiments that have measured adult body condition, survival and/or future fecundity. Although the empirical evidence suggests that long‐lived species are more likely to experience survival costs than short‐lived species, we believe the opposite may be true. We suggest that shifting the experimental protocol of cost of reproduction studies from brood enlargements (an approach taken in most prior studies) to brood reductions will provide more accurate quantifications of naturally occurring costs.

7. The cost of reproduction is one mechanism proposed to explain the reduced survival rates reported for kittiwake populations in the North Atlantic relative to those in the North Pacific ocean. Oceanographic data, however, suggest that lower food availability may limit survival of kittiwakes in the North Atlantic where a deeper mixed layer and reduced primary production combine to make conditions less favourable for this seabird during the winter months.
Population dynamics of apparent competition in a host–parasitoid assemblage
Authors: BONSALL MICHAEL B. , HASSELL MICHAEL P.
Published: March 2003

The population dynamics of two moth species, Plodia interpunctella (Hübner) and Ephestia kuehniella Zeller in the presence of their shared parasitoid, Venturia canescens (Gravenhorst), were studied in well replicated time series experiments.

Moths were prevented from competing for resources and could therefore only interact via the shared parasitoid. This study examines the consequences of apparent competition on the population dynamics of a simple laboratory insect assemblage.

Ephestia kuehniella suffers severly in the presence of the shared parasitoid. In all eight replicates, this moth species is eliminated. Time series analysis reveals that the E. kuehniella populations show divergent oscillations.

Plodia interpunctella and V. canescens populations show persistent populations. Time series analysis reveals that there is a delayed density dependence acting on these populations and the dynamics are either stable equilibrium or damped oscillations.

Repeated‐measures analysis of the strength of the indirect interaction reveals that the effects of apparent competition before E. kuehniella is lost are amensal. The indirect interaction between E. kuehniella and P. interpunctella is [–, 0] rather than [–, –].
The spatial structure of populations
Authors: Thomas Chris D. , Kunin William E.
Published: March 2003

1. Studies of the spatio‐temporal dynamics and structure of populations have identified many categories of population type. However, recognized categories intergrade, making it difficult to assign empirical population systems to single categories.

2. We suggest that most population categories can be arranged along two axes that combine per capita birth (B), death (D), emigration (E) and immigration (I) rates. The ‘Compensation Axis’ describes the source‐sink component of population structure, with source populations exporting individuals (B > D, E > I) and sinks and pseudosinks consuming individuals (B < D, E < I). The ‘Mobility Axis’ describes the involvement of a local population in regional (I + E) rather than local (B + D) processes, running from separate populations, through metapopulations, to patchy populations.

3. Each sample area within a spatially structured population system can potentially be assigned to a position along each of these axes, with individual sample areas weighted by local population size. The positions of these sample areas and their relative weightings allow the relative importance of different types of process to be judged. A worked exampled is provided, using the butterfly Hesperia comma. This approach shifts the emphasis from pattern (categories that real population systems do not fit) onto process.

4. In many systems, continuous variation in habitat quality and demographic parameters make clear distinctions between ‘habitat’ and ‘non‐habitat’ difficult to sustain. In such cases, we advocate the use of a spatial grid system, with effects of patch size and isolation combined into a single, weighted distance function (neighbourhood).

5. The relative importance of different processes depends on the spatial scale at which the system is observed. This again emphasizes the value of a process‐based approach.
The equilibrium assumption in estimating the parameters of metapopulation models
Authors: Moilanen Atte
Published: March 2003

1. The construction of a predictive metapopulation model includes three steps: the choice of factors affecting metapopulation dynamics, the choice of model structure, and finally parameter estimation and model testing.

2. Unless the assumption is made that the metapopulation is at stochastic quasi‐equilibrium and unless the method of parameter estimation of model parameters uses that assumption, estimates from a limited amount of data will usually predict a trend in metapopulation size.

3. This implicit estimation of a trend occurs because extinction‐colonization stochasticity, possibly amplified by regional stochasticity, leads to unequal numbers of observed extinction and colonization events during a short study period.

4. Metapopulation models, such as those based on the logistic regression model, that rely on observed population turnover events in parameter estimation are sensitive to the implicit estimation of a trend.

5. A new parameter estimation method, based on Monte Carlo inference for statistically implicit models, allows an explicit decision about whether metapopulation quasi‐stability is assumed or not.

6. Our confidence in metapopulation model parameter estimates that have been produced from only a few years of data is decreased by the need to know before parameter estimation whether the metapopulation is in quasi‐stable state or not.

7. The choice of whether metapopulation stability is assumed or not in parameter estimation should be done consciously. Typical data sets cover only a few years and rarely allow a statistical test of a possible trend. While making the decision about stability one should consider any information about the landscape history and species and metapopulation characteristics.
Density–distribution relationships in British butterflies. II. An assessment of mechanisms
Authors: Cowley M. J. R. , Thomas C. D. , Wilson R. J. , León‐Cortés J. L. , Gutiérrez D. , Bulman C. R.
Published: March 2003

The interspecific density–distribution relationship is a general and robust pattern that has been described as a rule in community ecology. Many theoretically plausible causes of the relationship have been described, but it is still disputed which factor(s) are most important.

 Using data on the densities and distributions of butterflies and their host plants collected in a 35‐km2area of north Wales, and data on butterfly mobility, niche breadth, habitat breadth and distance from range margins, we examined five of the principal explanatory mechanisms.

 We found that several variables were significantly correlated with density or distribution. Habitat breadth, mobility and distance from range margin had significant positive effects on butterfly distribution. Host‐plant density was significantly positively related to butterfly density; mobility was significantly negatively related to density.

 Despite these results, we could not unambiguously demonstrate that one hypothesis (or several interacting hypotheses) generated density–distribution correlations. The most conclusive evidence was that statistical patterns of distribution (aggregation models) underpinned the positive density–distribution relationship seen amongst the more mobile butterflies. The results provided evidence against the metapopulation dynamic explanation, and were equivocal with respect to the contributions of range position, niche breadth and resource availability.

 An alternative approach was to explore deviations from the underlying relationship between density and distribution, rather than concentrating on the correlation itself. This approach wasmuchmore successful: we demonstrated that species that occurred at high densities relative to their distributions used aggregated resources and were relatively sedentary; whereas those that occurred at low densities relative to their distributions used less aggregated resources, and were more mobile. Mobile species had less aggregated distributions than did relatively sedentary species.

 Given that the interspecific density–distribution pattern appears to be almost ubiquitous and that the proposed explanations are not mutually exclusive, faster progress may be made by examining deviations from the pattern than from further analysis of the pattern itself.
Food limitation explains most clutch size variation in the Nazca booby
Authors: Clifford L. D. , Anderson D. J.
Published: March 2003

Natural selection is expected to optimize clutch size, but intrapopulation variation is maintained in many bird species. The Nazca booby provides a simple system in which to investigate clutch size evolution because clutch size and brood size are decoupled due to obligate siblicide. The indirect effect of brood size on clutch size evolution can therefore be eliminated.

 In Nazca boobies, second eggs provide insurance against the failure of the first egg or early death of the first hatchling, but approximately half of all females lay only one egg. We tested the hypothesis that one‐egg clutches result from food limitation by providing female Nazca boobies with supplemental food.

 A higher proportion of supplemented females produced two‐egg clutches than did control females. Supplemented females produced larger second‐laid eggs than did control females, but not first‐laid eggs. Laying date and laying interval were not affected.

 Comparisons of clutch size and egg volume between years indicated that the supplemental feeding experiment was not conducted in a year with a poor natural food supply. Thus supplemented females produced larger clutch sizes despite apparently normal natural food levels.

 This experiment nearly completes our understanding of clutch size variation in the Nazca booby, and indicates that food limitation and the costs of egg‐laying should be considered carefully in studies of clutch size evolution.
Using individual‐based simulations to test the Levins metapopulation paradigm
Authors: Keeling Matt J.
Published: March 2003

Levins metapopulations have become a standard tool for modelling spatially heterogeneous populations. The acceptance of these models by ecologists may be attributed to their simple structure and their use of presence–absence data.

 Using structured‐metapopulations, which possess stochastic dynamics at the local subpopulation level, the extinction and subsequent recolonization rates can be calculated and compared to those of the classical Levins model.

 Single‐species metapopulations conform to the Levins ideal, validating the widespread use of this conceptual model. However, multispecies systems are shown to deviate in a consistent manner. This deviation, which is explained in terms of a correlation between patch occupancy and average population levels of the species, can be used to identify the signature of enemy–victim interactions.
Longevity of kings and queens and first time of production of fertile progeny in dampwood termite (Isoptera; Termopsidae; Zootermopsis) colonies with different reproductive structures
Authors: Thorne Barbara L. , Breisch Nancy L. , Haverty Michael I.
Published: March 2003

We report age‐specific survivorship of founding kings and queens and colony age of first production of fertile progeny (alates) of two cohorts, containing 52 and 42 complete colonies, respectively, in the primitive dampwood termite Zootermopsis nevadensis ssp. nevadensis.

Longevity of kings and queens was determined and compared in various experimental manipulations of reproductive structure of incipient colonies (removal of king or queen or both vs. unmanipulated pairs as controls) performed one year after pairing. Life span of reproductives was also evaluated in circumstances of interactions between young colonies, a treatment inspired by field observations of natural nest spacing and intraspecific competition between young dampwood termite colonies.

In our first experimental series, founding pairs survived 2–7 years (x̄ = 4·5 ± 0·3 SE) after pairing. Kings lived significantly longer (x̄ = 4·7 ± 0·3 years after pairing; range 2·2–7·3 years) in treatments initiated as pairs than when left as the remaining founder in the queen removal treatment (x̄ = 3·2 ± 0·6 years after pairing; range 1·5–5·3 years), even though one or more female replacement reproductives differentiated within several months after queen loss. Queen life span in the absence of kings averaged 4·9 ± 0·4 years (range 3·6–6·3 years) after pairing, not significantly different from the life span of queens living with kings. There was no significant difference between king and queen life spans in non‐interaction treatments in our first experiment. Results from the second experimental series (35 colonies) are presented to date.

Survival of pairs until death of one mate was significantly shorter in interaction treatments compared with control colonies, suggesting that intraspecific competition between young colonies may create opportunities for replacement reproductives.

The first alates were produced between 1·8 and 6·5 years after pairing in our first experimental series, and between 2·4 and 5 years, to date, in the second experiment.

Ecological and evolutionary correlates of long life span in social insect reproductives and other animals are discussed.
Long‐term recolonization patterns of ants in Western Australian rehabilitated bauxite mines with reference to their use as indicators of restoration success
Authors: Majer J.D. , Nichols O.G.
Published: March 2003

1.  The return of invertebrate animals to rehabilitated mine pits is desirable for the re‐establishment of ecosystem functioning. A long‐term ant monitoring programme is reported over 14 years in a jarrah Eucalyptus marginata forest control plot and in three bauxite mine pits, one of which had been left unvegetated, one planted with marri trees E. calophylla and the other seeded with mixed native plant species.

2.  The results confirm published findings for the first 2 years of the succession that seeding with mixed species results in a more rapid attainment of a forest‐like ant fauna, although in the last 6 years of the study the ant fauna of the planted plot had become more similar to that of the seeded plot.

3.  Changes in the nature of the ant fauna are described and it is concluded that although composition has substantially converged on that of the forest by the end of the study, differences still persist.

4.  Research on vegetation, spiders and ants in bauxite mined areas which have been rehabilitated using more recent technology suggest that these differences will lessen with time and with the introduction of improved rehabilitation prescriptions.

5.  An additional aim of the study was to validate the chronosequence approach to studying ecosystem recovery following disturbances such as mining. It is concluded that long‐term studies provide important information that is missed by the chronosequence approach. Ideally, rapid‐feedback chronosequence approaches should be augmented by long‐term case studies.
Effects of delayed hay removal on the nutrient balance of roadside plant communities
Authors: Schaffers A. P. , Vesseur M. C. , Sýkora K. V.
Published: March 2003

1. Mass losses and nutrient losses from fresh roadside cuttings were studied in the field during a 6‐week period. Large amounts (over 50%) appear to be lost from the cuttings. The losses were positively related to initial nutrient concentrations during this short‐term study. Mass and nitrogen losses were best explained by the initial C:N ratio, phosphorus and potassium losses by the initial phosphorus concentration.

2. For potassium the losses were particularly large (up to 90%). For this element only, the observed relationship between loss rate and initial chemical composition could not be established significantly. It is concluded that potassium is mainly lost by leaching whereas the major nitrogen, phosphorus and mass losses are most probably caused by rapid microbial decomposition of readily soluble substances.

3. Using existing data on chemical composition of other roadside cuttings, nutrient losses after different hay removal delay times were modelled for different plant communities. All or most of the losses were assumed to return to the soil system.

4. When soil impoverishment is aimed for, cuttings should be removed within 1 or 2 weeks in most plant communities. If removal is delayed longer, the amounts of nutrients removed will often fall below the annual atmospheric input. In plant communities where annual above‐ground production of nitrogen and phosphorus are lower than the annual atmospheric deposition already, rapid removal of the cuttings may be the only way to maintain at least potassium at a limiting level.

5. The main effect of hay‐making on the soil nutrient status most likely consists of a reduction of the potassium availability, at least on sandy soils with a low cation exchange capacity and provided there is little delay in hay removal.
Response of soybean to attack by stemfly Melanagromyza sojae in farmers' fields in Indonesia
Authors: VAN DEN BERG H. , SHEPARD B. M. , NASIKIN
Published: March 2003

To determine the effect of Melanagromyza sojae, a common pith‐boring agromyzid fly, on soybean under field conditions in Indonesia, physiologically mature plants from 70 farmers' field sites were uprooted. Plant parameters and exit holes in the stem (created by M. sojae prior to pupation) were recorded.

Melanagromyza sojae was present at all sites and infested 84% of the plants. Farmers' applications of insecticides had no influence on the infestation level by M. sojae. Most exit holes occurred above the cotyledons.

Exit holes in the hypocotyl (i.e. the stem section below the cotyledons), indicative of early attack, were associated with a decrease in the number of seeds per plant, stem diameter and plant height. This suggests that early attack adversely affects plant development. Exit holes above the hypocotyl, indicative of attack later in the season, were associated with an increase in plant parameters, suggesting that late attack occurred in response to the plant's size or vigour.

Multiple regression was conducted to evaluate the influence of infestation on seed production. Separate models were used to analyse early and late attack. For late attack, the plant variables ‘stem diameter’ and ‘plant height’ were added to the regression.

Early attack caused less than 2% yield loss on a per‐plant basis. Possible compensation by neighbouring plants was not considered. Later attack did not reduce yield. Therefore measures to control M. sojae would have been unwarranted.

Infestation had no effect on the 100‐seed weight, confirming that the number of seeds per plant reliably predicted yield.
Testing large‐scale hypotheses using surveys: the effects of land use on the habitats, invertebrates and birds of Himalayan rivers
Authors: Manel S. , Buckton S.T. , Ormerod S.J.
Published: March 2003

1. Piecemeal changes in land use might have cumulative effects on regional biodiversity. However, this hypothesis is difficult to test experimentally at the scales involved, so alternative approaches are required. Here, we illustrate some of the strengths and weaknesses of surveys for evaluating the effects of land use on rivers and river birds over a large area of the Himalayan mountains.

2. We surveyed 180 streams and their catchments in north‐west India and Nepal in 1994–96. We then used analysis of covariance (ancova), multiple linear regression and multiple logistic regression to assess how stream habitat structure, stream chemistry, aquatic invertebrate abundance and the occurrence of river birds were affected by land use after accounting for altitudinal pattern.

3. Streams draining terraced catchments differed significantly in habitat structure from other streams. They had more physical modifications, wider channels, fewer cascades, finer substrata and simpler riparian vegetation with fewer trees. We detected no clear effects of land use on stream chemistry, but terracing was accompanied by significantly increased abundances of benthic dipterans, ephemeropterans and total aquatic invertebrates.

4. River bird occurrence was best explained by altitude, and secondarily by habitat structure. Some of the habitat features influenced by terracing significantly affected birds both positively (grey wagtailMotacilla cinerea) and negatively (little forktailEnicurus scouleri, river chatChaimarrornis leucocephalus, brown dipperCinclus pallasii, plumbeous redstartRhyacornis fuliginosus). However, only in the grey wagtail did the presence of terracingper seaffect occurrence unequivocally; effects on other species were either small or confounded by altitude.

5. We cannot refute the hypothesis that catchment land use affects Himalayan river ecology, but our data on the regional consequences for river birds were equivocal. We suggest that large‐scale surveys, although providing one of the few pragmatic methods of assessing large anthropogenic effects on ecosystems, will need careful design to factor out potential confounds if they are to be used to test hypotheses robustly. They should also be supported where possible with process studies, intervention studies and model applications to independent data.
Biological control using sterilizing viruses: host suppression and competition between viruses in non‐spatial models
Authors: Hood G.M. , Chesson P. , Pech R.P.
Published: March 2003

1. Research is currently underway to develop genetically engineered viruses that can sterilize pest animals. The technique, known as viral‐vectored immunocontraception (VVIC), promises to control mammalian pests such as the European rabbit, the house mouse and domestic cats.

2. Using host–parasite models we explored the degree of control of the host population that can be attained when hosts that recover from infection become permanently infertile. The models assume some demographic compensation for reduced fertility in the host population, and are tailored to address issues raised by the use of the myxoma virus as an agent to sterilize rabbits. A ‘pay‐off’ function is developed, which defines the degree to which host density is suppressed by a sterilizing agent.

3. The results show that sterilizing viruses can reduce host abundance, and that hosts with low birth rates and moderate mortality rates are the best targets for VVIC. High transmissibility increases the pay‐off from VVIC, but because virulent parasites kill most of the hosts that they infect, the pay‐off is highest if benign parasites are used as the vector of contraceptive antigens. We argue that appropriate pay‐off functions should be developed as a basis for research and development on genetically modified organisms.

4. The host–parasite models are extended to include a competing strain of virus that does not sterilize the host. We analysed these models using a general approach to the analysis of competition, which has not often been applied to epidemiological models. The extended model shows that host sterilizationper sedoes not affect the competitive ability of viruses, a result that applies to a broad class of models in which the per capita growth rates of competing parasites are linear functions of limiting competitive factors.
Bee diversity along a disturbance gradient in tropical lowland forests of south‐east Asia
Authors: Liow Lee Hsiang , Sodhi Navjot S. , Elmqvist Thomas
Published: March 2003

Bees are believed to be dominant pollen vectors in tropical forests, yet studies specific to bees in south‐east Asia are rare. Regeneration and restoration of the rapidly disappearing lowland forests of this region are reliant on bees, thus there is an urgent need for forest bee data at the community level.

 Bee communities of eight forested sites in Johor (Malaysia) and Singapore were surveyed three times each from February to August 1999 at the below‐canopy level. These sites ranged from relatively undisturbed primary lowland dipterocarp forests to late secondary forests and exotic forests, including an oil palm plantation. We attempted to elucidate the environmental factors that correlated with the distribution of bees.

 Bee abundance, in particular that of Apidae, was significantly higher in larger primary forests than other types of forests. However, bee species richness was higher in disturbed forests.

 The distribution of bees was apparently influenced by variables closely related to forest disturbance and resource abundance, such as the density of big trees (diameter at breast height 30–40 cm), temperature and flowering intensity of trees and shrubs.

 More stingless bees (Trigona spp.) were found where trees were larger and ambient conditions more constant but flowering intensities lower.

 The differences between the bee communities in forests of urban Singapore and primary forests in Johor may indicate that ecological processes in the forests of Singapore, in particular pollination, may be changing. However, pollination may not be totally intact in the primary forests surveyed, as their bee communities seemed to be depauperate.

 The role of important pollinators, especially bees, for the long‐term survival of tropical lowland forests is poorly understood. Our study indicates that we urgently need more thorough understanding of pollination and pollinators, as some bee species appear to be disappearing from disturbed tropical lowland forests.
Meadow pipits, red grouse and the habitat characteristics of managed grouse moors
Authors: Smith A.A. , Redpath S.M. , Campbell S.T. , Thirgood S.J.
Published: March 2003

The abundance of meadow pipits appears to be a good indicator of the breeding density of hen harriers on moorland managed for red grouse in Scotland. High densities of hen harriers can limit grouse populations at low density and reduce shooting bags, with repercussions for grouse moor management and conservation. We therefore examined the habitat characteristics of managed grouse moors, asking whether changes in vegetation could alter the ratio of pipits, and thus harriers, to grouse.

We examined grouse abundance and habitat on 69 sites of 1 km2 in upland Britain, of which pipit abundance was studied on 36. Similar data were collected on 73 sites of 25 ha within the Langholm estate in south‐west Scotland, in order to make a within‐estate and among‐moor comparison.

The distribution of pipit abundance on the Langholm estate was similar to that seen in the extensive among‐moor study. Pipit and grouse abundance were related to habitat in similar ways in the two data sets.

Pipits were the most frequent passerine, but their abundance was not related to grouse abundance. Pipit abundance declined with increasing muirburn and heather, but increased with grass cover. In a linear regression model Calluna, Sphagnum and muirburn cover accounted for 42% of the variation in pipit abundance across Britain.

Grouse abundance was influenced by the regional location of the grouse moor and to a lesser extent by its altitude. There were more grouse on English moors with less patchy habitats. Bird species declined with increasing Calluna and Sphagnum cover and habitat patchiness. Bird species diversity increased from west to east and on moors with more muirburn.

This study provides evidence that meadow pipits are influenced by habitat characteristics on moorland managed for grouse. This work also illustrates how habitat management may be able to mitigate human–wildlife conflicts: long‐term increases in heather cover and management of this habitat by muirburn on grouse moors may reduce pipit numbers and thus reduce the ratio of hen harriers to grouse. However, the effects of such vegetation change on other components of the upland bird assemblage requires further investigation.
Predation on livestock by an expanding reintroduced lynx population: long‐term trend and spatial variability
Authors: Stahl P. , Vandel J.M. , Herrenschmidt V. , Migot P.
Published: March 2003

In recent decades, the Eurasian lynxLynx lynxhas recolonized former habitat, bringing it into potential conflict with livestock. We studied the spatial and temporal distribution of lynx attacks on sheep in the French Jura between 1984 and 1998, during and after its population expansion. We estimated the local and regional impact of lynx predation on livestock.

The number of attacks increased from three in 1984 to 188 in 1989, concurrently with the colonization of the main sheep range by lynx. During subsequent years, 66–131 attacks were recorded annually (92–194 sheep killed per year).

On average, 1·6 sheep were killed per attack. Lynx preyed disproportionately on lambs and subadult sheep. A small percentage of flocks (9·5–22·9%) were attacked, most of which (75·2%) were attacked once or twice a year. At the regional level, annual sheep losses to lynx were 0·14–0·59% of the total number of sheep.

The major lynx–livestock problem was due to clustered attacks in a few small areas. Each year, two to six ‘hot spots’ (33–69% of the attacks) were identified. Hot spots covered 0·3–4·5% of the total area where attacks occurred (1835–4061 km2). Roe deer abundance was higher in hot spots and, even here, sheep only made up 3·1% of the lynx diet. These data show that lynx were not killing sheep due to shortages of alternative prey or in response to an increased need for food when rearing young.

The concentration of hot spots in only nine small areas between 1984 and 1998 indicated that only a few individual lynx were involved. The reappearance of hot spots at the same sites, after years of interruption and despite the removal of lynx, suggested that the ultimate factors causing hot spots were factors inherent to those sites. Further investigation is needed to identify causal factors with a view to eliminating them. These may relate to landscapes features, animal husbandry practices or the behavioural ecology of lynx.

In future, where large predator reintroductions are planned, the potential for concentrated, localized, impact should be evaluated and mitigation measures put in place. For scattered and episodic lynx damage, financial compensation is the only realistic option at present. In hot spots, the cost‐effectiveness of guard‐dogs or the selective removal of some individual lynx should be evaluated.
The selection of stubble fields by wintering granivorous birds reflects vegetation cover and food abundance
Authors: Moorcroft D. , Whittingham M. J. , Bradbury R. B. , Wilson J. D.
Published: March 2003

Fields left fallow after harvest (i.e. stubble fields) support high wintering densities of many species of granivorous bird. We examined correlates of use by eight such species of different types of intensively managed wheat and barley stubble fields, organic wheat fields and set‐aside fields on mixed lowland farmland in central England. Field occupancy was studied in relation to the physical characteristics of fields and seed abundance.

 Higher seed abundance was associated with greater occupancy by linnet Carduelis cannabina, grey partridge Perdix perdix, chaffinch Fringilla coelebs, yellowhammer Emberiza citrinella, reed bunting Emberiza schoeniclus and corn bunting Miliaria calandra. Larger areas of bare earth within stubble fields were associated with greater occupancy by linnet, yellowhammer, reed bunting and corn bunting, but lower occupancy by woodpigeon Columba palumbus.

 On conventional intensively farmed sites, seed abundance and area of bare earth were significantly greater on barley stubbles than on wheat stubbles.

 Seed numbers fell throughout the winter in all stubble types, although reductions were greatest on intensive barley stubbles, intermediate on intensive wheat stubble and lowest on undersown organic wheat stubbles.

 Within fields occupied by linnets, areas used for feeding had significantly greater quantities of seeds known to be important in their diet. Feeding areas also had a greater area of bare earth than randomly selected ‘non‐feeding areas’.

 Linnets and reed buntings were rarely found on fields where densities of weed seeds important in their diets fell below 250 seeds m−2. In autumn, yellowhammers and grey partridges rarely fed on fields where cereal grain density was below 50 m−2. However, in spring, both species fed on these fields irrespective of grain density, perhaps indicating a switch to other food sources.

 We suggest that land managers wishing to maximize the value of overwinter stubble fields for granivorous birds locate such fields where there is a substantial natural regeneration of weed flora and where previous cropping (e.g. barley) is likely to offer a sparse stubble with substantial areas of bare ground.
Opposing functional effects of cyclic GMP and cyclic AMP may act through protein phosphorylation in rabbit cardiac myocytes
Authors: Yan L. , Lee H. , Huang M. W. , Scholz P. M. , Weiss H. R.
Published: March 2003

1 We tested the hypothesis that the negative functional effects of cyclic GMP (cGMP) oppose the positive effects of cyclic AMP (cAMP) in cardiac myocytes through interaction at the level of their respective protein kinases.  2 Cell shortening was studied using a video‐edge detector. The O2 consumption of a suspension of rabbit ventricular myocytes was measured using O2 electrodes. Protein phosphorylation was measured autoradiographically following SDS‐PAGE. Data were collected with: (1) 8‐bromo‐cGMP (8‐Br‐cGMP) 10−7 or 10−5
m; (2) 8‐bromo‐cAMP (8‐Br‐cAMP) 10−7 or 10−5
m; (3) 8‐Br‐cAMP 10−5
m followed by 8‐Br‐cGMP 10−7 or 10−5
m; (4) 8‐Br‐cGMP 10−5
m followed by 8‐Br‐cAMP 10−7 or 10−5
m; (5) 8‐Br‐cGMP 10−7 or 10−5
m followed by KT 5720 (cAMP‐dependent protein kinase inhibitor) or KT 5823 (cGMP‐dependent protein kinase inhibitor) 10−6
m; and (6) 8‐Br‐cAMP 10−7 or 10−5
m followed by KT 5720 or KT 5823 10−6
m.  3 8‐Br‐cGMP 10−5
m decreased percent shortening (Pcs) from 6.3±0.6 to 3.6±0.4% and rate of shortening (Rs) from 66.7±4.4 to 41.8±4.2 μm s−1. 8‐Br‐cAMP 10−5
m increased Pcs (from 3.7±0.2 to 4.8±0.2) and Rs (from 50.0±3.0 to 60.0±3.1). With 8‐Br‐cAMP 10−5
m, 8‐Br‐cGMP 10−5
m decreased Pcs and Rs less. The positive functional effects of 8‐Br‐cAMP 10−7 or 10−5
m were also diminished with 8‐Br‐cGMP 10−5
m. Following 8‐Br‐cGMP 10−7 or 10−5
m, KT 5720 10−6
m further decreased Pcs to 2.5±0.3 and Rs to 30.0±4.1. KT 5823 10−6
m returned Pcs to 4.7±0.4 and Rs to 61.3±5.3. Following 8‐Br‐cAMP 10−7 or 10−5
m, KT 5720 decreased the elevated Pcs and Rs significantly and KT 5823 10−6
m further increased these parameters.  4 cGMP and cAMP phosphorylated the same five protein bands. With KT 5720 or KT 5823, all of the bands were lighter at the same concentration of 8‐Br‐cAMP and 8‐Br‐cGMP.  5 We conclude that, in rabbit ventricular myocytes, the opposing functional effects of cGMP and cAMP are related to the interaction at the level of their respective protein kinases.
Functional identification of β3‐adrenoceptors in the guinea‐pig ileum using the non‐selective β‐adrenoceptor antagonist (±)‐bupranolol
Authors: Horinouchi T. , Koike K.
Published: March 2003

1 To clarify whether there is a species difference or a tissue difference in β3‐adrenoceptors, the β3‐adrenoceptors mediating relaxations to catecholamines ((–)‐isoprenaline, (–)‐noradrenaline and (–)‐adrenaline), a selective β3‐adrenoceptor agonist BRL37344 and a non‐conventional partial β3‐adrenoceptor agonist (±)‐CGP12177A (a potent β1‐ and β2‐adrenoceptor antagonist with a partial β3‐adrenoceptor agonist property) were investigated in the guinea‐pig ileum.

2 Catecholamines and β3‐adrenoceptor agonists induced concentration‐dependent relaxations of pre‐contracted strips of the guinea‐pig ileum. The rank order for their relaxing potency was (–)‐isoprenaline (pD2: 7.60) > BRL37344 (7.05) > (–)‐noradrenaline (6.38) > (±)‐CGP12177A (6.25) > (–)‐adrenaline (6.07).

3 In the presence of the non‐selective β1‐ and β2‐adrenoceptor antagonist (±)‐propranolol (1 μM), only small rightward shifts of the concentration–response curves (CRCs) to these agonists were observed and the rank order of potency of agonists was BRL37344 (pD2: 7.00) > (±)‐CGP12177A (6.17) > (–)‐isoprenaline (6.01) > (–)‐noradrenaline (5.69) > (–)‐adrenaline (5.41).

4 In the presence of (±)‐propranolol (1 μM), the additional presence of (±)‐bupranolol (3–30 μM), a non‐selective β1‐, β2‐ and β3‐adrenoceptor antagonist, caused a concentration‐dependent rightward shift of the CRCs to catecholamines and β3‐adrenoceptor agonists. Schild plot analyses of (±)‐bupranolol against these agonists gave pA2 values of 6.02 ((–)‐isoprenaline), 6.03 ((–)‐noradrenaline), 6.01 ((–)‐adrenaline), 6.56 (BRL37344) and 5.74 ((±)‐CGP12177A), respectively. All Schild plot slopes were not significantly different from unity. The pA2 values of (±)‐bupranolol obtained for the guinea‐pig β3‐adrenoceptors were about one log unit less than the values obtained for the rat β3‐adrenoceptors and about two log units less than the values obtained for dog β3‐adrenoceptors.

5 These results confirm that functional β3‐adrenoceptors are present in the guinea‐pig ileum and that the relaxations of these agonists are mainly mediated via β3‐adrenoceptors in this tissue. The differential antagonistic potency of (±)‐bupranolol may suggest that there is a species difference between the three species (guinea‐pig, dog and rat) in their β3‐adrenoceptors.
The effects of thiol compounds and ebselen on nitric oxide activity in rat aortic vascular responses
Authors: Kim H. R. , Kim J. W. , Park J. Y. , Je H. D. , Lee S.‐Y. , Huh I. H. , Sohn U. D.
Published: March 2003

1 Thiols have been implicated to play a role in a variety of aspects of nitric oxide (NO) generation and activity. Thiol dependence of nitric oxide synthase (NOS) has remained controversial and its mechanism is not clear. This study investigates possible mechanisms between thiol (SH group) and NOS activation, through thiol compounds (glutathione, dithiothreitol, N‐acetyl‐L‐cysteine) and Ebselen [2‐phenyl‐1,2‐benzisoselenazole‐3(2H)‐one] on rat aortic vascular responses.

2 In rat thoracic aorta, acetylcholine (10–6–10–9 M) induced a relaxation of phenylephrine (PE) (10–7 M)‐induced tone, which was inhibited dose dependently by increasing concentration of ebselen (1–10 μM).

3 In rings of rat thoracic aorta, ebselen and NOS inhibitors (NG‐monomethyl‐L‐arginine, NG‐nitro‐L‐arginine methyl ester) produced an augmentation of phenylephrine (10–7 M)‐ induced tone and acetylcholine induced a relaxation of PE (10–7 M)‐induced tone in rat thoracic aorta, which was inhibited by ebselen (10 μM) like NOS inhibitor.

4 The thiol compounds (glutathione, dithiothreitol, and N‐acetyl‐L‐cysteine) alone did not change vascular tone in rat thoracic aorta. Pretreatment with thiol compounds before ebselen treatment, however, reversed the inhibitory effect of ebselen which acts like the NOS inhibitor in rat thoracic aorta. Posttreatment with thiol compounds after ebselen treatment did not reverse the inhibitory effect of ebselen by as much as pretreatment.

5 Calcium ionophore A23187 (10–7 M)‐induced vasodilation was inhibited in ebselen pretreated rat thoracic aorta, but sodium nitroprusside (SNP, 10–7 M)‐induced relaxation was not inhibited by ebselen. This suggests that NOS is involved in the inhibitory effect of ebselen on rat thoracic aorta relaxation.

6 These results suggest that ebselen exerts an inhibitory action on the nitric oxide synthesis in rat thoracic aorta by interacting with thiol groups.