bluuebunny/crossref_metadata_2025 huggingface dataset:
Density‐dependent life histories in female bank voles from fluctuating populations
Authors: TKADLEC EMIL , ZEJDA JAN
Published: March 2003

Using long‐term data sets from two lowland floodplain forest bank vole populations in central Europe, we tested two predictions that with increasing densities: (i) proportions of nonparous females in winter populations would increase; and (ii) age of both nonparous and parous females would increase. These two predictions follow from the assumption that changes in age structure are driven by density‐dependent shifts in age at first reproduction. Both populations were sampled by snap trapping between 1956 and 1976.

For each year, we examined samples of animals collected between November and April for proportions of females with and without breeding experience and analysed their variation in age relative to the population density. The presence or absence of placental scars was used to discriminate between the parous and nonparous animals. Age was determined by measuring the length of the first mandibular molar (M1) roots.

Both populations exhibited multi‐annual fluctuations in numbers closely resembling those in northern Fennoscandia. The proportion of nonparous females in our total sample was 0.73, suggesting that it is uncommon for parous female bank voles to breed in two successive years and that their life histories are largely designed for breeding in one season only as a major reproductive strategy.

Using a logistic‐binomial regression model, we found that the probability of females being nonparous or parous at capture varied significantly with time, space and population density. The final model producing the best fit to data predicted that the proportion of nonparous females would be slightly larger over winter and substantially larger after high‐density breeding seasons, which is consistent with the tested prediction.

With increasing densities during the breeding seasons, both the nonparous and parous females became older at the onset of winter. Again, the field evidence was consistent with the predicted pattern. The age of parous females in the autumn at high densities was older, mainly because of an increased proportion of females entering their second winter.

We propose a new intrinsic mechanism by which a delayed density dependence in age‐specific fitness components can arise in microtines. This mechanism, based on an increased bimodality in age at first reproduction towards northern latitudes, has a potential to explain the south‐north gradient in cyclicity observed in microtine populations in Fennoscandia.
Resource control by territorial male cichlid fish in Lake Malawi
Authors: Genner Martin. J. , Turner George. F. , Hawkins Stephen. J.
Published: March 2003

1. The rocky habitat communities of Lake Malawi contain a high diversity of ecologically similar, predominantly herbivorous, cichlid fish species. How so many species can coexist is still unknown.

2. Adult males of the majority of these species hold permanent territories which form dense multispecies mosaics across the shores.

3. The study examined six coexisting species of cichlids from the rocky habitat where males are known to control access to the algal food resources within their territorial space. These included four sibling species of the Pseudotropheus (Tropheops) species complex, which are specialized epilithic algal herbivores, and two sibling species of the trophically more generalist P. (Maylandia) species complex which feed upon both epilithic algae and plankton.

4. The hypotheses that both intraspecific and interspecific territoriality occur in these communities and that interspecific aggression initiated by territorial males is preferentially directed at species with the most similar diets to their own were tested.

5. It was found that males preferred to exclude conspecific intruders, while they tolerated intruders with different diets to their own. Also, male P. (Tropheops) preferentially excluded similar heterospecific dietary specialists, while male P. (Maylandia) tolerated similar heterospecific dietary generalists.

6. Based on this study, it is proposed that interspecific territoriality may be reducing competition between species with different diets and promoting their coexistence, while it may be enhancing competition between species with the same diet. Furthermore, it suggests that ecological generalism may be reducing the intensity of interspecific competition, while specializations for the same resources may be increasing competition.
Can population growth rates vary with the spatial scale at which they are measured?
Authors: Steen Harald , Haydon Daniel
Published: March 2003

1. The ratio of successive population censuses is often assumed to reflect population growth rates. We identify three simple potential sources of bias in the estimation of population growth rates that relate to either the total number of censused individuals or the spatial areas over which censuses are conducted.

2. The commonly used method of adding a constant to time series data to avoid problems caused by division by zero can lead to underestimation of growth rates at low densities in increasing populations.

3. Variances associated with density estimates can lead to positive bias in estimation of growth rates when populations are distributed in ephemeral patches. The spatial variance and spatio‐temporal covariance in bank vole census data suggest that this bias could be severe when small trapping grids are used. Use of logged estimators of growth rate avoids this problem.

4. Using census data from non‐randomly placed trapping grids that are smaller than twice the maximum range of natal dispersal to estimate population growth rates can lead to negatively biased estimates, particularly at low population densities.

5. These three sources of bias are evaluated as explanations for scale‐dependent changes in the estimates of growth rates identified in populations of snowshoe hare (Lepus americanus), bank voles (Clethrionomys glareolus) and lemmings (Lemmus lemmus).
Weather‐mediated regulation of olive scale by two parasitoids
Authors: Rochat Jacques , Gutierrez Andrew Paul
Published: March 2003

The effects of temperature and interspecific competition among two parasitoids (Aphytis maculicornis (=paramaculicornis) (Masi)–Coccophagoides utilis Doutt) of the olive scale (Parlatoria oleae (Colvée)) were examined, and the reason for the successful biological control of olive scale explained.

 An age‐structure distributed maturation time model of this system was developed that simplifies many of the details of prior physiologically based models.

 Temperature‐dependent physiological indices were used to scale fecundity and survivorship rates from their maximum values.

 The distributed maturation time population dynamics model captured the variance in temperature‐related development times required to simulate the dynamics of the system.

 A type III ratio‐dependent functional response was used to estimate parasitism rate on olive scale and also served to stabilize our single patch model.

 The model confirms the Huffaker & Kennett (1966) conclusions concerning the role of weather and the relative contribution of the two parasitoids in the regulation of olive scale in California olive.
Maternal effects and the stability of population dynamics in noisy environments
Authors: Benton Tim G. , Ranta Esa , Kaitala Veijo , Beckerman Andrew P.
Published: March 2003

It is widely appreciated that complex population dynamics are more likely in systems where there is a lag in the density dependence. The transmission of maternal environmental conditions to offspring phenotype is a potential cause of such a lag. Maternal effects are increasingly found to be common in a wide range of organisms, and might thus be a frequent cause of nonequilibrium population dynamics.

We show that a maternal effects’ lag generally increases population variability. This may result from the lag inducing cycles (or more complex dynamics) in a deterministic environment or, in a stochastic environment, from the lag interacting with environmental noise to produce more variable dynamics than would otherwise occur. This may happen whether the underlying dynamics are equilibrium, periodic or more complex.

Although maternal effects may generally destabilize dynamics there are a clear set of exceptions to this. For example, including a maternal lag may convert cycles to equilibrium dynamics, which may revert to cycles when external noise is added.

The influence of the maternal effect depends importantly on the details of the model, whether it is structured or unstructured, the life‐history traits which are maternally affected, and the type of density dependence.

Our results indicate that, if maternal effects are possible, failure to include them in models used predictively may result in quantitatively, and perhaps qualitatively, poor predictions.
The cleaner wrasse, Labroides dimidiatus, is a key organism for reef fish diversity at Ras Mohammed National Park, Egypt
Authors: Bshary Redouan
Published: March 2003

In marine cleaning symbioses, small fish or shrimps remove ectoparasites and other material from cooperating ‘client’ fish. Until now, there has been conflicting evidence with respect to the importance of cleaning for client health and in particular with respect to the impact of cleaning organisms on local fish diversity.

Data are provided on the impact of the cleaner wrasse Labroides dimidiatus on reef fish distribution at Ras Mohammed National Park, Egypt. During four field seasons, I regularly sampled fish species composition in 46 reef patches. Natural fluctuations in cleaner fish presence or absence at these reef patches allowed me to assess how this variable correlates with reef fish diversity. In addition, cleaner fish were removed experimentally from some reef patches and added at others to test whether the presence or absence of cleaner fish causes changes in fish diversity.

Both cleaner fish disappearance and cleaner fish removal had no immediate effects on fish abundance, i.e. within the first few weeks. A significant decline in fish diversity was only detectable after 4–20 months.

In contrast, cleaner immigration or experimental addition led to a significant increase in fish diversity within the first few weeks.

Generally, effects were most pronounced for client species that visit reef patches and soon move off again, and less pronounced (but still significant) for resident clients that do not move between reef patches. Surprisingly, the presence or absence of cleaner fish also affected the distribution of resident fish that hardly ever interact with them.

This study demonstrates that cleaner fish are a key organism for local reef fish diversity.
Population dynamics of the Mongolian gazelle Procapra gutturosa: an historical analysis
Authors: Milner‐Gulland E.J. , Lhagvasuren Badamjavin
Published: March 2003

1.  The Mongolian gazelle Procapra guttorosa is legally hunted, but has no scientifically‐based management strategy. It has suffered a range contraction in recent years, but the reasons for this are unclear. This paper addresses both of these issues.

2.  The available data on the population dynamics and human influences on the Mongolian gazelle are presented and evaluated. Districts which currently contain Mongolian gazelles had a significantly lower human population density in 1969 than those which no longer contain gazelles.

3.  A discrete‐time age‐ and sex‐structured model is developed for the Mongolian gazelle. The model includes stochastically determined mortality rates, depending on whether the winter is harsh and/or the summer has a disease epidemic. The model results suggest that given the poor data available, a relatively safe strategy for managers, producing reasonable yields, would be to hunt at a low hunting mortality rate, taking up to 6% of the population each year, while selecting strongly for males.

4.  A simpler lumped‐parameter model is developed using the climate and disease‐determined rates of population increase derived from the age‐ and sex‐structured model. Comparison between the two models shows that the lumped parameter model is an adequate simplification of the age‐ and sex‐structured model, although it underestimates equilibrium population sizes somewhat.

5.  The simplified model is used to investigate the available data on the Mongolian gazelle. It is shown that the population must have been larger than previous estimates in order to have sustained the level of recorded hunting over the last 64 years.

6.  The model suggests that the population declined rapidly from 1979 to 1986, then stabilized. Variation in natural mortality rates has had an effect on the rate of decline since 1932, but recorded hunting has not. It is not possible to tell whether the rates of unrecorded hunting or habitat degradation have changed since 1932. The results are robust to parameter variation.
Traditional farming and key foraging habitats for chough Pyrrhocorax pyrrhocorax conservation in a Spanish pseudosteppe landscape
Authors: Blanco Guillermo , Tella JosÉ L. , Torre Ignacio
Published: March 2003

1.  Agricultural land devoted to low‐intensity practices supports many declining bird species in Europe. The potential effects of intensification or abandonment of traditional farming practices are assessed from the point of view of the conservation of the chough Pyrrhocorax pyrrhocorax.

2.  The study was conducted in Los Monegros (north‐east Spain), in a pseudosteppe landscape of special relevance for this species. In this area traditional farming survives in the form of low‐intensity arable systems including fallowing and extensive sheep grazing.

3.  Foraging choughs showed a strong selection for field margins, avoided any remnant of the original scrubland and halophitic vegetation, and utilized other habitats maintained by traditional crop rotation (e. g. fallow, stubble) at different times of the year.

4.  A highly complex pattern of habitat selection was found which was not only related to seasonal changes in habitat availability, but also differed between territorial pairs and the non‐breeding population. This emphasizes the importance of taking all the different components of bird populations into account when analysing interactions between habitat selection and the annual farming cycle.

5.  Chough habitat selection suggests that both agricultural intensification and land abandonment would have detrimental consequences for this species in Los Monegros. The maintenance of traditional farming is recommended, especially by promoting the use of long fallow rotations grazed extensively by livestock, encouraging the increase of grassland edges around landholdings and sand roads, and maintaining a low input of biocides. These management measurements could also favour most other endangered species of steppe birds, and could be supported by the establishment of Zonal Programmes under the CAP Agri‐Environment Regulation (2078/92).
Using species abundance models as indicators of habitat disturbance in tropical forests
Authors: Hill Jane K. , Hamer Keith C.
Published: March 2003

1. In temperate communities, species abundance distributions have been used to detect ecosystem disturbance: in undisturbed habitats, distributions are claimed to generally fit log‐normal models, whereas in disturbed habitats, distributions fit log‐series models.

2. There is a growing literature on the effects of habitat disturbance in tropical ecosystems and several studies suggest that species abundance models may be useful in detecting disturbance, although data are lacking.

3.
Nummelin (1998) claims that these models are not universal indicators of forest disturbance, but we highlight a number of problems with the data presented in Nummelin's study and conclude that it is too soon to dismiss these models. We discuss several important points arising from Nummelin's study which need to be considered if species abundance models are to be used appropriately.
Identifying trends in land degradation in non‐equilibrium rangelands
Authors: Pickup G. , Bastin G. N. , Chewings V. H.
Published: March 2003

1. Change in environmental conditions in the complex non‐equilibrium rangelands of arid Australia is difficult to monitor. We show how trends in rangeland condition can be identified from changes over time in the pattern of vegetation growth across gradients of differing grazing intensity.

2. Grazing intensity was measured indirectly using distance from water. Vegetation growth was derived from remotely sensed vegetation index values before and after large rainfalls. The amount of growth was adjusted for initial vegetation cover to give a standard measure of vegetation response.

3. A vegetation response ratio was derived by comparing areas less than 4 km from water with benchmark areas further away. Systematic changes in this ratio over time indicate a trend.

4. Ratio values from test areas suggested decline, improvement and no change, consistent with recent management history.

5. The method can be applied where the whole area is affected by grazing and relatively pristine benchmarks are unavailable. It could therefore be useful in the semi‐arid rangelands where paddocks are smaller than in the arid part of Australia. It also has possible uses in the rangelands of Africa and the Americas. There is potential for applying the method to traditional grazing systems as well as to commercial pastoralism.

6. The method is cheaper and more effective than other techniques and increases the capacity of grazing gradient‐based monitoring schemes for arid and semi‐arid areas.
Macroinvertebrate distributions and the conservation value of aquatic Coleoptera, Mollusca and Odonata in the ditches of traditionally managed and grazing fen at Wicken Fen, UK
Authors: Painter Duncan
Published: March 2003

1. Water‐filled ditches are an important ecological feature of lowland Britain. Originally dug to facilitate wetland drainage, ditches often provide refuges for aquatic flora and fauna of high conservation value.

2. The ditches, ponds and major waterways of a traditionally managed undrained fen and the ditches of a previously drained cattle‐grazed fen meadow were sampled at Wicken Fen National Nature Reserve for Coleoptera, Mollusca and Odonata, and for physical, chemical and biological variables.

3. Multivariate analysis showed a clear division between ditches on the two fens, and between larger and smaller waterbodies.

4. Individual ditches possessed distinctive faunas. Ditch age and bank profile were important factors influencing faunal species composition.

5. Invertebrate distributions were shown to be significantly correlated with macrophyte distribution.

6. Waterbodies were ranked in terms of their species quality, using a point‐scoring system; there was no correlation between rankings for the three invertebrate groups; only ditch age and detritus levels were correlated with species quality score (for Coleoptera).

7. Ditch management recommendations are discussed in the light of these results.
Breeding success and causes of breeding failure of curlew Numenius arquata in Northern Ireland
Authors: Grant Murray C. , Orsman Chris , Easton Jon. , Lodge Chris , Smith Malcolm , Thompson Guy , Rodwell Stephen , Moore Niall
Published: March 2003

1. The present study investigated breeding success and causes of breeding failure of curlew, a species for which the UK holds internationally important breeding numbers. Studies were undertaken between 1993 and 1995 in two areas of Northern Ireland, where the species’ breeding range has recently contracted and breeding numbers are declining. Avian nest predators were abundant in both areas, whereas foxes were abundant on the Antrim study area but generally were absent from the Lough Erne study area, which was mainly islands.

2. Productivity was estimated to be 0·14–0·26 fledglings per pair in Antrim and 0·20–0·47 fledglings per pair on Lough Erne. These figures are lower than most estimates of productivity from other studies of breeding curlew. The differences between the recorded productivity levels and those estimated to be required to maintain a stable population are sufficient to account for the observed decline in Northern Ireland's breeding curlew population.

3. Predation was the main proximate cause of breeding failure, with nest predation being of most importance in reducing productivity. Only 3·6–19·0% of all nests hatched on each study area in each year, with nest predation accounting for 85–97% of failures. Survival of chicks from hatching to 31 days of age was 38·5% in Antrim and 19·1–29·2% on Lough Erne. Predation accounted for 74% of chick mortality.

4. Nest failure rates were not related to the vegetation height around nests nor to clutch laying date on either study area. They differed among the islands and one shoreside site on Lough Erne. Almost all nest predation on Lough Erne was attributable to avian predators, but in Antrim foxes probably accounted for most nest predation. The likelihood of predation on chicks was not related to their hatching date, hatching weight or body condition.

5. The results from this study suggest that predation rates on curlew nests in Northern Ireland may have increased in recent decades. Levels of predator control in Northern Ireland have declined but there have also been considerable changes in land‐use that could benefit generalist predator species or increase the vulnerability of curlew nests to predation. It is recommended that large‐scale trials of legalized predator control and land‐use manipulation should be undertaken to identify appropriate conservation management methods.
Restoration of ecosystem function in an abandoned sandpit: plant and soil responses to paper de‐inking sludge
Authors: Fierro Alejandro , Angers Denis A. , Beauchamp Chantal J.
Published: March 2003

1. In minesoil reclamation, the establishment of a sustainable plant cover requires the improvement of limiting conditions and the re‐initiation of carbon (C) and nutrient cycling.

2. The approach used in this study for reclaiming an abandoned sandpit in Quebec, Canada, was based on a heavy organic amendment as an attempt to accelerate the reconstruction of a functional ecosystem.

3. The one‐time intervention consisted of incorporating paper de‐inking sludge into soil at two rates (0 and 105 dry t ha–1), supplemented with nitrogen (N) at three rates (3, 6 and 9 g kg–1 sludge) and phosphorus (P) at two rates (0·5 and 1·0 g kg–1 sludge) followed by seeding (mid‐summer) of Agropyron elongatum (Host) Beauv. (tall wheatgrass).

4. Standing biomass increased in the presence of sludge after both the first and second full growing seasons. High N application rates further increased yield, more importantly in the second season. The high P rate improved grass establishment in all cases. Ground cover increased with time and doubled in the presence of sludge whereas it declined in the absence of sludge. Phosphorus and N uptake was improved consistently in the presence of sludge.

5. Sludge application resulted in improved water retention and cation exchange capacities, and an increase in pH and bulk density of sandpit minesoil, all of which may have accounted for the significant improvement in plant responses. Levels of soil C and N suggest that this reconstructed system is approaching sustainability.

6. Adequate N and P supplements will accentuate the positive influence of sludge on revegetation.
The persistence of a SIS disease in a metapopulation
Authors: Foley Janet E. , Foley Patrick , Pedersen Niels C.
Published: March 2003

1. Deterministic models predict that susceptible‐infective‐susceptible (SIS) disease, where there is no immunity to reinfection following recovery, will become infinitely persistent in a host population. We explored the incorporation of stochasticity into SIS models; modelled interacting host‐disease agents in metapopulations; and examined model predictions in a real system involving viral infection in domestic cats.

2. SIS models incorporating stochasticity predicted that disease persistence would be finite and dependent on the host population size, provided the host population was isolated. However, the disease may persist by dynamic spread among interacting host metapopulations.

3. Feline enteric coronavirus (FECV) dynamics in domestic cats were well predicted by stochastic metapopulation models.

4. The models we present are mathematically tractable, generalizable, and mechanistically realistic. The findings from the cat‐virus system are immediately applicable to the management of cattery populations and could be adapted to inform eradication programmes for other infectious diseases in animal and human populations. The most practical methods to eradicate feline enteric coranovirus would be to remove small catteries (islands) from interactions with large catteries (mainlands) and to convert mainlands to islands by depopulation.
Age structure and density of red‐capped robin populations vary with habitat size and shape
Authors: Major Richard E. , Christie Fiona J. , Gowing Greg , Ivison Tessa J.
Published: March 2003

1. In order to determine the influence of habitat shape on aspects of the population dynamics of birds, 196 male red‐capped robins Petroica goodenovii were surveyed using song playback in large non‐linear woodland remnants and linear roadside remnants in the wheatbelt of south‐eastern Australia.

2. The average density of male robins was significantly higher in large non‐linear remnants [0·86 ± 0·09 (SD) birds ha–1] than in small linear remnants [0·35 ± 0·16 (SD) birds ha–1].

3. Red‐capped robins exhibit delayed plumage maturation, and 14% of the males captured were yearlings. This percentage was significantly higher in roadside remnants (20%) than in large, non‐linear remnants (8%).

4. These results indicate that different population processes are occurring in the individual remnants and the dynamics of the metapopulation are potentially complex.

5. Land managers must not focus excessively on wildlife corridors (narrow, linear habitats) at the expense of appropriate management and restoration of large areas of native vegetation.
Can population surveys show if the Mediterranean monk seal colony at Cap Blanc is declining in abundance?
Authors: Forcada Jaume
Published: March 2003

1. The Mediterranean monk seal is an endangered marine mammal with only a few populations thought to be viable. The largest aggregation of this species is found at the Peninsula of Cap Blanc, on the western Sahara, where a colonial structure is maintained. The size of this colony is estimated by annual capture–recapture surveys, but it is unclear if the attained level of precision is enough to detect changes in numbers in the short term.

2. In this study, simulated capture–recapture experiments were used to investigate the relationship between population estimates and abundance. The statistical power necessary to detect a population decline with ongoing surveys was estimated, and the requirements for an improvement in precision were evaluated. Additionally, changes in abundance over consecutive surveys were examined for comparison with an alternative method of Bayesian inference.

3. Results indicated that the power to detect trends from the actual surveys was lower than should be required for the conservation of a small population, such as the colony at Cap Blanc. A 5% annual rate of decline in abundance would only be detected with high power after 12 years, with a population of 317 seals being reduced to 172. If the annual rate of decline was 10%, 8 years would be required to detect a reduction of 317 to 136 seals.

4. Capture–recapture surveys can produce reliable data but do not identify moderate or low population declines. The increase in precision of surveys is costly and time consuming, and other monitoring methods are needed to detect early signs of a decline. Bayesian methods cannot provide a better result because they are not robust to small sample size and heterogeneity in capture probabilities. Despite the need for alternative methods for earlier detection, capture–recapture surveys are still required to estimate the size of the colony, and precision in population estimates can be evaluated in relation to cost effectiveness.
Impact of the Onopordum capitulum weevil Larinus latus on seed production by its host‐plant
Authors: Briese D.T.
Published: March 2003

1.
 The impact of the oligophagous capitulum weevil Larinus latus on seed production by its host Onopordum species was studied in its native range in order to assess its potential as a biological control agent of these thistles in Australia.

2.
 Field surveys in Greece during 1988–89 showed a strong positive relationship between attack levels of L. latus and seed destruction in Onopordum species Differences in attack levels were found between populations of different species, with heavier attack on those having larger capitula.

3.
 In the case of O. bracteatum, attack levels attained 100% with total seed destruction. More detailed studies at one location over a full season in 1991 confirmed that L. latus is the dominant capitulum insect, being responsible for the loss of 37% of seed, compared with 8% for the lepidopteran Homeosoma nebulella and 2% for the tephritid fly Tephritis postica.

4.
 A regression surface was produced that estimated seed loss in terms of capitulum size and number of developing L. latus larvae. This provides a tool for measuring overall population seed loss from easily measurable parameters.

5.
 While able to reduce seed production by Onopordum thistles severely in a single season, the longer‐term impact of these weevils on their host‐plant population dynamics may not be as great. Onopordum species have long‐lived seed banks and thus escape in time will dampen the effects of high seed loss in any one year. Moreover, populations of L. latus are themselves subject to density‐dependent regulatory processes that would further buffer the system.

6.
 This weevil was released in Australia in 1992 for the control of Onopordum thistles, and these findings suggest that L. latus would be most effective as part of a complementary guild of biological control agents.
Quantifying changes in abundance of food plants for butterfly larvae and farmland birds
Authors: Smart S. M. , Firbank L. G. , Bunce R. G. H. , Watkins J. W.
Published: March 2003

1. Recent changes in population size of butterflies and farmland birds across north‐west European landscapes have been linked to the effects of agricultural intensification. Reduction in food supply has been postulated as one of the proximal causes of these trends but the generality of this explanation has not been tested at a large scale and across animal species.

2. Changes in abundance of food plants for butterfly larvae and lowland farmland birds in the British countryside were analysed for the period 1978–90 using data from fixed plots recorded as part of the countryside surveys of Britain.

3. Associations were sought between these changes and trends in population size of selected butterflies and birds recorded from long‐term monitoring schemes.

4. No associations were found between change in abundance of food plants and either increasing, stable or decreasing animal groups. At the level of individual animal species, significantly more decreases than increases in food plant frequency were found for herbivorous bird species irrespective of population trend. The size of the reduction in food plant frequency was also significantly greater for the declining bird group than for stable or increasing groups.

5. Few significant associations were detected between population trend and food plant trend for butterfly species. However, the results suggested a positive relationship between increasing butterflies and increased abundance of Elytrigia repens and Urtica dioica.

6. Food plants that increased in abundance comprised species favoured by lack of management and increased nutrient availability. Increases in abundance were also associated with linear landscape features such as hedges and streamsides. Decreasing plant species included arable weeds and stress‐tolerant species typical of unimproved grasslands.

7. Based on evidence of local associations between animal and food plant change and the need for viable populations of food plants to exist within the range of each animal species, we support measures designed to enhance and maintain populations of declining food plants. Much evidence now exists to identify practical measures that husband food resources for many bird and butterfly species. The challenge for conservation policy is to manage their implementation at scales necessary to influence national trends.
Time budgets and foraging of breeding golden plover Pluvialis apricaria
Authors: Whittingham M.J. , Percival S.M. , Brown A.F.
Published: March 2003

1. The golden plover Pluvialis apricaria is of high conservation concern in Europe. Previous studies have concentrated on how birds utilize moorland. We used radio‐telemetry to study their habitat selection and behaviour, during both night and day, in an upland landscape of enclosed fields and moorland in county Durham, UK.

2. During incubation adult golden plover fed principally in enclosed fields 1·1–3·7 km from their moorland nests, but spent less than 5% of their foraging time on moorland. In contrast, birds with broods spent around 85% of their time foraging on moorland.

3. Birds on moorland selected calcareous grassland and avoided old stands of dense tall heather (> c. 12 cm). Younger, shorter (< c. 5–8 cm), sparser heather was used as much as would be expected by chance. Mires of harestail cotton grass Eriophorum vaginatum, the dominant community type when heather Calluna vulgaris is heavily grazed, was selected on both moorland sites.

4. Only 17 of 85 fields in the study area were used for foraging by breeding golden plover. The number of molehills, a reported indicator of earthworm abundance, was the best single variable explaining field choice. Both field size and distance from road had small but significant effects on field choice.

5. We advocate that groups of enclosed fields regularly used by golden plover during the breeding season be afforded specific protection under conservation schemes (e.g. environmentally sensitive area agreements). Conservationists wishing to locate such fields should look for areas with high earthworm populations, as indicated by molehills, close (< 4 km) to breeding populations of golden plover. Rank heather on flat or gently sloping ground should be kept short by appropriate burning or grazing. Areas of calcareous grassland should be preserved.

6. These data illustrate the value of detailed radio‐telemetry in informing equally detailed habitat management for important bird species.
An improved method for the rapid assessment of forest understorey light environments
Authors: Brown Nick , Jennings Steve , Wheeler Phil , Nabe‐Nielsen Jacob
Published: March 2003

1.  The high spatial and temporal variability of forest understorey light environments requires lengthy and/or extensive sampling in order to characterize it by direct measurement. As this is often impractical, a number of surrogate measures have been developed that estimate light availability from assessments of forest canopy structure.

2.
 The subjective crown illumination index developed by Clark & Clark (1992) was compared with Garrison's (1949) moosehorn and two new methods: (i) the crown illumination ellipses method, which compares the size of canopy gaps with a series of standard area ellipses printed on a transparent screen; and (ii) the canopy‐scope that, like the moosehorn, uses an array of 25 dots printed on a transparent screen to assess canopy openness, but is more robust and portable, measuring the largest canopy gap visible from the point of measurement rather than canopy openness overhead.

3.  The new measures were more highly correlated with canopy openness in the range 0–30%, measured from hemispherical photographs, than the crown illumination index, and showed lower levels of between‐observer variability.

4.  The canopy‐scope has the potential to be widely used for the simple and rapid assessment of forest understorey light environments. It has the advantage of giving ratio scale measurements that can be used in parametric statistics. The crown illumination ellipses can be used to score the illumination of crowns that are above head height.
Heterogeneous grazing causes local extinction of edible perennial shrubs: a matrix analysis
Authors: Hunt L.P.
Published: March 2003

Population modelling and field measurements of births, growth and deaths were used to investigate the long‐term change in abundance of Atriplex vesicaria (Chenopodiaceae), a long‐lived, palatable, perennial shrub, under sheep grazing. Of particular interest was whether A. vesicaria is at risk of being eliminated throughout grazed paddocks when the recommended practice of continuous grazing at conservative stocking rates is employed.

Time‐invariant matrix population models indicated that the A. vesicaria population was in decline over much of the study paddock, but the rate of decline was greatest nearer to the water point (population growth rate λ ≈ 0·8). Time‐varying stochastic matrix models projected that the A. vesicaria population would become locally extinct at most sites up to approximately 2200 m from water, occurring first closer to water (within 12–29 years). The population was stable (i.e. λ ≥ 1) at sites greater than 2200 m from water over the projection period of 100 years.

Decreases in adult survival and recruitment made the largest contributions to reductions in the population growth rate. However, there were spatial patterns centred on the water point in the degree to which particular demographic processes contributed to these reductions, because of a grazing gradient and the differential sensitivity of demographic processes to grazing. Thus decreases in recruitment contributed to reductions in the population growth rate at greater distances. Such responses, together with the sensitivity of the population growth rate to these processes, determined the spatial pattern in population growth.

The results suggest that piospheres (i.e. the zone of impact) continue to expand over many years under set‐stocking so that the area around the water point that is devoid of A. vesicaria becomes larger. The process of expansion appears to first involve the inhibition of recruitment, followed by eventual mortality of established shrubs.

The large contribution of adult survival to the population growth rate in A. vesicaria suggests that minimizing the mortality of established adults should be a priority for management. This is likely to involve resting from grazing at critical times such as during extended dry periods. This may also permit increased levels of recruitment during subsequent moister periods.
Sustainable timber harvesting in Venezuela: a modelling approach
Authors: Kammesheidt Ludwig , Köhler Peter , Huth Andreas
Published: March 2003

Reliable data on the growth and yield of logged‐over forest, to determine sustainable cutting cycles, are widely missing for the tropics.

 We used the process‐based model formind2.0 to analyse the growth and yield of logged‐over forest in Venezuela under different logging scenarios over a period of 240 years, and compared results with unlogged stands. The performance of the model was evaluated with a detailed stability and sensitivity analysis.

 In the absence of further logging, the logged‐over stand approached the stand structure of mature forest in terms of bole volume and basal area after about 50–100 years.

 Thirty‐year cutting cycles with conventional logging methods and net extraction volumes of 45 and 60 m3 ha−1 cycle−1 did not provide sustainable yields under either of two minimum felling diameters (35 and 50 cm) that were applied. Only the 60‐year cutting cycle provided sustainable yields under conventional and reduced‐impact logging, with the different minimum felling diameters and a range of net volumes extracted (30–60 m3 ha−1 cycle−1).

 With the longest cutting cycle (60 years), bole volume recovered to levels similar to the mature unlogged stand, but the species composition was very different.

 Scenarios with reduced‐impact logging provided a significantly higher timber volume than under conventional logging. The conservation of forest resources will only be possible with long cutting cycles (at least 60 years) in combination with reduced‐impact logging.
Application of laser scanning cytometry followed by epifluorescent and differential interference contrast microscopy for the detection and enumeration of Cryptosporidium and Giardia in raw and potable waters
Authors: De Roubin M.-R. , Pharamond J.-S. , Zanelli F. , Poty F. , Houdart S. , Laurent F. , Drocourt J.-L. , Van Poucke S.
Published: March 2003

Aims: The main goal of this study was to validate a new laser scanning cytometry method (ChemScanRDI) that couples immunofluorescence detection with differential interference contrast (DIC) confirmation, against manual microscopic enumeration of Giardia and Cryptosporidium (oo)cysts. This study also assessed the basic performance of the new Association Française de Normalisation (AFNOR) NF T 90-455 method for Giardia and Cryptosporidium (oo)cyst enumeration with respect to (oo)cyst yield, linearity, repeatability, influence of turbidity and detection limit in raw and potable waters. Methods and Results: The new standard method relies on cartridge (Envirocheck) filtration, immunomagnetic separation purification, immunofluorescence staining and detection followed by DIC confirmation. The recovery was 30–50% for both parasites at seeding levels from 30 to 230 (oo)cysts. The method is linear from 0 to around 400 seeded (oo)cysts and the yield does not significantly vary for turbidity levels from 10 to 40 Formazin Nephelometric Units (FNU). The results were obtained using manual microscopic enumeration of the (oo)cysts. The ChemScanRDI yielded counts that were at least equivalent to those obtained using manual microscopy for both parasites in raw and potable water concentrates, for seeding levels of 10–300 or 10–100, respectively. The purification and labelling method proposed by the supplier of theChemScanRDI (Chemunex) reached very similar recoveries to the AFNOR protocol (70–86% in both cases). Conclusions: Laser scanning cytometry can be used as a more standardized alternative to manual enumeration as part of the new AFNOR standard method. Significance and Impact of the Study: By using laser scanning cytometry instead of manual microscopy, laboratories could circumvent the limitations of manual microscopy, namely: low sample throughput, operator subjectivity and operator fatigue. The study further supports the drive to incorporate laser scanning cytometry in the standard methods for Giardia and Cryptosporidium enumeration.
Enhancement of acetylcholine‐induced desensitization of guinea‐pig ileal longitudinal muscle in Ca2+‐free conditions
Authors: Horio S. , Nagare T. , Moritoki H.
Published: March 2003

1 To determine the role of cellular Ca2+ in desensitization, acetylcholine(ACh)‐induced desensitization was studied under Ca2+‐free condition in guinea‐pig ileal longitudinal muscle.

2 Pretreatment of the tissue with 10−−4 m ACh (desensitizing treatment) in normal Tyrode solution caused desensitization of the responses both to ACh and histamine. The desensitizing treatment performed in Ca2+‐free solution enhanced desensitization of the responses to ACh and histamine significantly.

3 The desensitizing treatment with ACh caused suppression of the responses to high K+ (tonic component) and Bay K 8644. The desensitizing treatment performed in Ca2+‐free solution potentiated the suppression of the responses to high K+ and Bay K 8644 significantly.

4 ACh‐induced desensitization was enhanced significantly in the presence of a protein kinase C inhibitor, 1‐(5‐isoquinolinesulfonyl)‐2‐methylpiperazine(H‐7, 10−−4m) to a similar extent as desensitization obtained under Ca2+‐free condition, but not in the presence of a non‐specific and less potent kinase inhibitor, N‐(2‐guanidinoethyl)‐5‐isoquinolinesulfonamide hydrochloride(HA1004, 10−−4 m).

5 These results suggested that voltage‐gated Ca2+ channels were involved in ACh‐induced desensitization and that intracellular Ca2+, which was increased during the stimulation with ACh, inhibited desensitization through the activation of protein kinase C. This kinase could have activated or protected Ca2+ channels during the desensitization process to reduce desensitization.
Spontaneous baroreflex sensitivity as a dynamic measure of cardiac anticholinergic drug effect
Authors: Penttilä J. , Vesalainen R. , Helminen A. , Kuusela T. , Hinkka S. , Rahi K. , Kaila T. , Scheinin H.
Published: March 2003

1 In this study, the analysis of spontaneous baroreflex sensitivity (BRS) was applied to the dynamic assessment of cardiac anticholinergic drug effect in healthy male volunteers.

2 The anticholinergic effects of single intravenous (i.v.) injections of atropine (10 μg kg–1), glycopyrrolate (5 μg kg–1) and scopolamine (5 μg kg–1), as well as a 2‐h infusion of glycopyrrolate (5 μg kg–1 h–1) were investigated. Baroreflex sensitivity, a validated measure of cardiac parasympathetic reflex regulation, was repeatedly measured from 5‐min recordings of electrocardiogram (ECG) and continuous blood pressure by using the sequence technique, a method based on detection of spontaneous fluctuations in blood pressure and heart rate.

3 Single injections of atropine, glycopyrrolate and scopolamine decreased the mean BRS by 71 ± 32, 68 ± 23 and 27 ± 45%, respectively, whereas the slow glycopyrrolate infusion gradually decreased BRS (up to 83 ± 11% reduction) and increased both systolic (SAP) and diastolic arterial pressures (DAP) (on an average, by 9 mmHg).

4 During the withdrawal of the parasympathetic blockade (indicated by increasing BRS), the proportion of baroreflex sequences in the recordings increased transiently from 10 up to 20–25%, probably reflecting the restoration of the baroreflex integrity and the baroreflex‐induced attempt to counteract the blood pressure increase.

5 The sequence method to study BRS seems to be feasible in the assessment of cardiac anticholinergic drug effects, and it also provides good time resolution for the dynamic measurements.
The dynamics of plant invasions: a case study of three exotic goldenrod species (Solidago L.) in Europe
Authors: Weber Ewald
Published: March 2003

The patterns of spread of the three exotic species Solidago altissima L., S. gigantea Ait. and S. graminifolia (L.) Salisb. after their introduction to Europe were investigated, based on herbarium specimens and literature records. The spread was analysed by mapping the localities for each decade since 1850. Cumulative numbers of localities as well as numbers of occupied grid squares showed a continuous increase since 1850 for all three species. The slopes, however, were significantly different among the species. Solidago gigantea had the highest colonization rate, followed by S. altissima, and finally S. graminifolia. The latter showed only a slight increase in abundance over time. The increase in diameter of the range in central Europe was logistic for S. altissima and S. gigantea with a rapid increase between 1850 and 1880. The spread of the species in area and time over Europe showed no clear front; new localities at large distances were simultaneously colonized. A large part of the actual range of S. altissima and S. gigantea was already achieved about 1950. It is assumed that the spread of the species followed the hierarchical diffusion model with several independent foci from which the species began to spread. The data suggest that S. altissima and S. gigantea will successfully spread further, leading to an increase in abundance and area, while S. graminifolia seems to spread slowly.