bluuebunny/crossref_metadata_2025 huggingface dataset:
Seed‐crop size and eruptions of North American boreal seed‐eating birds
Authors: Koenig Walter D. , Knops Johannes M. H.
Published: March 2003

Eruptions occur when a species appears in unusually high densities within and often outside of its normal range. We used 30 years of Christmas Bird Counts combined with cone/seed‐crop data on boreal coniferous trees, breeding bird surveys, and weather records to test correlates of winter eruptions by 11 species of primarily boreal North American seed‐eating birds.

 Eruptions of six species in eastern (red‐breasted nuthatch Sitta canadensis L., black‐capped chickadee Parus atricapillus L., evening grosbeak Hesperiphona vespertina Cooper, pine grosbeak Pinicola enucleator L., red crossbill Loxia curvirostra L. and bohemian waxwing Bombycilla garrulus L.) and five species in western North America (pine grosbeak, pine siskin Carduelis pinus Wilson, evening grosbeak, bohemian waxwing and red‐breasted nuthatch) correlated with a combination of large coniferous seed crops in the previous year followed by a poor crop. Breeding population size in the year of the eruption was also correlated positively with the event in two of the species. Eruptions in these species apparently occur when large boreal seed crops resulting in high population densities (via high overwinter survivorship and/or high reproductive success) are confronted with a relatively poor seed crop the next autumn.

 Eruptions of common redpolls Carduelis flammea L. and black‐capped chickadees in the west followed only large seed crops the previous year, suggesting that high density is a more important factor leading to eruptions than seed crop failure. The opposite was true for white‐winged crossbills (Loxia leucoptera Gmelin) in the east, where eruptions correlated only with poor current year seed crops. This was the only species supporting the ‘seed‐crop failure’ hypothesis as the sole cause of eruptions.

 Purple finches Carpodacus purpureus Gmelin erupted following years when breeding population densities were high for reasons apparently unrelated to the seed crop. Eruptions of three species in both regions were uncorrelated with any of the variables tested.

 We conclude that seed crops of boreal trees play a pivotal role in causing eruptions for a majority of boreal species, usually through a combination of a large seed crop resulting in high population densities followed by a poor seed crop rather than seed‐crop failure alone. Weather conditions were not a significant factor correlating with eruptions in any of the species.
Review of methodology of quantitative reviews using meta‐analysis in ecology
Authors: Gates Simon
Published: March 2003

Statistical methods for combination of independent results have been well publicized in the ecological literature, and have begun to be used for reviewing research. They provide a considerable advance in scientific rigour over traditional narrative or ‘vote‐counting’ reviews.

However, other methodological developments for research synthesis have not yet been widely adopted.

This review briefly summarizes some of the techniques used for carrying out rigorous reviewing and synthesis of results in medical science, and surveys techniques used by ecological meta‐analyses.

Many of the methods used to reduce bias and enhance the accuracy, reliability and usefulness of reviews in medical science have not yet been widely used by ecologists.

The quality of ecological reviews could be improved by adoption of some of these methods, such as specifying the methods used for literature searching, stating the types of study combined in the review and the strength of evidence they provide, presenting results as a point estimate with a confidence interval, investigating bias in selection of studies using funnel plots, making a clear distinction between the main analysis and subsidiary analyses and interpreting the latter with caution, and performing sensitivity analyses.
Dynamics of regional coexistence for more or less equal competitors
Authors: Doncaster C. Patrick , Pound Graeme E. , Cox Simon J.
Published: March 2003

Competition between two species in a metapopulation involves each inhibiting the other's ability firstly to colonize an already occupied area and then to persist in it. Models for regional competition of this kind have 3‐D dynamics, from which it has proved difficult to extract useful predictions except for special conditions. We introduce a 2‐D general model for species that are equally vigorous at inhibiting the ability of others to remain in an occupied patch as to arrive there. The model covers the full spectrum of competitive interactions, from weak to strong and symmetrical to asymmetrical. Its Lotka–Volterra dynamics extend the general theory of competitive coexistence by generating clear predictions for community structure, amenable to cross‐system comparisons and experimental manipulations.

Previous 2‐D models of interactions between dominant and fugitive species are special cases of the 2‐D general model. Moderately asymmetrical competition has two outcomes distinctly different from dominant–fugitive interactions, at both the scale of metapopulation and population: (i) slow growing and weak competitors coexist with faster growing superior competitors, albeit at reduced densities; and (b) habitat removal always yields relative gains in abundance for species with higher growth capacity, but the gains are absolute only for species subjected to competitive impacts that exceed within‐species impacts. Extinctions of slow growing and weak competitors provide the most sensitive indication of habitat degradation, and their losses also have the least effect on community structure.

The 2‐D general model further predicts that highly productive communities will tolerate differences between species in their capacity for population growth, whereas less productive communities will tolerate stronger competitive interactions between species. This prediction applies equally to a population of resource consumers as to a metapopulation of colonists. The model explicitly links local and regional population dynamics tor–Kselection in community structure by predicting a prevalence of growth‐orientated species in resource‐poor habitats and competition‐orientated species in resource‐rich habitats.
A comparison of two pollinators: the introduced honey bee Apis mellifera and an indigenous bee Centris tarsata on cashew Anacardium occidentale in its native range of NE Brazil
Authors: Freitas Breno M. , Paxton Robert J.
Published: March 2003

1.  Aspects of the flowering biology of wild cashew Anacardium occidentale, an andro monoecious, self‐fertile tree, were studied in the north‐east of Brazil, where this species is endemic. Comparison was made among two bee species, Apis mellifera and Centris tarsata, in their pollination of cashew flowers using a number of measures including single bee visits to marked flowers.

2.  Cashew flowering is protandrous within a day. Male flowers greatly outnumber hermaphrodite flowers. Stigmas lose receptivity rapidly and pollen is quickly removed from anthers yet flowers remain intact for several days.

3.  Only females of C. tarsata collected pollen from cashew flowers, and then only from male flowers. The similar foraging behaviour of the nectar collectors of the two bee species under investigation when visiting hermaphrodite cashew flowers suggests that they may both act as good pollinators.

4.  We develop an index of efficiency of pollen removal from anthers (PREi) whereby the relative benefits of flower visitors to a component of a plant’s male reproductive success can be quantified.

5.  Comparisons of single bee visits to flowers with unvisited flowers and others receiving unlimited visits were used to show that: C. tarsata pollen collectors were more efficient than nectar collectors of either bee species at removing pollen from anthers; nectar collectors of both bee species had similar pollen removal efficiencies; C. tarsata was more efficient at depositing pollen on stigmas than A. mellifera; both bee species had statistically similar efficiencies at setting seed.

6.  The indices of efficiency for some of the stages in the pollination of cashew suggest that C. tarsata flower visits may enhance plant reproductive success over flower visits by A. mellifera but that both bee species may be suitable for the pollination of commercially grown cashew.

7.  Despite cashew’s single ovule per flower, high nut set demands a high rate of pollinator visitation during the peak time of stigma receptivity. Provision of additional bee pollination in commercial orchards is recommended to obtain good nut yields.
Responses of slug numbers and slug damage to crops in a silvoarable agroforestry landscape
Authors: Griffiths J. , Phillips D.S. , Compton S.G. , Wright C. , Incoll L.D.
Published: March 2003

1.  Alternative farming practices such as set‐aside and agroforestry are likely to be of continuing interest to European agriculture but may have associated problems, such as increased populations of crop pests such as slugs.

2.  A silvoarable agroforestry experiment has been in progress since 1987 at Leeds University Farms at Bramham, West Yorkshire, UK. It consists of four replicate blocks, each with rows of trees separating alleys of arable crops; all four blocks have their own arable control areas in adjacent fields.

3.  Pitfall trap catches within the experiment indicate that the slug population increased over the period 1991–94. The increase was greatest, and most consistent, within the tree rows in the agroforestry blocks. The increase was slower and less consistent in the arable controls and the arable areas within the agroforestry blocks.

4.  In spring 1994, the slugs in each of the treatments in the agroforestry experimental area were sampled using pipe traps, refuge traps and pitfall traps. The number and diversity of slugs were highest in the grassed understorey beneath the rows of trees and significantly higher in the alleys between the rows of trees than in the arable control areas.

5.  The levels of slug damage to a pea crop were assessed by surveys that recorded the number of emerging plants and the number of damaged leaves per plant. There were significant correlations between the number of slugs caught and the damage to the crop by slugs. It is concluded that slugs have the potential to be important pests of some crops in silvoarable agroforestry landscapes and that this could influence the choice of crops for this type of farming.

6.  Major conclusions are emboldened in the Discussion.
The effects of refuge size and number on acarine predator–prey dynamics in a pesticide‐disturbed apple orchard
Authors: Lester P.J. , Thistlewood H.M.A. , Harmsen R.
Published: March 2003

1.  In apple orchards, the use of pesticides such as pyrethroids for the control of lepi dopteran and dipteran pests can severely disturb natural equilibria by killing or repelling acarine predators. After spraying, phytophagous mite populations will often subsequently increase to densities which are above economic thresholds. To conserve predator populations we manipulated the size and number of predator refuges. Refuges were made with various sizes of polyethylene sheeting placed over 0, 10, 30, 60 or 100% of the leaves on trees before spraying with the pyrethroid permethrin.

2.  At the time of spraying the phytoseiid predator Typhlodromus caudiglans and the stigmaeid predator Zetzellia mali were present in similar densities. The main phytophagous mites present were the tetranychid mites Panonychus ulmi and Tetranychus urticae. After spraying, Typhlodromus caudiglans was virtually eliminated from sprayed leaves, but not from refuge leaves. Recolonization of sprayed leaves by T. caudiglans was slow, probably due to toxic or repellent effects of the pyrethroid residue. Densities of Z. mali were only slightly affected by the pyrethroid, but this species was unable to control tetranychid densities on sprayed leaves in the absence of T. caudiglans. After spraying, P. ulmi and Tetranychus urticae increased on sprayed leaves to densities well in excess of crop economic thresholds, while densities remained low on refuge leaves.

3.  The major effect of refuge size was a high positive correlation between entire‐tree densities of T. caudiglans and refuge size, and a high negative correlation with P. ulmi densities. The refuge size necessary to control P. ulmi to below economically damaging densities was predicted to be in excess of 60% of each tree. Thus, only 40% of each tree would receive a pyrethroid spray. This is not practical for management purposes as the reduced spray coverage is unlikely to control target lepidopteran and dipteran pests. No significant effects of refuge number were observed.

4.  The application of a pyrethroid spray resulted in a major disturbance to natural acarine population dynamics in this orchard for up to 11 weeks after spraying. While refuges were useful in conserving a population of the predator Typhlodromus caudiglans and reducing entire‐tree densities of phytophagous mites, the use of refuges may be more valuable when using pesticides with a lower residual effect.
An experimental investigation, using stomatal conductance and fluorescence, of the flood sensitivity of Boltonia decurrens and its competitors
Authors: SMITH MARIAN , MOSS JAMES SCOTT
Published: March 2003

Boltonia decurrens, a perennial floodplain species endemic to the Illinois River Valley, USA, is threatened with extinction due to destruction of habitat. Extant populations of B. decurrens have become isolated and restricted to human‐disturbed, alluvial soil habitats. In sites that are not disturbed, B. decurrens is replaced by competing vegetation after 3–5 years. If further decline in size and number of populations is to be avoided, strategies for management of the species must be developed.

To assess the feasibility of using controlled flooding to reduce competition in sites where B. decurrens occurs, we compared the effects of 10 weeks of root‐zone saturation on mortality, biomass, stomatal conductance and the ratio of variable to maximum fluorescence (the fluorescence ratio) in B. decurrens and three of its competitors: an annual, Conyza canadensis; a non‐rhizomatous perennial, Aster pilosus; and a rhizomatous perennial, Aster ontarionis.

Boltonia decurrens was unaffected by the 10‐week treatment, but all other species showed increases in mortality, reduction or re‐allocation of biomass, and decreases in stomatal conductance. There was no effect of flooding on the fluorescence ratio. Because reductions in stomatal conductance were accompanied by changes in mortality and biomass, we concluded that measurement of stomatal conductance could be used as a non‐destructive technique to determine differential flood tolerance. The order of tolerance among species in this study was B. decurrens > A. ontarionis > A. pilosus > C. canadensis; therefore, controlled flooding may be an effective management tool in preserving populations of B. decurrens.
Biorational management tactics to select against triazine‐resistant Amaranthus hybridus: a field trial
Authors: Jordan Nicholas , Kelrick Michael , Brooks John , Kinerk Wesley
Published: March 2003

1. The individual and joint effectiveness of two biorational tactics (crop interference and exploitation of negative cross‐resistance to certain herbicides) in the management of triazine‐resistant Amaranthus hybridus L. (smooth pigweed) were estimated. Biorational tactics exploit biological idiosyncracies of resistant (R) genotypes to maximize fitness cost(s) of resistance. We quantified selection against triazine resistance by relative performance comparisons between lines having comparable nuclear genomes but either resistant or susceptible cytoplasm. Increasing soybean density by reducing row spacing (from 76 cm to 25 cm) did not significantly increase the fitness cost of resistance.

2. Low doses of bentazon (100 and 300 g active ingredient ha–1) did strongly increase the cost of resistance. Over 2 years, the mean relative performance of R genotypes in bentazon treatments was 0·40, compared to 0·60 in the absence of bentazon. Therefore, use of bentazon in soybean production has the potential to delay evolution of triazine resistance in maize–soybean rotations using triazines.

3. There was no consistent indication that increased soybean density and bentazon herbicide could act synergistically to increase costs of triazine resistance in Amaranthus hybridus. Nor were differences in response to biorational tactics evident between the two populations of origin (Maryland and Virginia, USA) from which experimental lines were derived.

4. Effects of the biorational tactics differed markedly between years, highlighting that resistance management depending primarily on these tactics would have widely variable results. Use of such tactics is likely to be most effective in the context of diversified weed management.
The impact of great skua predation on seabird populations at St Kilda: a bioenergetics model
Authors: Phillips Richard A. , Thompson David R. , Hamer Keith C.
Published: March 2003

1. The number of great skuas Catharacta skua Brünnich breeding at St Kilda, Outer Hebrides, has increased rapidly in recent years, making it currently the second largest colony outside Shetland and the fastest growing in the UK. In comparison with Shetland, where the diet consists mostly of sandeel Ammodytes marinus Raitt and discarded gadoid fish, and very rarely of birds, great skuas at St Kilda feed far more extensively upon seabirds. This paper incorporates metabolic, dietary and demographic data to estimate the total mass of different prey consumed at St Kilda and to assess the potential impact of this predation on other seabird populations.

2. On the basis of a bioenergetics model incorporating fundamental life‐history parameters, the great skua population at St Kilda was estimated to require 141 × 106 kJ of energy per season, most of which (88·0%) was necessary for the maintenance and activity of breeding adults. Energy demand was considerably lower for non‐breeders (2·5% of the total), and for chicks and fledglings (9·2%).

3. In addition to seabirds, great skua diet at St Kilda also included a considerable proportion of fish and goose barnacles Lepas sp. However, because of differences in mean meal mass and caloric density, meals of larger seabird prey were more important in terms of their energetic contribution in the diet than in terms of their relative abundance.

4. Combining the bioenergetics and prey consumption models, it was estimated that a total mass of 12·2 tonnes of fish, 1·6 tonnes of goose barnacles and 8·8 tonnes of seabirds was consumed by the great skua population at St Kilda to fulfil its total energy requirement in 1996. Overall seabird consumption was estimated to be 40,800 seabirds of seven different species. Although a proportion of birds killed are likely to be visiting non‐breeders, the magnitude of this figure nonetheless suggests that great skuas may have a considerable impact on the internationally important populations of some seabirds at St Kilda.
Does variation in census area confound density comparisons?
Authors: Gaston Kevin J. , Blackburn Tim M. , Gregory Richard D.
Published: March 2003

1. Estimates of density are not always independent of the area over which populations are censused. Instead, lower densities tend to be recorded for species when they are censused over larger areas. This may have serious implications for both intra‐ and interspecific comparisons of density, with relevance to such issues as conservation prioritization and management strategies, because differences in density may simply result from differences in census areas.

2.Here, we use long‐term population census data for British birds in the period 1968–91, drawn from the Common Birds Census (CBC), to examine relationships between density and census area within species, and the consequences of these relationships for intraspecific and interspecific density comparisons.

3.Most British bird species exhibit statistically significant negative relationships between density and census area. We used these relationships to standardize mean density estimates for all species to a common census area. These area‐adjusted estimates were usually very similar to geometric mean density estimates calculated without reference to census area.

4.For a subset of species recorded from a large number (> 30) of census sites in each year in the period 1968–91, we used intraspecific density–area relationships for each year to standardize mean density estimates to a common census area in all years. Again, the area‐adjusted estimates for each year were usually very similar to the simple geometric mean density estimates calculated for the species in the same year.

5.These results are encouraging, but are certainly a consequence of the relatively limited range of census areas used here, and the fact that the mean census area varies little across species, or across years within species. Moreover, those species occupying few sites are the most likely to have area‐biased densities, but are the species for which area‐correction will be most difficult.

6.Overall, the results suggest that past analyses conducted using the CBC data are unlikely to have been seriously confounded by variation in census area. Nevertheless, they do highlight that the effects of census area will require consideration by anyone planning to measure or use densities for comparative purposes either within or among species.
Factors influencing molehill distribution in grassland: implications for controlling the damage caused by molehills
Authors: Edwards G. R. , Crawley M. J. , Heard M. S.
Published: March 2003

1. Moles are perceived as pests of farms, gardens, sports fields and nature reserves, mainly because they form molehills. The danger and inhumaneness of current methods of mole control (e.g. poisoning with strychnine or the use of mole traps) means that non‐lethal methods are sought. We examined the possibility of controlling molehill distribution by using management procedures that alter the availability of earthworms, the principal food of moles.

2. The abundance of molehills and earthworms was monitored over 2 years in an acid grassland where pesticide (with and without insecticides and molluscicides), grazing (continuous grazing by rabbits vs. hay meadow), soil pH (with and without lime), herbicide (with and without herb‐ and grass‐specific herbicides) and fertilizer (N, P, K, Mg) treatments were imposed.

3. In the experimental area of 4608 m2, a total of 1062 molehills formed, each with an average area of 0·14 m2; a disturbance rate equivalent to 3·2% of the soil surface over 2 years. Peak molehill production occurred in spring and autumn, with few molehills formed at other times of the year.

4. Molehill production in grazed areas was one‐third that of hay meadows. Half as many molehills formed in unlimed as limed plots. Significantly fewer molehills formed in areas where grass species were removed (herb‐rich) than areas where no species were removed. Insecticide, molluscicide and fertilizer application had no significant effect on molehill production.

5. The treatments that had fewer molehills also had less earthworms, indicating that molehill production was decreased, indirectly, through the treatments reducing food availability.

6. Reducing the number of molehills through management procedures that decrease earthworm availability offers an alternative to lethal control of moles. This could be achieved by allowing (or encouraging) soil pH to fall (e.g. withholding lime application; through the use of acidifying nitrogen‐fertilizers), by creating herb‐rich swards or by preventing plant biomass from accumulating for long periods. These methods will be more applicable to gardens, sports fields and nature reserves than to farms, where conflicts with normal farming practices would make them difficult to implement.
Effects of forest fertilization on the radial growth and resin exudation of insect‐defoliated Scots pines
Authors: Kytö Maarit , Niemelä Pekka , Annila Erkki , Varama Martti
Published: March 2003

1. Scots pine trees that had been defoliated by the pine sawfly Diprion pini were fertilized with various nutrient combinations in the growing season following defoliation in order to study the possibility of accelerating tree recovery. Resin exudation, vertical resin duct density and vigour index of the trees were measured 3 years after defoliation, and radial growth 6 years after defoliation.

2. Defoliation reduced stem growth, and annual rings were missing particularly in the severely defoliated trees. Nitrogen fertilization enhanced radial growth even in the severely defoliated trees.

3. Nitrogen fertilization increased the number of vertical resin ducts in both defoliated and undefoliated trees, but resin duct density tended to be lower in the nitrogen‐fertilized trees than in trees that had not received nitrogen fertilizer. Resin duct density did not correlate with resin flow rate.

4. Resin exudation was strongest from trees that had been almost totally defoliated, intermediate from trees that had lost half of their foliage, and weakest from undefoliated trees, indicating that defoliation had induced resin production in the stem. Resin flow was not affected by fertilization.

5. There was a weak negative correlation between vigour index and resin flow. No trees with a high vigour index had strong resin exudation, while resin exudation varied from minimal to very strong in trees with a low vigour index.

6. The results indicate that nitrogen fertilization can be used to stimulate growth of defoliated trees without affecting resistance traits on infertile sites.
Can arbuscular mycorrhizal fungi be used to control the undesirable grass Poa annua on golf courses?
Authors: Gange A.C. , Lindsay D.E. , Ellis L.S.
Published: March 2003

1. 
Poa annua (annual meadow‐grass or annual bluegrass) is the most problematic weed of temperate zone golf putting greens. In the UK there are no chemicals approved for its control, although several herbicides and plant growth regulators are available in the USA. Reducing P. annua levels in fine turf would greatly reduce the heavy reliance on pesticides and water that currently exists.

2. This paper reports on an observational and a manipulative study in golf putting greens, aimed at determining whether arbuscular mycorrhizal (AM) fungi have any potential for the reduction of this weed in fine turf.

3. All 18 greens on three golf courses were sampled, and in two courses a negative relation between AM fungi and P. annua abundance was found, upholding previous results. In greens where AM fungi were relatively common (as measured by root colonization), P. annua was rare, and vice versa. Furthermore, when the fungi were common, abundance of the desirable turfgrass Agrostis stolonifera was greater.

4. Two explanations are suggested for these relations, a competitive one, in which AM fungi alter the balance of competition between the two grasses, and an antagonistic one, in which the fungi may directly reduce the growth of P. annua.

5. In a manipulative experiment, where mycorrhizal inoculum was added to a golf green, the colonization level of A. stolonifera roots was enhanced, as was the abundance of this grass. Furthermore, there was a suggestion that adding inoculum could decrease the abundance of P. annua.

6. AM fungi have the potential to be a much more environmentally sound method of P. annua control in sports turf than the currently used chemicals.
Vegetation response to grazing management in a Mediterranean herbaceous community: a functional group approach
Authors: Sternberg Marcelo , Gutman Mario , Perevolotsky Avi , Ungar Eugene D. , Kigel Jaime
Published: March 2003

1.  A 4‐year study was conducted in a Mediterranean herbaceous community in north‐eastern Israel to investigate the effects of cattle grazing management on the structure and composition of the community. Understanding the effects of grazing on the dynamics of Mediterranean herbaceous communities is important in formulating rational management plans for both conservation and sustainable animal production.

2.  The relationships among plant functional groups were studied in the context of inter‐annual variation in rainfall. Treatments included manipulations of stocking rates (moderate, heavy and very heavy) and grazing regimes (continuous vs. seasonal), in a factorial design.

3.  The herbaceous community was rich in species, with 166 species recorded at the site, of which 74% were annuals. Plant cover was dominated by 10 species that accounted for 75% of the total cover.

4.  Inter‐seasonal rainfall variation was a dominant factor in the expression of different grazing treatments on the structure of the plant community. Grazing effects were stronger in wet years than in dry years.

5.  Paddocks under continuous grazing were higher in number of species compared with paddocks subjected to seasonal grazing, independently of grazing intensity.

6.  Functional group analyses showed that reduction in cover of tall grasses was correlated with an increase in cover of prostrate annual legumes and less palatable groups such as annual and perennial thistles, crucifers and forbs.

7.  Cover of functional groups composed of hemicryptophytic species was less variable (lower coefficient of variation) in response to grazing treatments and inter‐annual variation in climatic conditions compared with functional groups with annual species.

8.  The persistence of the dominant species and the relatively small amplitude of change in plant cover of the functional groups suggest that the community was rather stable in spite of wide variation in grazing regimes and climatic conditions. East‐Mediterranean grasslands appear to be adapted to grazing due to their long history of human association.
Predicting spatial variation in heather utilization by sheep and red deer within heather/grass mosaics
Authors: Palmer S.C.F. , Hester A.J.
Published: March 2003

1. Recent work has shown that the dynamics of woody and herbaceous vegetation mosaics under grazing or browsing can be strongly affected by the spatial pattern of the vegetation. A suite of models is described here to predict spatial variation in the utilization of an internationally important woody species, heather Calluna vulgaris, within heather/grass mosaics when grazed by sheep or red deer Cervus elaphus. This type of information is needed for the successful management of free‐ranging herbivores grazing these extensive vegetation types.

2. The models predict: (i) heather utilization at the edge of grass patches; (ii) utilization distant from the grass edge; and (iii) the rate of change of utilization with distance from the edge of grass patches as functions of (a) the proportion by area of grass in the mosaic, (b) the length of heather/grass edge per unit area, and (c) the overall heather utilization on a site. Differences between species of grazers and seasons are also taken into account.

3. The models were fitted to data from two series of grazing experiments conducted on natural and artificial heather/grass mosaics in north‐east Scotland.

4. Overall heather utilization in the experiments was estimated using a geographical information system (GIS), taking into account higher levels of utilization in proximity to grass patches.

5. A modelling approach for predicting how the heather/grass mosaic pattern will change through time under heavy grazing is proposed. As no field data are yet available on this process, this model was developed by simulation within a GIS.

6. This work demonstrates how incorporation of spatial information can improve the accuracy of utilization predictions, and thus the design of appropriate management practices. As with many other similar systems, the paucity of data on spatial variation in heather utilization by grazing ungulates, and the effects of utilization at the heather/grass edge, particularly under high grazing pressures, is highlighted. This is considered to be a major limitation to the efficacy of currently available decision support tools to aid the management of heterogeneous grazing systems.
Habitat‐based statistical models for predicting the spatial distribution of butterflies and day‐flying moths in a fragmented landscape
Authors: Cowley Matthew J. R. , Wilson Robert J. , León‐Cortés Jorge L. , Gutiérrez David , Bulman Caroline R. , Thomas Chris D.
Published: March 2003

1. Most species’ surveys and biodiversity inventories are limited by time and money. Therefore, it would be extremely useful to develop predictive models of animal distributions based on habitat, and to use these models to estimate species' densities and range sizes in poorly sampled regions.

2. In this study, two sets of data were collected. The first set consisted of over 2000 butterfly transect counts, which were used to determine the relative density of each species in 16 major habitat types in a 35‐km2area of fragmented landscape in north‐west Wales. For the second set of data, the area was divided into 140 cells using a 500‐m grid, and the extent of each habitat and the presence or absence of each butterfly and moth species was determined for each cell.

3. Logistic regression was used to model the relationship between species’ distribution and predicted density, based on habitat extent, in each grid square. The resultant models were used to predict butterfly distributions and occupancy at a range of spatial scales.

4. Using a jack‐knife procedure, our models successfully reclassified the presence or absence of species in a high percentage of grid squares (mean 83% agreement). There were highly significant relationships between the modelled probability of species occurring at regional and local scales and the number of grid squares occupied at those scales.

5. We conclude that basic habitat data can be used to predict insect distributions and relative densities reasonably well within a fragmented landscape. It remains to be seen how accurate these predictions will be over a wider area.
A landscape‐scale test of the predictive ability of a spatially explicit model for population viability analysis
Authors: D.B. Lindenmayer , Ball I. , Possingham H.P. , Mccarthy M.A. , Pope M.L.
Published: March 2003

Although population viability analysis (PVA) is widely employed, forecasts from PVA models are rarely tested. This study in a fragmented forest in southern Australia contrasted field data on patch occupancy and abundance for the arboreal marsupial greater glider Petauroides volans with predictions from a generic spatially explicit PVA model. This work represents one of the first landscape‐scale tests of its type.

 Initially we contrasted field data from a set of eucalypt forest patches totalling 437 ha with a naive null model in which forecasts of patch occupancy were made, assuming no fragmentation effects and based simply on remnant area and measured densities derived from nearby unfragmented forest. The naive null model predicted an average total of approximately 170 greater gliders, considerably greater than the true count (n = 81).

 Congruence was examined between field data and predictions from PVA under several metapopulation modelling scenarios. The metapopulation models performed better than the naive null model. Logistic regression showed highly significant positive relationships between predicted and actual patch occupancy for the four scenarios (P = 0·001–0·006). When the model‐derived probability of patch occupancy was high (0·50–0·75, 0·75–1·00), there was greater congruence between actual patch occupancy and the predicted probability of occupancy.

 For many patches, probability distribution functions indicated that model predictions for animal abundance in a given patch were not outside those expected by chance. However, for some patches the model either substantially over‐predicted or under‐predicted actual abundance. Some important processes, such as inter‐patch dispersal, that influence the distribution and abundance of the greater glider may not have been adequately modelled.

 Additional landscape‐scale tests of PVA models, on a wider range of species, are required to assess further predictions made using these tools. This will help determine those taxa for which predictions are and are not accurate and give insights for improving models for applied conservation management.
The comparative demography of the pasture weed Echium plantagineum between its native and invaded ranges
Authors: Grigulis K. , Sheppard A.W. , Ash J.E. , Groves R.H.
Published: March 2003

Echium plantagineum is native to the western Mediterranean Basin, where it is a common, but not dominant, component of species‐rich annual grasslands. Since its introduction into Australia, E. plantagineum has spread to infest vast areas of predominantly agricultural land in south‐east and south‐west Australia, where it can be the dominant pasture species.

To unravel the ecological factors responsible for the high population abundance of E. plantagineum in Australia, its demography was compared between sites in the invaded and native ranges. Demographic parameters of E. plantagineum populations were estimated at a site near Canberra in south‐eastern Australia, and at a site near Evora in southern Portugal. Identical factorial experiments were set up at each site with treatment combinations of the presence or absence of grazing and pasture competition.

The recruitment, survival, fecundity and seed bank dynamics of E. plantagineum populations were measured for each of the treatment combinations over 2 years at each site. These data allowed the estimation of demographic parameters describing the proportion of E. plantagineum individuals moving from one life‐cycle stage to the next.

Seedling establishment fractions were two to five times greater at Canberra than at Evora, and seed bank incorporation rates were three times greater at Canberra than Evora. These demographic differences were those most likely to play an important role in the greater abundance of E. plantagineum in Australia compared with Mediterranean Europe. Neither seed bank survival rates nor seed production differed between populations at Canberra and Evora, while seedling survival rates were always lower at Canberra than at Evora.

Neither grazing nor pasture competition limited the seed production or seedling survival of E. plantagineum populations at Evora more than at Canberra.

An effective approach for the control of E. plantagineum in Australia may thus be through the reduction of the seedling establishment fraction. This may be achieved by maintaining significant pasture vegetation cover and reducing the available space for E. plantagineum establishment during autumn.
Differences in the capture rate of cage‐trapped red foxesVulpes vulpesand an evaluation of rabies control measures in Britain
Authors: Baker Philip J. , Harris Stephen , Robertson Charles P.J. , Saunders Glen , White Piran C.L.
Published: March 2003

Methods used to control canids may differ in their relative effectiveness and how they ‘sample’ age and sex classes. However, there is little information on such biases. We utilized data from a population of known size and structure to quantify differences in the seasonal capture rate of foxesVulpes vulpesof different age, sex and social status. The effects of home‐range utilization and trap experience were also investigated.

The capture rate of juvenile (< 1 years) foxes was highest in spring and declined throughout the year. Adult (≥ 1 years) trap rates were equivalent to those of juveniles in winter.

Neither juveniles nor adults exhibited sex differences in trappability.

Adults were classified as dominant or subordinate based upon patterns of dyadic interaction. Subordinate foxes were trapped more frequently than dominants.

Trappability did not differ inside or outside of core areas, after controlling for trap effort.

Previous trap experience did not affect the capture rate of adult foxes.

Captures of non‐resident foxes peaked in winter (52% of captures), associated with dispersing juveniles and adult males, and were lowest in summer (13%).

In Britain, 75–90% of foxes would need to consume poison or vaccine baits to control a rabies epizooty. During simulated rabies control operations, where cage‐trapping was used to measure the proportion of foxes taking dummy baits containing a biomarker, < 30% of foxes consumed baits. However, non‐resident foxes present during the period of baiting but not during trapping, or vice versa, may bias these calculations. We used the frequency of capture of non‐resident foxes to re‐examine the success rate of these trials.

Revised estimates still suggest that < 45% of foxes were reached during the simulated control operations. This is significantly below the levels necessary for rabies control. Further biomarker trials are required that do not rely only on trapping for sample collection and where the residency status of captured foxes has been determined.
Modelling the effects of plant species on biocontrol effectiveness in ornamental nursery crops
Authors: Skirvin David J. , De Courcy Williams Michael E. , Fenlon John S. , Sunderland Keith D.
Published: March 2003

The development of biological control strategies for ornamental crops is challenging due to the high diversity of crops grown and zero tolerance to pest presence. In an attempt to provide a biological basis for the development of biological control, an individual‐based stochastic modelling approach was developed.

 This approach has been used to examine the impact of tritrophic interactions on biological control of the spider mite Tetranychus urticae by the predatory mite Phytoseiulus persimilis. The effect of differences in the biology of T. urticae and P. persimilis on three nursery stock crops, Ceanothus thyrsiflorus var. ‘Autumnal Blue’, Choisya ternata and Euonymus japonicus, was investigated through simulation experiments.

 The effect of pest aggregation and frequency of predator introduction on the control of T. urticae was examined at a range of initial pest and predator densities. Control was assumed to occur when T. urticae was driven to extinction, due to zero tolerance to pest presence on these ornamental crops.

 ‘One‐off’ introductions of P. persimilis rarely caused T. urticae to become extinct, but repeated weekly introductions always led to pest extinction, regardless of the plant species, at the highest introduction rate of 1000 predators (10 stem−1). Time to pest extinction was similar on all plant species with repeated introductions, but was influenced by differences in the biology of pest and predator on the three plant species.

 Increased aggregation of T. urticae led to greater extinction at lower predator introduction rates, but time to extinction was increased due to the time taken for the predator to cope with the increased pest density.

 These predictions highlight the importance of plant species and spatial dynamics of both pest and predator in determining the efficiency with which biological control can be achieved on ornamental crops, suggesting that prophylactic application of predatory mites may be preferable to reactive application.
Modelling the effects of an oil spill on open populations of intertidal invertebrates
Authors: Forde Samantha E.
Published: March 2003

Knowledge of the impact of oil spills on coastal communities, in California and elsewhere, is currently limited by a lack of long‐term data, the inability to infer causality from monitoring studies, and the necessarily limited spatial and temporal scales of experimental studies.

This study therefore used a modelling approach to investigate the combined effects of different intensities of an oil spill and recruitment variation on a barnacleChthamalus fissuspopulation. The methodology and results are likely to apply to any similarly open marine populations with dispersive larval forms.

The model consisted of a source population comprising individuals that reproduced based on size and probability of mortality. Larvae from the source population entered a larval pool. A proportion of the larvae from the larval pool recruited to a focal population within the region.

The model was used to assess the effects on recruitment to the focal population of (i) the size structure of the source population, (ii) the intensity of oil spills in the source population, and (iii) recruitment intensity to the focal population.

Differences in the size structure of the source population had little effect on the reproductive output of the population relative to the intensity of the oil spill. Similarly, the intensity of the oil spill had a stronger influence on recruitment to the focal population than the size structure of the source population. Size structure of the source population was important, however, when evaluating the seasonal trajectory of the focal population.

Modelling provides a format in which questions about the effects of human impacts can be addressed that would be intractable using experiments. The results of this model suggest that recruitment variation, along with the processes underlying recruitment variation, are critical to predicting the effects of disturbance on open marine populations.
Phenotypic and molecular characterization of chickpea rhizobia isolated from different areas of Morocco
Authors: Maâtallah J. , Berraho E.B. , Muñoz S. , Sanjuan J. , Lluch C.
Published: March 2003

Aims: To determine the biodiversity of rhizobial strains nodulating Cicer arietinum L. in representative soils from various areas of Morocco.

Methods and Results: Symbiotic traits, utilization of 49 carbohydrate sources, resistance to antibiotics and heavy metals, tolerance to salinity, to extreme temperatures and pH were studied as phenotypic markers. In addition, restriction fragment length polymorphism (RFLP) of PCR-amplified 16S rDNAs were compared with those of reference strains. Numerical analysis of the phenotypic characteristics showed that the 48 strains studied fell into three distinct groups. RFLP analysis of 16S rRNA genes revealed an additional heterogeneity and four ribotypes were identified.

Conclusions: Chickpea rhizobia isolated from Moroccan soils are both phenotypically and genetically diverse. Most of these rhizobia belong to the Mesorhizobium genus. However, some strains originating from a particular soil appeared to have 16S rRNA genes similar to Sinorhizobium as well as very distinct auxanographic characteristics compared with Mesorhizo- bium isolates.

Significance and Impact of the Study: A well characterized collection of chickpea-nodulating rhizobia in representative soils of Morocco has been generated, which can be used to develop efficient inoculants for this crop. This is the first report evidencing that chickpeas may be nodulated by bacteria from the Sinorhizobium genus.
Bacteriology of the Labrador dog gut: a cultural and genotypic approach
Authors: Greetham H.L. , Giffard C. , Hutson R.A. , Collins M.D. , Gibson G.R.
Published: March 2003

Aims: To carry out an extensive study of the microflora composition of the Labrador dog gut. Methods and Results: Faecal specimens from four Labradors were collected and plated onto growth media designed to recover total anaerobes, bacteroides, bifidobacteria, lactobacilli, clostridia, Gram-positive cocci, total aerobes and coliforms. Morphologically different isolates were collected from all agars inoculated with faeces from one canine individual (repeated four times). A total of 157 out of 171 isolates were identified using 16S rRNA gene sequencing. Sequence analysis showed that agar selectivity was poor, especially when bacteroides and Gram-positive cocci were the targets. Bifidobacteria were not detected in any of the samples analysed, indicating their presence at low or negligible levels. The gene sequences of many of the isolates (n=45, representing 29% of the total) did not correlate with known species in the Ribosomal Database Project and EMBL databases, suggesting the presence of novel gut diversity. Conclusions: Traditional culture methods fail to reflect the bacterial diversity present in Labrador dog faeces. Significance and Impact of the Study: This study has shown the value of molecular-based methodologies for determining bacterial profiles in the Labrador dog gut microbiota, but has also exposed the limitations of purportedly selective agars.