bluuebunny/crossref_metadata_2025_split 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

Summary

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

Summary

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

SummaryCompetition 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

Summary

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.