bluuebunny/crossref_metadata_2025_split huggingface dataset:
Identifying disease reservoirs in complex systems: mountain hares as reservoirs of ticks and louping‐ill virus, pathogens of red grouse
Authors: Laurenson M. K. , Norman R. A. , Gilbert L. , Reid H. W. , Hudson P. J. 
Published: March 2003

Summary

We examined the role of mountain hares in the louping‐ill virus/Ixodes ricinus tick system to determine whether hares were reservoirs of these pathogens for red grouse. A field experiment, which involved reducing mountain hare densities was undertaken and changes in tick abundance, louping‐ill virus seroprevalence and red grouse densities recorded.
Hares were found to be important hosts for all stages of ticks at two study sites and, where sheep were frequently treated with acaricide, hares fed the greatest proportion of adult ticks. Hare densities were reduced at the experimental site between 1993 and 2001 but remained relatively constant at a control site. Both nymph and larvae tick burdens on red grouse chicks declined over this period to very low levels at the treatment site, but not at the control site. The estimated size of the tick population at the treatment site decreased by more than 99% by 1999.
Louping‐ill prevalence, as measured by antibody prevalence in shot young red grouse, also declined at the treatment site, lagging behind the tick decline by approximately 2 years. The number of young grouse produced per hen grouse at this treatment site increased in comparison to a second control area. However, no change was found in summer grouse densities and thus we cannot demonstrate parasite‐mediated competition.
A deterministic SIR‐type model describing the dynamics of this pathogen/vector/host system was constructed and used to examine the role of mountain hares in louping‐ill virus and tick dynamics. The model predicted a decline in tick numbers and seroprevalence as hare densities reduced. The inclusion of hares as both tick hosts and vector–host–vector transmitters of louping‐ill virus gave the best fit to the observed data.
Comparative nesting and feeding ecology of skylarks Alauda arvensis on arable farmland in southern England with special reference to set‐aside
Authors: Poulsen John Grynderup , Sotherton Nick W. , Aebischer Nicholas J. 
Published: March 2003

1.  A study of skylark Alauda arvensis L. breeding ecology in relation to crop type was carried out from April to August 1992 on arable land in southern England. Set‐aside land was included in this comparative study. 2.  Territory density averaged 0·15 ha−1. It was 2–3 times higher in fields of set‐aside and grass, especially permanent pasture, than in winter and spring‐sown cereals. 3.  Territory size was nearly twice as large in fields of winter cereals (4·5 ha) than in other crop types (2·5 ha). Where set‐aside was present on one farm, territory size in set‐aside (1·7 ha) was a third lower than in cereals and grass. 4.  Nesting began in set‐aside and permanent pasture in April and peaked in late May. Nesting was not detected in spring barley until late May and in silage grass until early June. The density of successful nests in set‐aside fields was more than double that in any of the arable crop types. 5.  Average clutch size at hatching was 3·91 eggs in fields of set‐aside, over 15% higher than in silage grass (3·40) and in spring barley (3·27). 6.  Fledging success did not differ according to crop type, but productivity, expressed as the number of fledglings produced per hectare, was 0·50 in set‐aside, 0·13 in silage grass, and 0·21 in spring barley. Nests with chicks were not found in fields of winter cereals. The causes of chick death were thought to be predation in set‐aside fields, farming practices in silage grass fields, and suspected starvation in spring cereals. 7.  The potentially high nesting success of skylarks in set‐aside implies that sympathetic set‐aside management could play an important part in reversing its decline across the European Union.
Recovery of tropical rainforest avifauna in relation to vegetation succession following shifting cultivation in Mizoram, north‐east India
Authors: Raman T.R. Shankar , Rawat G.S. , Johnsingh A.J.T. 
Published: March 2003

1.  Recovery of rainforest bird community structure and composition, in relation to forest succession after slash‐and‐burn shifting cultivation or jhum, was studied in Mizoram, north‐east India. Replicate fallow sites abandoned after shifting cultivation 1, 5, 10, 25 and ≈100 years ago, were compared with primary evergreen and semi‐evergreen forest using transect and quadrat sampling. 2.  Vegetation variables such as woody plant species richness, tree density and vertical stratification increased with fallow age in a rapid, non‐linear, asymptotic manner. Principal components analysis of vegetation variables summarized 92·8% of the variation into two axes: PC1 reflecting forest development and woody plant succession (variables such as tree density, woody plant species richness), and PC2 depicting bamboo density, which increased from 1 to 25 years and declined thereafter. 3.  Bird species richness, abundance and diversity, increased rapidly and asymptotically during succession paralleling vegetation recovery as shown by positive correlations with fallow age and PC1 scores of sites. Bamboo density reflected by PC2 had a negative effect on bird species richness and abundance. 4.  The bird community similarity (Morisita index) of sites with primary forest also increased asymptotically with fallow age indicating sequential species turnover during succession. Bird community similarity of sites with primary forest (or between sites) was positively correlated with both physiognomic and floristic similarities with primary forest (or between sites). 5.  The number of bird species in guilds associated with forest development and woody plants (canopy insectivores, frugivores, bark feeders) was correlated with PC1 scores of the sites. Species in other guilds (e. g. granivores, understorey insectivores) appeared to dominate during early and mid‐succession. 6.  The non‐linear relationships imply that fallow periods less than a threshold of 25 years for birds, and about 50–75 years for woody plants, are likely to cause substantial community alteration. 7.  As 5–10‐year rotation periods or jhum cycles prevail in many parts of north‐east India, there is a need to protect and conserve tracts of late‐successional and primary forest.
Long‐term harvesting and male migration in a New Zealand population of Himalayan tahr Hemitragus jemlahicus
Authors: Forsyth David M. 
Published: March 2003

1. Sexual differences in behaviour and ecology have important implications for the management of harvested ungulate populations. 2. This study investigated the long‐term effects of harvesting on the abundance and distribution of sexes within an introduced population of Himalayan tahr in the Two Thumb and Sibbald Ranges, New Zealand. Annual counts of tahr were made from 1984 to 1996 in two catchments subject to different harvest regimes. 3. Although populations in the two catchments increased at similar rates over the study period, their adult sex ratios diverged significantly in the late 1980s. In Carneys Creek, which was subject to unrestricted harvest, the adult sex ratio was initially equivalent to the estimated population sex ratio, but from 1991 it was significantly male‐biased. In North Branch, 10 km from Carneys Creek but subject only to adult (trophy) male harvest, the population was significantly female‐biased in all years. 4. There was a large and male‐biased harvest in Carneys Creek in 1993, suggesting that immigration of males may have been responsible for the long‐term changes in sex ratio observed there. In contrast, the harvest of males in North Branch was insufficient to explain its female‐biased population. 5. Monthly counts of male and female tahr in Carneys Creek between December 1993 and February 1996 revealed a consistent seasonal change in the abundance of sub‐adult males, and perhaps adult males, but not females. Sub‐adult males immigrated into Carneys Creek during spring, increasing to a summer maximum before emigrating during autumn; few sub‐adult males were present during winter. 6. Counts at six additional sites during summer and autumn 1996 indicated that the probable source of these males was an adjacent hunting reserve. This hunting reserve, which included North Branch, contained a female‐biased population with moderate female density. 7. The observed changes appear to have been a consequence of sexual differences in habitat selection and mobility. In particular, outside the rut the larger‐bodied males avoided habitats containing high densities of females. 8. Harvesting has the potential to affect the spatial distribution of age–sex classes for sexually dimorphic ungulates. Managers need to consider these effects when designing and interpreting harvest and monitoring programmes.
The use of trapping records to monitor populations of stoats Mustela erminea and weasels M. nivalis: the importance of trapping effort
Authors: Mcdonald Robbie A. , Harris Stephen 
Published: March 2003

Summary 1. Trapping and hunting records are frequently used as an index of animal abundance. This study demonstrates that these records can be misleading if sampling effort is not controlled for. 2. Mean numbers of stoats Mustela erminea and weasels M. nivalis trapped by British gamekeepers have been decreasing since 1975 and 1961 respectively, giving rise to concern that populations of both species may be declining. However, trapping effort has not been quantified over this period. 3. A total of 203 gamekeepers in England were questioned about the trapping effort they expended and the number of stoats and weasels they trapped in 1997. The most significant factor affecting the number of stoats and weasels trapped was trapping effort. 4. Gamekeepers that relied on hand‐rearing game birds for shooting regarded stoats and weasels as a less serious problem, and made substantially less trapping effort, than gamekeepers that relied on wild game birds. 5. The national decline in the numbers of stoats and weasels trapped may be the result of a decline in stoat and weasel populations. However, the decline is equally consistent with a reduction in trapping effort, corresponding to a national increase in reliance on hand‐rearing game birds for shooting. 6. When the effect of trapping effort was controlled for, the number of weasels trapped by gamekeepers in 1997 was significantly lower in the south‐west than in other regions of England and was unusually low in some local areas. 7. Trapping records can be used effectively to monitor populations of stoats and weasels, as long as gamekeepers record the number of traps set in each month and monthly totals of animals killed. Ideally, the sex of each animal and whether it was trapped or shot should also be recorded. Similar modifications should also be made to other wildlife monitoring schemes based on trapping and hunting records.
Modelling the effect of cultivation on seed movement with application to the prediction of weed seedling emergence
Authors: Grundy A.C. , Mead A. , Burston S. 
Published: March 2003

Summary 1. Effective weed control is essential in field vegetables. However, the range of available herbicides has been continually reduced for commercial and toxicological reasons over the last decade. In order to predict the optimum weeding period and to apply alternative control strategies successfully, a realistic estimate is needed of the size, timing and duration of a flush of weed emergence in a crop. The soil weed seed bank is the primary source of future weed populations, and therefore provides a unique resource for predictive management purposes. 2. Models have previously been developed to predict the emergence of weed species from different burial depths and to simulate the vertical movement of weed seeds following seed bed preparation. 3. In this investigation a vertical movement model was extended to include the effects of four cultivation implements on the horizontal displacement of weed seeds. These implements were a rotavator, a spring tine, a spader and a power harrow. 4. The rotavator caused a backward movement of seeds; neither the spring tine nor spader had a significant effect on the horizontal displacement of seeds; whilst the power harrow had the greatest capacity to move seeds forward > 0·5 m in the soil. 5. This investigation combined depth of burial and vertical movement models to simulate the likely outcome of different sequences of spring tine, spader, rotavator and power harrow on subsequent weed seedling emergence. For example, sequences including multiple passes of a spader increased the numbers of emerged seedlings, whilst for those where the rotavator dominated the sequence, a marked reduction in seedling numbers was predicted. The findings of a series of simulations are viewed in the light of existing methods of weed control based on soil cultivation, for example the stale seed bed technique. 6. The combined model provides the basis for a decision support system to aid the control of weeds. Additionally, it provides a research tool to improve understanding of the dynamics of the weed seed bank and the implications of seed bed preparations for future populations. The combined model has helped to identify areas of weed seed ecology requiring further study, essential for the development of true dynamic models.
Demography and the decline of the grey partridgePerdix perdixin France
Authors: Bro E. , Sarrazin F. , Clobert J. , Reitz F. 
Published: March 2003

Summary1. Bird populations can be efficiently managed only if the demographic mechanisms that cause change are correctly understood. Here we illustrate the demographic variables causing decline among grey partridgePerdix perdixpopulations in France by comparing populations that show contrasting trends. The analysis combined a field survey at 10 contrasting sites during 3 years, modelling and statistical analyses; survival rates and reproductive success were estimated through the largest‐ever radio‐tracking study of hens, while density was estimated through counts.2. Population viability analyses showed that, in France, north‐western populations of grey partridge were healthy whereas south‐eastern populations were declining.3. Elasticity analyses accounting for environmental stochasticity indicated that the survival rate during shooting, over winter and at the time of the first nesting attempt were the most important demographic influences on population growth rate. The hatching rate, covey size at hatching of first clutches and chick survival rate were secondary. The contribution of replacement clutches to population change was low.4. Multiple regression showed that hen survival during the first nesting attempt explained 33% of the variability in the population growth rate across populations. The shooting pressure increased with the health of the population.5. Improving survival rate during winter and the first nesting attempt was not sufficient for recovery in a declining population. It was also necessary to increase simultaneously the hatching rate of first clutches and chick survival rate to produce a stable population that could sustain shooting.6. Low hen survival rates, in particular during the breeding period, explain the recent decline of grey partridge populations in some regions of France. However, the recovery of populations will need a simultaneous improvement of several demographic parameters.
Responses of ants to selective logging of a central Amazonian forest
Authors: Vasconcelos H.L. , Vilhena J.M.S. , Caliri G.J.A. 
Published: March 2003

Summary 1. Relatively little information exists on the effects of logging on rain forest organisms, particularly in the Neotropics where logging operations have increased dramatically in recent years. In this study we determined experimentally the effects of selective logging of a central Amazonian forest on ground‐living ants. 2. The experimental design consisted of three 4‐ha replicated plots representing control unlogged forest, forest logged 10 years prior to the start of the study (1987), and forest logged 4 years prior to the start of the study (1993). The logging operation removed 50% of the basal area of trees of commercial value, or about eight trees per hectare. This resulted in a significant decrease in canopy cover, and an increase in understorey vegetation density in logged plots relative to controls. 3. Collection and identification of ants from a total of 360 1‐m2 samples of leaf‐litter revealed 143 ant species, of which 97 were found in the control plots, 97 in the plots logged in 1987, and 106 in those logged in 1993. Species richness, evenness and mean abundance (ants m−2) per plot did not vary among treatments. Most of the species found in the control plots were also present in the logged plots. However, population density of many species changed as a result of logging, an effect that persisted for at least 10 years after logging. Species commonly found in sites that were directly disturbed by logging (gaps and tracks) were rare in the undisturbed forest, as revealed by an additional collection of ants. 4. These results suggest that the persistence of ant assemblages typical of undisturbed forest is likely to depend on the amount of structural damage incurred by logging. Thus management techniques that minimize logging impacts on forest structure are likely to help maintain the conservation value of logged forests for ground‐dwelling ants. It is particularly important to minimize the extent of logging roads and tracks created by heavy machinery because these areas appear more prone to invasion by non‐forest species.
Consequences of large‐scale processes for the conservation of bird populations
Authors: Baillie Stephen R. , Sutherland William J. , Freeman Stephen N. , Gregory Richard D. , Paradis Emmanuel 
Published: March 2003

1. Detailed studies of population ecology are usually carried out in relatively restricted areas in which emigration and immigration play a role. We used a modelling approach to explore the population consequences of such dispersal and applied ideas from our simulations to the conservation of wild birds.2. Our spatial model incorporates empirically derived variation in breeding output between habitats, density dependence and dispersal. The outputs indicate that dispersal can have considerable consequences for population abundance and distribution. The abundance of a species within a patch can be markedly affected by the surrounding habitat matrix.3. Dispersal between habitats may result in lower population densities at the edge of good quality habitat blocks and could partially explain why some species are restricted to large habitat fragments.4. Habitat deterioration may not only lead to population declines within that habitat but also in adjacent habitats of good quality. This may confound studies attempting to diagnose population declines.5. Although mobile species have the advantages of colonizing sites within metapopulations, dispersal into poorer quality territories may markedly reduce total populations.6. There are two main approaches to conservation: one is to concentrate on establishing and maintaining protected areas, while the other involves conservation of the wider countryside. If dispersal is an important process then protecting only isolated areas may be insufficient to maintain the populations within them.
Vegetation structure and prey abundance requirements of the Iberian lynx: implications for the design of reserves and corridors
Authors: Palomares F. 
Published: March 2003

Summary Habitat alteration and fragmentation are two of the greatest threats to biodiversity. The conservation of most species in highly encroached areas requires reserves that are connected by suitable habitat corridors to increase the effectiveness of the area under protection. However, the quality required for such corridors is still debated. This study investigated the habitat characteristics (vegetation structure and prey abundance) of sites used by resident and dispersing Iberian lynx in south‐western Spain. Vegetation structure and an index of rabbit abundance (the staple prey of lynx) were measured at sites used by radio‐collared lynx in 1996 and 1997. Data from 128 plots used by resident lynx and 310 plots used by dispersing individuals were compared with data from 162 randomly located plots in sites considered to be unused by lynx.3. Resident sites had a lower percentage of tree cover, shorter tree height, higher percentage of tall shrub cover, higher percentage of overall understorey and higher number of rabbit pellets than both dispersal and unused sites. The height of the short shrub layer was taller and the rabbit abundance index was higher in dispersing sites than in unused sites. Gender did not affect habitat selection by lynx. During dispersal, lynx frequently (50% of cases) used vegetation patches narrower than 300 m. In these cases, sites used by lynx had higher understorey cover and taller shrub height than adjacent unused sites. The percentage of short shrub cover used by lynx increased with the length of time taken to disperse; this was the only variable that changed over time. Range size of resident individuals declined significantly with the index of rabbit abundance but increased with the percentage of short shrub cover. Both variables were good predictors of range size. The study shows that corridors connecting reserves do not have to be prime habitats; they can even support moderate habitat degradation due to human activity. This result has implications both for the conservation of existing corridors, and for the restoration of the many corridors between reserves that have been lost.