bluuebunny/crossref_metadata_2025_split huggingface dataset:
Enhancing food supplies for waders: inconsistent effects of substratum manipulations on aquatic invertebrate biomass
Authors: Sanders Mark D. 
Published: March 2003

Summary 1. The potential of substratum manipulations as a technique for enhancing food supplies for waders was investigated in 98 constructed ponds at six sites in the Upper Waitaki Basin, New Zealand. Substrata were manipulated by using different construction methods, and by adding barley straw or stones to some ponds. Total invertebrate biomass and chironomid biomass were measured 3 and 15 months after ponds were constructed. 2. Food supplies in many newly constructed ponds contained large proportions of chironomid larvae, an attractive food for waders. However, this pattern was not universal; food supplies in many other newly constructed ponds were dominated by various nektonic invertebrates, or, at one site, by molluscs. 3. Food supplies developed rapidly; 3 months after construction most ponds contained similar or greater total invertebrate biomass (mean, range: 1·20, 0·10–7·66 g m−2 dry mass) and greater chironomid biomass (0·66, 0–5·41 g m−2) than nearby ‘pre‐existing’ wetlands (1·79, 0·39–6·18 g m−2 total invertebrate dry mass; 0·01, 0–0·08 g m−2 chironomid dry mass). However, ponds with stony substrata contained relatively low total invertebrate and chironomid biomass. 4. Substratum manipulations affected chironomid or total invertebrate biomass at all sites. Differences in biomass between substrata in constructed ponds were large at some sites (up to 2·7 g m−2 dry mass for chironomids, and up to 3·39 g m−2 dry mass for total invertebrates), indicating that substratum manipulations have good potential as a tool for increasing food supplies for wetland birds. 5. Despite the sometimes large effects of substratum manipulations, no technique achieved consistently positive results. The absolute and relative effects of any given substratum manipulation varied greatly among sites. This inconsistency indicates that, although substratum manipulations can be worthwhile, they need to be evaluated on a site by site basis.
Factors affecting the species composition of arable field boundary vegetation
Authors: Kleijn David , Verbeek Marein 
Published: March 2003

Summary 1.  In recent decades the botanical diversity of arable field boundaries has declined drastically. To determine the most important factors related to the species composition of arable field boundaries, the vegetation composition of 105 herbaceous boundaries, 1‐m wide, in the central and eastern Netherlands was surveyed. Biomass samples of the boundary were taken at 0–33, 34–66 and 67–100 cm from the adjacent arable field. 2.  Farmers were interviewed with respect to boundary management and land use on the adjacent arable field. The two data sets containing the botanical data and the environmental variables were linked and analysed by multivariate analysis and analysis of variance. 3.  The nitrogen and phosphorus inputs to the crop were closely correlated to another environmental variable, crop rotation. Crop rotations dominated by maize cultivation received significantly higher nutrient inputs than the other rotations. 4.  Nitrogen, phosphorus and crop rotation were strongly correlated with the composition of the boundary vegetation. Species richness of the boundary vegetation was negatively related to nitrogen and phosphorus inputs to the crop, while total boundary biomass was negatively related to nitrogen inputs only. Furthermore, there was a significant relationship between the partitioning of the boundary vegetation between different functional groups and both nitrogen inputs and crop rotation on the adjacent arable field. No significant relationships were found between the vegetation composition and either herbicide use in the boundary or boundary management. This may have been due to the descriptive approach of the study: little variation in boundary management as well as herbicide use in the boundary was observed in the study area. 5.
The boundary vegetation was characterized by a peak in biomass production in the zone near the arable field. In this zone the perennial arable weed Elymus repens, as well as annual dicot species, were significantly more abundant, while perennial dicots and monocots were significantly less abundant compared with the zones further from the arable field. 6.  Efforts to protect field boundary vegetation need to focus on a reduction or cessation of fertilizer applications in the outer metre(s) of crops that require high nutrient inputs. The determination of the exact nature of the relationship between the vegetation composition of arable field boundaries and the intuitively important management and herbicide use in the boundary requires an experimental approach.
Monitoring mammal populations with line transect techniques in African forests
Authors: Plumptre Andrew J. 
Published: March 2003

Summary1. Line transect survey techniques have been used to estimate population density for a variety of mammal species in tropical forests. In many cases indirect methods, surveying signs of animals such as counts of dung or nests, have been used because of the poor visibility in these forests. The estimates of the production and decomposition rates of these signs each have their associated errors; however, for the majority of published studies these errors have not been incorporated into the estimate of the standard errors or confidence limits of the density estimate. An equation is given showing how this should be done.2. An equation is also given relating the resolution (R) of a density estimate to the coefficient of variation (CV) of the estimate. This shows that to detect a 10% change in a population the CV must be 3·6% (with a power of 50%) or 2·4% (with 80% power). Using this equation and data from studies in Africa, it is shown that differences of less than 10–30% change in the population are unlikely to be detected between two surveys where visual sightings of animals are made. When indirect methods of estimating the population are used, it is unlikely that less than a 30–50% change in the population could be detected.3. Some studies have surveyed primate groups using estimates of an average group spread. Data from primate groups in Budongo Forest, Uganda, show that group spread is highly variable and varies at different times of day and between months. This survey technique is not recommended.4. If line transects are used for monitoring populations, conversion factors should be minimized as each contributes to an increase in the CV and a reduction in the ability to detect small changes in population density.5. Monitoring trends in abundance over several survey periods can improve the detection of change, although this is costly and requires several surveys before any conclusions can be reached. Re‐using transects in subsequent surveys can also reduce the variation around the estimate and will improve the resolution. Focusing survey efforts in areas of high density is an alternative strategy, but one that could lead to other errors as high‐density areas may be the safest and hence the last to show change. Using biased survey methods is also a promising technique that can increase the precision of surveys. It is concluded that a combination of different survey methods will ensure that changes in abundance are identified.
Effects of intensive harvesting on moose reproduction
Authors: Laurian Catherine , Ouellet Jean‐Pierre , Courtois Réhaume , Breton Laurier , St‐Onge Sylvain 
Published: March 2003

Summary1. It has been hypothesized that a balanced adult sex ratio is necessary for the full participation of ungulate females in reproduction and therefore high productivity. We tested this general hypothesis by combining two complementary approaches.2. First, using telemetry (n = 60) and annual aerial censuses between 1995 and 1998, we compared two mooseAlces alcespopulations in Quebec, Canada, one non‐harvested and the other subject to intensive sport harvesting from the end of September to mid‐October. We tested the following predictions for the harvested population: (i) females increase movements and home ranges during the mating period; (ii) the mating system is modified, with the appearance of groups of one male and many females; (iii) subadult males participate in reproduction; (iv) the mating period extends over two to three oestrus cycles; (v) the calving period extends over several months; and (vi) productivity declines.3. Daily movements and home range sizes during the mating period did not differ between harvested and non‐harvested populations. Most groups observed were male–female pairs. Subadult males (1·5–2·5 years old) were only observed with females in the harvested population. Mating and calving periods did not differ between populations. The proportion of females that gave birth and the number of calves produced were also comparable in the two populations.4. Secondly, we also assessed the existence of a relationship between population productivity and percentage of males in various management units of the province of Quebec that were characterized by a wide range in sex ratios. Contrary to prediction (vi), the number of calves per 100 adult females was not related to the percentage of adult males in the population.5. The participation of young adult males (subadults) in reproduction in our harvested population may have compensated for the lower percentage of adult males, and thus productivity was unaffected. We therefore reject the hypothesis that intensive harvesting, at least at the level we observed, affects reproduction and population productivity.6. As there are some uncertainties regarding the long‐term effects of high hunting pressure, however, managers should favour sex ratios close to levels observed in non‐harvested populations.
Habitat models of bird species' distribution: an aid to the management of coastal grazing marshes
Authors: Milsom T. P. , Langton S. D. , Parkin W. K. , Peel S. , Bishop J. D. , Hart J. D. , Moore N. P. 
Published: March 2003

1. Coastal grazing marshes comprise an important habitat for wetland biota but are threatened by agricultural intensification and conversion to arable farmland. In Britain, the Environmentally Sensitive Area (ESA) scheme addresses these problems by providing financial incentives to farmers to retain their grazing marshes, and to follow conservation management prescriptions.2. A modelling approach was used to aid the development of management prescriptions for ground‐nesting birds in the North Kent Marshes ESA. This ESA contains the largest area of coastal grazing marsh remaining in England and Wales (c. 6500 ha) and supports nationally important breeding populations of lapwingVanellus vanellusand redshankTringa totanus.3. Counts of ground‐nesting birds, and assessments of sward structure, surface topography and wetness, landscape structure and sources of human disturbance were made in 1995 and again in 1996, on 19 land‐holdings with a combined area ofc. 3000 ha. The land‐holdings varied from nature reserves at one extreme to an intensive dairy farm at the other.4. Models of relationship between the presence or absence of ground‐nesting birds and the grazing marsh habitat in each ofc. 430 marshes were constructed using a generalized linear mixed modelling (GLMM) method. This is an extension to the conventional logistic regression approach, in which a random term is used to model differences in the proportion of marshes occupied on different land‐holdings.5. The combined species models predicted that the probability of marshes being occupied by at least one ground‐nesting species increased concomitantly with the complexity of the grass sward and surface topography but decreased in the presence of hedgerows, roads and power lines.6. Models were also prepared for each of the 10 most widespread species, including lapwing and redshank. Their composition differed between species. Variables describing the sward were included in models for five species: heterogeneity of sward height tended to be more important than mean sward height. Surface topography and wetness were important for waders and wildfowl but not for other species. Effects of boundaries, proximity to roads and power lines were included in some models and were negative in all cases.7. Binomial GLMMs are useful for investigating habitat factors that affect the distribution of birds at two nested spatial scales, in this case fields (marshes) grouped within farms. Models of the type presented in this paper provide a framework for targeting of conservation management prescriptions for ground‐nesting birds at the field scale on the North Kent Marshes ESA and on lowland wet grassland elsewhere in Europe.
Patterns of incubation and nest‐site attentiveness in relation to organochlorine (PCB) contamination in glaucous gulls
Authors: Bustnes J.O. , Bakken V. , Erikstad K.E. , Mehlum F. , Skaare J.U. 
Published: March 2003

SummaryAlthough experimental studies show that organochlorines (OC) can affect bird behaviour, field assessments are invariably confounded by ecological differences between contaminated and uncontaminated sites. The behaviour of individual birds in the field has rarely been related to the contaminant burden.We examined individual patterns of incubation and nest‐site attentiveness in relation to OC burden, measured as polychlorinated biphenyl (PCB) concentration in the blood, of 27 glaucous gullsLarus hyperboreusin two breeding areas at Bear Island, in the north‐eastern Atlantic.Blood PCB concentrations ranged from 52 ng g‐1to 1079 ng g‐1(wet weight). There were significant differences between the two breeding areas, and females had significantly lower concentrations than males.Gull behaviour differed significantly between breeding areas and sexes independently of PCB. Females incubated more than males (54% vs. 46%) but spent more time away from the nest site than males, both overall (23% vs. 12%) and when not incubating (50% vs. 21%). They were also absent for longer periods (4·5 vs. 2·8 h). Moreover, length of incubation bouts (6·4 vs. 4·4 h), the amount of time absent from the nest site when not incubating (51% vs. 25%) and length of absences (5·6 vs. 1·8 h) differed between breeding areas, probably due to different feeding specializations.After controlling for these area and sex effects, the proportion of time absent from the nest site when not incubating, and the number of absences, were both significantly related to blood concentration of PCB.Increased absence from the nest site in individual glaucous gulls with high blood concentrations of OC suggests effects on reproductive behaviour. We speculate that endocrine disruption or neurological effects might be involved, leading to increased energetic costs during incubation and reduced reproductive output.
Factors affecting predation by buzzards Buteo buteo on released pheasants Phasianus colchicus
Authors: Kenward R.E. , Hall D.G. , Walls S.S. , Hodder K.H. 
Published: March 2003

Summary

Information on the effects of wildlife predation on game and livestock is required to allow improved management of all organisms involved. Monitoring of prey, predators and predation mechanisms each suggests important methods, illustrated here by data from common buzzards Buteo buteo and ring‐necked pheasants Phasianus colchicus.
Location data from 136 radio‐tagged common buzzards, together with prey remains from 40 nest areas, records from 10 gamekeepers and vegetation surveys, were used to investigate raptor predation at 28 pens from which pheasants were released in southern England.
Among 20 725 juvenile pheasants released in 1994–95, gamekeepers attributed 4·3% of deaths to buzzards, 0·7% to owls, 0·6% to sparrowhawks, 3·2% to foxes and 0·5% to other mammals.
Fresh pheasant remains were found on 7% of 91 visits to buzzard nests, and 8% of radio‐tagged buzzards had significantly more association than other buzzards with pheasant pens.
Predation by buzzards was most likely to be recorded at release pens with little shrub cover, deciduous canopies and a large number of released pheasants. The number of pheasants killed was greatest in large pens with extensive ground cover, and the highest proportion of released pheasants was killed in large pens where few were released. However, only 21% of 55 releases had > 2 pheasant kills per week.
Radio‐tagged buzzards were located most often at pheasant‐release pens with open, deciduous canopies. Pens were most likely to be visited by buzzards that had fledged nearby, but the proximity of buzzard nests had little influence on how much predation occurred.
Only a minority of buzzards associated frequently with pheasant pens, and predation was heavy at only a minority of sites, where pen characteristics and release factors probably made it easy for individual buzzards to kill pheasants. We suggest that the occasional heavy losses could be avoided by encouraging shrubs rather than ground cover in pens, by siting pens where there are few perches for buzzards, and perhaps also by high‐density releases.
Post‐war changes in arable farming and biodiversity in Great Britain
Authors: Robinson Robert A. , Sutherland William J. 
Published: March 2003

Summary

Agriculture represents the dominant land use throughout much of western Europe, and a significant part of European biodiversity is associated with this habitat. We attempted to quantify the changes in agriculture and biodiversity in Britain since the 1940s.
There have been widespread declines in the populations of many groups of organisms associated with farmland in Britain and north‐west Europe. The declines have been particularly marked amongst habitat specialists; many of the taxa still common on farmland are habitat generalists.
Farming practices have become increasingly intensive in the post‐war period, with a dramatic reduction in landscape diversity. Since 1945, there has been a 65% decline in the number of farms, a 77% decline in farm labour and an almost fourfold increase in yield. Farms have become more specialized; the greatly increased use of machinery has made operations quicker and more efficient, but has resulted in the removal of 50% of the hedgerow stock. Autumn sowing of crops has become predominant, with winter stubbles now far less prevalent. The number and extent of chemical applications has increased greatly, but the net amount applied, and their persistence, has decreased in recent years.
Intensification has had a wide range of impacts on biodiversity, but data for many taxa are too scarce to permit a detailed assessment of the factors involved. Reduction in habitat diversity was important in the 1950s and 1960s; reduction in habitat quality is probably more important now.
As a case study, the declines in populations of seed‐eating birds populations were assessed in relation to changing agricultural management. Generally, the declines were likely to be caused by a reduced food supply in the non‐breeding season, although other factors may be important for particular species.
Agriculture will face a number of challenges in the medium term. While research into the mechanisms underlying species and habitat associations, and their interaction with scale, will be critical in under‐pinning management, consideration of farmer attitudes and socio‐economic factors is likely to be as important. Biodiversity may benefit from integrated farming techniques but these need to incorporate environmental objectives explicitly, rather than as a fringe benefit.
Long‐term changes in the trophic level of the Celtic Sea fish community and fish market price distribution
Authors: Pinnegar J. K. , Jennings S. , O’Brien C. M. , Polunin N. V. C. 
Published: March 2003

Summary

The intensive exploitation of fish communities often leads to substantial reductions in the abundance of target species, with ramifications for the structure and stability of the ecosystem as a whole.
We explored changes in the mean trophic level of the Celtic Sea (ICES divisions VII f–j) fish community using commercial landings, survey data and estimates of trophic level derived from the analysis of nitrogen stable isotopes.
Our analyses showed that there has been a significant decline in the mean trophic level of survey catches from 1982 to 2000 and a decline in the trophic level of landings from 1946 to 1998.
The decline in mean trophic level through time resulted from a reduction in the abundance of large piscivorous fishes and an increase in smaller pelagic species which feed at a lower trophic level.
Similar patterns of decline in the trophic level of both catches and landings imply that there have been substantial changes in the underlying structure of the Celtic Sea fish community and not simply a change in fishery preferences.
We suggest that the reported changes in trophic structure result from reductions in the spawning stock biomass of traditional target species associated with intensive fishing, together with long‐term climate variability.
The relative distribution of fish market prices has changed significantly over the past 22 years, with high trophic level species experiencing greater price rises than lower trophic level species.
Although decreased abundance of high trophic level species will ultimately have negative economic consequences, the reduction in mean trophic level of the fish community as a whole may allow the system to sustain higher fishery yields.
Management objectives in this fishery will depend on the relative values that society attaches to economic profit and protein production.
Functional and numerical responses do not always indicate the most effective predator for biological control: an analysis of two predators in a two‐prey system
Authors: Lester P. J. , Harmsen R. 
Published: March 2003

Summary

Functional and numerical responses are key components in the selection of predators for biological control. We examined the relevance of these responses for predicting the effectiveness of generalist predators, taking into account effects of alternative prey and multiple predators. Our system involved two acarine predators of two prey species on apple. Responses were measured on leaf discs in the laboratory, and predictions assessed on small potted apple trees. In particular, we tested three hypotheses.
Hypothesis I: the species with the higher predatory responses will be more effective in limiting prey populations. Neither predator had a consistently higher functional response, which depended on prey stage and species. Amblyseius fallacis had a (approximately two times) higher ovipositional response than Typhlodromus pyri. We therefore hypothesized that A. fallacis would be more effective in controlling prey. No evidence was found to support this hypothesis.
Hypothesis II: alternative prey reduce the functional response of predators to target prey. Alternative prey did or did not reduce the functional response to target prey, depending on the predator, stage and species of alternative prey. The only consistent trend for both predators was that the predation of Panonychus ulmi deutonymphs was reduced when Tetranychus urticae was present.
Hypothesis III: the predator species with the highest mean ovipositional response will out‐compete the other predator species. The number of predators observed in the mixed predator treatments depended on the prey composition. Although A. fallacis had a higher ovipositional response, it was never more abundant. Intraguild predation probably played a role in determining predator abundance, although prey composition altered intraguild effects.
These results highlight the complex nature of predator and prey interactions. Because of these interactions, functional and numerical assays on single predator–single prey systems in simplified laboratory environments do not allow predictions of the growth of mixed populations in realistic habitats, or of the effectiveness of predators as biological control agents in the field.