bluuebunny/crossref_metadata_2025_split huggingface dataset:
Metapopulation moments: coupling, stochasticity and persistence
Authors: Keeling Matt J. 
Published: March 2003

1. Spatial heterogeneity has long been viewed as a reliable means of increasing persistence. Here, an analytical model is developed to consider the variation and, hence, the persistence of stochastic metapopulations. This model relies on a novel moment closure technique, which is equivalent to assuming log‐normal distributions for the population sizes.2. Single‐species models show the greatest persistence when the mixing between subpopulations is large, so spatial heterogeneity is of no benefit. This result is confirmed by stochastic simulation of the full metapopulation.3. In contrast, natural‐enemy models exhibit the greatest persistence for intermediate levels of coupling. When the coupling is too low, there are insufficient rescue effects between the subpopulations to sustain the dynamics, whereas when the coupling is too high all spatial heterogeneity is lost.4. The difference in behaviour between the one‐ and two‐species models can be attributed to the oscillatory nature of the natural‐enemy system.
Prey diversity, prey composition, and predator population dynamics in experimental microcosms
Authors: Petchey Owen L. 
Published: March 2003

Summary1.Food‐web complexity‐stability relations are central to ecology, and many empirical studies show greater food‐web complexity leads to lower population stability. Here, predator population variability decreased with increasing prey diversity in aquatic microcosm experiments, an example of greater food‐web complexity leading to greater population stability.2.Prey diversity as well as different sets of prey species within each level of prey diversity produced differences in predator population dynamics, demonstrating the importance of both prey composition and prey diversity in determining predator population stability.3.Prey diversity can affect predator population dynamics through at least three groups of mechanisms: prey reliability, prey biomass, and prey composition mechanisms. The results suggest that greater prey reliability at higher prey diversities enhances predator stability and provide support for MacArthur (1955).
Plastic daily fattening routines in willow tits
Authors: Koivula Kari , Orell Markku , Lahti Kimmo 
Published: March 2003

Summary

Each day small birds must build up sufficient energy reserves, largely fat deposits, for the following night and for the periods when foraging is not possible. The earlier the birds acquire the reserves and the more they carry them, the higher is the insurance value of the reserves. Still, small birds do not forage at maximal capacity during the day and, even at dusk, body reserves are usually below the physiological upper limit. A popular explanation for this is that birds’ fatness levels reflect an optimal compromise between starvation risk and risks associated with reserve carrying and acquisition.
Theoretical works suggest that uncertain or variable feeding conditions should promote high reserve levels, and that in the daily perspective, feeding should peak in the morning hours. In more favourable conditions, reserve levels should be smaller and the acquisition peak should be delayed towards the end of the day. These predictions were tested by experimentally manipulating winter feeding conditions and monitoring subsequent daily body mass increase in northern population of the willow tit Parus montanus (Conrad), a small‐sized forest passerine.
The birds using feeders appeared heavier than the control birds throughout the day. This contradicts the prevailing theory, but is understandable since the feeding procedure probably not only affected food amount but may also have decreased acquisition costs in terms of predation.
Daily mass gain and the gain rates were fairly similar in the food‐manipulated and the control birds. However, the mass gain schedules differed between the treatment groups: the food‐supplemented birds gained mass at a roughly constant rate while among the control birds the gain rate was higher in the morning than in the afternoon. Probably to avoid associated costs, birds abandon early build‐up of reserves if foraging conditions become favourable enough.
Management procedures required to increase chironomid availability to waders feeding on artificial lagoons remain unclear
Authors: Green A.J. , Hilton G.M. 
Published: March 2003

1.  Rehfisch (1994) made various recommendations for how to increase chironomid biomass and its availability to waders in artificial lagoons. We argue that his studies form an insufficient basis for some of these recommendations. 2.  He suggested protocols for depth manipulation based on a model predicting biomass in terms of depth and depth squared which was not a meaningful representation of his data. This model should therefore not be used as a guide for managing water levels. 3.  He predicted that biomass would peak at a depth of about 117 cm, yet he only studied depths of up to 54 cm. We used data from a large, permanent, brackish lake to illustrate how biomass at shallow depths cannot be used to predict that found at greater depths. 4.  His aim of a simple model allowing managers to predict chironomid biomass on the basis of depth in artificial lagoons was unrealistic, owing to wide variation in the biomass–depth relationship within and between sites. 5.  The value of his ‘inverted sombrero’ design for a wader lagoon needs to be demon strated empirically. He advocated regular drying‐out of lagoons followed by immediate refilling, a flooding cycle that may not maximize chironomid biomass.
Modelling topoclimatic patterns of egg mortality of Epirrita autumnata (Lepidoptera: Geometridae) with a Geographical Information System: predictions for current climate and warmer climate scenarios
Authors: Virtanen Tarmo , Neuvonen Seppo , Nikula Ari 
Published: March 2003

1.  Our aim was to quantify the effects of a warmer winter climate on the egg mortality (and, consequently, the risk of an outbreak) of Epirrita autumnata, a serious defoliator of mountain birch. 2.  The egg survival of E. autumnata was studied in northernmost Finland from 1993 to 1996, when minimum temperatures were also recorded. Utilizing a digital elevation map with a GIS (Geographical Information System), models were developed for egg survival and minimum temperature, taking into account altitude, local topography and temperatures at a meteorological station in the study area. 3.  Areas of high egg mortality of E. autumnata can be modelled in the GIS with reasonable accuracy by the model describing areal distribution of minimum winter temperatures, taking account of the fact that the critical limit for egg survival of E. autumnata in midwinter is about −35·5°C. The approach can be applied in short‐term forecasting of outbreak areas when previous year population densities and minimum winter temperatures at meteorological stations are known. 4.  In our study area, from 1961 to 1991 more than one‐third of the years were egg‐killing winters in the mixed birch‐pine forests zone, and 15% of years in the birch forest zone. In order for an outbreak to take place, at least three consecutive seasons with a high population growth rate are needed; in the mixed birch‐pine forests the possibilities of an E. autumnata outbreak during the period 1961–91 were very rare, while in the birch forest zone outbreak possibilities were also noticeably restricted by winter minimum temperatures. 5.  If winter warming takes place according to the scenarios presented, by the middle of the next century the birch‐growing areas in our study area protected by low temperatures from outbreaks of E. autumnata will be only one‐third as great as those of today, and by the end of the next century only one‐tenth of those of today. 6.  The models and methods described in this paper can be applied to other ecological processes. The modelling strategies and techniques described here serve as intermediate tools for linking large scale climate models (general circulation models, GCMs) and ecological processes happening at a smaller scale.
Changes in decomposition rates and Collembola densities during the forestry cycle in conifer plantations
Authors: Butterfield J. 
Published: March 2003

1.Conifers have a tendency to produce detrimental changes in the soil that suppress decomposition. It is also possible that clear‐felling and the short plantation rotation (40–50 years), usual in Britain, will eventually cause nutrient depletion. Decomposition rates are important in determining the level of nutrients available, to both the crop and the soil invertebrate community, and this study has compared them at three stages during the plantation cycle.2.Cotton cloth buried in the soil of open areas decomposed at twice the rate of cloth buried in the soil of closed canopy plantations.3.The rate of decomposition in the soil layer 0–80 mm from the surface was 1·5 times that in the 81–160 mm layer.4.In young plantations, the decomposition rate of cloth decreased with an increase in the age of the plantation. It is suggested that the decrease in decomposition rate with plantation age is associated with increased shading and a decrease in the amplitude of the diurnal temperature cycle.5.Springtail (Collembola) densities were high in spring on an open area and decreased in summer. The opposite occurred in the closed canopy plantation. Drying on the exposed open area is suggested as the cause of the decreased summer densities.6.On the site where Collembola densities were monitored, decomposition rates were higher in the upper soil layer of the closed canopy plantation than in an open area. It is probable that this was due to the upper layers on the exposed area drying, rather than to the high Collembola densities checking fungal decomposition.7.The nutrient release that accompanies decomposition has potential importance for the rate of growth of the conifer crop. This preliminary study suggests that the decomposition rate is highest in the years immediately after felling, probably favouring the establishment of the next rotation.8.This study has not detected suppression of decomposition on open or clear‐felled areas in Hamsterley Forest (NZ0530), suggesting that present planting and harvesting methods are appropriate and should continue. However, further investigation of the interactions between fungi, meso‐ and macrofauna is needed to understand both nutrient cycling and the invertebrate community structure in plantation forestry.
A history of change: causes of miombo woodland decline in a protected area in Malawi
Authors: Abbot Joanne I. O. , Homewood Katherine 
Published: March 2003

1. Tropical dry woodlands are thought to be declining as a result of human activity. Aerial photograph analysis showed measurable conversion of closed canopy miombo* to sparse woodland in Lake Malawi National Park, Malawi, from 1982 to 1990. This multi‐disciplinary study investigates the possible contributions to these impacts by local use of domestic fuelwood, construction poles and fuelwood for commercial fish smoking. 2. Domestic fuelwood use was measured in 30 households over an 11‐month period. Domestic fuelwood is collected by women and is headloaded to the village. It comprises a large biomass of mainly dead wood and small branches over a wide species range. Mean total annual domestic fuelwood consumption by the total enclave population was less than half the mean annual production of fallen dead wood in the Park, estimated from three quadrats harvested monthly over an 11‐month period. 3. Construction poles are mostly small, have extended durability and come from a broad species range. Fencing poles frequently take root to form live hedges. Eucalyptus trees are commonly grown for poles. Construction pole use appears sustainable and shows signs of substitution. 4. The 305 commercial fish smoking stations in the enclaves used less fuelwood annually than domestic fuelwood users. However, the men who undertake this activity target large branches and logs from a narrow species range, involving destructive felling of canopy species. 95% of men collecting fuel for fish smoking use cutting tools and three‐quarters transport the wood by boat or bicycle. 5. The scale, size classes and species involved in commercial fish smoking suggest that this activity drives the observed degradation of closed canopy to sparse woodland. Traditional local fishing focused on small species sun‐dried for preservation. Commercial fish smoking was introduced relatively recently by immigrants, along with gill netting that harvests larger fish requiring smoking for preservation. Demand for fish by ever‐increasing urban populations underpins the continuing growth of the fish smoking industry. 6. Disaggregation of different wood use practices allows informed management policy for the Park. Currently, management targets and penalizes domestic fuelwood collectors. While seeking to reduce demand and provide alternative fuelwood sources, law enforcement and forestry extension should be reorientated to address the extraction of fuelwood for fish smoking.
Determinants of human–elephant conflict in a land‐use mosaic
Authors: Hoare R.E. 
Published: March 2003

Summary1. The resolution of direct conflict between humans and elephants in Africa has become a serious local political issue in recent years, and a continental conservation problem. ‘Problem elephants’ damage crops, food stores and water sources, and sometimes threaten human life.2. Eighty per cent of the African elephant's range lies outside formally protected areas, and inadequate management of human–elephant conflict is frequently a precursor to further decline in the numbers and distribution of elephants. Conflict appears to be increasing in an assortment of African ecosystems as the agricultural interface with elephant range expands.3. The present study recorded incidents by problem elephants in small subdivisions of a 15 000 km2elephant range. The level of problem elephant activity over 3 years showed huge variation and could not be explained by elephant density, proximity of a protected area, area of human settlement, human density or local rainfall.4. It is proposed that the irregular and unpredictable nature of human–elephant conflict incidents in the study area mainly depended upon the behavioural ecology of individual elephant bulls.5. This study proposes a statistic to quantify problem elephant activity in Africa which can be used to compare the intensity of problem incidents between different ecosystems at different times: ‘elephant incidents per square kilometre of human settlement area per year’. Spatial analyses of appropriate data at the human–elephant interface may yield a more predictive understanding of the conflict process.
Patterns of otterLutra lutraroad mortality in Britain
Authors: Philcox C.K. , Grogan A.L. , Macdonald D.W. 
Published: March 2003

Summary1. This paper examines patterns of otter road traffic accidents and the possibilities for reducing this mortality.2. Records of otter road casualties in Britain (673 between 1971 and 1996) were compiled and accident sites were plotted on 1:50000 scale Ordnance Survey maps. Casualty records were categorized by geographical region, road type, distance to watercourses and presence and type of river crossings. The data were analysed for demographic, seasonal, temporal and spatial trends.3. A rapid increase in numbers of road traffic accident records has occurred since 1983. Fifty‐six per cent of fatalities were males, representing a statistically significant bias.4. The number, but not the sex ratio, of otter road casualties differed between seasons and in all areas was positively correlated with either seasonal rainfall or river flow.5. Significant effects of geographical region, road density and year were found on the annual number of casualties recorded in mainland regions, and the regional rates of increase in numbers of road traffic accidents were significantly different. There is also evidence that road traffic accidents are influenced by otter site occupancy of a region.6. Trunk and A‐roads accounted for 57% of road traffic accident records, even though they comprise only 13% of the road network.7. A 100‐m wide zone surrounding fresh water and the coast accounted for 67% of all casualty records. Measures to reduce road mortality should target this zone.8. The seasonal correlations of otter road traffic accidents with rainfall and river flow, and the fact that 91% of accidents occurred where a road crossed a watercourse, suggest that substantial reductions in road mortality could be achieved by improving the design of road crossings of watercourses.9. We suggest that the optimal approach to road crossing design is to maintain a continuous, and where possible, natural bank above the level of high flows, using either wide‐span bridges, over‐sized culverts or artificial ledges.10.The use of otter‐proof fencing may be required to reduce mortality where roads pass close to watercourses, but care must be taken that this does not create a barrier to all movements of otters and other wildlife.
Predation onPinus sylvestrisseeds and juvenile seedlings in Swedish boreal forest in relation to stand disturbance by logging
Authors: Nystrand Ove , Granström Anders 
Published: March 2003

Summary1. Forest management involving live tree retention and natural regeneration after cutting is currently increasing in boreal areas. This calls for further analysis of the optimal conditions for seedling establishment from seed following stand disturbances due to logging.2. We studied post‐dispersal predation on seeds and juvenile seedlings ofPinus sylvestrisover 3 years in 32 north Swedish boreal forest stands with different levels of stand disturbance by logging. The aims were to identify the most important predator species and to quantify the damage inflicted upon seeds and seedlings in relation to disturbance.3. In most stands and years, seed predation resulted in < 20% seed mortality, although occasionally it reached 60%. Predation on juvenile seedlings ranged from 5% to 100%, with > 70% mortality in 10 cases and < 30% in 44 cases (of a total of 79 observations).4. The most important seed predators were the carabidsPterostichus oblongopunctatusandCalathus micropterus, and seed predation was correlated with the number of seed‐eating carabids caught in pitfall traps. Microtine rodents caused high damage levels only on a single occasion.5. Logging affected both catches of carabids and seed predation levels, but the relationship between tree stand density and predation was not linear and, generally, seed predation decreased in the order shelterwood > unlogged forest > clear‐cut.6. The most important predator on juvenile seedlings was the slugArion subfuscus, which attacked seedlings during the first weeks after germination. Pitfall trap catches ofHylobius abietis, which commonly damage planted (1–3‐year‐old) conifer seedlings, were not related to the levels of seedling predation.7. Seedling predation was negatively related to stand disturbance, with the highest predation levels by slugs in unlogged forests and the lowest in clear‐cuts. Seedling predation was higher in wet than in dry summers, probably because slugs are moisture‐limited.8. There was a large between‐site variation in both seed and seedling predation, but predation was not strongly related to forest site types. The fact that predation was strongly affected by logging operations indicates that there may be opportunities to reduce damage through modification of the silvicultural practices.
Large−scale disturbances, biological control and the dynamics of gorse populations
Authors: Rees M. , Hill R.L. 
Published: March 2003

Summary

Simulation and analytical models were developed for gorse Ulex europaeus. The simulation model incorporated spatially local density−dependent competition, disturbance, asymmetric competition between seedlings and established plants, a seed bank, local seed dispersal, an age structured established plant population, and temporal variation in the probability of disturbance. The analytical models were simple approximations of the simulation.
The models extended our previously published model for Scotch broom Cytisus scoparius to include large−scale disturbances and possible management options, such as the use of fire, herbicides and oversowing with perennial grasses. Fire was assumed to influence established plant mortality, seed survival in the seed bank, and the probability of germination.
We reviewed published data on the demography of gorse in New Zealand, the current management techniques, and the ongoing biological control programme.
Over a wide range of biologically reasonable parameter values, the analytical models accurately predicted the outcome of the simulations. The analytical models worked well, providing gorse occupied a high proportion of the available sites and large−scale disturbances did not occur too frequently.
The potential impact of seed−feeding biological control agents on gorse abundance was assessed, using the models, for several environmental and management scenarios. In particular, we explored how large−scale disturbance, such as fire and herbicide application, influences the outcome of biological control.
The success of a biological control programme was found to depend critically on the frequency and intensity of disturbance, whether disturbed sites became suitable for recruitment, and the effects of disturbance on germination and seed mortality.
The models highlight the need to manage recruitment opportunities carefully in order to maximize the effect of biological control agents. The models also indicate that details of plant population biology can have a profound effect on the success of any management strategy.
Linking agricultural practice to insect and bird populations: a historical study over three decades
Authors: Benton Tim G. , Bryant David M. , Cole Lorna , Crick Humphrey Q. P. 
Published: March 2003

Summary

There is continuing debate about the impact of agricultural practices on farmland wildlife. In particular, it has been postulated that a general decline in insect abundance linked with intensification of agriculture may have contributed to farmland bird decline. While some autecological studies have supported this hypothesis, larger‐scale and long‐term studies are needed.
Suction traps mounted on 12·2‐m towers (Rothamsted‐type) have been sampling aerial insects for nearly 40 years throughout the UK. Their catches are correlated over large spatial scales. We analysed insect catch data from a single suction trap run for 27 years in a rural location in Scotland, and showed that insect numbers have changed significantly over time, although non‐linearly. The multivariate data set (numbers from the 12 common arthropod groups) was summarized using principal components analysis (PCA) to extract three components explaining 62% of the variation.
We also used PCA to describe agricultural change, using published agricultural data for eight measures of farming in Scotland. Arthropod abundance and principal component (PC) scores were significantly related to the agricultural PC scores as well to summary climatic measures.
Using Scottish data from the British Trust for Ornithology Common Birds Census, we extracted three PC to describe the time‐dependent average densities of 15 common farmland birds in Scotland. Measures of bird density were significantly related to insect abundance and PC scores and, independently, to measures of agriculture and climate.
These data from a broad suite of species provide support for linked temporal change between farmland birds, invertebrate numbers and agricultural practice in Scotland. Although entirely correlative, the results are consistent with the view that agricultural change has influenced birds through changes in food quality or quantity. The work also shows how large‐scale invertebrate sampling, in this case using suction traps, is useful for monitoring farmland biodiversity.