bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of pH and resources on a processing chain interaction in simulated treeholes
Authors: Paradise Christopher J. 
Published: March 2003

1. Both resources and abiotic factors may affect biotic interactions. One interaction that occurs in treehole habitats involves leaf shredders that facilitate growth of detritivores, and it may be affected by both leaf litter quantity and changes in water quality. 2. Water chemistry in central Pennsylvania treeholes has been impacted by acid deposition, and the most common insects therein have differential survival under low pH conditions. Experimental microcosms that mimic treehole habitats were used to test the hypothesis that this abiotic factor, pH, also affects facilitative interactions. Leaf litter resources and pH were varied independently of presence of leaf‐shredding scirtid beetles (Helodes pulchella and Prionocyphon discoideus), and the mosquito Aedes triseriatus, to examine interactions among pH, resources and insects. 3. pH affected the interaction between the insects, such that effects of scirtids were more evident at pH 4·5 than at 6·5. Female mosquitoes were larger in the presence of scirtids, low resource and low pH conditions than in absence of scirtids, low resource and low pH conditions. 4. There were also effects of A. triseriatus on scirtids. The size of individual scirtids was smaller in the presence of A. triseriatus, but total scirtid biomass was unaffected as survival was also higher in the presence of A. triseriatus. 5. The effects observed on a resource‐mediated biotic interaction led to the conclusion that this interaction is pH dependent, and gives support to the concept that abiotic factors play a role in determining the outcome of biotic interactions, and that acidification can have complex effects on communities.
Density–distribution relationships in British butterflies. I. The effect of mobility and spatial scale
Authors: Cowley M. J. R. , Thomas C. D. , Roy D. B. , Wilson R. J. , León‐Cortés J. L. , Gutiérrez D. , Bulman C. R. , Quinn R. M. , Moss D. , Gaston K. J. 
Published: March 2003

Summary Positive relationships between the density and distribution of species in taxonomic assemblages are well documented, but the underlying mechanisms remain poorly understood. Two factors that are expected to be important in explaining variation in these relationships are the spatial scale of analysis and the relative mobility of the study species. We examined density–distribution relationships in British butterflies at a variety of spatial scales. Distributions were proportions of grid squares occupied: 50 m grid within 0·25 km2areas (local), 500 m grid in 35 km2(regional), 10 km grid across England, Wales and Scotland (national), 153 000 km2grid squares across Europe (European), and also seven categories of international distribution (Global; 1 = European endemic to 7 = in 5 + continents). Densities were measured using transect counts at local, regional and national scales. Different relationships between density and distribution occurred at different scales of analysis. When we controlled for the effects of mobility and/or phylogenetic association, a positive relationship between density and distribution was apparent at local, regional and national scales. Species’ national densities in Britain were positively correlated with their European distribution sizes, but significantly negatively correlated with their global range sizes. Butterfly mobility had a positive effect on distribution and a negative effect on density at all spatial scales. For a given total abundance, more mobile species had lower densities but wider distributions, i.e. they were less aggregated than more sedentary species. The decreasing strength of the density–distribution correlation, and the eventual reversal of the pattern, with the increasing magnitude of difference between the scale at which density was measured relative to distribution, suggests that some element of niche may be important in determining densities and distributions. However, the measure of niche breadth analysed did not explain significant variation in density, distribution, or in the density–distribution relationship.
The formation and growth of seabird colonies: Audouin’s gull as a case study
Authors: Oro Daniel , Ruxton Graeme D. 
Published: March 2003

Summary

Simulations of a stochastic, individual‐based predictive model were used to investigate the ecological processes relating to the formation and growth of colonies (local populations) of Audouin’s Gull (Larus audouinii Payraudeau). A colony was established in 1981 at the Ebro Delta (in the north‐western Mediterranean) and since then, the colony has grown dramatically at an average rate of 44% per year, such that by 1997 it held 65% of the total world population of this species.
Our model shows that the observed growth in the colony cannot be explained without large‐scale immigration of individuals into the colony. Although immigration occurred in most of the years throughout the study, years with an absence of immigration and even with net emigration from the colony also occurred.
The most likely source of immigrants was the colony on the Chafarinas Islands (655 km southwards from the Ebro Delta), which has been the largest known colony excluding the Delta in every year since 1981. However, immigrants from other neighbouring colonies apart from the Chafarinas, and even from other colonies beyond the western Mediterranean metapopulation were presumably also involved.
Immigration from other colonies is likely to be driven by temporal heterogeneity in the relative quality of the different colonies, combined with individuals dispersing to search for and select the most suitable breeding place, in order to increase their fitness. However, breeding success at the Ebro Delta colony was not autocorrelated from one year to the next, suggesting that the predictability of the environment was low.
Predictability was also low in other colonies within the metapopulation, independently of their size or relative quality. Results suggest that the presence of conspecifics (rather than local reproductive success) may be more important for immigrants in breeding site selection.
Colonization of the Ebro Delta was probably facilitated by the effective protection of the site against human disturbances, which produced a new, empty, high quality site for prospecting gulls. This may be considered a stochastic and density independent event, of a type that may have been a much more important influence on seabird colony formation than has been appreciated.
Dispersal and metapopulation dynamics of an oceanic seabird, the wandering albatross, and its consequences for its response to long‐line fisheries
Authors: Inchausti Pablo , Weimerskirch Henri 
Published: March 2003

Summary

We measured for the first time in a pelagic seabird the dispersal rate of wandering albatrosses and show that while adults are highly philopatric to breeding sites the dispersal rate of young birds is not negligible, even at large distances. We show that the wandering albatross has metapopulation dynamics, i.e. migration events are sufficient to influence the dynamics of populations at other islands.
The spatial dynamics of wandering albatross has important consequences when analysing and making projections of the effects that incidental by‐catch related to long‐line fishery activities at different spatial scales can have on the persistence of local populations of wandering albatross.
Modelling state‐dependent interference in common cranes
Authors: Stillman Richard A. , Bautista Luis M. , Alonso Juan C. , Alonso Javier A. 
Published: March 2003

Summary

Interference is a key component of food competition, but is difficult to measure in natural animal populations. Using data from a long‐term study, we show that interference between common cranes Grus grus L., feeding on patches of cereal seeds, reduces intake rates at high competitor densities, and that the strength of interference is unrelated to food abundance.
An alternative to measuring interference directly is to predict its strength using behaviour‐based models. We test an interference model, originally developed for shorebirds feeding on invertebrate prey, for cranes. We compare the predictions of a rate‐maximizing
model, in which animals steal food if this increases intake rate, and a
state‐dependent model, in which they only rate‐maximize if their intake rate is below a target value, otherwise they minimize injury risk by not stealing food. State‐dependent aggression occurs in cranes.
The state‐dependent model predicts more accurately the relative aggression rates of cranes of different dominance. However, both models predict accurately the observed strength of interference, that the strength of interference is unrelated to food abundance, at least within the observed range of crane and seed densities, and that cranes of a higher dominance have a higher intake rate than those of lower dominance.
This paper shows how state‐dependent behaviour can be incorporated into an interference model, and that the model can produce accurate predictions for a system quite different to that for which it was developed.
A 20‐year study on life‐history traits of a harvested long‐lived temperate coral in the NW Mediterranean: insights into conservation and management needs
Authors: Garrabou J. , Harmelin J. G. 
Published: March 2003

Summary

Long‐lived species play a paramount role in the structure and functioning of terrestrial and marine ecosystems. The dramatic increase of human‐induced disturbances may be irremediably affecting populations of long‐lived species. Data on life‐history traits on these species taking into account relevant temporal and spatial scales are very scarce for marine ecosystems, though these data are key to guarantee the conservation of these species and the communities that they shape.
This study examined long‐term data on life‐history traits of the precious red coral (Corallium rubrum L., 1758) in the NW Mediterranean. This was performed by surveying the fate of 67 red coral colonies during 21 years in a shallow‐water habitat (27 m depth).
Photographic monitoring provided data on survivorship, whole and partial mortality, recruitment and growth of colonies allowing about 1000 observations on life‐history traits.
Red coral showed a high survivorship, 60% of colonies reaching 22 years of age. Whole mortality was significantly higher in juvenile colonies while partial mortality displayed the inverse pattern. Recruitment showed a pulse mode with a single peak at the beginning of the study and low rates thereafter. Average growth rates over the study period were extremely low: 0·24 ± 0·05 mm year−1 for the basal diameter, 1·78 ± 0·7 mm year−1 for colony height and 3·40 ± 0·31 branches in 22 years.
This study also examined size‐related effects of harvesting on red coral populations since shallow‐water populations (between 10 and 40 m depth) have long been submitted to intensive harvesting.
Measurements (basal diameter and height) of 400 colonies corresponding to the largest ones dwelling in 10 currently harvested and two non‐harvested populations were compared to analyse the effects on the population's recovery and potential colonies’ maximum sizes. Harvested populations showed values that were about twice as low on average and up to four times lower for maximum values in colony size than in the non‐harvested populations.
Our study provides indisputable data on the longevity of colonies and the parsimonious population dynamics of C. rubrum. Current populations have shown a dramatic shift in their size structures characterized by the absence of large colonies. Taking into account results obtained in this study full recovery time of shallow‐water harvested populations may be measured by several decades or even centuries.
Intertidal habitat loss and wildfowl numbers: applications of a spatial depletion model
Authors: Percival S.M. , Sutherland W.J. , Evans P.R. 
Published: March 2003

1.  A spatial depletion model of the responses of grazing wildfowl to the availability of intertidal vegetation at Lindisfarne National Nature reserve, north‐east England, was used to investigate the capacity of the site’s beds of Zostera and other intertidal vegetation to support brent geese Branta bernicla hrota and wigeon Anas penelope. 2.  Recent total winter counts of brent geese and wigeon were both only 40% of the maximum that the food supply at the site could theoretically support. Other factors must have been restricting their numbers. Earlier arrival of brent geese at the site could increase the number of brent goose‐days which could be supported, but would have only a slight negative effect on the wigeon‐days. 3.  The model was used to examine three conservation issues: encroachment of Spartina anglica, sea level rise and loss of food plants from the whole site (which could result from increased autumn storms or plant disease). Loss from the top of the shore through encroachment by Spartina anglica had the greatest effect on the site’s capacity to sustain geese and wigeon. Loss from the bottom of the shore, as would occur through sea level rise, had less impact. Increased loss of vegetation over the whole site would have an intermediate effect. 4.  This work has important implications for the management of the site. Factors such as hunting, that may be restricting current numbers below those that could be supported by the food supply, require urgent investigation. Model predictions indicate that encroachment of Spartina is likely to depress local populations of brent geese and wigeon under current conditions only if it results in the complete loss of Zostera from the top 500 m of the shore.
Post‐burn reproduction of woody plants in a neotropical savanna: the relative importance of sexual and vegetative reproduction
Authors: Hoffmann William A. 
Published: March 2003

1. Burning typically occurs at intervals of 1–3‐years in the Brazilian cerrado, a rate that exceeds the precolonization fire regime. To determine if woody plants of the cerrado successfully reproduce within the short span of time between burns, experimental burns were used to quantify the effects of fire on sexual and vegetative reproduction of six species of resprouting trees and shrubs.2.Four of the six species reproduce vegetatively by producing root suckers. For three of these species,Rourea induta,Myrsine guianensisandRoupala montana, sucker production was seven to 15 times greater in burned plots than in unburned controls.3.Fire had a negative impact on sexual reproduction. Fire caused an immediate reduction in sexual reproductive success by destroying developing reproductive structures and seeds. Additionally, five of the six study species exhibited overall reductions in seed production in the years following fire. Fire had this effect by reducing the individual size of all species and, for three species, by reducing size‐specific reproductive output. Only the treePiptocarpha rotundifoliaexhibited increased seed production following burning.4.Fire caused substantial mortality to both seedlings and suckers. Suckers were larger than seedlings and experienced lower mortality rates for two of three species. Fire‐induced mortality of seedlings varied greatly among species, ranging from 33% to 100%.5.The results indicate that vegetative reproduction is much more successful than sexual reproduction under the high fire frequency typical of current fire regimes. It is concluded that current fire regimes must be causing a shift in species composition, favouring species capable of vegetative reproduction.
Movements and foraging areas of grey seals in the North Sea
Authors: Mcconnell B.J. , Fedak M.A. , Lovell P. , Hammond P.S. 
Published: March 2003

Summary 1. Grey seals Halichoerus grypus Fab. are large, numerous marine top predators. Fears concerning competition with fisheries have prompted calls for control measures. However, little is known about the areas where grey seals forage or the distances they may travel. 2. The movements of 14 grey seals caught at the Farnes in north‐east England (12) and Abertay in eastern Scotland (2) between August 1991 and July 1993 were investigated using Argos Satellite Relay Data Loggers (SRDLs). A total of 1461 seal days of location and behavioural data (mean 104·3 days per seal) covered all months of the year except February and March. 3. The seal movements were on two geographical scales: long and distant travel (up to 2100 km away); and local, repeated trips from the Farnes, Abertay and other haul‐out sites to discrete offshore areas. 4. Long distance travel included visits to Orkney, Shetland, the Faroes, and far offshore into the Eastern Atlantic and the North Sea. During travel the seals moved at speeds of between 75 and 100 km day–1 (0·87 and 1·16 m s–1). Most of the time, long distance travel was directed to known haul‐out sites. The large distances travelled indicate that grey seals that haul out at the Farnes are not ecologically isolated from those at Orkney, Shetland and the Faroes. 5. In 88% of trips to sea, individual seals returned to the same haul‐out site from which they departed. The durations of these trips were short (mean 2·33 days) and their destinations at sea were often localized areas characterized by a gravel/sand seabed sediment. This is the preferred burrowing habitat of sandeels, an important part of grey seal diet. This, and the fact that dives in these areas were primarily to the seabed, leads us to conclude that these were foraging areas. The limited extents of return‐trips from a haul‐out site (mean 39·8 km) suggest that the direct impact of seal predation may be greater on fisheries within this coastal zone, especially those near seal haul‐out sites, rather than on fisheries further offshore. 6. An average of 43% of all the seals’ time was spent within 10 km of a haul‐out site, although localized foraging areas were identified considerably further offshore. Proximity to a haul‐out may provide safety from predation. Alternatively, these periods may be used for rest or social interaction, or we may be underestimating foraging activity near haul‐out sites. 7. We suggest that the movement patterns observed in this study may persist through time and across the grey seals which haul‐out at the Farnes. We also suggest that a study such as this could be combined with diet studies and haul‐out censuses to map foraging intensity. Such information is an essential component of seal–fishery interaction models, upon which management decisions should be based.
Restoration of drained peatlands in southern Finland: initial effects on vegetation change and CO2 balance
Authors: Komulainen Veli‐Matti , Tuittila Eeva‐Stiina , Vasander Harri , Laine Jukka 
Published: March 2003

Summary 1. Components of the CO2 balance for a drained minerotrophic fen and a drained ombrotrophic bog were measured for permanent plots using static chamber techniques for 1 year before and 2 years after a rewetting treatment in part of both sites. During the same period, changes in ground and bottom layer vegetation composition were monitored. 2. After the treatment, the water table rose, the average increase being 25 cm for the fen site and 20 cm for the bog site. In the untreated areas the average water table remained at the pretreatment level. 3. There was a clear change in vegetation composition in the rewetted area of the fen site where the cover of cottongrass Eriophorum vaginatum L. increased drastically. The change in vegetation composition seemed to be dependent on the nutrient status of the sites, being faster at the more nutrient‐rich fen site. 4. The rates of CO2 efflux from the soil surface decreased on those rewetted plots where all vegetation had been removed. In 1996, the CO2 efflux rates from the soil surface of the untreated plots were about twice as high as from the rewetted plots with a high water table. 5. The change in water table levels and vegetation composition affected the seasonal (mid‐May to end of September) CO2‐C balances. For the rewetted area of the fen site, the CO2‐C balance varied from 162 to 283 g m–2, being greatest in a plot with dense E. vaginatum cover and a high water table. For the rewetted area of the bog site, the CO2‐C balance varied from 54 to 101 g m–2, being greatest in a hollow‐level plot with a high water table and mire vegetation. For the untreated areas, the CO2‐C balance was close to zero (3 g m–2 at the bog site) or negative (–183 g m–2 at the fen site), when carbon fixation by the tree stand was omitted. 6. The results are encouraging from the practical point of view as restoration of both fen and bog sites initiated vegetation succession and CO2‐C balance development towards those of pristine mires.
The use of sighting data to analyse Iberian lynx habitat and distribution
Authors: Palma Luís , Beja Pedro , Rodrigues Miguel 
Published: March 2003

Summary 1. Over a large part of its very restricted and fragmented range, Iberian lynx Lynx pardinus occur in remote mountainous country at low density, where the only information about the species comprises records of incidental sightings obtained by inquiry. In this study we developed an approach for quantifying lynx–habitat relationships and distribution patterns from sighting data, using records from western Algarve (Portugal) in 1990–95. 2. Habitat was described in terms of land cover, topography, human disturbance and rabbit abundance, in 25‐km2 cells surrounding lynx sightings and at random locations within the study area. 3. Lynx sightings were consistently associated with predictable habitat features. Sighting probabilities estimated from a logistic regression model increased with the abundance of rabbits and the proportion of land covered by tall Mediterranean maquis, and declined with road density and the amount of developed land. This model identified correctly 85·7% of lynx sightings; at the same time only 20·7% of the random locations were misclassified. 4. Indices of human presence were never associated positively with lynx sightings, suggesting that observation patterns were not influenced by the spatial distribution of potential observers. 5. Kriging was used to interpolate spatially between sighting probabilities derived from the logistic model in order to produce a map of sighting potential for the Iberian lynx in western Algarve. Jack‐knife resampling assessed the accuracy of this map. Three well‐defined areas of high sighting potential were identified, probably representing the lynx core areas in this region. 6. Our analysis of lynx sighting records suggests that these data may provide a first approximation to lynx habitat and distribution when further information is lacking. The application of this approach to other rare and reclusive species is discussed.