bluuebunny/crossref_metadata_2025 huggingface dataset:
Distribution ofCrassiphiala bulboglossa, a parasitic worm, in shoaling fish
Authors: Krause Jens , Ruxton Graeme D. , Godin Jean‐Guy J.
Published: March 2003

1. The distribution of transmittable parasites in group‐living host species has been investigated in a number of studies. However, little is known about the distribution of parasites with indirect life cycles in this context. This study investigates the relationship between parasitism and shoal composition by looking at the distribution ofCrassiphiala bulboglossa(Haitsma), a trematode worm which uses fish as an intermediate host, within and between fish shoals in a lake. In particular, tests aimed at establishing whether the parasite distribution was affected by parasite‐assortative shoaling behaviour, host group size, host habitat characteristics, and other factors (such as species identity and body length) that potentially covary with parasite infection.

2.Overall, 34 fish shoals were caught. For each shoal member, the fish species was identified, its standard body length measured and its parasites (C. bulboglossa) counted. Three habitat characteristics were also recorded for each shoal: water depth and distances to shore and to vegetation.

3.Crassiphiala bulboglossaprevalence and load varied with fish species. Only 6% of the golden shiners [Notemigonus crysoleucas(Mitchill)] were parasitized, whereas 24% of the killifish (Fundulus diaphanus(Lesueur)] and 98% of the white suckers [Catostomus commersoni(Lacépède)] were infected. Infected shiners and killifish had very low parasite loads, whereas suckers were heavily parasitized. Parasite prevalence within shoals was not correlated with the average body lengths of killifish and shiners in shoals (sample size was too small for testing in suckers).

4.Killifish shoals showed parasite prevalences significantly different from those expected under a null hypothesis that assumes assortment of fish between shoals by size and species but not by parasitism. In shiners and suckers, no evidence for non‐random distribution of parasites among shoals was found, which may have been because of lack of statistical power.

5.Parasite prevalence was related to the number of conspecifics in a shoal for shiners but not for killifish.

6.There was no significant relationship between parasite prevalence and habitat characteristics in shiners and killifish.
Increasing returns in the life history of Columbian ground squirrels
Authors: Dobson F. Stephen , Risch Thomas S. , Murie Jan O.
Published: March 2003

1. We examined positive associations and trade‐offs of maternal and reproductive traits in a population of Columbian ground squirrels, Spermophilus columbianus.

2. Structural size, body condition, mother's personal allocation to body mass during reproduction, and timing of littering were estimated for live‐trapped reproductive females that were observed during an 8‐year period, and were compared to litter mass, litter size, and average pup mass using path analyses.

3. Mothers exhibited age‐structured traits that influenced reproductive patterns. Yearling mothers were significantly smaller, bred later, and had smaller litters than older females. Mothers that gained more body mass during reproduction and older mothers in good body condition that were structurally large had larger litters.

4. Early seasonal timing of littering was an important positive influence on successful reproduction by older mothers only in early breeding seasons and in years when conditions for reproduction were good for all females.

5. The number of offspring that survived to 1 year of age was most strongly associated with litter mass and litter size; date of breeding was of secondary influence, with earlier litters exhibiting greater success.

6. In general, mothers that gained the most in body mass during reproduction were concurrently more successful in weaning large litters (perhaps due to better quality of foraging habitat).

7. In addition to expected reproductive trade‐offs, reproduction by Columbian ground squirrels exhibited positive associations of life‐history traits that may reflect evolutionary increasing returns.
Dispersal in a metapopulation of the bush cricket,Metrioptera bicolor(Orthoptera: Tettigoniidae)
Authors: Kindvall Oskar
Published: March 2003

1. I present a stochastic simulation model that describes individual movements ofMetrioptera bicolorPhilippi in a heterogeneous landscape, consisting of patches of suitable habitat surrounded by a matrix of unprofitable habitats. Although the model is parameterized with information about daily movement behaviour, it can generate spatially explicit predictions about inter‐patch dispersal rates for much longer periods, e.g. one generation.

2.Long‐term dispersal experiments were conducted to evaluate model predictions. Patch‐specific emigration rates and the total distance moved by individuals could be predicted with satisfactory precision. Because of the stochastic nature of the model, it failed to predict which recipient patches emigrating individuals actually chose in a particular situation.

3.Spatially explicit simulations of the movement model were made for the whole natural distribution area ofM. bicolor. The results suggest that emigration rates are negatively correlated with patch size. Local populations occurring on small patches may be more prone to extinction than those on large patches, by losing more emigrants than are compensated for by immigration.
Consequences of maternal size for reproductive expenditure and pupping success of grey seals at North Rona, Scotland
Authors: Pomeroy P. P. , Fedak M. A. , Rothery P. , Anderson S.
Published: March 2003

1. The reproductive performance of individually marked mothers aged between 4 and 36 years breeding at the established grey seal colony of North Rona, Scotland was studied. Natality rate was between 0·805 and 0·975 for these females during 1979–95 and 57% of females produced 74% of the pups born. Mothers pupped successfully on N. Rona after absences of up to 5 years.

2. The average maternal postpartum mass (MPPM) of mothers was 190 ± 23 (SD) kg, larger than had been recorded from this colony previously. Although annual mean MPPM increased during the study, there were increases and decreases in individuals’ MPPM between years.

3. Pup mass at birth and pup growth rate were related to MPPM and date of parturition. No evidence of differential postpartum expenditure in the sexes was found. Relative pup birth mass decreased with MPPM but relative pup weaning mass remained constant over the range of MPPM.

4. Maternal mass expenditure during lactation averaged 39% of MPPM, and the consequences for MPPM in the year following either high or low relative expenditure were inversely related to relative expenditure in the first year. However, mothers increased their mass after skipping breeding in a year.

5. General Linear Models and REML analyses indicated that expenditures were significantly different between mothers when other variables and factors had been taken into account. In general, maternal expenditure was greater for animals of larger masses and duration of lactation, but corrected maternal expenditure of longer individuals was less than expected. Pup mass at weaning was influenced by mother's identity and year and there was evidence that individual mothers which were longer for their weight raised smaller pups.

6. The life history consequences of reproductive expenditure in any year appeared in subsequent breeding patterns. The cost of breeding for larger animals and larger expenditures was indicated by lower pupping success rates in years following births and skipped breeding years.
Asymmetric competition between two tit species: a reciprocal removal experiment
Authors: Torok JÁnos , TÓth LÁszló
Published: March 2003

1. In a 5‐year field experiment, competition for food was tested between great tit (Parus major L.) and blue tit (P. caeruleus L.), two common hole‐nesters in Central Europe. Experimental (‘allopatric’) populations of both species were created during the breeding seasons by preventing the nesting or egg laying of one of the competing species.

2. An asymmetric relationship was found between the two tits; blue tits were more successful in the competitive interaction. Detectable effects were found only in nestling condition. Great tits raised lighter nestlings when breeding sympatrically with blue tits.

3. A possible mechanism is suggested that could be responsible for the different competitive abilities of the two species; blue tits are more effective in utilizing the most abundant size categories of caterpillar food supply than great tits.
Synchrony, scale and temporal dynamics of rock partridge (Alectoris graeca saxatilis) populations in the Dolomites
Authors: Cattadori Isabella. M. , Hudson Peter. J. , Merler Stefano , Rizzoli Annapaola
Published: March 2003

1. Harvesting records of rock partridge (Alectoris graeca saxatilis) were examined first to identify the presence of cycles in a species with a southern European distribution and then to examine synchrony between populations at a range of scales.

2. Hunting records from 1965 to 1994 were obtained from 210 hunting areas and analysed at three spatial scales: subpopulation, population and metapopulation. Rock partridge exhibited cyclic fluctuations in about 40% of the time series with a period of 4–7 years. The results did not change with spatial scale. The density‐dependent structure of the populations showed that most populations exhibited damped oscillations.

3. The proportion of populations that were in synchrony increased with scale from the population to metapopulation level. There was no decline in synchrony with distance but a large variation between populations irrespective of distance.

4. The populations clustered into dry and wet habitats, with those in the dry habitat being more cyclic. We suggest the lack of spatial synchrony with distance but greater synchrony within habitats may reflect the influence of stochastic events operating on populations with different density dependence structures.
Rabbits killing birds: modelling the hyperpredation process
Authors: Courchamp Franck , Langlais Michel , Sugihara George
Published: March 2003

1. Introduced rabbits are known to have catastrophic effects on oceanic islands, either by direct destruction of the vegetative cover, or by the resulting disturbance of indigenous vertebrates.

2. Another dramatic effect, less well known, but potentially of major importance, is the hyperpredation process. This process, related to apparent competition, predicts that an introduced prey species, well adapted to high predation pressure, could induce the extinction of an indigenous prey, through the sudden increased population size of an introduced predator. In many island ecosystems, the simultaneous presence of introduced feral cats and rabbits is thus potentially a further threat for small vertebrates endemic of these islands.

3. Through a mathematical model, we tested this hypothesis, using a tri‐trophic system comprising an indigenous prey (birds), an introduced prey (rabbits) and an introduced predator (cats), and we demonstrated the theoretical existence of the hyperpredation process.

4. In addition, the numerical analysis of the model allowed a quantification of this process. It shows that the conditions required for an indigenous species to cope with the hyperpredation process imply very high intrinsic growth rates and/or carrying capacity, as well as behavioural anti‐predator response to the introduced predator. Since these conditions are unlikely to be met, this process is a further potential threat to most indigenous vertebrate prey.

5. Finally, our model shows that, although it can be induced by both types of adaptation together or alone, behavioural adaptations alone are more powerful in generating the hyperpredation process, than are life history traits adaptations.
Spatial dynamics of predation by carabid beetles on slugs
Authors: Bohan David A. , Bohan Anna C. , Glen David M. , Symondson William O. C. , Wiltshire Christopher W. , Hughes Louise
Published: March 2003

1. An explicitly spatial sampling approach was employed to test the null hypothesis that the predation on slugs by the carabid beetle Pterostichus melanarius (Illiger) was opportunistic.

2. The beetles and slugs were sampled across a nested series of grids of sampling points, in a field of winter wheat during June and July 1997.

3. The spatial distribution of all slugs in June was found to change with the scale of the sampling grid, from random on the 0.25 m scale, through aggregation at 1 m, to random at 4 m. At the highest scale of 16 m, the slugs were significantly spatially aggregated.

4. The distribution of beetles in June was also spatially dynamic, with randomness observed at the 4 m and 8 m scales. At 16 m, significant aggregation was observed.

5. The dynamic distributions of slugs and beetles, at 16 m, were found not to be associated with, and thus were not determined by, soil or crop factors.

6. Comparison of slug and beetle populations showed, however, that the distributions at 16 m were dynamically associated with each other. In June where there were many slugs there were also many carabids, whilst in July where there were many carabids there were few slugs.

7. Approximately 11% of the beetles sampled across the 16 m grid in June and July were found to have ingested slug protein, following intensive enzyme‐linked immunosorbent assay (ELISA) testing.

8. The spatial distribution of these slug‐positive beetles was significantly associated with the distribution of the larger slug classes, over 25 mg. Where there were many large slugs in June there were many slug‐positive beetles. Conversely, in July few large slugs were found where there were many slug‐positive beetles.

9. Parametric analysis revealed that these changes in the large slug class, at each sampling point between June and July (growth), were negatively related to the local numbers of slug‐positive beetles, and that growth declined as the local numbers of beetles increased.

10. These findings suggest that predation was not opportunistic, but direct and dynamic, falsifying the null hypothesis. Moreover, this predation elicited significant changes in the spatial distribution and local density of the slugs, in a manner that may be termed spatially density dependent.
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

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

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

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

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

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

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

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

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.
A study of the restoration of heathland on successional sites: changes in vegetation and soil chemical properties
Authors: Mitchell R.J. , Marrs R.H. , Le Duc M.G. , Auld M.H.D.
Published: March 2003

1. Lowland heaths are high‐profile ecosystems for conservation action in Britain, but many areas have been invaded by Betula spp., Pinus sylvestris, Pteridium aquilinum and Rhododendron ponticum. As succession occurs on heaths, changes occur in both the vegetation and the soil chemical properties of the site.

2. Nine heathland sites in the Poole Basin area of Dorset were studied, where management of successional sites to restore heathland had occurred. The efficacy of heathland restoration in terms of both the vegetation and the soil chemical properties was assessed.

3. The management had allowed many heathland species to establish and the majority of sites to start to become similar to the neighbouring heathland. The reversion of increased soil nutrients was found to be more problematic, with levels of ammonium–nitrogen, phosphorus, pH, calcium and magnesium remaining greater than those of the heathland soils.

4. The vegetation and soil data were analysed using canoco (canonical correspondence analysis) and were then used to test four hypothetical models that related changes in biotic factors (vegetation) and abiotic variables (soil nutrients) following management to the success of the restoration of heathland on successional sites.

5. A second canoco analysis was carried out in which the managed sites were treated as passive samples. This model was used to measure the distances between the heath, successional and managed sites. These distances provided measures of management success and the resilience of the treated late‐successional ecosystem.

6. The successional species present before management affected the success of reversion; management of Pinus sylvestris sites was generally more successful than management of others sites, especially those invaded by Betula. The most significant effect of different management techniques resulted from litter‐stripping, which reduced the nutrients available and improved and accelerated the success of reversion.
Successional response of a tropical forest termite assemblage to experimental habitat perturbation
Authors: Davies Richard G. , Eggleton Paul , Dibog Luc , Lawton John H. , Bignell David E. , Brauman Alain , Hartmann Christian , Nunes Lina , Holt John , Rouland Corinne
Published: March 2003

1. Research into the successional responses of tropical forest communities following disturbance has potential applications for habitat restoration. Currently little is known of how these responses relate to the recovery of biodiversity and ecosystem processes. Succession of assemblages of decomposer arthropods is essential for the recovery of the soil community and nutrient cycling processes.

2. This study investigated the successional response of a termite assemblage to the experimental perturbation of forest habitat in southern Cameroon, examining the implications for tropical forest restoration. A randomized block design consisting of four experimental perturbations of differing severity was established in an old secondary forest in the Mbalmayo Forest Reserve. Isolated control sites were left in undisturbed forest. Recovery of the termite assemblage was assessed by measuring termite species richness and abundance at regular intervals over the subsequent 12 months.

3. The speed of recovery of the termite assemblage varied with the type and extent of perturbation. In treatments involving severe soil and canopy disturbance, termite species richness and abundance recovered more rapidly when dead wood was left on the ground following perturbation. The availability of dead wood also resulted in recolonization by a subset of the termite assemblage that was distinct compositionally from that sampled from all other treatments. This subset at sites with additional dead wood included not only certain wood‐feeding species, but also soil feeders.

4. The positive effects upon the termite assemblage of leaving substantial dead wood on the ground has implications for the restoration of tropical forests following human‐induced disturbances such as logging. The accelerated recovery of termite diversity and assemblage composition is a significant component of soil community recovery and the restoration of nutrient cycles. These benefits are expected to influence soil fertility and, ultimately, forest regeneration. The duration and persistence of these effects will depend crucially on the type, scale and intensity of the original disturbance. The impact of termites on soil properties, and vice versa, clearly deserves more attention in studies of tropical forest regeneration and recovery.
Extending Ellenberg's indicator values to a new area: an algorithmic approach
Authors: Hill Mark O. , Roy David B. , Mountford J. Owen , Bunce Robert G. H.
Published: March 2003

1. Ellenberg's indicator values scale the flora of a region along gradients reflecting light, temperature, continentality, moisture, soil pH, fertility and salinity. They can be used to monitor environmental change.

2. Ellenberg values can be extended from central Europe, for which they were defined, to nearby parts of Europe. Given a database of quadrat samples, they can be repredicted by a simple algorithm consisting of two‐way weighted averaging, followed by local regression.

3. A database of British samples was assembled from two large surveys. Ellenberg values were repredicted.

4. Except for the indicator of continentality, the correlation of repredicted and original values was in the range 0·72 (light) to 0·91 (moisture). The continentality indicator could not be adequately repredicted by the algorithm, and is unusable in Britain.

5. Discrepancies between original and repredicted values can be attributed to various causes, including wrong original values, differing ecological requirements in Britain and central Europe, biased sampling of the British range of habitats, and the occurrence of small plants in shaded or basic microhabitats within well illuminated or predominantly acid quadrats.

6. The repredicted values were generally reliable, but a small proportion was clearly wrong. Wrong values were due to either inadequate sampling of species’ realized niches in Britain or sampling with quadrats that were too large and included species that were not close associates.
Optimal release strategies for biological control agents: an application of stochastic dynamic programming to population management
Authors: Shea K. , Possingham H. P.
Published: March 2003

1. Establishing biological control agents in the field is a major step in any classical biocontrol programme, yet there are few general guidelines to help the practitioner decide what factors might enhance the establishment of such agents.

2. A stochastic dynamic programming (SDP) approach, linked to a metapopulation model, was used to find optimal release strategies (number and size of releases), given constraints on time and the number of biocontrol agents available. By modelling within a decision‐making framework we derived rules of thumb that will enable biocontrol workers to choose between management options, depending on the current state of the system.

3. When there are few well‐established sites, making a few large releases is the optimal strategy. For other states of the system, the optimal strategy ranges from a few large releases, through a mixed strategy (a variety of release sizes), to many small releases, as the probability of establishment of smaller inocula increases.

4. Given that the probability of establishment is rarely a known entity, we also strongly recommend a mixed strategy in the early stages of a release programme, to accelerate learning and improve the chances of finding the optimal approach.
Habitat structure and egg distributions in the processionary caterpillar Ochrogaster lunifer: lessons for conservation and pest management
Authors: Floater Graham J. , Zalucki Myron P.
Published: March 2003

1. The spatial and temporal distribution of eggs laid by herbivorous insects is a crucial component of herbivore population stability, as it influences overall mortality within the population. Thus an ecologist studying populations of an endangered butterfly can do little to increase its numbers through habitat management without knowledge of its egg‐laying patterns across individual host‐plants under different habitat management regimes. At the other end of the spectrum, a knowledge of egg‐laying behaviour can do much to control pest outbreaks by disrupting egg distributions that lead to rapid population growth.

2. The distribution of egg batches of the processionary caterpillar Ochrogaster lunifer on acacia trees was monitored in 21 habitats during 2 years in coastal Australia. The presence of egg batches on acacias was affected by host‐tree ‘quality’ (tree size and foliar chemistry that led to increased caterpillar survival) and host‐tree ‘apparency’ (the amount of vegetation surrounding host‐trees).

3. In open homogeneous habitats, more egg batches were laid on high‐quality trees, increasing potential population growth. In diverse mixed‐species habitats, more egg batches were laid on low‐quality highly apparent trees, reducing population growth and so reducing the potential for unstable population dynamics. The aggregation of batches on small apparent trees in diverse habitats led to outbreaks on these trees year after year, even when population levels were low, while site‐wide outbreaks were rare.

4. These results predict that diverse habitats with mixed plant species should increase insect aggregation and increase population stability. In contrast, in open disturbed habitats or in regular plantations, where egg batches are more evenly distributed across high‐quality hosts, populations should be more unstable, with site‐wide outbreaks and extinctions being more common.

5. Mixed planting should be used on habitat regeneration sites to increase the population stability of immigrating or reintroduced insect species. Mixed planting also increases the diversity of resources, leading to higher herbivore species richness. With regard to the conservation of single species, different practices of habitat management will need to be employed depending on whether a project is concerned with methods of rapidly increasing the abundance of an endangered insect or concerned with the maintenance of a stable, established insect population that is perhaps endemic to an area. Suggestions for habitat management in these different cases are discussed.

6. Finally, intercropping can be highly effective in reducing pest outbreaks, although the economic gains of reduced pest attack may be outweighed by reduced crop yields in mixed‐crop systems.