bluuebunny/crossref_metadata_2025 huggingface dataset:
Interference among insect parasitoids: a multi‐patch experiment
Authors: Visser Marcel E. , Jones T. Hefin , Driessen Gerard
Published: March 2003

1. Interference among insect parasitoids leads to a reduction in the overall search rate (the population equivalent of searching efficiency) with increasing parasitoid population density. When this reduction is due to behavioural responses of individuals to increased intraspecific competition, interference can serve as a stepping stone from individual behaviour to population phenomena.

2. Interference can take different forms: (1) a direct within‐patch reduction of searching efficiency with parasitoid density (direct mutual interference); (2) a decrease in overall search rate with increasing parasitoid density if parasitoids have a non‐uniform distribution over patches where this distribution remains unaltered with increasing density (pseudo‐interference); (3a) a decrease in the time spent on patches by each individual, i.e. more or longer travelling at higher parasitoid densities; and (3b) a decrease in overall search rate due to a change in the distribution of parasitoid effort over patches with increasing parasitoid density. These last two forms arise from behavioural responses to increased parasitoid density and are forms of indirect mutual interference.

3. We present an expression for the overall search rate in a patchy environment where individual parasitoids travel between patches. We use this to show how the different forms of interference affect the overall search rate, contrasting environments with aggregated and uniform host distributions.

4. Using the data of Jones (1986) we explore the different forms of interference in a multipatch experiment. In these experiments, different numbers of parasitoids were introduced in an arena where the distribution of hosts over patches was either aggregated or uniform. We show that both pseudo‐interference and indirect mutual interference play a role, and that they have an opposite effect for a uniform host distribution, but amplify one another for aggregated host distributions.

5. The indirect mutual interference arises from a shift towards a more uniform distribution of parasitoid effort over patches with increasing parasitoid densities. This shift is caused by a behavioural response to parasitoid density, and is likely due to changes in the parasitoids’ patch arrival and departure decisions. These decisions underlie the distribution of time spent on patches, thereby linking individual behaviour to a phenomenon at the population level.

6. Finally, we put forward a more general framework for indirect mutual interference to also include behavioural responses in sex allocation, clutch size and host acceptance to parasitoid density as forms of interference.
Dynamics of a harvested moose population in a variable environment
Authors: Solberg Erling Johan , Saether Bernt‐Erik , Strand Olav , Loison Anne
Published: March 2003

1.Population size, calves per female, female mean age and adult sex ratio of a moose (Alces alces) population in Vefsn, northern Norway were reconstructed from 1967 to 1993 using cohort analysis and catch‐at‐age data from 96% (6752) of all individuals harvested.

2.The dynamics of the population were influenced mainly by density‐dependent harvesting, stochastic variation in climate and intrinsic variation in the age‐structure of the female segment of the population.

3.A time delay in the assignment of hunting permits in relation to population size increased fluctuations in population size.

4.Selective harvesting of calves and yearlings increased the mean age of adult females in the population, and, because fecundity in moose is strongly age‐specific, the number of calves per female concordantly increased. However, after years with high recruitment, the adult mean age decreased as large cohorts entered the adult age‐groups. This age‐structure effect generated cycles in the rate of recruitment to the population and fluctuations introduced time‐lags in the population dynamics.

5.An inverse relationship between recruitment rate and population density, mediated by a density‐dependent decrease in female body condition, could potentially have constituted a regulatory mechanism in the dynamics of the population, but this effect was counteracted by a density‐dependent increase in the mean age of adult females.

6.Stochastic variation in winter snow depth and summer temperature had delayed effects on recruitment rate and in turn population growth rate, apparently through effects on female body condition before conception.
Brood parasitism by the cuckoo on patchy reed warbler populations in Britain
Authors: Lindholm Anna K.
Published: March 2003

1. Reed warblers are not known to be parasitized by cuckoos in Wales, and are rarely parasitized in some English populations, despite the presence of cuckoos. Nine hypotheses are proposed to explain regional differences in parasitism frequencies. They are tested against national and international data from the BTO, RSPB and EURING, and data from four study sites.

2. The frequency of parasitism of reed warbler populations was found to be negatively correlated with habitat patch size. Thus the frequency of parasitism experienced by reed warblers and the number of cuckoos parasitizing a reed warbler population do not increase in direct proportion to host abundance.

3. Population sizes of two unparasitized (Llangorse Lake and Oxwich) and one rarely parasitized population of reed warblers (Pannel Valley) are neither too large nor too small to be suitable for parasitism by cuckoos.

4. Cuckoos are not excluded from these populations by lack of perches in the habitat, because of a lack of prey in the immediate area, or by territorial competition with cuckoos of other host preferences.

5. There has been no decline in frequency of parasitism of reed warblers in Britain since 1932. Thus, reed warbler cuckoos are probably not declining in numbers and contracting their range away from these three geographically marginal sites.

6. Cuckoos parasitizing reed warbler populations at Llangorse Lake, Oxwich and Pannel Valley would achieve reproductive success equal to or higher than that attained with other local hosts, so that any host switches away from reed warblers would be unprofitable.

7. Reed warbler cuckoos may have dispersed to all or most of these study populations in the past. However, the cuckoo populations would have been small and highly vulnerable to extinction. Cycles of increases, declines and extinctions of local populations could explain the variance in parasitism frequencies and number of cuckoos often observed.

8. The most important factors considered in this study that affect the presence and number of cuckoos at a site appear to be competition between females, habitat patch size and structure, rates of dispersal and demographic stochasticity.
Structural change in an exploited fish community: a consequence of differential fishing effects on species with contrasting life histories
Authors: Jennings Simon , Greenstreet Simon. P. R. , Reynolds John. D.
Published: March 2003

1.An understanding of the links between life histories and responses to exploitation could provide the basis for predicting shifts in community structure by identifying susceptible species and linking life‐history tactics with population dynamics.

2.We examined long‐term trends in the abundance of species in the North Sea bottom‐dwelling (demersal) fish community. Between 1925 & 1996 changes in species composition led to an increase in mean growth rate, while mean maximum size, age at maturity and size at maturity decreased. The demersal fish community was increasingly heavily fished during this period.

3.Trends in mean life‐history characteristics of the community were linked to trends in abundance of component species. An approach based on phylogenetic comparisons was used to examine the differential effects of fishing on individual species with contrasting life histories.

4.Those species that decreased in abundance relative to their nearest relative, matured later at a greater size, grew more slowly towards a greater maximum size and had lower rates of potential population increase. The phylogenetically based analyses demonstrated that trends in community structure could be predicted from the differential responses of related species to fishing.

5.This is the first study to link exploitation responses of an entire community to the life histories of individual species. The results demonstrate that fishing has greater effects on slower growing, larger species with later maturity and lower rates of potential population increase. The comparative approach provides a basis for predicting structural change in other exploited communities.
The intra‐ and interspecific relationships between abundance and distribution in helminth parasites of birds
Authors: Poulin Robert
Published: March 2003

1.Positive correlations between local abundance and distribution on a larger spatial scale are commonly observed among related species.

2.Within parasite species, the same relationship may be expected between prevalence and intensity of infection across host species used. Across parasite species, a positive relationship is expected between average abundance in a host population and the number of host species that can be exploited based on the resource breadth hypothesis. Trade‐offs between the ability to exploit many host species and the potential for heavy infections, however, could result in a negative relationship.

3.Intraspecifically, using data on 51 helminth species parasitic in birds, prevalence and intensity of infection among host species used are generally only weakly correlated. Only in nematodes is there an overall positive relationship between prevalence and intensity.

4.A comparative analysis was performed on data from 389 species of cestodes, trematodes and nematodes parasitic in birds to determine how host specificity covaries interspecifically with abundance, measured both as prevalence and intensity of infection.

5.After controlling for phylogenetic influences and sampling effort, the number of host species used correlated positively with prevalence in all three parasite taxa, and with intensity of infection in trematodes only.

6.These results do not support the existence of a trade‐off between abundance and the use of many host species, as has been found for fish parasites. Instead, whatever makes helminth parasites of birds abundant within a host population may facilitate their successful colonization of new host species.
Scaling of metabolic rate with body mass and temperature in teleost fish
Authors: Clarke Andrew , Johnston Nadine M.
Published: March 2003

1.We examined published studies relating resting oxygen consumption to body mass and temperature in post‐larval teleost fish. The resulting database comprised 138 studies of 69 species (representing 28 families and 12 orders) living over a temperature range ofc.40 °C.

2. Resting metabolic rate (Rb; mmol oxygen gas h–1) was related to body mass (M;wet mass, g) byRb = aMb, where a is a constant and b the scaling exponent. The model was fitted by least squares linear regression after logarithmic transformation of both variables. The mean value of scaling exponent, b, for the 69 individual species was 0·79 (SE 0·11). The general equation for all teleost fish was 1nRb = 0·80(1nM) – 5·43.

3. The relationship between resting oxygen consumption and environmental temperature for a 50‐g fish was curvilinear. A typical tropical fish at 30°C requires approximately six times as much oxygen for resting metabolism as does a polar fish at 0°C. This relationship could be fitted by several statistical models, of which the Arrhenius model is probably the most appropriate. The Arrhenius model for the resting metabolism of 69 species of teleost fish, corrected to a standard body mass of 50 g, was 1nRb = 15·7 – 5·02.T–1, whereTis absolute temperature (103 × K).

4.The Arrhenius model fitted to all 69 species exhibited a lower thermal sensitivity of resting metabolism (mean Q10 = 1·83 over the range 0–30 °C) than typical within‐species acclimation studies (median Q10 = 2·40,n = 14). This suggests that evolutionary adaptation has reduced the overall thermal sensitivity of resting metabolism across species. Analysis of covariance indicated that the relationships between resting metabolic rate and temperature for various taxa (orders) showed similar slopes but significantly different mean rates.

5. Analysis of the data for perciform fish provided no support for metabolic cold adaptation (the hypothesis that polar fish show a resting metabolic rate higher than predicted from the overall rate/temperature relationship established for temperate and tropical species).

6. Taxonomic variation in mean resting metabolic rate showed no relationship to phylogeny, although the robustness of this conclusion is constrained by our limited knowledge of fish evolutionary history.
A general framework for the aggregation model of coexistence
Authors: Hartley Stephen , Shorrocks Bryan
Published: March 2003

The aggregation model of coexistence has been used widely to explain the coexistence of competing species that utilize patchy and ephemeral resources. Over the years, it has been reformulated in many different ways, using different assumptions, indices and analyses, leading sometimes to contradictory conclusions. We present a general framework, from which many of the alternative approaches are derived as special cases.

A generalized distribution, composed of the distribution of visits across patches and the distribution of eggs per visit, is used to model changes in the mean individual‐level experience of density that occur at different population‐level densities.

New and more general criteria for coexistence are derived, based upon standard invasability analysis of Lotka–Volterra competition equations applied to a patchy system.

An important parameter in the new coexistence criteria is the mean per capita density of individuals in a single clutch (). Until now this measure has been relatively ignored, experimentally and theoretically.

We confirm earlier findings that the random distribution of clutches may be a sufficient cause of aggregated egg distributions to allow coexistence between species of unequal competitive ability, but only if the product of competition coefficients is less than one.
Foraging ranges of solitary bees
Authors: Gathmann Achim , Tscharntke Teja
Published: March 2003

Habitat requirements of solitary bees include nesting sites, food resources and nesting material. We used translocation experiments to establish foraging distances and measured foraging trip duration to analyse how solitary bees cope with the distance between nesting sites and suitable food plants in different habitat types.

Maximum foraging distance between nesting site and food patch was 150–600 m for the 16 bee species examined. Foraging distance was correlated positively with body length. Mean foraging trip duration, measured for seven bee species, ranged from 6 to 28 min and was also correlated with body length. In a study of the polylectic species Osmia rufa
, we found a significant decrease in foraging trip duration with increasing number of plant species. Logistic regressions showed that the oligolectic
Megachile lapponica
nested in trap nests with a probability of 50% if the distance between trap nest and food patch was less than 250 m. The oligolectic
Chelostoma rapunculi utilized trap nests when the distance to the nearest food patch was less than 300 m.

These experiments showed that solitary bees have a rather small foraging range so local habitat structure appears to be of more importance than large‐scale landscape structure. All requirements for sustaining viable populations must be within this range. Therefore, it is necessary to maintain and restore a dense network of habitat patches in landscapes to ensure long‐term sustainability of wild bee diversity and their ecological function as pollinators.
Reduced applications of metaldehyde pellets for reliable control of the slug pests Arion lusitanicus and Deroceras reticulatum in oilseed rape adjacent to sown wildflower strips
Authors: FRIEDLI JÜRG , FRANK THOMAS
Published: March 2003

Slugs have been shown to cause severe damage in oilseed rape crops adjacent to sown wildflower strips. Rape can be protected from this damage by broadcasting a recommended dose of metaldehyde over the whole field area. This paper investigates whether severe slug damage can be prevented by applications of metaldehyde just along the wildflower strips thereby reducing the input of chemical molluscicide.

In this study, untreated control plots suffered severe crop loss at 1 m from all wildflower strips studied. However, all treatments of molluscicide protected rape from severe crop loss without significant differences among the three treatments (two different concentrations of metaldehyde applied in 50‐cm wide barriers along the strips and a recommended dose of metaldehyde broadcast over the whole study area).

Arion lusitanicus and Deroceras reticulatum were by far the most abundant slug pests found in the studied rape fields. Arion lusitanicus was very abundant in the wildflower strips and up to 1 m into the field; however, it was almost entirely absent at 3 m from the strips. Since D. reticulatum was evenly distributed over the whole field area, A. lusitanicus appeared to be responsible for the majority of damage in control plots 1 m from the wildflower strips.

Application of metaldehyde in a 50‐cm wide band has been shown to be practicable and efficient in protecting rape from severe slug damage near to wildflower strips. These reduced applications of molluscicide mean savings of time and money for farmers and can be recommended for practical application.
Long‐term changes in agricultural practices and wildfowling in an internationally important wetland, and their effects on the guild of wintering ducks
Authors: Duncan P. , Hewison A. J. M. , Houte S. , Rosoux R. , Tournebize T. , Dubs F. , Burel F. , Bretagnolle V.
Published: March 2003

1. The Marais Poitevin, one of the principal wintering and passage sites for ducks and waders in the East Atlantic flyway, underwent agricultural intensification in the 1980s. The numbers of ducks declined in the period 1979–96 in the main roost, Baie de l’Aiguillon; this was a site‐specific phenomenon for which local factors were responsible. We describe here long‐term changes in some key characteristics of the wetlands, paying particular attention to the principal factors affecting the quality of waterbird habitat: the area of semi‐natural grasslands, water management and wildfowling.

2. The area of grasslands declined by 50% between 1970 and 1995, principally as a result of conversion to arable farmland. The pattern was observed over the whole area and was slightly more marked close to the day‐roost of the ducks. The rate of change was greatest in the 1980s. Water levels, and therefore the flooded area, were reduced over the study period during the months of May to November. The numbers of wildfowlers declined from the 1970s, but the number of artificial wildfowling ponds increased, especially after 1980. The number of birds killed did not decline and may have increased. The quality of the ducks’ habitat therefore declined by all three measures.

3. Four species, mallard, shoveler, teal and gadwall, showed an increase in other sites in north and west France either over the whole period or over the last part (1984–96), while declining (shoveler and mallard) or remaining stable in the Baie de l’Aiguillon. Pintail remained stable in the other sites, while showing a long‐term decline (over 30 years) in the Baie. Wigeon did not use the Baie in large numbers in the 1996 cold spell as they did until the 1980s.

4. The uncoupling of the trends for these species in the Baie from their trends in the other sites may reflect the loss of grassland feeding habitat in the Marais Poitevin. However, for mallard, pintail and shoveler the declines in the Baie were much stronger than the 50% loss of grasslands so other factors, such as the reduction in autumn flooding and/or shooting, are likely to have played a part.

5. Since the three measures of long‐term trends in duck habitat co‐varied it was not possible to separate their effects statistically. The hypotheses arising from this study need to be tested: this should be done using comparative and experimental approaches. Suggestions are made for the management of water levels and shooting in the feeding habitat close to the Baie de l’Aiguillon.
Prediction of weed density: the increase of error with prediction interval, and the use of long‐term prediction for weed management
Authors: Wallinga J. , Grasman J. , Groeneveld R. M. W. , Kropff M. J. , Lotz L. A. P.
Published: March 2003

1. This paper addresses the errors that are associated with the long‐term prediction of weed densities, and the effect of these errors on the performance of weed management decisions based on those long‐term predictions.

2. A model of weed population dynamics was constructed and its parameters were estimated from experimental observations of population dynamics of the weed species Stellaria media in a crop rotation.

3. The observations showed that estimates of weed population growth rate differed between two locations.

4. The model was used to analyse error propagation for predicted weed densities in an enlarged prediction interval. It is concluded that errors due to an uncertain population growth rate increase linearly with the length of the prediction interval, and thus pose an upper limit to the horizon for long‐term predictions.

5. It is shown that a limited ability to predict weed densities does not necessarily impair the practical use of weed population dynamic models in planning for long‐term weed control programmes.
Recent rise to dominance of Molinia caerulea in environmentally sensitive areas: new perspectives from palaeoecological data
Authors: Chambers F.M. , Mauquoy Dmitri , Todd Pamela A.
Published: March 2003

1. A characteristic of some heath and moorland areas in maritime north‐west Europe is the widespread dominance of Molinia caerulea (purple moor grass). The overwhelming local supremacy of this species concerns farmers, owing to its relatively low palatability for grazing stock, and conservationists, owing to the monotonous, species‐poor landscapes that often result under Molinietum.

2. In some environmentally sensitive areas (ESAs) in England and Wales, Molinietum is believed to have ousted Callunetum in recent decades; experiments sponsored to control the species have predicated its infiltration and replacement of heather‐dominated stands.

3. Experimental control of Molinia in ESAs on Exmoor, England, was paralleled by palaeoecological studies to verify its recent rise, assess its status in moorland, and test the utility of the techniques for such research.

4. Peat profiles from two localities on Exmoor were sampled and subjected to recently developed techniques of plant macrofossil counting and to conventional pollen analysis. One locality was ‘white moor’, clearly dominated by Molinia; the other was ‘grey moor’ (an admixture of ericaceous shrubs) that had become invaded (allegedly recently) by Molinia.

5. Dating of profiles employed a range of methods, including conventional radiocarbon dating, Accelerator Mass Spectrometry (AMS) dating and the counting of spheroidal carbonaceous particles, to attempt to delimit horizons of recent peat growth.

6. The pollen and macrofossil data confirmed the recent ousting of Calluna and rise to dominance of Molinia in the grey moor, but also provided evidence of an earlier unsuspected (pre‐Callunetum) presence of Molinia. The overwhelming dominance of Molinia in the white moor was also a recent phenomenon, but was only partly at the expense of Calluna. The palaeoecological data indicated a greater antiquity and former abundance of Molinia than is often appreciated and suggested that, over the past millennium, vegetation dominance has alternated between Callunetum and grass moor containing at least some Molinia, while the former Calluna‐dominated grey moor itself developed originally from grass moor.

7. These findings have implications for conservation management and for restoration targets in ‘degraded’ moorland. Similar palaeoecological studies have since been adopted in Wales, directly to inform conservation and management policy.
Factors associated with wolverine Gulo gulo predation on domestic sheep
Authors: Landa A. , Gudvangen K. , Swenson J.E. , Røskaft E.
Published: March 2003

1. Following a long history of eradication campaigns against predators, wolverine Gulo gulo distribution and numbers became critically low in Norway in the 1960s. Consequently, wolverines were protected by law during the 1970s and 1980s. This led to an increase in wolverine numbers and re‐establishment in some formerly occupied habitats, resulting in increased depredation on domestic reindeer Rangifer tarandus and sheep Ovis aries. Wolverine control and licensed hunting have been used increasingly as tools to reduce the depredation since protection was introduced. However, the factors influencing the level of this depredation have not been studied. We therefore examined losses of domestic sheep grazing unattended on upland summer ranges in the Snøhetta plateau of south central Norway during 1979–94, in relation to wolverine population numbers, reproduction and control measures. This area was recently re‐occupied by wolverines and reproduction has been recorded regularly from the beginning of the study period.

2. The number of ewes and lambs recorded in organized grazing areas increased more than fivefold during the period, and losses increased proportionally with sheep numbers. The differences in losses among municipalities and grazing co‐operatives were probably related to sheep breeds and local variation in wolverine density.

3. The heavy Dala sheep breed was most at risk, whereas losses from the lighter Norwegian short‐tailed and Norwegian fur‐bearing breeds were lower than expected.

4. Killing of wolverines led to fewer lambs being lost in the same year that the wolverine killing took place, but the effect quickly declined, implying a rapid re‐establishment of wolverines in the local area.

5. Lambs were more vulnerable to wolverine predation than ewes, and losses were higher in wolverine cub‐rearing areas than in the area as a whole.

6. We conclude that: (i) control programmes for wolverines, as practised today, will have little long‐term effect in reducing sheep losses, unless wolverines are eradicated or severely reduced in numbers; (ii) the introduction of more agile sheep breeds will probably reduce losses; (iii) in areas where wolverine control to protect sheep is a threat towards wolverine conservation, the present sheep husbandry system of grazing unguarded sheep in the mountains should be replaced by alternative forms that provide the sheep with more protection. This is particularly important in wolverine denning areas.
Colobus monkeys and coconuts: a study of perceived human–wildlife conflicts
Authors: Siex Kirstin S. , Struhsaker Thomas T.
Published: March 2003

1. Approximately half of the remaining Zanzibar red colobus Procolobus kirkii, one of Africa's most endangered primates, reside permanently outside protected areas, many within agricultural areas. Consequently, conservation of this endangered species is strongly dependent on the development of effective management plans that address the potential human–wildlife conflicts in these agricultural areas.

2. There are a growing number of complaints about red colobus consumption of coconuts in the agricultural areas and requests by local farmers for compensation and/or removal of the colobus. Prior to taking actions that would hinder the conservation of this highly endangered species, it is necessary to quantify and compare the actual impact of the colobus on coconut harvest with that perceived by the farmers.

3. In this study we monitored five experimental and two control plots to quantify the potential impact of red colobus on coconut crops and to assess the ecological variables that may influence this impact.

4. We found that red colobus consumption of coconuts was highest in areas of high red colobus density and low availability of alternative red colobus food resources. Despite these correlations, red colobus feeding on immature coconuts did not appear to limit coconut harvest. On the contrary, red colobus consumption of coconuts was found to be positively correlated with harvest. This correlation is probably due to a pruning effect.

5. Based upon our findings that red colobus are having no significant negative impact on coconut harvest and are actually a source of tourist revenue to the region, we recommend no action be taken to remove colobus from the agricultural areas.

6. This study illustrates the importance of scientific documentation of perceived human–wildlife conflicts.
Assessing the completeness of bat biodiversity inventories using species accumulation curves
Authors: Moreno Claudia E. , Halffter Gonzalo
Published: March 2003

1. In this study we used species accumulation models to solve one of the most serious problems encountered when comparing species richness between different communities. The problem is how to compare data among inventories in which different methodologies or measures of sampling effort have been employed. The methods used here for bats may be applied to any other biological group. We fit two asymptotic models to species accumulation curves for bat inventories to evaluate local or within‐community diversity (alpha) and landscape diversity (gamma) in central Veracruz, Mexico.

2. Species accumulation models allow us to: (i) measure within‐inventory efficacy and completeness; (ii) obtain an estimate of species richness that is based on a standardized measure of sampling effort, which makes valid comparisons between inventories possible; and (iii) estimate the minimum sampling effort required to reach a satisfactory level of completeness.

3. The applied models fit well in all cases (r2 >  0·95). The linear dependence model predicted lower asymptotes and the Clench model predicted higher asymptotes than the observed species richness. These models are useful as predictors representing the lower and upper limits between which the true species richness value should lie.

4. Alpha diversity for bats in all vegetation communities (11–18 species) was lower than the gamma diversity (20 species), suggesting that species richness and the sampling effort required are related to environmental heterogeneity.

5. We propose that 90% of the total fauna predicted by either of the models is an acceptable standardized value for comparing species richness between communities.

6. We assessed the within‐inventory completeness as the proportion of the models’ asymptote, where 90% is the desired minimum level of completeness. Except in palm stands, all bat inventories had an acceptable level of completeness, at least for the linear dependence model.

7. For conditions similar to those of our study area, the minimum effort required to obtain a satisfactory level of completeness is 5–18 nights for plant communities and 18 nights for more heterogeneous landscapes.

8. We make recommendations for improving the efficacy and completeness of bat surveys based on the application of species accumulation models.
Abundance–occupancy relationships
Authors: Gaston Kevin J. , Blackburn Tim M. , Greenwood Jeremy J.D. , Gregory Richard D. , Quinn Rachel M. , Lawton John H.
Published: March 2003

1. The abundance and distribution of species tend to be linked, such that species declining in abundance often tend also to show declines in the number of sites they occupy, while species increasing in abundance tend also to be increasing in occupancy. Therefore, intraspecific abundance–occupancy relationships are commonly positive.

2. The intraspecific pattern is mirrored by more general positive interspecific abundance–occupancy relationships: widespread species tend to be abundant, and narrowly distributed species rare.

3. Here, we review recent research on these patterns based on the flora and fauna of the British Isles. We assess their generality, describe what is currently known about their structure, and summarize the results of tests of the several hypotheses proposed to explain their existence.

4. The positive form generally exhibited by abundance–occupancy relationships, intraspecific or interspecific, has consequences for several areas of applied ecology, including conservation, harvesting, biological invasions and biodiversity inventorying. These implications are discussed briefly.
Lamb predation and fox control in south‐eastern Australia
Authors: Greentree Carolyn , Saunders Glen , Mcleod Lynette , Hone Jim
Published: March 2003

1.  Wild predators sometimes kill livestock. In Australia the red fox kills lambs, but there are limited experimental data to demonstrate the effects of controlling foxes on the predation level.

2.  Using a balanced experimental design over 2 years, we investigated the effects of three levels of fox control, using poisoning with sodium monofluoroacetate (compound 1080), on lamb production, lamb predation and fox abundance in south‐eastern Australia.

3.
 There was no effect of fox control on lamb production. Fox predation was the probable cause of lamb death for a minimum of 0·8% and a maximum of 5·3% of 1321 lamb carcasses. Fox control significantly (P < 0·05) reduced the minimum percentage of lamb carcasses classified as killed by foxes from 1·50% (no fox control) to 0·90% (fox control once per year) or 0·25% (fox control three times per year). Fox control also significantly (P < 0·005) reduced the maximum percentage of lamb carcasses classified as killed by foxes from 10·25% (no fox control) to 6·50% (fox control once per year) or 3·75% (fox control three times per year). Poisoning did not affect fox abundance in spring.

4.  We estimated the number of treatment replicates needed to detect an effect of predator control on the number of lambs successfully reared to lamb marking (10 weeks old). The estimated numbers were high if predation effects were small. It is recommended that the effects of fox control should be evaluated carefully to determine if the present results are widespread, as some fox control may be wasted.

5.  The general effects of predator control on livestock predation requires more experimental investigation and economic evaluation. However, field experiments of sufficient power to detect effects will present considerable challenge.
Dynamics of shrub encroachment in an African savanna: relative influences of fire, herbivory, rainfall and density dependence
Authors: Roques K.G. , O'Connor T.G. , Watkinson A.R.
Published: March 2003

Shrub encroachment has been widely observed in savanna regions. This study analysed the causes of shrub encroachment in the lowveld savanna of north‐eastern Swaziland, southern Africa, and highlighted management regimes that can be used to reduce or prevent it.

The rates and dynamics of shrub encroachment were quantified for the period 1947–90 using aerial photographs, and for 1997 using a ground survey. Five similar areas with different land‐use histories were compared to investigate the relative importance of fire, herbivory, rainfall, soil type and shrub density in driving shrub dynamics.

In the study area as a whole, shrub cover increased from a mean of 2% in 1947 to 31% in 1990. Dichrostachys cinerea accounted for most of the increase in cover, contributing 81% to total shrub cover during 1997. Shrub cover was strongly correlated with shrub density and weakly negatively correlated with tree cover.

Shrub encroachment varied across land‐use fence lines. The key determinants of shrub dynamics were grazing, through its negative effect on fire frequency and an interaction between drought frequency and high shrub cover. Browsing pressure had a significant but minor impact on dynamics, while soil type had no significant effect. High grazing pressures through their effect on fire frequency were critical throughout the study period in promoting shrub encroachment, while the interaction between drought and high shrub cover produced declines in the later stages. Browsing had an impact on encroachment only in the early stages.

Frequent fires, facilitated by low grazing pressures, were capable of preventing shrub encroachment. When coupled with drought, frequent fires could reduce high shrub densities.

As cover and density were strongly correlated, it can be inferred from the negative correlation between change in cover (density) and initial cover (density) that the rate of shrub encroachment was cover (density)‐dependent and that there was a shrub equilibrium of 40% cover, approximating to 2400 plants ha−1. Shrub population growth was driven by events (fire, drought) as well as continuous agents (density dependence, mean browsing and grazing pressure).

Bush encroachment can be reversed by a combination of management (frequent fires) and climatic events (drought). The implications for savanna management are discussed.
Local declines in the abundance of harbour seals: implications for the designation and monitoring of protected areas
Authors: Thompson Paul M. , Van Parijs Sofie , Kovacs Kit M.
Published: March 2003

Information on the abundance of European pinnipeds is required to assess interactions with fisheries and to meet new conservation obligations under the European Community (EC) Habitats Directive. A detailed time‐series of data has documented increases in grey seal populations, but there remains considerable uncertainty over the current status of UK harbour seal populations.

 We present data on changes in the abundance of harbour seals in a study area within Orkney, Scotland, UK, previously considered a stronghold for this species. In 1998, intensive shore‐based counts of both adults and pups were only 16–36% of similar counts made between 1984 and 1987. Furthermore, a significant reduction in the proportion of yearlings present in haul‐out groups indicated a reduction in local recruitment.

 Current monitoring of UK harbour seals, using wider‐scale aerial survey techniques, has provided important estimates of site distribution and relative abundance at regional and national scales. However, these larger‐scale surveys lack associated data on within‐year variation in counts at particular sites. Consequently, they cannot currently be used to explore the spatial scale of the changes in seal numbers that we report here. Similarly, current data from wider‐scale monitoring cannot be used to determine whether observed local changes in abundance result from redistribution or a change in survival or reproduction.

 Management and monitoring plans are currently being developed for special areas of conservation (SAC) for harbour seals in response to the EC Habitats Directive. We suggest that more intensive research is required to assess whether or not similar changes in the abundance and age structure of seals have occurred in these areas. Without a better understanding of the current status of harbour seals both within and outside proposed SAC, future efforts to monitor the effectiveness of management initiatives will be constrained.
The impact of a root‐crown weevil and pasture competition on the winter annual Echium plantagineum
Authors: A.W. Sheppard , M.J. Smyth , A. Swirepik
Published: March 2003

Root‐feeding insect herbivores may suppress their host populations by altering the competitive balances within the plant community of the host‐plant. In this study, repeated field experiments using caged and natural populations of a root‐crown weevil, Mogulones larvatus, on the annual weed Echium plantagineum (Boraginaceae) were conducted with and without pasture competition in its exotic range.

The experiment used a split‐plot design, excluding weevils with insecticide and plant competition through weeding.

The greatest effect of the weevils was observed when natural densities of weevils occurred on naturally growing E. plantagineum rosettes in the field. Weevils reduced plant survival by 43%, and the size and seed weight of survivors by 58% and 74%, respectively.

Pasture competition had a similar impact on E. plantagineum as the weevils for plant size and seed weight, except that there was no impact on rosette survival. There were also no significant interactions between the effects of weevils and competition. Most impact occurred in the second half of the growing season.

The number of weevil eggs and larvae and all plant reproductive parameters measured per unit biomass were independent of plant size.

Such impact experiments help develop simplified impact assessment methodologies for assessing the success of biological control projects in the field.
Modelling landscape‐scale habitat use using GIS and remote sensing: a case study with great bustards
Authors: Osborne P.E. , Alonso J.C. , Bryant R.G.
Published: March 2003

Many species are adversely affected by human activities at large spatial scales and their conservation requires detailed information on distributions. Intensive ground surveys cannot keep pace with the rate of land‐use change over large areas and new methods are needed for regional‐scale mapping.

We present predictive models for great bustards in central Spain based on readily available advanced very high resolution radiometer (AVHRR) satellite imagery combined with mapped features in the form of geographic information system (GIS) data layers. As AVHRR imagery is coarse‐grained, we used a 12‐month time series to improve the definition of habitat types. The GIS data comprised measures of proximity to features likely to cause disturbance and a digital terrain model to allow for preference for certain topographies.

We used logistic regression to model the above data, including an autologistic term to account for spatial autocorrelation. The results from models were combined using Bayesian integration, and model performance was assessed using receiver operating characteristics plots.

Sites occupied by bustards had significantly lower densities of roads, buildings, railways and rivers than randomly selected survey points. Bustards also occurred within a narrower range of elevations and at locations with significantly less variable terrain.

Logistic regression analysis showed that roads, buildings, rivers and terrain all contributed significantly to the difference between occupied and random sites. The Bayesian integrated probability model showed an excellent agreement with the original census data and predicted suitable areas not presently occupied.

The great bustard's distribution is highly fragmented and vacant habitat patches may occur for a variety of reasons, including the species’ very strong fidelity to traditional sites through conspecific attraction. This may limit recolonization of previously occupied sites.

We conclude that AVHRR satellite imagery and GIS data sets have potential to map distributions at large spatial scales and could be applied to other species. While models based on imagery alone can provide accurate predictions of bustard habitats at some spatial scales, terrain and human influence are also significant predictors and are needed for finer scale modelling.
Suppression of weeds by spring wheat Triticumaestivum increases with crop density and spatial uniformity
Authors: Weiner Jacob , Griepentrog Hans‐Werner , Kristensen Lars
Published: March 2003

Recent advances in our understanding of the advantage of initial size in competition among individual plants (size‐asymmetric competition) suggest that the potential for many crops to suppress weeds is much greater than generally appreciated. We hypothesize that this potential can be realized if: (i) the crop density is increased significantly and (ii) the crop is regularly (uniformly) distributed in two‐dimensional space rather than sown in traditional rows.

We tested these hypotheses by sowing four varieties of spring wheat Triticum aestivum at three densities (200, 400 and 600 m−2) and in two spatial patterns (normal rows and a uniform grid pattern) in the presence of high weed pressure.

There were strong and significant effects of both crop density and spatial distribution on weed growth. Weed biomass decreased with crop density and was 30% lower in the grid pattern.

There was a negative linear relationship between above‐ground weed biomass in early July and crop yield at harvest, so weed suppression translated directly into yield. The treatment with high crop density and the grid sowing pattern contained 60% less weed biomass and produced 60% higher yield than the treatment closest to normal sowing practices (crops sown in rows at 400 m−2).

The results were similar when the experiment was repeated in the following year, even though weed abundance was lower and the weed community was very different. There was 30% less weed biomass and 9% higher yield when the crop was sown in a grid pattern.

While weed biomass decreased monotonically with density for all varieties, a significant variety–density interaction suggested that the attributes resulting in good weed suppression at high crop density may not be the same as those most advantageous at low crop density.

A more crowded, uniform, distribution of some crops could contribute to a strategy to reduce the use of herbicides and energy‐intensive forms of weed control.
Assessment of light and soil conditions in ancient and recent woodlands by Ellenberg indicator values
Authors: Dzwonko Zbigniew
Published: March 2003

The system of Ellenberg indicator species is widely accepted and used to characterize climate, light and soil conditions in central Europe and beyond. The aim of this study was to examine the extent to which Ellenberg indicator values can be used to characterize environmental conditions in ancient and recent woodlands.

The study was based on data from 264 plots in ancient deciduous woodlands and adjacent 70‐year‐old recent woodlands located on the same soils in the Carpathian foothills. Vegetation data were related to information on light intensity and a range of soil variables.

Despite a similar number of species on the plots in the ancient and recent woodlands, the correlations between the mean indicator values for light (mL), reaction (mR) and nitrogen (mN) and measured light intensity, soil pH and cation exchange capacity, respectively, were significantly lower in the recent woodlands than in the ancient woodlands.

Due to a very slow and differentiated regeneration rate of the field layer, the species with the lowest indicator values for reaction and nitrogen were significantly less abundant in the recent woodlands than in the ancient woodlands, while the species with higher values of these indicators were more frequent. The change of the reaction of many species to light conditions was the main reason for poor prediction of light intensity in the recent woodlands by the mean indicator values for light.

The mean Ellenberg indicator values for light, reaction and nitrogen were relatively good predictors of the environmental conditions in the ancient woodlands, with stabilized species composition determined mainly by the environmental regime. They were, however, much weaker indicators in the recent woodlands. This implies that the mean indicator values for secondary woodlands should be interpreted with caution and verified by measurements of environmental variables.