bluuebunny/crossref_metadata_2025 huggingface dataset:
The effect of landscape composition on colonization success, growth rate and dispersal in introduced bush‐crickets Metrioptera roeseli
Authors: Berggren Å. , Carlson A. , Kindvall O.
Published: March 2003

Fragmentation and habitat loss affects both existing and introduced populations. Small habitat areas may have harsher biotic and abiotic conditions, as well as restricting population sizes. Loss of connectivity reduces the opportunities for individuals to move between patches to rescue populations or to re‐colonize patches. Knowledge of how landscape composition affects the introduced populations is therefore essential for successful management and future re‐introductions.

To study the effect of landscape composition and structure on the success of colonization, population growth and dispersal distances, we introduced Roesel’s bush‐crickets Metrioptera roeseli to 70 habitat islands in areas previously unoccupied by the species. The introduction sites differed in habitat area and connectivity. The population survival and dispersal were then studied for 5 years after initial introductions.

In addition to results showing the importance of suitable habitat for population persistence, connectivity in form of linear landscape elements and nodes was also crucial. Linear landscape elements and/or nodes were important for colonization success, growth and dispersal. Linear landscape elements and nodes also reduced the negative effects of unsuitable habitat (matrix) and isolation from suitable habitat and on the populations.

These results stress the importance of connectivity in the landscape for population survival and establishment. Consideration of this should be taken into account in both management and re‐introductions of bush‐crickets and other invertebrates with similar population characteristics and behaviour.
Patterns of reproductive effort and success in birds: path analyses of long‐term data from European ducks
Authors: Blums Peter , Clark Robert G. , Mednis Aivars
Published: March 2003

We tested ecological hypotheses about timing of breeding and reproductive effort in birds, by analysing > 15‐year data sets for individually marked females in three species of Latvian ducks (northern shoveler, tufted duck, common pochard).

Duckling survival and recruitment declined with advancing hatch date in pochard and tufted duck, after controlling for effects of female age and other factors with path analysis, a novel finding which indicates that fitness advantages associated with early hatching extended beyond the prefledging period. Logistic regression analysis suggested further that individual duckling prefledging survival was moderate in the earliest phase of the breeding season, greatest in mid‐season and lowest later on.

However, selection acting against early hatched ducklings was surpassed by strong directional selection favouring recruitment of the earliest hatching females. The absolute and relative numbers of female recruits produced by a breeding female declined sharply with advancing hatch date in all species.

Unlike previous studies, an hypothesized intraspecific trade‐off between duckling mass and brood size was detected, being very robust in two of three species.

Unexpectedly, female age effects on recruitment were manifested only indirectly by several pathways, the most important being the earlier hatching dates of older females. Size‐adjusted body mass (i.e. condition index) was positively related to reproductive success, and was 2–8‐fold more influential than female size (indexed by wing length).

Overall, fecundity‐independent variables (e.g. hatching date, weather, indices of duckling production and habitat quality) generally had 2–10 times greater influence on recruitment rates than did fecundity‐dependent variables such as female size or condition, duckling mass and brood size, suggesting a critical role for external environmental factors vs. individual female‐specific traits in the recruitment process.
Model complexity and population predictions. The alpine marmot as a case study
Authors: Stephens Philip A. , Frey‐roos Fredy , Arnold Walter , Sutherland Wlliam J.
Published: March 2003

During the past 15 years, models have been used increasingly in predictive population ecology. Matrix models used for predicting the fates of populations are often extremely basic, ignoring density dependence, spatial scale and behaviour, and often based on one sex only. We tested the importance of some of these omissions for model realism, by comparing the performance of a variety of population models of varying levels of complexity.

Detailed data from more than 13 years of behavioural and demographic research on a population of alpine marmotsMarmota marmotain Berchtesgaden National Park, southern Germany, were used to parameterize four different population models. The models ranged from a simple population‐based matrix model, to a spatially explicit behaviour‐based model.

The performance of the models was judged by their ability to predict basic population dynamics under equilibrium conditions. Only a spatially explicit individual‐based model ignoring optimal behaviour predicted dynamics significantly different to those observed in the field, highlighting the importance of considering realistic patterns of behaviour in spatially explicit models.

Using realistic levels of environmental and demographic stochasticity, variance in population growth rates predicted by all models was high, even within the range of population densities experienced in the field. This emphasizes the difficulty of using population‐level field data to determine overall patterns of density dependence for use in population models.

All models were also used to predict potential density‐dependent effects on alpine marmot population growth. In this regard, the models differed greatly. It was concluded that the simplest matrix model was adequate for making predictions regarding population sizes or densities under equilibrium conditions, but that for predictions requiring an understanding of transient dynamics only the behavioural model would be adequate.

An emergent feature of this study of alpine marmot population dynamics was the prediction of a demographic Allee effect with a profound influence on population dynamics across a very broad range of population sizes. Three mechanisms were identified as underlying this Allee effect: stochastic skews in sex ratio and demographic composition at low population sizes; less efficient social thermoregulation during hibernation in small groups; and difficulties with mate finding during dispersal, even at relatively high population sizes.
Colonization rates and distances of a host butterfly and two specific parasitoids in a fragmented landscape
Authors: Van Nouhuys Saskya , Hanski Ilkka
Published: March 2003

We describe the pattern of colonization of suitable, but currently empty, habitat by a host butterfly and two specialist parasitoids living in a highly fragmented landscape.

Using survey data collected over 8 years, field sampling and small‐scale experiments we show that the ability of the Glanville fritillary butterfly (Melitaea cinxia) to colonize new habitat is intermediate between that of its two larval primary parasitoids.

The butterfly forms a classic metapopulation, which the parasitoidHyposoter horticolaexperiences as a single patchily distributed host population because of its high rate of dispersal and long colonization distances. In contrast, most of the local butterfly populations are presently inaccessible to the parasitoidCotesia melitaearum,which has a limited dispersal range and therefore persists only in tightly clustered networks of host populations.

At the regional scale, the butterfly may escapeC. melitaearumby colonizing empty habitat, but host dispersal does not limit parasitism byH. horticola,which consequently must be limited by local interaction.

The parasitoidH. horticolamostly avoids direct competition withC. melitaearumbecause the majority ofH. horticolapopulations are outside the range of dispersal by currentC. melitaearumpopulations. In contrast, allC. melitaearumpopulations experience competition withH. horticola.
The consequences of disrupted dispersal in fragmented red‐cockaded woodpeckerPicoides borealispopulations
Authors: Schiegg Karin , Walters Jeffrey R. , Priddy Jeffery A.
Published: March 2003

Habitat fragmentation may adversely affect animal populations through several mechanisms. However, little is known about how the impacts of some of these mechanisms are manifested in altered dynamics of wild populations.

We used a spatially explicit individual‐based simulation model to examine the potential effects of disrupted dispersal due to fragmentation on the population dynamics of the endangered, co‐operatively breeding, red‐cockaded woodpeckerPicoides borealis.

We simulated population dynamics as a function of population size and spatial aggregation of territories. Dispersal success (but not mortality or fecundity) was an emergent property of model runs. In the model all female and some male fledglings dispersed in straight lines in random directions, and the remaining males stayed on their natal territories as helpers and competed for breeding vacancies in their immediate neighbourhood.

Population trend was tied to the higher dispersal success of both males and females in larger and less fragmented populations. Helpers were more successful than dispersing males. Male breeder recruitment depended entirely on helpers when populations were small (25 or 100 territories).

Declining populations were characterized by high emigration rates and both failure and delay in female recruitment. The large numbers of unpaired males resulted in lowered reproductive output at the population level and in the loss of territories. Populations of 25 territories were stable when territories were highly aggregated, despite high emigration rates. These results closely match empirical observations.

A number of co‐operatively breeding species are endangered. The unusual dispersal behaviour of helpers may make such species sensitive to habitat fragmentation but also resilient to reductions in population size when territories are aggregated. Small populations of co‐operative breeders may have considerable conservation value as a source of genetic diversity.
Stability and complexity in microcosm communities
Authors: Fox Jeremy W. , McGrady‐Steed Jill
Published: March 2003

Theory predicts that communities comprising many species connected randomly by strong interactions are unlikely to exhibit stable, feasible equilibria (i.e. positive equilibria to which all species will return following perturbation), making the observed complexity of natural communities very surprising. This prediction has never been tested experimentally in speciose communities.

We tested this prediction using long‐term data from experimental communities of bacteria, protists and small metazoans in laboratory microcosms. Initial communities varied in species richness ( S
), composition and connectance (
C ; the fraction of possible interspecific interactions that are actually realized).

Many initial communities lost species to extinction (unstable and/or infeasible communities), but population densities and species compositions subsequently stabilized.

We used logistic regression to describe the probability that an initial community would be stable and feasible as a function of complexity [( SC
)
1/2 ]. Probability of a stable, feasible equilibrium declined with complexity, as predicted by theory.

We also found that communities converged in connectance over time, so that at the end of the experiment connectance was independent of species richness. Monte Carlo simulations indicated that this result was highly improbable if extinctions occurred at random with respect to connectedness. Connectance is also independent of species richness in well‐resolved natural food webs, a pattern usually ascribed to phylogenetic and/or physiological constraints on diet breadth. However, such constraints cannot explain our results. Trophic interactions causing non‐random extinctions may provide a novel explanation for patterns in the connectance and species richness of whole food webs.
Individual variation in prey selection by sea otters: patterns, causes and implications
Authors: Estes J. A. , Riedman M. L. , Staedler M. M. , Tinker M. T. , Lyon B. E.
Published: March 2003

Longitudinal records of prey selection by 10 adult female sea otters on the Monterey Peninsula, California, from 1983 to 1990 demonstrate extreme inter‐individual variation in diet. Variation in prey availability cannot explain these differences as the data were obtained from a common spatial‐temporal area.

Individual dietary patterns persisted throughout our study, thus indicating that they are life‐long characteristics.

Individual dietary patterns in sea otters appear to be transmitted along matrilines, probably by way of learning during the period of mother–young association.

Efficient utilization of different prey types probably requires radically different sensory/motor skills, each of which is difficult to acquire and all of which may exceed the learning and performance capacities of any single individual. This would explain the absence of generalists and inertia against switching, but not the existence of alternative specialists.

Such individual variation might arise in a constant environment from frequency‐dependent effects, whereby the relative benefit of a given prey specialization depends on the number of other individuals utilizing that prey. Additionally, many of the sea otter's prey fluctuate substantially in abundance through time. This temporal variation, in conjunction with matrilineal transmission of foraging skills, may act to mediate the temporal dynamics of prey specializations.

Regardless of the exact cause, such extreme individual variation in diet has broad ramifications for population and community ecology.

The published literature indicates that similar patterns occur in many other species.
Preliminary estimates of fallen dead wood and standing dead trees in managed and unmanaged forests in Britain
Authors: Kirby K.J. , Reid C.M. , Thomas R.C. , Goldsmith F.B.
Published: March 2003

1.  The amount of dead wood, particularly as fallen dead wood and standing dead trees, in British forests is attracting attention from forest managers as part of their interest in increasing biodiversity within forests managed for timber. Existing levels of dead wood in managed and unmanaged forests were assessed to provide a basis for what might be considered high or low amounts of dead wood under present conditions.

2.  Estimates of fallen dead wood, derived from line‐intersect sampling, were collated for 63 sites (87 stands) in Britain. The values obtained ranged from virtually zero in recently cut coppice to 60–140 m3 ha−1 in stands largely undisturbed over at least the last 80 years. The highest values (from unmanaged stands) overlap with estimates for the volumes of fallen logs in old‐growth broadleaved forests in North America and continental Europe. Forests currently managed for timber had less than 20 m3 ha−1 of fallen logs.

3.  In unmanaged stands, localized accumulation of fallen material was often associated with exceptional events such as the 1976 drought or the 1987 great storm. Following the 1987 storm the amounts of fallen dead wood in unmanaged forests in eastern England appear to have doubled from about 10 m3 ha−1 to 23 m3 ha−1.

4.  Large standing dead trees (snags), > 40 cm diameter, were rarely recorded in the forests surveyed because most forests in Britain have been cut over at least once this century and any large timber removed.

5.  The following, based on the range of values found in this survey, are proposed as provisional benchmarks for amounts of dead wood in British broadleaved forests: low <20 m3 ha−1 fallen dead wood, 0–10 snags ha−1 (all below 10 cm diameter); medium 20–40 m3 ha−1 fallen dead wood, 11–50 snags ha−1 (of which some are more than 10 cm diameter); high >40 m3 ha−1 fallen dead wood, more than 50 snags ha−1 (of which some are more than 40 cm diameter).

6.  Further work on assessing the dead wood resource in British forests is needed.
Long‐term population studies and the development of an integrated management programme for control of Opuntia stricta in Kruger National Park, South Africa
Authors: Hoffmann J.H. , Moran V.C. , Zeller D.A.
Published: March 2003

1.  A cactus, Opuntia stricta, has invaded almost 16 000 ha of conserved, natural habitatand has become a major weed problem in Kruger National Park (KNP), South Africa.

2.  The main objectives in the control of O. stricta are to reduce the density of the weed and to curb long‐range dispersal of seeds by preventing young plants from reaching the size (28 cladodes) at which they start to produce fruits.

3.  Herbicides have failed to provide satisfactory control of O. stricta because the weed infestations are replenished from seeds in the soil and from small plants that are overlooked during spraying.

4.  A phycitid moth, Cactoblastis cactorum, was released in KNP during 1988 in an attempt to control O. stricta biologically.

5.  Population counts of the biological control agent and of the weed over a 5‐year period showed that, even though C. cactorum has not provided complete control of O. stricta in KNP, the moderate levels of larval damage have stunted the growth of O. stricta and have considerably extended the time that the young plants take to reach sexual maturity.

6.  Comparisons of modelled (i.e. with no C. cactorum) and actual populations of O. stricta showed that C. cactorum is making a substantial contribution to the control of O. stricta in residual infestations of the weed that have been treated with herbicides.

7.  The need for long‐term evaluation studies in biological weed control is demon strated by the development of an integrated management programme for effective control of O. stricta.
Log‐normal distribution of species abundances is not a universal indicator of rain forest disturbance
Authors: Nummelin Matti
Published: March 2003

1. The fit to log‐normal distribution of species abundances of grasshoppers, ladybird beetles, tortoise beetles and dung beetles and forest floor vegetation in unlogged and selectively felled sites in Kibale Forest, western Uganda was analysed. It was shown that the fit to log‐normal distribution cannot be used as a straightforward universal indicator of rainforest disturbance.
Experimental refuges for migratory waterfowl in Danish wetlands. I. Baseline assessment of the disturbance effects of recreational activities
Authors: Madsen Jesper
Published: March 2003

1. Potential human sources of disturbance, including fishing, sailing, windsurfing and different types of waterfowl hunting, are described and their effects on autumn‐staging waterbirds, including mute swan, wigeon and coot, were examined at a coastal wetland in Denmark from 1985 to 1988.

2. Bird and human distributions were superimposed on the distribution of submerged vegetation and water depths to identify the extent of spatial overlap; likewise, seasonal and diurnal temporal overlap in bird abundance, and human activities were defined. Behavioural and distributional reactions of waterbirds to different human activities, in terms of escape distances, disruption of activity patterns and redistribution, were assessed to establish their relative effects.

3. Sailing and windsurfing showed little spatial overlap, and fishing partial spatial overlap with bird distributions; these activities almost ceased before the peak in autumn bird numbers. Hunting showed a high degree of spatial and temporal overlap with bird presence.

4. Birds responded to windsurfing at greatest distances, whereas hunting (especially from mobile punts) caused the longest disruptions to activities of waterfowl. In terms of behaviour and redistribution, wigeon was more affected by shooting than was mute swan or coot. One or two mobile shooting punts reduced wigeon numbers, whereas numbers were unaffected by the presence of up to 4–6 stationary punts; fishing boats had no effect on wigeon abundance.

5. Hunting, especially shooting from mobile punts, was identified as the most disturbing human activity in relation to staging waterfowl in this area. Similar results and conclusions were reached in another comparable study area. The results have implications for refuge designs and zoning of disturbing recreational activities.
Experimental refuges for migratory waterfowl in Danish wetlands. II. Tests of hunting disturbance effects
Authors: Madsen Jesper
Published: March 2003

1. In most situations that have been studied, the creation of refuge areas for migratory waterfowl has generally increased the number of waterfowl using a site. However, experimental evidence to show that the increases were caused by reduced disturbance and not by confounding factors, e.g. improvement of habitat quality of the sites or general population increases, is generally lacking.

2. In two Danish coastal wetlands, waterfowl hunting was the most critical source of disturbance to autumn‐staging waterfowl (Madsen 1998). To test whether hunting disturbance displaced birds from sites, experimental refuge areas were established, with hunting‐free areas manipulated annually during a 4‐year period, followed by permanent refuge establishments, monitored for a further 4 years.

3. In both areas, experiments showed that quarry geese and dabbling ducks redistributed according to the position of the hunting‐free areas, whereas protected species did not. In quarry geese, there was a 6–8‐fold increase in numbers from before to after the experiments; in quarry dabbling ducks there was a 4–50‐fold increase. Dabbling ducks extended the staging period into the winter. Protected waterfowl as well as goldeneye and coot (both quarry species) did not redistribute; their numbers either fluctuated or increased (2 to > 50 fold).

4. In quarry geese and dabbling ducks, changes in food supplies (of the herbivorous species), intensities of recreational activities outside the refuge areas, weather or overall population sizes could not explain the increases. In protected species, as well as goldeneye and coot, trends in local numbers were in accordance with overall population trends for some species; in others, the rate of increase in local numbers was higher than in overall population size.

5. In both areas, species richness increased from before to after the experiments. This was most pronounced in one of the areas where the refuge included shallow‐watered areas in association with salt marshes.

6. It is concluded that prior to experiments, waterfowl hunting caused a displacement of quarry species, resulting in a species‐poor waterfowl community. Refuge creation is an efficient management tool to improve the conservation value and biodiversity of wetlands of importance to waterfowl.
Improving grasslands: the influence of soil moisture and nitrogen fertilization on the establishment of seedlings
Authors: Haugland Espen , Froud‐Williams Robert J.
Published: March 2003

1. In order to investigate the factors influencing the establishment of seedlings in permanent grassland, the influence of soil moisture and nitrogen fertilization on competition between established plants of Lolium perenne and seedlings of Phleum pratense or Trifolium pratense was studied in two experiments under greenhouse conditions using the ‘split‐box’‐technique.

2. There was no difference in the production of plant dry matter of P. pratense or T. pratense between 30% volumetric soil water content (−0·005 MPa) and 22% (−0·04 MPa), but 15% soil moisture (−0·33 MPa) reduced plant growth. L. perenne yields were linearly reduced by reduced soil moisture content.

3. Shoot competition from L. perenne reduced the plant dry matter yield of P. pratense and T. pratense more than did root competition in these experiments. When shoot competition was present, differences between moisture contents were not detected, indicating that light was probably the limiting resource under such conditions. No significant interaction between root competition and soil moisture was observed for plant weight.

4. Root competition was not prevented even though sufficient water and nitrogen were supplied. This indicated either that some other growth factor was limiting or the plants competed for resources at the root hair level even though sufficient resources were supplied at the pot or field scale. Therefore, in the situation of direct drilling of species during grassland renovation, it may be difficult to alleviate competition by adequate provision of water and nitrogen.
Do wood‐pigeons avoid pesticide‐treated cereal seed?
Authors: MKay H. V. , Prosser P. J. , Hart A. D. M. , Langton S. D. , Jones A. , MCoy C. , Chandler‐Morris S. A. , Pascual J. A.
Published: March 2003

1. Pesticides applied to seeds before sowing may present a high risk to seed‐eating birds. Some of these chemicals are highly toxic but are avoided by captive birds in laboratory tests. However, evidence for birds avoiding them in the field is lacking. The objective of this study is to investigate avoidance and other factors affecting risk of poisoning, using the model of wood‐pigeons Columba palumbus L. feeding on winter‐drilled cereal seed treated with the organophosphorus insecticide fonofos.

2. Wood‐pigeons feeding on arable fields in Cambridgeshire, UK, were counted once or twice per week over four winters from 1992 to 1996. In autumn, newly drilled cereal fields are shown to be preferred to alternative crops such as stubble and ploughed fields and root crops. In spring, newly drilled cereal fields are sometimes preferred to older cereal fields, stubble, ploughed fields and drilled onions.

3. Fewer fields drilled with fonofos‐treated cereal seed were used by wood‐pigeons than untreated (without fonofos) fields for the first week after drilling only. The extent of the avoidance reaction was related to the concentration of fonofos on the seed left exposed on field surfaces.

4. The concentration of fonofos on newly drilled seed exposed on field surfaces (mean of 241 mg kg–1) was much lower than expected from the approved application rate (1080 mg kg–1). Residues decayed linearly at a rate of 2% per day after drilling and varied widely between fields.

5. The density of seed left exposed after drilling also varied widely between fields, being greater on headlands (field edges) than the main field and declining at a rate of 2% per day after drilling.

6. Of 61 wood‐pigeons shot within the study area over three winters, 26 had been feeding on cereal seed and of these, six contained fonofos residues at levels similar to poisoned birds submitted to the MAFF Wildlife Incident Investigation Scheme.

7. In conclusion, fonofos‐treated cereal seed may be partially avoided in the wild. Avoidance fails to prevent poisoning under some (rare) conditions, possibly when seed density, concentrations of fonofos and levels of hunger are all above average. The implications for risk assessment are discussed.
A strategy for minimizing waterfowl deaths on toxic waterbodies
Authors: Read J. L.
Published: March 2003

1.A deterrent was used in conjunction with engineering and management techniques to discourage nomadic waterfowl from landing and remaining on toxic waterbodies.

2.Four behavioural traits of nomadic waterfowl were exploited in the development of the deterrent: nocturnal movements, attraction to reflective surfaces, fear of diurnal predators, and naivety to local conditions and deterrents.

3.A rotating, intermittent beacon directed at a shallow angle across the water surface effectively discouraged most waterfowl. This beacon was floating and solar‐powered and built to be acid resistant.

4.A series of deterrents, with gas‐powered sonic guns and provision of clean alternative waterbodies nearby, significantly lessened the likelihood of waterfowl injury or mortality on toxic waterbodies.
Clearcutting and burning of northern spruce‐fir forests: implications for small mammal communities
Authors: Sullivan Thomas P. , Lautenschlager R. A. , Wagner Robert G.
Published: March 2003

1.This study was designed to test the hypotheses that (i) abundance and related demographic parameters of small mammal populations would decline after clearcutting of northern spruce‐fir forest, and (ii) prescribed burning, following clearcutting, an approach to emulating natural disturbance, would enhance the species richness and diversity of the small mammal community relative to unharvested and clearcut forests.

2.Intensive live‐trapping of small mammal populations was conducted in replicated forest (uncut), clearcut and clearcut‐burned sites from 1988 to 1992 in west‐central British Columbia, Canada.

3.Mean abundance of southern red‐backed volesClethrionomys gapperiwas significantly higher on forest sites (11·74 ha–1) than on clearcut (0·60 ha–1) or clearcut‐burned (0·02 ha–1) sites. Mean numbers of deer micePeromyscus maniculatuswere significantly higher on the clearcut‐burned sites (16·88 ha–1) than on forest sites (9·04 ha–1). Demographic parameters of reproduction, survival and body weight of deer mice were similar across all sites.

4.The long‐tailed voleMicrotus longicaudushad a strong annual fluctuation in abundance, particularly on clearcut sites (14·04 ha–1), where there were significantly more animals than on either forest (1·53 ha–1) or clearcut‐burned (2·67 ha–1) sites. Meadow volesM. pennsylvanicuswere relatively uncommon but occurred more often on clearcut and clearcut‐burned sites than on forest sites.

5.The north‐western chipmunkTamias amoenusoccurred at significantly higher numbers on clearcut (4·16 ha–1) and clearcut‐burned (3·88 ha–1) sites than on forest sites, where it was rarely captured. ShrewsSorexspp. were at similar numbers across forest, clearcut and clearcut‐burned sites. WeaselsMustelaspp. were captured more often on clearcut and clearcut‐burned sites than on forest sites. A rare species, the western jumping mouseZapus princeps, was captured on clearcut and clearcut‐burned sites only.

6.Mean species richness of small mammals was significantly higher on clearcut sites (3·51) than on forest (2·73) or clearcut‐burned (2·72) sites. Species diversity was similar over all sites. Although species composition was altered by clearcutting, abundance of all species, exceptC. gapperi, was the same or higher than that in uncut forest.

7.Prescribed burning of clearcuts may not be necessary to mimic natural disturbance regimes. Clearcutting of northern spruce‐fir forest may provide diverse habitats for small mammals through different stages of succession (along with old growth forest) much as wildfires formerly did.
ADVANCES IN APPLIED ECOLOGICAL TECHNIQUES A novel mark–recapture technique and its application to monitoring the direction and distance of local movements of rangeland grasshoppers (Orthoptera: Acrididae) in the context of pest management
Authors: Narisu  , Lockwood Jeffrey A. , Schell Scott P.
Published: March 2003

1. Rangeland grasshopper movement was studied in Wyoming, USA, with respect to the biological and ecological factors (population density, developmental stage and weather) influencing net displacement and directionality.

2. A novel adaptation of the mark–recapture method was developed to monitor grasshopper dispersal. The method used fluorescent powder and resighting marked grasshoppers in the field with ultraviolet light, rather than physical recapturing of individuals.

3. Rangeland grasshoppers exhibited a strong tendency for directional movement. Adult grasshoppers demonstrated a significant tendency for dispersal in a north‐westerly direction across a range of population densities (5–8, 10–15 and ≥ 18 grasshoppers m–2). Although not a definitive explanation, weather might have influenced this behaviour, as the grasshoppers consistently moved upwind.

4. The mean displacement of grasshoppers in a 36‐h period ranged from 2·3 m in nymphs to 3·7 m in adults, with the distance of displacement being positively correlated with population density.

5. An understanding of grasshopper movement in terms of directionality and displacement has immediate applicability to reduced agent–area treatments for rangeland grasshopper management.
Survey of badger Meles meles damage to agriculture in England and Wales
Authors: Moore Niall , Whiterow Anne , Kelly Paul , Garthwaite David , Bishop Julie , Langton Steve , Cheeseman Chris
Published: March 2003

1. In response to reported increases in badger numbers and associated agricultural damage, a questionnaire survey of 3600 land owner/occupiers was conducted in 1997 to determine the extent and significance of badger damage in England and Wales. We assess the significance of badger‐induced damage and highlight problem regions, farm types and specific crops to allow targeting of future research efforts at amelioration. (This survey investigated alleged badger damage to agriculture but did not address the role of badgers in the transmission of bovine tuberculosis.)

2. The return rate of the questionnaire was 55·1% (n = 1982) and 150 of the responses were ground‐truthed.

3. Almost 30% of those land owner/occupiers who responded reported that badger damage had occurred in the previous 12 months, and 57% reported an increase in damage during the past 5 years.

4. Badger damage was widespread, but its incidence was highly dependent on region and farm type. The most frequently reported damage (25·5%) resulted from badgers’ burrowing activities (especially those causing damage to fences). Crop damage was also frequently reported (21·2%), with wheat, forage maize and vines being damaged most frequently.

5. Ground‐truthing showed that incorrect attribution to badgers of damage was negligible and that the majority of respondents had assessed correctly the extent and cost of badger damage, except for predation on livestock where most ‘evidence’ was circumstantial.

6. Most reported damage was of little economic consequence to individual land owners/occupiers; however, approximately 5% estimated that they had incurred costs of over £1000.

7. Assuming that the questionnaires returned were a random subset of those distributed, the mean estimated national cost was £41·5 million per annum (62% of which was due to burrowing activity). Assuming that all the non‐respondents had no damage, the estimate was £21·5 million per annum.

8. Future research into management options for damage limitation should be targeted at the areas and situations of most significant damage. These are primarily burrowing damage and direct crop damage to wheat, maize, vines, fruit and vegetables. The region suffering the most intense damage was the south‐west of England. The highly seasonal nature of the damage to some crops will allow preventative action to be taken at the most appropriate times. Predation by badgers on livestock is considered a small‐scale and unproven problem.
Effects of surgically imposed sterility on free‐ranging rabbit populations
Authors: Twigg Laurie E. , Lowe Tim J. , Martin Gary R. , Wheeler Amanda G. , Gray Garry S. , Griffin Sandra L. , O’Reilly Catherine M. , Robinson David J. , Hubach Peter H.
Published: March 2003

1. Demographic changes in response to surgically imposed female sterility were monitored in 12 free‐ranging rabbit populations in south‐western Australia over a 4‐year period. This was part of a research programme aimed at examining the potential for virally vectored immunocontraception to limit the abundance of rabbits (e.g. using a recombinant myxoma virus) and other mammalian pests. Sterility levels were 0%, 40%, 60% and 80% of all females in year 1, with a similar proportion of female recruits sterilized surgically in subsequent years.

2. There was a significant decrease in rabbit productivity with increasing sterility level. This was overcome by increased survival of kittens and adults on the high‐sterility sites, such that the base‐level numbers of rabbits were maintained, and mean annual rates of increase (r) were near zero for all treatments in all years. However, in the high‐sterility populations this compensation was insufficient to overcome the effects of sterility totally, and there was a marked decrease in the seasonal peaks in rabbit abundance for these treatments.

3. Survival and recruitment were dependent upon the level of sterility, and consequently the density of rabbits, with greatest survival of adult rabbits occurring on the 80% sites. Survival of sterile females was greater than that of other adults, probably because of their increased ability to maintain body condition during times of low pasture biomass (summer drought). Thus two density‐dependent processes were identified: the first was operating through increased survival of juvenile rabbits, the second through increased adult survival, particularly sterilized females.

4. Because the proportional impact of immigration was greater (i.e. immigrants constituted a greater proportion of the population) and emigration was less, from the 80% sites, the effects of sterility may have been underestimated on these sites.

5. The abundance of European rabbit fleas, a vector of myxomatosis, was significantly lower on the 80% sites, but this did not appear to affect the transmission of myxoma. Myxomatosis occurred as an annual epizootic in three of four years, with > 90% of rabbits on site after each epizootic testing positive for myxoma antibodies.

6. To achieve a sustained long‐term reduction in rabbit abundance, 60–80% of female rabbits would need to be prevented from breeding. This could be achieved by a recombinant strain of myxoma provided the strain retained good transmissibility and all infected rabbits became sterile for life.
Interactions between nutrient status and weevil herbivory in the biological control of water hyacinth
Authors: Heard Tim A. , Winterton Shaun L.
Published: March 2003

1. Despite the widespread release of effective biocontrol agents, water hyacinth remains the world’s most problematic aquatic weed, particularly in eutrophic waterbodies. However, understanding of the interaction between control and trophic status is still incomplete.

2. Growth of water hyacinth plants was measured at two water nutrient concentrations (high and medium) and in the presence and absence of two insect biocontrol agents in a large circulating hydroponic system in a glasshouse.

3. At the high nutrient concentration (1·6 mg l−1 N and 1·0 mg l−1 P), plants multiplied more quickly, attaining greater biomass. Both insect species reduced plant growth at both nutrient concentrations. Neochetina bruchi, however, performed better than N. eichhorniae at the high nutrient concentration by inflicting more damage on the plants and reducing biomass by a greater extent.

4. Insect damage reduced the concentrations of nitrogen and phosphorus found in plants growing in high nutrient water but not in medium nutrient water (0·4 mg l−1 N and 0·025 mg l−1 P).

5. The developmental and reproductive performance of N. bruchi was determined at both nutrient concentrations. Water hyacinth plants grown at higher nutrient concentration were superior hosts to N. bruchi than plants grown at medium concentrations. Net reproductive rate and intrinsic rate of increase were significantly greater at the high concentrations. Greater damage by N. bruchi to water hyacinth at the high nutrient concentration was due to the greater production of offspring, and hence greater larval damage.

6. We predict that water hyacinth problems will be greater in eutrophic waterbodies, where N. bruchi will be a superior biocontrol agent to N. eichhorniae. In low‐nutrient waterbodies, local nutrient enrichment of water may assist the establishment of control agents. These results illustrate the importance of wider ecological factors on the success of biological control.
How environmental stress affects density dependence and carrying capacity in a marine copepod
Authors: Sibly Richard M. , Williams Timothy D. , Jones Malcolm B.
Published: March 2003

1. Management of the effects of stress on populations – for instance in ecotoxicology – requires understanding of the effects of stressors on populations and communities. Attention to date has too rarely been directed to relevant ecological endpoints, such as carrying capacity and density dependence. Established procedures are instead based on measuring the Life Tables of individual organisms exposed to differing concentrations of a pollutant at low population density, but this approach does not take into account population effects that may occur through interactions between individuals. Here we introduce an approach that allows direct measurement of the effects of stressors on carrying capacity and density dependence.

2. Using the marine copepod Tisbe battagliai Volkmann‐Rocco, we report replicated experiments establishing the effects of 100 µg L−1 pentachlorophenol (PCP) in combination with varying diet and food concentrations. Population density was measured as population biomass in 10 mL volumes. Diet was either the alga Isochrysis galbana Parke (here designated ‘poor diet’) or a mix of two algal species (I. galbana and Rhodomonas reticulata Novarino: ‘good diet’). Each was given at three food concentrations (520, 1300 and 3250 µgC L−1), selected on the basis that at low population density these cover the range between limited and maximal population growth.

3. Carrying capacity increased linearly with food concentration. On the poor diet the increase was 1·2 μg L−1 for each μgC L−1 increase in food concentration. On the good diet the increase was 2·3 μg L−1/μgC L−1 in the absence of PCP, and 1·9 μg L−1/μgC L−1 with PCP. Maximum carrying capacity was in the region of 60–80 μg per 10 mL volume. Population growth rate (pgr) decreased linearly with population biomass when the latter was plotted on a logarithmic scale. Increasing biomass reduced pgr by 1·70 week−1 for each unit increase in log10 biomass. Increasing food concentration and improving diet both increased pgr, but did not affect the slope of the density‐dependent relationship. Presence or absence of PCP had no effect except that at some higher food concentrations non‐PCP populations initially increased faster than PCP populations, and at high concentration on the good diet the effect of density‐dependence was decreased in PCP populations.

4. The results show that a stressor's effects at high population density may differ from its effects at low density, and emphasizes the importance of finding new protocols, such as those introduced here, with which to study the joint effects of a stressor and population density. Managers and researchers of threatened species, harvested species and pest species need to know the joint effects of stressors and population density, in order to be able to predict the effects of stressors on carrying capacity and on the course of recovery from environmental perturbations.
Effects of spring drought and irrigation on farmland arthropods in southern Britain
Authors: Frampton Geoff K. , Van Den Brink Paul J. , Gould Philip J. L.
Published: March 2003

1. Information is lacking on how possible future changes in the seasonal occurrence and intensity of precipitation in Europe will affect the arthropod community of arable farmland.

2. We used a novel experimental approach to investigate the responses of farmland arthropods to spring precipitation in a spring‐sown legume. Replicated plots were subjected to spring drought (plots shielded from rainfall), actual rainfall (reference) and spring irrigation. Shielding plots extended an existing drought to 58 days.

3. The response of epigeic arthropods was investigated using principal components analysis (PCA) and principal response curves (PRC). Temporal changes in treatment effects at the community level were more clearly displayed by PRC than by PCA, while PRC improved the interpretation of individual species' responses. PRC analysis has potential for wider application in ecological experiments and monitoring.

4. Short‐term manipulation of precipitation in May affected the arthropod community for at least 97 days, despite exceptionally high rainfall in June. The effects of drought on the abundance of herbivores, mycophages, omnivores and predators were negative, while those of irrigation were positive. There were no differences in the responses of beneficial and pest taxa.

5. In addition to their intrinsic importance, these findings illustrate that spring weather might affect the availability of arthropod prey for insectivorous wildlife. Food availability has been implicated in the population declines of several insectivorous farmland birds.

6. The difficulty of manipulating rainfall in a temperate climate precludes realistic field studies of how farmland arthropods respond to precipitation. We suggest that automated rain shielding of experimental plots provides a technique for wider application in drought studies.
Effects of agricultural intensification on the breeding success of corn buntings Miliaria calandra
Authors: Brickle Nick W. , Harper David G.C. , Aebischer Nicholas J. , Cockayne Simon H.
Published: March 2003

1. Corn buntings Miliaria calandra have declined steeply in Britain and north‐western Europe since the mid‐1970s; changes in farming practice are believed to have been partly responsible.

2. We studied nesting corn buntings on the South Downs in west Sussex between 1995 and 1997 to examine the possible effects of agricultural intensification on breeding success. The abundance of invertebrates around individual nests was sampled by sweep‐netting in July.

3. Corn buntings provisioning nestlings foraged in grassy margins more than any other habitat relative to their availability within the maximum foraging range. The other habitats used more than expected were spring‐sown barley, unintensified grass and set‐aside. Those used less than expected included winter‐sown wheat and intensively managed grassland. The invertebrates most commonly fed to chicks were more abundant in foraging areas than elsewhere. Their density was negatively correlated with the number of insecticide applications both when cereal fields only were considered and when all foraging habitats were included.

4. The lower the abundance of chick‐food invertebrates close to nests, the greater the distance from the nest at which parents foraged, and the longer such trips were in duration. The weights of nestlings, corrected for age using tarsus length, were positively correlated with the abundance of chick‐food invertebrates.

5. The probability of nest survival was negatively correlated with the abundance of chick‐food invertebrates close to the nest, apparently as a result of an increased risk of predation.

6. Agricultural intensification in Britain, including the increased use of pesticides, has led to a widespread decrease in the availability of chick‐food invertebrates on lowland farmland. If our results are typical of corn buntings in an arable environment, this decrease correlates with reduced breeding success. Depending on the mortality rates for fledged chicks and older birds, this reduction may have contributed to the corn buntings' decline and may hamper recovery.

7. Farming practices that increase invertebrate availability ought to benefit breeding corn buntings. Large‐scale measures such as set‐aside and the spring‐sowing of cereals (especially if undersown with grass) depend heavily on overall agricultural policy. Small‐scale initiatives might therefore be more feasible; these include the provision of grassy margins or beetle banks and selective spraying of headlands.