bluuebunny/crossref_metadata_2025 huggingface dataset:
Structure of a diverse tropical forest insect–parasitoid community
Authors: Lewis Owen T. , Memmott Jane , Lasalle John , Lyal Chris H.C. , Whitefoord Caroline , Godfray H. Charles J.
Published: March 2003

Quantitative host–parasitoid food webs are descriptions of community structure that include data on the abundance of hosts and parasitoids, and the frequency of links between them, all expressed in the same units.

Quantitative host–parasitoid food webs were constructed describing the community of leaf‐mining insects (Diptera, Coleoptera and Lepidoptera) and their parasitoids (Hymenoptera) in an 8500‐m2area of moist tropical forest in Belize, Central America, over a 1‐year period.

The summary food web, containing data for the whole year, is we believe the most diverse quantitative host–parasitoid web yet described. It contains 93 species of leaf‐miner, 84 species of parasitoid and 196 links between hosts and parasitoids.

Most parasitoids were generalists, with individual parasitoid species recorded as parasitizing up to 21 host species. In contrast, most leaf‐miners were specialists, with 114 links documented between leaf‐miners and their host plants.

A robustness analysis was used to reveal the effects of different sampling intensities on food web statistics. The results suggest that the sampling had revealed most of the species of host and parasitoid in the community, but further interactions among species would continue to be detected with additional sampling. Measures of the ratio of hosts to parasitoids and of realized connectance were relatively insensitive to sampling intensity.

Three seasonal webs were constructed, revealing temporal changes in the structure of the community. There was greater turnover in host species composition than parasitoid species composition among seasons, but most web statistics remained relatively constant across seasons.

Both the summary web and the seasonal webs show low levels of compartmentalization, suggesting that the host–parasitoid community is not divided into relatively discrete subwebs with largely independent dynamics.

The extent of potential indirect interactions between pairs of hosts was assessed by constructing quantitative parasitoid overlap graphs. These suggest that abundant species are likely to have greater indirect effects on less abundant species thanvice versa, and that species in the same taxonomic order are more likely to interact indirectly. The graphs do not support the hypothesis that species sharing the same host plant are more likely to interact via shared parasitoids.
Scientific quality of tourism environmental impact assessment
Authors: Warnken J. , Buckley R.
Published: March 2003

1.  The scientific quality of environmental impact assessment (EIA), as exemplified by major tourism developments in Australia, is very poor.

2.  Methods are inadequately specified.

3.  Sampling is inadequately replicated in space or time.

4.  Significant parameters are often ignored.

5.  Impact predictions are rarely quantitative or testable and frequently are inaccurate.

6.  Monitoring programmes generally are inadequate to detect likely impacts.

7.  As an exercise in applied science, EIA fails to meet the most fundamental quality criteria.

8.  As a tool in public decision‐making, EIA needs much better applied science.
Structure and function in two tropical gallery forest communities: implications for forest conservation in fragmented systems
Authors: Kellman Martin , Tackaberry Rosanne , Rigg Lesley
Published: March 2003

1.  Composition, growth and turnover of trees in two species‐rich tropical gallery forests were examined to evaluate what community reorganization may be needed to transform recently created tropical forest fragments into stable refugia for regional forest biotas.

2.  Rates of tree growth and turnover over a 5‐year interval were comparable to those recorded in continuous forests and in both communities there had been some tree species turnover in the measured stem size classes during the 5‐year interval.

3.  The more abundant tree species in both communities formed three functional groups along gradients between streams and forest edges: edge‐concentrators, core‐concentrators and generalists.

4.  Soil fertility showed no consistent increase close to streams and neither tree growth nor recruitment rates were increased in this zone. In contrast, forest edge zones exhibited increased rates of tree growth and recruitment indicating that growth processes in these forests are light‐limited rather than soil‐limited, and that forest edge zones are generally favourable habitats for tree populations.

5.  Both communities showed signs of past fire incursions, and the tendency of a subset of tree species to concentrate in the more growth‐limited core habitats is attributed to their fire sensitivity.

6.  Rapid development of an edge zone of fire‐insensitive tree species is considered to be essential to the survival of forest community fragments in the fire‐prone landscapes of the tropics, and the edges of gallery forests are recommended as potential sources of species with which to fashion these protective ecotones.

7.  Preservation of a diverse forest biota in the fire‐protected interiors of fragments will require natural or artificially enhanced immigration rates that are sufficient to offset local extinctions.
Maximum likelihood population size estimation of harbour seals in the Dutch Wadden Sea based on a mark–recapture experiment
Authors: Ries Edith H. , Hiby Lex R. , Reijnders Peter J.H.
Published: March 2003

1.  The harbour seal population Phoca vitulina in the entire Wadden Sea was severely depleted due to a virus‐epizootic during 1988. A comprehensive study on the population biology and activity patterns was subsequently initiated to design a management and conservation plan. The main objective of this study was to estimate harbour seal abundance in the different regions of the Wadden Sea.

2.  We investigated the potential of a mark–recapture experiment using VHF radio‐tags in combination with repeated aerial surveys to estimate the number of harbour seals in the Dutch part of the Wadden Sea. The number of harbour seals hauled‐out and the presence of any radio‐tagged seals was monitored during seven aerial surveys of all known haul‐out sites in the Dutch Wadden Sea over the 1994 breeding season.

3.  A maximum likelihood (ML) estimator was developed to infer the rate of tag‐loss and the size of the local prepupping population.

4.  The ML estimate of the number of harbour seals in the Dutch Wadden Sea was 1536 (95% confidence limits were 1225 and 2200). The corresponding maximum proportion of seals hauled‐out was 68%.

5.  The use of VHF radio‐tags which can be monitored from the air provides a way of correcting aerial survey counts for the proportion of harbour seals hauled‐out during the surveys. Since haul‐out behaviour may be influenced by local conditions, such as exposure time of sand banks, we recommend this technique be repeated in other areas of the Wadden Sea rather than using the estimates from the current study in other areas.
Modelling pest population resurgence due to recolonization of fields following an insecticide application
Authors: Trumper E.V. , Holt J.
Published: March 2003

1.  To investigate the effect of insect recolonization on the insecticide‐induced resurgence of crop pests, a modified Lotka–Volterra predator–prey model was partitioned into two areas, ‘sprayed’ and ‘unsprayed’.

2.  The unsprayed area provided a source of insects to recolonize the sprayed area, resulting in a change in pest dynamics in both areas following an insecticide application.

3.  Model sensitivity to insecticide selectivity and rates of predation, insect dispersal and pest population increase were examined.

4.  Resurgence risk in the sprayed area increased with increasing pest dispersal rate, but decreased with increasing predator dispersal rate.

5.  Pest resurgence could also occur in the unsprayed area, especially when prey dispersal rates were low. The extent of resurgence in the unsprayed area could in some circumstances be worse than in the sprayed area itself.

6.  The more efficient and longer‐lived the predators, the greater the level of pest resurgence in both areas following insecticide use.

7.  More selective insecticides, killing the pest, but not the predator, reduced resurgence provided that the average life‐span of the predators was reasonably long. Even highly selective insecticides could cause resurgence of the pest in the unsprayed area.

8.  When the prey carrying capacity of the unsprayed area was increased relative to that of the sprayed area, resurgent effects in the unsprayed area were reduced, but could still be significant under some circumstances.
Foraging behaviour of sheep and red deer within natural heather/grass mosaics
Authors: Hester A. J. , Gordon I. J. , Baillie G. J. , Tappin E.
Published: March 2003

1. Heather moorland is an internationally important resource; it is valued as food and habitat for a range of herbivores as well as for landscape, conservation and recreation. In many parts of its range, grazing by large herbivores has impacted greatly on its current status and distribution. The interactions between two widespread herbivores, sheep and red deer, and the vegetation were examined within a naturally fragmented heather/grass mosaic in north‐east Scotland from 1991 to 1996. This paper reports their foraging behaviour and inter‐species interactions, and discusses the implications for grazing management within this vegetation type.

2. Both species foraged widely in this highly fragmented mosaic (red deer more widely than sheep) and consumed similar proportions of grass and heather. Neither species showed any major dietary shift as grass availability declined during experimental periods.

3. Grass patch size affected foraging behaviour differentially. Sheep spent more time grazing smaller grass patches (1–6 m2), whereas red deer showed no consistent grass patch size preferences (range: 1 m2 to over 200 m2). When lying down, red deer lay within heather almost exclusively, whereas sheep spent equal amounts of time within heather and small grass patches.

4. Faecal distribution also differed in a similar way, with concomitant implications for the spatial distribution of both physical and chemical impacts on the vegetation.

5. Contrary to previous hypotheses, the overall patterns of foraging behaviour by sheep and deer were little affected by the presence or absence of the other species. This suggests that range overlap between these species may have much less of an impact on their vegetation use than previously assumed.

6. Heather moorland is frequently found on sloping ground, which was shown to have a major effect on foraging, with a strong preference by both species for grazing facing either uphill or across the slope. This, and other slope‐related impacts, resulted in spatially different patterns of heather use around the edges of grass patches.

7. The primary conclusions are that, although the overall use of grass and heather by sheep and red deer was similar within this fragmented mosaic, vegetation pattern clearly affected their foraging behaviour differentially. Sheep appeared to be much more affected by the scale of heather fragmentation than were deer and their habitat use was more closely focused on paths and grass patches, which contrasts with the more even use of the mosaic by deer. The implications of these behavioural differences for the management of upland grazings under one or both of these herbivore species are discussed.
The conservation management of Imperata cylindrica grassland in Nepal with fire and cutting: an experimental approach
Authors: Peet Nicholas B. , Watkinson Andrew R. , Bell Diana J. , Sharma Uday. R.
Published: March 2003

1.
Imperata cylindrica dominated grassland in the Nepal Terai supports a number of threatened species including swamp deer Cervus duvauceli, hispid hare Caprolagus hispidus and Bengal florican Eupodotis bengalensis. It is also the main source of thatch material for local communities. Current widespread cutting and burning of the grasslands is deleterious to cover‐dependent vertebrates which would benefit from patches of grassland remaining unmanaged.

2. In Royal Bardia National Park, a randomized block experiment with four treatments (cutting, burning, cutting and burning, and no management) was established to examine the effects of these treatments on plant species abundance, species richness and grassland structure. The grassland was dominated by Imperata cylindrica, with Saccharum spontaneum, Vetiveria zizanioides, Desmostachya bipinnata and Schizachyrium brevifolium the other abundant species.

3. In year 3, 2 years after the first treatment, Imperata cylindrica remained the dominant grass species under all treatments. It increased in abundance in unmanaged plots and declined in abundance in managed plots. Desmostachya bipinnata showed the opposite response. Plant species richness was significantly higher in managed plots, which were structurally more heterogeneous.

4. The effects of cutting alone, burning alone, and cutting and burning combined on the structure and composition of the grassland were similar, despite additive effects on total grass cover, total forb cover and forb species richness in cut and burned plots. This allows the effects of cutting and burning to be reduced to a single treatment (cutting and burning) in future experiments to investigate the impacts of patch harvesting on community dynamics. Simpler factorial experiments can be designed than if cutting and burning had to be considered as separate treatments.

5. There was no difference in the establishment of tall grass species or woody species between managed and unmanaged plots.

6. Results suggest that patches of grassland could be left unmanaged on a 2‐year rotation without significantly altering the composition of the plant community, thereby providing refugia for cover‐dependent faunal species.
Rate of increase as a function of rainfall for house mouse Mus domesticus populations in a cereal‐growing region in southern Australia
Authors: Brown Peter R. , Singleton Grant R.
Published: March 2003

1. Mouse plagues are a significant problem to agricultural areas of Australia, causing millions of dollars of damage. This study was conducted to determine if rainfall could explain the occurrence of mouse plagues.

2. On average, data on mouse abundance were collected every month, using mark‐release‐recapture techniques, from the Victorian Mallee cereal‐growing region, from February 1983 to October 1994. No data were collected from December 1990 to September 1992. Three plagues of mice occurred during these 12 years. We examined the rate of increase of mouse populations as a function of antecedent rainfall.

3. The highest observed rate of increase per month was during 1986 (r = 1·86). The highest observed rate of decrease per month was during 1984 (r = –2·85). The maximum rate of increase of mouse populations used in the numerical response function was 1·16 month–1. The best estimate for the numerical response function was robs = –6·79 + 7·95 (1 – e–1·11V).

4. The numerical response of mouse populations to rainfall was examined against 6‐month accumulated rainfall that was lagged by 0, 3 and 6 months. The best fit of the model was to lag rainfall by 3 months.

5. Two systems for the response of mouse populations to rainfall are described. The plague system occurred when mouse populations responded to rainfall: populations increased following high rainfall and decreased following low rainfall. The non‐plague system occurred when the exponential rate of increase and rainfall were independent: populations crashed after a plague and were unable to respond to rainfall for at least 2 years thereafter.

6. The two systems suggest that there is ‘biological memory’ that masks the effect of rainfall for a minimum period after a mouse plague. This memory appears to be associated with the time since the last plague, the population response by mice (including shifts in age structure) in the previous year, and the abundance of mice after the spring decline. If rainfall is used to predict mouse plagues to assist in their management, the biology of the system must be known.
Identifying control strategies for tomato leaf curl virus disease using an epidemiological model
Authors: Holt J. , Colvin J. , Muniyappa V.
Published: March 2003

1. A number of insect vectors of plant‐virus diseases make only transitory visits to the crop in which the economic effects of the disease are important. The incidence of disease in the crop depends primarily on the immigration of vectors from alternative hosts which act as a reservoir of both the virus and vector.

2. An epidemiological model was developed to represent this situation and parameters were estimated for the case of tomato leaf curl virus disease (TLCVD) (Geminiviridae, Subgroup III) in India. From an analysis of the model, the following possibilities for the management of TLCVD emerged.

3. It was clear that varietal resistance to infection could be an important component of disease management but whether, once infected, the tomato plants acted as a source of inoculum had little impact on disease incidence in the tomato crop.

4. A very low rate of simulated vector immigration into a tomato crop sufficed to cause almost total infection. Around Bangalore, vectors may migrate into tomato crops in numbers in excess of those required for disease ‘saturation’, explaining why, using conventional insecticides, very efficient and intensive vector control is currently required to reduce disease incidence.

5. Disease incidence was sensitive to vector mortality only when vector numbers were low. In most cases, the immigration of viruliferous vectors made disease incidence insensitive to the mortality of vectors within the tomato crop.

6. A strategy for disease management which targets more than one of the parameters to which the model proved most sensitive is likely to be necessary. In particular, the use of protective netting combined with the growing of resistant varieties has the potential to reduce both B. tabaci immigration to the crop and to reduce virus inoculation by those insects which do reach the crop.
Tree performance on minespoils in the South Wales coalfield
Authors: Bending N.A.D. , Moffat A.J.
Published: March 2003

1. Variable growth of Larix leptolepis (Japanese larch) has been observed on restored opencast coal workings in South Wales. This has implications for the restoration of such sites. A study of the relationship of tree growth with minespoil chemical, nutritional, physical and hydrological factors was carried out.

2. Tree growth was positively related to nitrogen and phosphorus foliar concentrations, but negatively to those of magnesium. Seventy‐three per cent of the variation in tree growth was explained by variation in foliar chemistry.

3. Soil pH and extractable magnesium were negatively correlated with tree growth, with cation exchange capacity positively related to it.

4. Minespoils had bulk densities that commonly exceeded 1·7 g cm–3 below 0·2 m depth. Stone contents were high and typically 25% by volume.

5. Root systems of trees excavated were characterized by a high root density within 0·3 m of the minespoil surface. Restricted rooting was attributed to high bulk density and the incidence of shallow water tables.

6. Waterlogging during the spring and early summer, and the consequent presence of anaerobic soil conditions during periods of active growth, was found to be detrimental to tree growth.

7. The study suggests that landform design, selection of suitable soil or soil‐forming materials, spoil placement technique and appropriate species choice are central to the future success of forestry schemes on restored ground in South Wales.
Effects of mechanical cockle harvesting on intertidal communities
Authors: Ferns P.N. , Rostron D.M. , Siman H.Y.
Published: March 2003

1. Shellfish of marketable size can be harvested much more quickly and efficiently using mechanical methods such as tractor‐powered harvesters and suction dredgers than by traditional methods. The adverse effects of such machines on non‐target organisms need to be considered carefully before licensing such activities.

2. A tractor‐towed cockle harvester was used to extract cockles from intertidal plots of muddy sand and clean sand in order to investigate the effects on other benthic invertebrates and their predators.

3. Harvesting resulted in the loss of a significant proportion of the most common invertebrates from both areas, ranging in the muddy sand from 31% of Scoloplos armiger (Polychaeta) (initial density 120 m−2) to 83% of Pygospio elegans (Polychaeta) (initial density 1850 m−2). Significant effects could not be detected in most populations with a density of less than 100 m−2.

4. Populations of Pygospio elegans and Hydrobia ulvae (Gastropoda) remained significantly depleted in the area of muddy sand for more than 100 days after harvesting, and Nephtys hombergi (Polychaeta), Scoloplos armiger and Bathyporeia pilosa (Amphipoda) for more than 50 days.

5. Invertebrate populations in clean sand with relatively few cockles Cerastoderma edule (Pelecypoda) recovered more quickly than those in muddy sand with a more structured community, which included several tube‐dwelling species such as Pygospio elegans and Lanice conchilega (Polychaeta).

6. Bird feeding activity increased at first on the harvested areas, with gulls and waders taking advantage of invertebrates made available by harvesting. Subsequently, in the area of muddy sand, the level of bird activity declined compared with control areas. It remained significantly reduced in curlews Numenius arquata and gulls for more than 80 days after harvesting and in oystercatchers Haematopus ostralegus for more than 50 days.

7. It is concluded from this study that tractor dredging for cockles in high density areas causes a sufficiently large mortality of non‐target invertebrates that harvesters should be excluded from areas of conservation importance for intertidal communities such as invertebrates, fish and birds.
Importance of insect prey quality for grey partridge chicks Perdix perdix: a self‐selection experiment
Authors: Borg Claus , Toft Søren
Published: March 2003

1. The proportion of aphids in the cereal arthropod fauna has increased since the introduction of herbicides in the 1950s. In order to examine whether this increase has negative consequences for partridge chicks, a controlled experiment was carried out. Four groups of partridge chicks were fed different diets of fixed mixtures of grasshoppers and aphids, with aphid contents ranging from 0% to 45% wet weight. One additional group was allowed to select how much to eat of aphids and grasshoppers (self‐selection).

2. Over the run of the 5‐day experiment the self‐selecting chicks ate 7% wet weight of aphids and showed a higher growth rate than all groups on fixed diets.

3. Increasing the proportion of aphids in the chick diet above the self‐selected level had negative consequences for chick growth and flight feather development.

4. Food consumption and growth efficiency were markedly lower when chicks were fed a diet with a high proportion of aphids.

5. It is concluded that high densities of aphids cannot substitute for a diverse insect fauna as food for partridge chicks. Changes in the composition of the cereal arthropod fauna towards aphids constituting a greater proportion of available chick food may be detrimental to chick survival.
Estimates of forest elephant abundance: projecting the relationship between precision and effort
Authors: Peter D. Walsh , White Lee J.T. , Mbina Christian , Idiata Daniel , Mihindou Yves , Maisels Fiona , Thibault Marc
Published: March 2003

A key element of African elephant conservation is monitoring how different forms of human activity influence elephant distribution and abundance. Information on human–elephant interaction is critical for guiding conservation action at all levels, from very local management interventions, through national protected area planning, to international policy initiatives such as the ban on ivory trade. However, methods for monitoring elephant numbers often produce rather poor estimate precision. Therefore, a major challenge for elephant monitoring programmes at all levels is to allocate survey effort efficiently: the greatest possible statistical power to detect the effects of particular forms of human activity must be obtained from limited survey effort.

This study examined an approach to survey design based on the assumption that the precision of an abundance estimate is directly proportional to sampling effort. Field data from three sites in Central Africa were used to evaluate the potential of this approach for projecting how much effort will be necessary to survey and monitor forest elephants.

Variance in elephant dung pile encounter rate was proportional to sampling effort, but variance was also influenced by mean encounter rate. The relationship between variance and mean encounter rate followed a power law more closely than the linear model suggested by many previous authors. The linear model tended to substantially underestimate the effort level required for areas with high encounter rates. A bootstrapping exercise suggested that modelling the precision–effort relationship across strata should produce more accurate projections than estimating a distinct precision–effort relationship for each stratum.

Our results suggest that the survey design framework examined could substantially improve the statistical power of forest elephant monitoring programmes, although the use of a power law (rather than linear) model seems preferable. A similar approach should be appropriate for designing savanna elephant monitoring programmes and for addressing other issues, including rates of hunting and human elephant conflict. Furthermore, the parameter estimates reported in this study should be useful in designing elephant survey and monitoring programmes at other forested sites in Central Africa.
The effects of flooding lowland wet grassland on soil macroinvertebrate prey of breeding wading birds
Authors: Ausden Malcolm , Sutherland William J. , James Robert
Published: March 2003

Lowland wet grassland in western Europe is often managed for breeding wading birds, especially lapwingVanellus vanellus, redshankTringa totanus, snipeGallinago gallinagoand black‐tailed godwitLimosa limosa. Recommended conservation management often entails introducing winter flooding, and in Britain there is government funding to encourage this through the Environmentally Sensitive Area scheme.

Soil macroinvertebrates are important prey for breeding wading birds on lowland wet grassland. This study quantified the response of soil macroinvertebrates to flooding, their ability to survive in flooded grassland, and changes in the abundance and physical availability of soil macroinvertebrates for feeding wading birds as flood water subsides.

Unflooded grasslands contained high biomasses of soil macroinvertebrates, comprising mainly Tipulidae larvae and earthworm species that are widespread in pastures. Grasslands with a long history of winter flooding contained much lower biomasses of soil macroinvertebrates, comprising mainly a limited range of semi‐aquatic earthworm species.

Introducing winter flooding to previously unflooded grassland greatly reduced soil macroinvertebrate biomass. This was mainly due to the majority of earthworms vacating the soil soon after the onset of flooding. However, when earthworms were artificially confined in flooded soils, most species were capable of surviving periods of at least 120 days continual submergence. Winter flooding also expelled large numbers of overwintering arthropods from the soil.

Soil macroinvertebrates were slow to recolonize winter‐flooded grassland when it was re‐immersed in spring. Consequently, prey biomass for breeding wading birds remained low in areas that had been flooded during the preceding winter. However, winter flooding probably benefited breeding snipe by helping keep the soil soft enough for them to probe for prey. It also probably benefited breeding lapwings and redshank by helping keep the sward short and open enough for them to feed in during the latter part of their breeding season. Pools of winter flood water that remained in spring and early summer also provided a source of aquatic invertebrate prey for breeding wading birds.

We suggest that the best feeding conditions for breeding snipe will be provided by keeping the upper soil soft enough for them to probe in but without reducing soil macroinvertebrate biomass by flooding it beforehand. Optimal conditions for breeding lapwings and redshank will probably be provided by creating a mosaic of unflooded grassland, winter‐flooded grassland and shallow pools.
Grassland invasions: effects of manipulations of climate and management
Authors: S.M. Buckland , K. Thompson , J.G. Hodgson , J.P. Grime
Published: March 2003

Climate change, in combination with the impacts of land use, will give rise to new opportunities for grassland invasion. This paper reports on the repercussions of a field experiment.

Plant species, sown into experimental plots as part of a 6‐year study investigating factors limiting the success of seedling invasions, were resurveyed in 1999, 3 years after terminating experimental manipulations of climate, soil fertility and disturbance.

The most dramatic observation was the protracted expansion in populations of Brachypodium pinnatum, despite being at the northern limit of its distribution in Britain. In contrast, all other sown species, including those of both southern and widespread distribution in Britain, had become extinct, declined or remained unchanged in abundance.

Patterns of establishment were strongly deterministic. Populations of the southern grass, B. pinnatum, were highest in areas of the experimental plots unamended by fertilizer and physical disturbance, but expansion was apparently promoted by cessation of management. Among invaders of widespread distribution, two were dependent upon fertilizer addition (Arrhenatherum elatius and Dactylis glomerata), one significantly increased its cover with a combination of fertilizer and disturbance (Holcus lanatus), and one benefited from disturbance (Plantago lanceolata).

Two southern perennials, Origanum vulgare and Senecio erucifolius, both remained present in 1999 in plots that were formerly heated and subject to drought (1991–96), whereas they had become extinct in control plots.

Although the most successful invader was a rhizomatous perennial grass, an alternative strategy for survival and expansion was revealed after the severe drought in 1995: gap recolonization by annuals with a persistent seed bank.

Most notably, this study revealed the hidden potential of a native species to establish beyond its current range of distribution and, contrary to many recognized weeds, the capacity to achieve dominance in the absence of eutrophication or disturbance. This highlights the potent effects of climate change when plant traits effective for establishment coincide with the removal of current barriers to dispersal.
A model of bovine tuberculosis in the badger Melesmeles: an evaluation of control strategies
Authors: Smith G.C. , Cheeseman C.L. , Clifton‐Hadley R.S. , Wilkinson D.
Published: March 2003

An individual‐based stochastic simulation model was used to investigate the control of bovine tuberculosis (TB) in the European badger Meles meles. Nearly all population and epidemiological parameters were derived from one study site, and the transmission of TB from badgers to cattle was included. The latter is an essential step if reactive badger control strategies are to be modelled.

 The model appeared to underestimate slightly the rate of population recovery following widespread culling. This may have been due to simulating an isolated population with no immigration and no compensatory increase in fecundity. This should not affect the relative efficacy of each control strategy, but does require further investigation.

 Of the historical methods of badger control, gassing and the ‘clean ring’ strategies were the most effective at reducing disease prevalence in the badger and cattle herd breakdown rates. These results agree with those of earlier models.

 The proactive badger removal operation as part of the current field trial should cause a dramatic decrease in the number of cattle herd breakdowns, but also has the greatest effect on the badger population size.

 The proactive use of a live test to detect TB, followed by vaccination, appears to reduce substantially cattle herd breakdowns and disease prevalence in the badger.

 Three combined control strategies gave the best initial reduction in cattle herd breakdown rate and disease prevalence in the badger: (i) a proactive cull followed by reactive test and cull; (ii) a continued vaccination and proactive test and cull; and (iii) a continuous proactive test and cull.

 The results of simulation models suggest that badger vaccination is a very good method of TB control. This is at odds with simple models and requires further investigation.
Dung beetles as indicators of change in the forests of northern Borneo
Authors: Davis Andrew J. , Holloway Jeremy D. , Huijbregts Hans , Krikken Jan , Kirk‐Spriggs Ashley H. , Sutton Stephen L.
Published: March 2003

We reviewed the use of dung beetles as indicators of environmental change, highlighting the influence of natural forest dynamics on species distributions in primary forest and suggesting new ways in which this can be used to understand and interpret the effects of disturbance such as logging. These ideas were applied to rainforest dung beetle communities in Sabah, Malaysia.

 Dung beetle samples, using baited pitfall and flight intercept traps, were examined from primary, logged and plantation forests. Cluster analysis on dung beetle assemblages from primary forest samples showed clear species associations that had a high degree of fidelity to a particular biotope or vegetation type. Beetles were grouped into riverine‐edge, riverine, interior‐primary and ‘even’ (equitable distribution between biotopes) associations. Although biotope‐specific associations were spatially separate in primary forest, these associations overlapped at forest margins (riverine forest) and in logged forest (to form ‘composite assemblages’).

 Species associations showed different responses to disturbance: the riverine association included many species that showed a positive response to at least some types of disturbance, whereas others were neutral or negative in response; the even association species were mostly neutral; the primary forest associations were almost entirely negative in response.

The greatest faunal similarities were found between logged forest and riverine assemblages. Diversity was lower in logged compared with primary forest, and the lowest species richness and diversity were recorded in plantation forest. Small‐scale species richness in logged forest was generally higher than in individual transects from primary forest due to the presence of overlapping species ranges (composite assemblages) that were usually spatially separate in primary forest. Data suggested that increased species richness at a fine scale does not necessarily mean that species richness is greater at a larger scale, and that species mixing in derived ecosystems is dependent on the type of disturbance. Forest management should aim to minimize the mixing of the components of different biotopes, by implementing low impact (i.e. reduced‐impact logging) harvesting techniques.
The management of lowland neutral grasslands in Britain: effects of agricultural practices on birds and their food resources
Authors: Vickery J.A. , Tallowin J.R. , Feber R.E. , Asteraki E.J. , Atkinson P.W. , Fuller R.J. , Brown V.K.
Published: March 2003

The effects of agricultural intensification on biodiversity in arable systems of western Europe have received a great deal of attention. However, the recent transformation of grassland systems has been just as profound.

In Britain, the management of grassland has changed substantially in the second half of the 20th century. A high proportion of lowland grassland is managed intensively. The major changes include a doubling in the use of inorganic nitrogen, a switch from hay to silage, and increased stocking densities, particularly of sheep. Structurally diverse and species‐rich swards have been largely replaced by relatively dense, fast‐growing and structurally uniform swards, dominated by competitive species.

Most of these changes have reduced the suitability of grassland as feeding and breeding habitat for birds.

The most important direct effects have been deterioration of the sward as nesting and wintering habitat, and loss of seed resources as food. Short uniform swards afford poor shelter and camouflage from predators, whereas increased mowing intensities and trampling by stock will destroy nests and young. Increased frequency of sward defoliation reduces flowering and seed set, and hence food availability for seed‐eating birds.

The indirect effects of intensification of management on birds relate largely to changes in the abundance and availability of invertebrate prey. The effects of management vary with its type, timing and intensity, and with invertebrate ecology and phenology, but, in general, the abundance and diversity of invertebrates declines with reductions in sward diversity and structural complexity.

Low input livestock systems are likely to be central to any future management strategies designed to maintain and restore the ecological diversity of semi‐natural lowland grasslands. Low additions of organic fertilizer benefit some invertebrate prey species, and moderate levels of grazing encourage sward heterogeneity.

There is now a need to improve understanding of how grassland management affects bird population dynamics. Particularly important areas of research include: (i) the interaction between changes in food abundance, due to changes in fertilizer inputs, and food accessibility, due to changes in sward structure; (ii) the interaction between predation rates and management‐related changes in habitat; and (iii) the impact of alternative anti‐helminithic treatments for livestock on invertebrates and birds.
The use of nitrogen fertilizer on alternative grassland feeding refuges for pink‐footed geese in spring
Authors: Patterson I.J. , Fuchs R.M.E.
Published: March 2003

Intensive agriculture often reduces biodiversity on farmed land, but the converse situation, of wildlife damaging agriculture, is also important. A striking example is agricultural damage by increasing populations of wild geese. Alternative feeding refuges, designed to reduce damage, will be most effective if the grass swards are made as attractive to geese as possible. This paper describes an explicitly experimental study in north‐east Scotland during 1990–93, which investigated the effectiveness of different rates of application of nitrogenous fertilizer on the amount of grazing by pink‐footed geese in spring, compared split‐application with single‐application of spring fertilizer, and evaluated the use of slow‐release fertilizer in winter.

 The amount of goose grazing, measured from cumulative dropping density, increased with application rates of spring fertilizer, up to around 80 kg N ha−1, in parallel with a similar increase in grass production. Beyond this level there was little further increase, and cost‐effectiveness, measured as the percentage increase in dropping density per kg N ha−1 applied, was greatly reduced.

 Dropping density and grass production did not differ significantly between split‐application and single‐application of spring fertilizer. Split‐application should reduce the risk of nitrogen leaching in cold wet seasons, but the cost of application would be double that of single‐application.

 Overall, cumulative dropping density and grass production in late May were not significantly greater in plots treated over the winter with slow‐release fertilizer than in untreated plots. Dropping density was, however, higher in treated plots than in untreated ones during a short mild period in early spring. Slow‐release fertilizer may be of benefit in mild winters, but is more expensive than conventional nitrogenous fertilizer.

 This study has shown that nitrogenous fertilizer can greatly increase goose grazing on sacrificial grassland refuges in spring and is a useful tool in reducing conflict between farmers and increasing goose populations.
Impact of climatic factors on the developmental stability of mountain birch growing in a contaminated area
Authors: Jari Valkama , Mikhail V. Kozlov
Published: March 2003

We examined developmental stability in mountain birchBetula pubescensssp.czerepanoviialong a strong pollution gradient in the Kola Peninsula, north‐western Russia, over a period of 8 years (1993–2000). In particular, we investigated whether climatic factors or aerial pollution could increase developmental instability, which was assessed through leaf fluctuating asymmetry (FA).

Contrary to our expectations, leaf FA was not correlated with either distance from the pollution source, or with the levels of nickel and sulphur dioxide pollution in the study plots, or with shoot length or leaf size. There was, however, variation in FA between years: highest values of developmental instability were recorded during the coldest summers.

There was also considerable among‐tree variation in FA within plots, suggesting that birch genets either responded differently to environmental stress or demonstrated a different degree of genetic stress. The significant interaction between study year and birch genet suggests that the detected variation was a consequence of different sensitivity of the trees to climatic fluctuations rather than of different sensitivity to pollution.

Growth rate of birch correlated positively with developmental stability, i.e. faster leaf growth was associated with lower FA both at the scale of individual trees (presumably genetic differences) and at the scale of study years (environmental differences).

The lack of detectable response to aerial pollution by mountain birch in this study may be an outcome of selection for pollution‐resistant genotypes, which may have occurred due to an exceptionally high emission pressure during the past decades. On the other hand, resistance to temperature variations may not have evolved because warm and cold periods appear to occur somewhat regularly in the Kola Peninsula, and therefore variation in temperature optima between genotypes is favoured by natural selection.

Our results demonstrate that FA may serve as a useful measure of climatic stress in plants.
The occurrence of commensal rodents in dwellings as revealed by the 1996 English House Condition Survey
Authors: Langton S.D. , Cowan D.P. , Meyer A.N.
Published: March 2003

The presence of commensal rodents was assessed in the 1996 English House Condition Survey (EHCS). Logistic regression techniques were used to identify the key factors that might determine the susceptibility of dwellings to infestation.

 The overall percentages of dwellings that were infested, weighted to allow for the more intensive sampling used in certain categories of dwellings, were 1·83% for mice Mus domesticus, 0·23% for rats Rattus norvegicus living indoors and 1·60% for rats living outdoors. These figures excluded vacant properties, properties with some commercial use, and purpose‐built flats, as these groups showed different patterns of infestation and were therefore excluded from the logistic regressions.

 The prevalence of both rats and mice was significantly greater for dwellings where pets or livestock were kept in the garden.

 Dwellings classed as unfit for human habitation were more likely to be infested with mice.

 Dwellings in areas of low‐density housing had a significantly higher prevalence of both rat and mouse infestation. This probably reflects the general suitability of the rural environment for commensal rodents.

 Older properties had a relatively high prevalence of rats. This may be because their mature gardens provided suitable habitats for colonization. Once other confounding factors were taken into account, the age of the property did not influence the rate of infestation by mice.

 Dwellings in areas with substantial problems, such as dereliction, litter, vacant properties and unkempt gardens, had a significantly higher prevalence of rats and mice.

 This study reveals the value of applied ecological techniques, including logistic regression of presence–absence data, in understanding the distribution of commensal rodents in relation to dwellings, with the prospect of more effective management practices being developed as a consequence.
A new technique to measure spatial relationships within groups of free‐ranging coastal cetaceans
Authors: Denardo C. , Dougherty M. , Hastie G. , Leaper R. , Wilson B. , Thompson P.M.
Published: March 2003

The development and calibration of a land‐based technique to measure inter‐animal spacing in free‐ranging coastal cetaceans is described here. The technique was developed to study the behaviour of killer whales Orcinus orca in Norway.

A theodolite was used to measure the surfacing location of one reference individual while simultaneous video recordings of the whole group were made. Digitized video frames were then used to estimate the locations of all individuals in the video frame relative to the reference animal.

The technique was calibrated using a line of towed buoys with known separations. Estimated inter‐buoy distances were compared with actual values to calculate errors. There was no observable bias in measurements, with a mean error of −0·014 m (n = 304, SD = 0·880). At ranges up to 2 km from the observation site, 95% of measurements were accurate to within 1·7 m.

The accuracy of the measurement system was characterized with a set of Monte Carlo simulations. Simulations were run at offshore ranges from 100 m to 2000 m, with random perturbations applied to all variables. Errors in inter‐animal distances for n = 16 whales were estimated using 10 000 simulation runs for every range value. The results from the simulations agreed with experimental findings. The results showed no bias in inter‐animal distance measurements, with an overall mean error of 0·0864 m.

The results indicate that this technique is suitable for studies on a variety of coastal cetacean populations. It provides a new tool for quantitative studies on spatial behaviour of cetaceans, and will help underpin management efforts to monitor effects of anthropogenic disturbance. With modification, the technique might also be applicable to other coastal vertebrates where inter‐organism distances are required.