bluuebunny/crossref_metadata_2025_split huggingface dataset:
Lack of native species recovery following severe exotic disturbance in southern Californian shrublands
Authors: Stylinski Cathlyn D. , Allen Edith B. 
Published: March 2003

Summary 1. Urban and agricultural activities are not part of natural disturbance regimes and may bear little resemblance to them. Such disturbances are common in densely populated semi‐arid shrub communities of the south‐western US, yet successional studies in these regions have been limited primarily to natural successional change and the impact of human‐induced changes on natural disturbance regimes. Although these communities are resilient to recurrent and large‐scale disturbance by fire, they are not necessarily well‐adapted to recover from exotic disturbances. 2. This study investigated the effects of severe exotic disturbance (construction, heavy‐vehicle activity, landfill operations, soil excavation and tillage) on shrub communities in southern California. These disturbances led to the conversion of indigenous shrublands to exotic annual communities with low native species richness. 3. Nearly 60% of the cover on disturbed sites consisted of exotic annual species, while undisturbed sites were primarily covered by native shrub species (68%). Annual species dominant on disturbed sites included Erodium botrys, Hypochaeris glabra, Bromus spp., Vulpia myuros and Avena spp. 4. The cover of native species remained low on disturbed sites even 71 years after initial exotic disturbance ceased. Native shrub seedlings were also very infrequent on disturbed sites, despite the presence of nearby seed sources. Only two native shrubs, Eriogonum fasciculatum and Baccharis sarothroides, colonized some disturbed sites in large numbers. 5. Although some disturbed sites had lower total soil nitrogen and percentage organic matter and higher pH than undisturbed sites, soil variables measured in this study were not sufficient to explain variations in species abundances on these sites. 6. Non‐native annual communities observed in this study did not recover to a predisturbed state within typical successional time (< 25 years), supporting the hypothesis that altered stable states can occur if a community is pushed beyond its threshold of resilience.
Alternative methods for predicting species distribution: an illustration with Himalayan river birds
Authors: Manel Stéphanie , Dias J.M. , Buckton S.T. , Ormerod S.J. 
Published: March 2003

Summary1. Current emphasis on species conservation requires the development of specific distribution models. Several modelling methods are available, but their performance has seldom been compared. We therefore used discriminant analysis, logistic regression and artificial neural networks with environmental data to predict the presence or absence of six river birds along 180 Himalayan streams. We applied each method to calibration sites and independent test sites. With logistic regression, we compared performance in predicting presence–absence using map‐derived predictors (river slope and altitude) as opposed to detailed data from a standardized river habitat survey (RHS).2. Using the entire calibration data, overall success at predicting presence or absence was only slightly greater using artificial neural networks (89–100%) than either logistic regression (75–92%) or discriminant analysis (81–95%), and on this criterion all methods gave good performance.3. When applied to independent test data, overall prediction success averaged 71–80%, with logistic regression marginally but significantly out‐performing the other methods. Encouragingly for researchers with limited data, model performance in jack‐knife tests faithfully represented performance in more rigorous validations where calibration (n = 119) and test sites (n = 61) were in separate geographical regions.4. All three methods predicted true absences (83–92% success) better than true presences (31–44%). Results from logistic regression were the most variable across species, but positive prediction declined with increasing species rarity in each method.5. Applications with logistic regression illustrated that significant habitat predictors varied between data sets within species. Hypotheses about causal effects by habitat structure on distribution were thus difficult to erect or test. Logistic regression also showed that detailed data from the river habitat survey substantially improved positive prediction by comparison with prediction using slope or altitude alone.6. We conclude that discriminant analysis, logistic regression and artificial neural networks differ only marginally in performance when predicting species distributions. Model choice should therefore depend on the nature of the data, on the needs of any particular analysis, and on whether assumptions for each method are satisfied. All three methods share drawbacks due to systematic effects by species rarity on performance measures. They also share limitations due to the correlative nature of survey data often used for model development at the spatial scales required in macro‐ecology and conservation biology. Tests with independent data, using a wider range of performance measures than those used traditionally, will be important in examining models and testing hypotheses for such applications.
Sampling termite assemblages in tropical forests: testing a rapid biodiversity assessment protocol
Authors: Jones David T. , Eggleton Paul 
Published: March 2003

Summary 1. Termites play a key role in decomposition processes in tropical ecosystems. Rapid assessment of local termite assemblages requires a standardized sampling protocol capable of producing an accurate picture of species composition. This paper evaluates the efficacy of a sampling protocol designed to assess termite species richness and functional diversity in tropical forests. 2. The protocol entails a 100 m long transect consisting of 20 sections (each 5 × 2 m). One hour of human sampling effort per section is used to search for and collect termites from dead wood, soil, termite nests and other microhabitats up to a height of 2 m above ground. The protocol was tested in three forest sites where the local termite fauna was already comprehensively documented. Two transects were run at Danum Valley (Sabah, Borneo), one at Pasoh Forest Reserve (Peninsular Malaysia) and one at Mbalmayo Forest Reserve (Cameroon). 3. At the three sites the transect samples contained 31–36% of the known local termite species pool. The taxonomic and functional group composition of the transect samples did not differ significantly from that of the known local fauna. The two transects run at Danum Valley gave very similar patterns, suggesting that the protocol produces consistent within‐site results. After sampling 20 sections, pseudoturnover between the two Danum transects had declined to a relatively low level. 4. The transect method is effective because it utilizes collecting expertise within a protocol that standardizes sampling effort and area. The protocol provides a much more rapid and cost‐effective method for studying termite assemblage structure than sampling regimes designed to estimate population abundances. It was demonstrated that one supervised training transect was sufficient to ensure the protocol was conducted with the required level of sampling efficiency. 5. The protocol offers a rapid tool for investigating spatial and temporal patterns of termite assemblage structure in tropical forest sites. Existing data also suggest that termites warrant further investigation as ecological indicators. Termite assemblage composition shows a strong response to habitat disturbance and may be indicative of quantitative changes in the decomposition process. The termite transect has potential as a useful addition to any suite of organisms recommended for monitoring functional processes in tropical forests.
Modelling ecological half‐lives for radiocaesium in Norwegian brown trout populations
Authors: Hessen Dag O. , Skurdal Jostein , Hegge Ola , Andersen Tom 
Published: March 2003

Summary 1. Models of ecological half‐life may be valuable and cost‐effective predictive tools for authorities setting restrictions on human consumption of freshwater fish after environmental releases of radioactivity. This work aimed to validate such a model for radioactive caesium (134Cs and 137Cs) in brown trout Salmo trutta populations. Data were drawn from lakes with a wide variability in abiotic and biotic factors and initial caesium load. 2. In Norway, the highest fallout (more than 150 kBq m–2 of 137Cs) from the Chernobyl accident occurred in Oppland county, in south central Norway. Radioactivity was measured in more than 1800 samples of brown trout in nearly 100 localities in this region during 1986–95. 3. The back‐calculated maximum initial radioactivity on 1 January 1987 showed a strong regional variability (range 443–13 370; average 3855 Bq kg–1). Large variation in initial radioactivity was also recorded on a local scale (within 50 km). 4. The ecological half‐life model for caesium in brown trout populations for 1987–94/95 gave a close fit to real data from all localities with sufficient time series. Predicted half‐lives ranged from 1·2 to 4·2 years (average 2·5) but 95% confidence limits were narrow (2·7 and 2·3 years). 5. The overall variability in radioactivity levels over time was almost entirely related to the initial load and, with few exceptions, 88% of the changes in radioactivity was explained by the simple regression model. Modest variability in ecological half‐life was not correlated with initial activity, and no clear effects of water quality or season could be detected. For most lakes, levels of radioactivity in brown trout appeared to be predictable, with high accuracy after a fallout event, without extensive information on population ecology and water quality. However, more detailed work may be required to assess patterns within individual lakes.
Local extinction of British farmland birds and the prediction of further loss
Authors: Gates Simon , Donald Paul F. 
Published: March 2003

1. The populations of many UK farmland birds declined between 1970 and 1990, frequently accompanied by contractions in breeding ranges. Ornithological atlas data, land use data and environmental data at the scale of 10‐km squares were used to investigate the relationship between local extinctions and habitat suitability for six species, and to predict where future losses are most likely. 2. For each species we tested the hypothesis that local extinctions were concentrated in environments that were inherently less suitable. We also tested the hypothesis that spatial patterns of loss were not independent between species due to their concurrence in the same habitats. 3. Multivariate analyses (PCA) showed that areas where each species became extinct between 1970 and 1990 were more similar in land use type, climate and topography to areas where a species was never present than those where it was retained; local extinction was more likely in less suitable environments. Multiple logistic regression showed that for five of the six species the environmental gradient best predicting presence or absence in 1970 was also that best predicting loss between 1970 and 1990. For the six species studied, local extinctions were least likely in lowland arable areas. 4. For any pair of species, local extinctions were more frequent outside the area of overlap of the two species' ranges than inside. Within the area of overlap, species tended to be lost from the same squares. For each species, likelihood of local extinction declined with increasing number of the other five species present. 5. We used model parameters to map the probability of future local extinctions of the six species considered, allowing the identification of key areas for conservation management at a spatial scale appropriate to agri‐economic incentives.
The effect of pea cultivar and water stress on root and shoot competition between vegetative plants of maize and pea
Authors: Semere Tzehaye , Froud‐Williams Robert J. 
Published: March 2003

Summary

Improvements in intercrop yields may be achieved through an understanding of yield advantages due to above‐ground or below‐ground interactions.
Forage maize and two morphologically contrasting cultivars of pea (leafy cv. Bohatyr and semi‐leafless cv. Grafila) were grown alone and in additive mixtures, under two contrasting levels of soil moisture (± water stress).
The mechanism of competition between maize and pea was studied by separating the effects of root competition and shoot competition, using soil and aerial partitions. Plants were grown in rectangular tanks in a glasshouse.
Leafy pea cv. Bohatyr was as competitive as maize, both below‐ground and above‐ground, whereas semi‐leafless pea cv. Grafila was less competitive than maize or pea cv. Bohatyr. The greater competitive ability of the leafy pea, both above‐ and below‐ground, was probably due to its greater growth rate, associated with its greater leaf area.
The competitive ability of maize, relative to peas, was considerably reduced by water stress. Both the root and shoot competitive abilities of pea were greater under water stress, compared with those of maize.
Relative yield total (RYT) values were significantly greater when maize and pea were subjected to shoot competition only (RYT = 1·76) than when subjected to root competition (RYT = 1·17) or when subjected to both shoot and root competition (RYT = 1·13). This reflects the fact that the effects of root competition were greater than those of shoot competition.
Root competition decreased the shoot dry weights, plant height and leaf area of both maize and pea, whereas shoot competition had no significant effect on these attributes, indicating that soil resources, i.e. mineral nutrients and water, were more limiting than light.
Estimating deer abundance from line transect surveys of dung: sika deer in southern Scotland
Authors: Marques Fernanda F.C. , Buckland Stephen T. , Goffin David , Dixon Camilla E. , Borchers David L. , Mayle Brenda A. , Peace Andrew J. 
Published: March 2003

Summary

Accurate and precise estimates of abundance are required for the development of management regimes for deer populations. In woodland areas, indirect dung count methods, such as the clearance plot and standing crop methods, are currently the preferred procedures to estimate deer abundance. The use of line transect methodology is likely to provide a cost‐effective alternative to these methods.
We outline a methodology based on line transect surveys of deer dung that can be used to obtain deer abundance estimates by geographical block and habitat type. Variance estimation procedures are also described.
As an example, we applied the method to estimate sika deer Cervus nippon abundance in south Scotland. Estimates of deer defecation and length of time to dung decay were used to convert pellet group density to deer density by geographical block and habitat type. The results obtained agreed with knowledge from cull and sightings data, and the precision of the estimates was generally high.
Relatively high sika deer densities observed in moorland areas up to 300 m from the forest edge indicated the need to encompass those areas in future surveys to avoid an underestimate of deer abundance in the region of interest.
It is unlikely that a single method for estimating deer abundance will prove to be better under all circumstances. Direct comparisons between methods are required to evaluate thoroughly the relative merits of each of them.
Line transect surveys of dung are becoming a widely used tool to aid management and conservation of a wide range of species. The survey methodology we outline is readily adaptable to other vertebrates that are amenable to dung survey methodology.
Restoring resources for an endangered butterfly
Authors: Schultz Cheryl B. 
Published: March 2003

Summary

Recent changes in land use have resulted in dramatic habitat loss for numerous species. More than 99% of the habitat for Fender's blue butterfly Icaricia icarioides fenderi, an endangered butterfly in Oregon, USA, has been lost.
Fender's blue butterflies require larval host‐plants (Kincaid's lupine Lupinus sulphureus kincaidii) and nectar from native wildflowers.
An experiment was conducted at two degraded sites near Eugene, Oregon, to investigate methods for restoration of Fender's blue habitat. The experimental design included four soil treatments (tilling, reverse fertilization, solarization and a control) combined with two planting treatments (50% forb seed : 50% grass seed and 10% forb seed : 90% grass seed) and two weeding treatments (weeding or not weeding). Treatments were replicated in eight experimental blocks (9 × 28 m) at each site. Seeds from 12 native plant species were field collected and sown in September 1995.
Plant establishment was monitored in May 1996, 1997, 1998 and 1999. In 1999, flowers of all nectar species and leaves of Kincaid's lupine were counted.
Based on estimates of resource needs from previous work, resources were evaluated as insufficient, sufficient or ample.
Solarization combined with 50% forb : 50% grass planting promoted sufficient nectar to sustain butterflies at both sites. Control treatments provided insufficient nectar at both sites. None of the treatments produced sufficient larval resources.
This experiment demonstrates a method to quantitatively link habitat restoration to the resource needs of focal species. The results emphasize the importance of connecting restoration efforts to the life‐history features of focal species. In addition, they highlight the importance of using experiments conducted across a range of sites to test restoration methods before large‐scale efforts are implemented.
Short‐term effects of canopy openness on insect herbivores in a rain forest in Guyana
Authors: Basset Yves , Charles Elroy , Hammond David S. , Brown Valerie K. 
Published: March 2003

Summary

A before/after–control/impact experiment (BACI) was used to examine the short‐term effects of canopy openness on insect herbivores foraging on the seedlings of five rain forest species in an unlogged forest in Guyana. During the first and second study years, insects were collected monthly from 250 sites, representing 9750 seedlings spread over a plot of 1 km2. At the onset of the second collecting year, half of the parent trees at the sites were felled, creating an average canopy openness of 26%.
Comparisons of the control and impact sites before and after the felling showed that overall insect abundance, particularly of psyllids, and species richness increased at the impact sites, whereas evenness decreased markedly. These responses were consistent with the prediction that intermediate disturbance promotes high diversity in tropical systems.
Twenty‐nine per cent of insect species analysed showed a significant response to felling, with some populations doubling or halving at the impact sites after felling. The abundance of most species increased, although responses varied even between congeners.
A canonical correspondence analysis at the impact sites after felling indicated that most species responded to an increase in leaf production by seedlings, not to canopy openness per se. Species declining at the impact sites were more likely to feed indiscriminately on young and mature foliage and probably reacted to changes in microclimate.
The study illustrates the difficulty in identifying higher taxa, umbrella or indicator species that adequately integrate the responses of insect herbivores to forest disturbance. Because the integrity of insect communities in the understorey of this forest depends more on minimizing damage to plant resources than on canopy openness, we found some support for the conservation value of reduced impact logging in tropical wet forests.
The effect of plant competition and simulated summer browsing by deer on tree regeneration
Authors: Harmer Ralph 
Published: March 2003

SummaryDuring the last decade the use of natural regeneration has become an accepted method of restocking British woodlands after harvesting. However, in many broadleaved woodlands there are insufficient numbers of established tree seedlings of adequate size to ensure that restocking is successful. This lack of seedlings may be related to a number of factors, including competition from the ground flora and browsing by deer.The numbers of deer (Capreolus capreolus,Cervus elaphusandDama dama) are rising throughout Britain and population densities frequently exceed those known to have a significant impact on broadleaved trees. This experiment, which took place at four sites over a 5‐year period, studied the effects of competition from the ground flora and severe, simulated, browsing by deer during summer, on the growth and mortality of naturally occurringAcer pseudoplatanus,Fraxinus excelsior,Fagus sylvaticaandQuercus roburseedlings.The seedlings were initially 30–40 cm tall with stem diameters of 2·6–6·2 mm. Competition from the ground flora was removed by maintaining circular areas, 1 m in diameter, free of vegetation using a general herbicide. Browsing was simulated by clipping new shoots that were longer than 1 cm in June and August.The control of the ground flora had little effect on the growth and survival of seedling trees.In general, the number of tree seedlings producing sufficient growth to receive the simulated browsing treatment decreased with time, but for those seedlings that were clipped there were no consistent trends in either numbers or weights of shoots removed. Unclipped seedlings continued to grow. The height and stem diameter increments varied with species and site, but after 5 years unclipped plants were 50–200% taller with stem diameters 20–130% greater than at the start of the experiment.The mortality of unclipped seedlings was low and 80% or more survived. Clipping significantly reduced the survival ofFraxinus excelsiorandA. pseudoplatanus, butQ. roburandFagus sylvaticawere unaffected. On an annual basis, there was no relationship between mortality and accumulated number or dry weight of shoots clipped, initial stem diameter or height, and whether or not the seedling was under the overstorey canopy.The results from this study indicate that established seedlings ofA. pseudoplatanus,Fraxinus excelsior,Fagus sylvaticaandQ. roburthat are > 30 cm tall can survive several years of severe browsing under the shade provided by overstorey canopy covers of 50% or more. This suggests that management should aim to improve survival during the first 1–2 years of growth. This may be achieved by exclusion of animals by fencing, protection of individual seedlings using tree shelters, or culling to control herbivore numbers.