bluuebunny/crossref_metadata_2025_split huggingface dataset:
Additive partitioning of diversity across hierarchical spatial scales in a forested landscape
Authors: CHANDY SHIBI , GIBSON DAVID J. , ROBERTSON PHILIP A. 
Published: June 2006

SummaryEcological phenomena exist at multiple scales, but measurements of diversity frequently consider only the smallest scale, that of the original sample plots. Additive partitioning of diversity allows multiple, hierarchical spatial scales of analysis to reveal the scale at which diversity is maximized.We examined the spatial partitioning of diversity across 378 permanent plots established in 10 7–369‐ha research natural areas (RNA) in the 294 455‐ha Shawnee National Forest, Illinois, USA. Diversity (richness and Shannon's and Simpson's indices) was partitioned across four spatial scales, i.e. within and between plots, and between RNA and natural divisions (corresponding to α and three levels of β diversity), for two strata of vegetation (trees and woody understorey).For both strata, the highest contribution to diversity measured as species richness was between plots and between RNA. Diversity was lower than expected within plots, although Simpson's and Shannon's indices achieved their maximum values at this scale. However, Shannon's index values were higher than Simpson's index values at the between‐RNA scale and for all strata, indicating that the most common species were found at this scale.There was a simple asymptotic relationship between plot occupancy and local abundance, suggesting high colonization rates and rapid colonization of open habitat indicative of a wide niche breadth of the most abundant species.Synthesis and applications.The implications of these findings are that maximum diversity across a forested landscape is not necessarily at the scale of sampling (i.e. within plots) but may be at higher scales corresponding to larger landscape units. Moreover, the largest contribution of richness to total diversity occurred at a larger scale than diversity expressed using measures based upon information theory, which incorporate species abundance and evenness. Conservation efforts seeking to preserve diversity must identify and target the correct scales to allow effective management. In this study, management at and within the RNA represents the most appropriate scale for conserving maximum diversity.
The use of image analysis to estimate population growth rate in Daphnia magna
Authors: HOOPER HELEN L. , CONNON RICHARD , CALLAGHAN AMANDA , MAUND STEVE J. , LIESS MATTHIAS , DUQUESNE SABINE , HUTCHINSON THOMAS H. , MOGGS JONATHAN , SIBLY RICHARD M. 
Published: June 2006

Summary

Population growth rate (PGR) is central to the theory of population ecology and is crucial for projecting population trends in conservation biology, pest management and wildlife harvesting. Furthermore, PGR is increasingly used to assess the effects of stressors. Image analysis that can automatically count and measure photographed individuals offers a potential methodology for estimating PGR.
This study evaluated two ways in which the PGR of Daphnia magna, exposed to different stressors, can be estimated using an image analysis system. The first method estimated PGR as the ratio of counts of individuals obtained at two different times, while the second method estimated PGR as the ratio of population sizes at two different times, where size is measured by the sum of the individuals’ surface areas, i.e. total population surface area. This method is attractive if surface area is correlated with reproductive value (RV), as it is for D. magna, because of the theoretical result that PGR is the rate at which the population RV increases.
The image analysis system proved reliable and reproducible in counting populations of up to 440 individuals in 5 L of water. Image counts correlated well with manual counts but with a systematic underestimate of about 30%. This does not affect accuracy when estimating PGR as the ratio of two counts. Area estimates of PGR correlated well with count estimates, but were systematically higher, possibly reflecting their greater accuracy in the study situation.
Analysis of relevant scenarios suggested the correlation between RV and body size will generally be good for organisms in which fecundity correlates with body size. In these circumstances, area estimation of PGR is theoretically better than count estimation.
Synthesis and applications. There are both theoretical and practical advantages to area estimation of population growth rate when individuals’ reproductive values are consistently well correlated with their surface areas. Because stressors may affect both the number and quality of individuals, area estimation of population growth rate should improve the accuracy of predicting stress impacts at the population level.
Temporal and spatial development of red deer harvesting in Europe: biological and cultural factors
Authors: MILNER JOS M. , BONENFANT CHRISTOPHE , MYSTERUD ATLE , GAILLARD JEAN‐MICHEL , CSÁNYI SÁNDOR , STENSETH NILS CHR. 
Published: June 2006

SummaryDeer numbers have increased dramatically throughout Europe and North America over the last century, but empirical analyses of variation in harvesting and the influence of biological and cultural factors are lacking.We examined trends in size and composition of red deerCervus elaphusharvests over the last three to four decades in 11 European countries with contrasting deer productivity, management strategies and hunting traditions.The harvest increased exponentially in all countries except Austria and Germany, where it was stable, and Poland, where it has declined in recent years. Harvest growth rates ranged from 0·009 in Austria to 0·075 in Sweden and depended on the management system and harvest composition, being negatively related to the proportion of females in the adult harvest.Within four focal countries (France, Hungary, Norway and Scotland), there was considerable spatial variation in harvest growth rates. These tended to be higher in recently colonized areas than in traditional hunting areas and were often higher than the maximum possible population growth rate. Range expansion was an important component of the increase in total harvest in France and Scotland, but not in Hungary or Norway.Harvest composition was available for seven countries, all of which showed a strong increase in the proportion of calves in the harvest. The sex ratio of the adult harvest was relatively stable, being strongly male‐biased in Norway and marginally female‐biased elsewhere. The proportion of males in the harvest was unrelated to trophy hunting objectives.Synthesis and applications. Our study emphasizes that cultural aspects of management need to be accounted for, as well as biological factors, when interpreting the patterns of harvest growth and composition across Europe. Widespread sustained harvest growth has occurred, suggesting continued growth of deer populations with consequent social and economic impacts. Population control is therefore a major challenge for the future, currently hampered by inadequate population data and a decreasing number of hunters in some countries. Increasing the motivation of hunters to harvest female deer is one possible solution, although this may conflict with hunting traditions and economic considerations in some areas.
Genetic restoration of a stocked brown trout Salmo trutta population using microsatellite DNA analysis of historical and contemporary samples
Authors: HANSEN MICHAEL M. , BEKKEVOLD DORTE , JENSEN LASSE F. , MENSBERG KAREN‐LISE D. , NIELSEN EINAR E. 
Published: June 2006

Summary

Gene flow from domesticated to wild populations is a major threat to wild salmonid fish. However, few studies have addressed how populations could be restored after admixture has occurred. We analysed the prospects for restoring the previously intensively stocked brown trout population of the Skjern River, Denmark, by identifying remaining non‐admixed individuals to be used for supportive breeding.
We analysed microsatellite DNA markers in historical (1940–50s) and contemporary (1992–2004) samples from the Skjern River system, from the strain of domesticated trout previously used for stocking, and from the neighbouring Storå River. We analysed admixture proportions to estimate the genetic contribution by domesticated trout. We identified non‐admixed trout using assignment tests, and further analysed the possible sources of indigenous trout by estimating contemporary migration among populations.
Genetic differentiation between the historical Storå and Skjern river populations was low (θST = 0·004), suggesting considerable gene flow in the past. The contemporary Skjern and Storå river populations and a supportive breeding brood stock were strongly admixed, but some non‐admixed individuals nevertheless remained in the wild‐caught samples. In addition, two resident populations in isolated tributaries were found to be indigenous. The indigenous anadromous individuals from the Skjern River were unlikely to have been recruited from either the isolated tributary populations or the neighbouring Storå River and were presumably derived from unidentified spawning sites in the river system.
All but one non‐admixed anadromous Skjern River trout were females, which we ascribed to sampling bias. Moreover, all non‐admixed fish were late‐spawning (January–February) whereas the majority of all trout caught for the study were ripe by November–December. The difference in spawning time could be an important factor delaying complete admixture of domesticated and indigenous trout.
Synthesis and applications. This study demonstrates the feasibility of restoring populations that have been admixed with exogenous individuals, by identifying non‐admixed individuals using genetic markers. However, the results also highlight the problem that numbers of identified non‐admixed individuals may be small, necessitating identification of nearby, closely related populations that can be incorporated into breeding programmes.
Altering perceived predation risk and food availability: management prescriptions to benefit farmland birds on stubble fields
Authors: WHITTINGHAM MARK J. , DEVEREUX CLAIRE L. , EVANS ANDY D. , BRADBURY RICHARD B. 
Published: June 2006

Summary

European farmland bird populations have fallen dramatically and sympathetic management of key habitats is one crucial way to help boost these populations. Maximizing the value of habitats for foraging birds has largely focused on practical measures to increase food abundance, but energy intake, the key determinant of habitat quality, is also affected by food accessibility and perceived predation risk. We tested the importance of manipulating perceived predation risk and access to food on the distribution of birds on stubble fields, a key wintering habitat for many UK species and used by many species in different parts of the world.
Recent evidence suggests simple reductions in vegetation height alter perceived predation risk for some species. Light cultivation, by scarification of the soil surface, could potentially alter both perceived predation risk (via changes in vegetation structure) and food availability (by opening up the soil and bringing seeds to the surface) and so be a single solution to enhancing suitability of stubble fields for birds. In experiment 1, we investigated the effects of changing vegetation height (via topping) and scarification on vegetation structure, seed density and distribution of farmland birds, using a 2 × 2 factorial within‐field design. In experiment 2, we tested the temporal effects of scarification on bird distribution, using a similar within‐field design.
Scarified plots supported higher abundances of invertebrate feeders (e.g. thrushes). Plots that were scarified within the last 1–13 days were used more by invertebrate feeders and granivores (e.g. yellowhammer) than plots scarified 2–4 months ago. Both results were probably a consequence of food availability being temporarily increased by scarification making prey more accessible.
Granivorous passerines and invertebrate feeders preferred plots with shorter stubble while the abundance of skylarks, partridges, pigeons and meadow pipits was higher on plots with taller stubble. This was probably the result of differing anti‐predation strategies.
Synthesis and applications. Prescriptions that generate fine‐scale heterogeneity should benefit a range of species. Although our work was confined to stubble fields, the importance of simultaneous consideration of predation risk and access to food is likely to apply across European farmland landscapes and elsewhere, and could apply to other arable crops and potentially to grassland systems. On stubble fields specifically, topping of part of the field in the autumn could be combined with successive strip scarification treatments throughout the winter, to provide optimal conditions for a range of species. This could be incorporated as a management option in agri‐environment schemes such as the English Environmental Stewardship Scheme.
The ghost of past species occurrence: improving species distribution models for presence‐only data
Authors: LÜTOLF MICHAEL , KIENAST FELIX , GUISAN ANTOINE 
Published: June 2006

Summary

Model‐based approaches have been used increasingly in conservation biology over recent years. Species presence data used for predictive species distribution modelling are abundant in natural history collections, whereas reliable absence data are sparse, most notably for vagrant species such as butterflies and snakes. As predictive methods such as generalized linear models (GLM) require absence data, various strategies have been proposed to select pseudo‐absence data. However, only a few studies exist that compare different approaches to generating these pseudo‐absence data.
Natural history collection data are usually available for long periods of time (decades or even centuries), thus allowing historical considerations. However, this historical dimension has rarely been assessed in studies of species distribution, although there is great potential for understanding current patterns, i.e. the past is the key to the present.
We used GLM to model the distributions of three ‘target’ butterfly species, Melitaea didyma, Coenonympha tullia and Maculinea teleius, in Switzerland. We developed and compared four strategies for defining pools of pseudo‐absence data and applied them to natural history collection data from the last 10, 30 and 100 years. Pools included: (i) sites without target species records; (ii) sites where butterfly species other than the target species were present; (iii) sites without butterfly species but with habitat characteristics similar to those required by the target species; and (iv) a combination of the second and third strategies. Models were evaluated and compared by the total deviance explained, the maximized Kappa and the area under the curve (AUC).
Among the four strategies, model performance was best for strategy 3. Contrary to expectations, strategy 2 resulted in even lower model performance compared with models with pseudo‐absence data simulated totally at random (strategy 1).
Independent of the strategy model, performance was enhanced when sites with historical species presence data were not considered as pseudo‐absence data. Therefore, the combination of strategy 3 with species records from the last 100 years achieved the highest model performance.
Synthesis and applications. The protection of suitable habitat for species survival or reintroduction in rapidly changing landscapes is a high priority among conservationists. Model‐based approaches offer planning authorities the possibility of delimiting priority areas for species detection or habitat protection. The performance of these models can be enhanced by fitting them with pseudo‐absence data relying on large archives of natural history collection species presence data rather than using randomly sampled pseudo‐absence data.
Seasonal migration of thornback rays and implications for closure management
Authors: HUNTER EWAN , BERRY FIONA , BUCKLEY AINSLEY A. , STEWART CHRISTIE , METCALFE JULIAN D. 
Published: June 2006

Summary

Sharks and rays are vulnerable to fisheries exploitation because of late maturation and low fecundity, highlighting the need for effective conservation strategies. Area closures have been proposed as an appropriate management option for thornback rays in the southern North Sea, where they appear to form local subpopulations between which there is limited mixing.
To gain a fishery‐independent estimation of stock distribution, 197 thornback rays Raja clavata tagged with electronic data storage tags (DST) were released in the Thames Estuary in 1999 and 2000.
The tidal location method was used to estimate the positions of individual fish between time of release and recapture. The fishery‐independent seasonal stock distributions were integrated with landings data and a simple model was developed to estimate monthly fishing effort per International Council for the Exploration of the Sea (ICES) rectangle by different fleets and gear types.
The potential impacts of closed area management, in terms of reducing thornback ray mortality in the southern North Sea, were calculated. Spatial closures were applied either (i) as permanent closures of individual ICES rectangles or (ii) seasonally, at the level of the Thames Estuary. Catch reductions were calculated allowing for the redistribution of fishing effort.
The results confirmed the importance of the Thames Estuary for thornback rays. However, 77% of rays moved outside the estuary over winter, with seasonal migration into the Thames to spawn between March and August.
The effects of closures varied between areas and gear types. Permanent closures of individual ICES rectangles were less effective at reducing fishing mortality on rays than a spring or summer closure of the Thames Estuary as a whole, which would have a major impact on the commercially more valuable sole fishery.
Synthesis and applications. The results presented illustrate the potential impacts of a range of closure scenarios, prior to their implementation, as a basis for advice on sustainable exploitation of thornback rays. These models could be further refined by additional studies of juvenile behaviour and of other ray subpopulations in the southern North Sea.
Decline in alkali meadow vegetation cover in California: the effects of groundwater extraction and drought
Authors: ELMORE ANDREW J. , MANNING SARA J. , MUSTARD JOHN F. , CRAINE JOSEPH M. 
Published: June 2006

Summary

Throughout arid regions of the world, groundwater is extracted for human population centres. In the Great Basin and Range region of the USA, we lack basic information regarding some plant communities detailing the extent to which vegetation is threatened by groundwater extraction. This is particularly true for alkali meadow vegetation, which is restricted to zones of shallow groundwater yet is not a riparian plant community with obligate wetland properties.
To increase our understanding of the relative importance of groundwater and precipitation in maintaining alkali meadow vegetation cover, we used a 16‐year record of plant cover derived from satellite data of Owens Valley, California, USA, in conjunction with concurrent depth‐to‐water and precipitation measurements, to analyse vegetation response to anthropogenic and climatic changes in water availability.
Groundwater decline varied from 0·5 to 5·0 m throughout the study area, with the largest changes occurring at sites closest to pumping wells. The entire region experienced a 6‐year drought (1987–92), during which annual precipitation remained below the 50‐year median.
Meadow plant cover over the 16‐year study period was correlated with groundwater depth, but plant cover was generally unresponsive to annual precipitation variability. Sensitivity to groundwater decline was greatest for plots with a higher cover of herbaceous perennials.
The results showed that this plant community is groundwater dependent, and that this characteristic buffers the system from the effects of drought. However, at sites with extensive groundwater decline, the remaining plant cover became weakly correlated with precipitation only after groundwater declined below a threshold depth located at 2·5 m, representing the average plant rooting depth.
Synthesis and applications. Sustainable water development that seeks to pump groundwater without adversely affecting vegetation cover and plant assemblages must recognize the maximum rooting depth of groundwater‐dependent plant species. When groundwater is within the root zone, management decisions can be made to either increase or decrease vegetation cover through modification of groundwater depth. When groundwater is below the root zone, vegetation cover is low and susceptible to changes in precipitation. Quantitative satellite measurements of vegetation cover might aid the monitoring and sustainable management of water resources.
Chloroplast microsatellites reveal colonization and metapopulation dynamics in the Canary Island pine
Authors: NAVASCUÉS MIGUEL , VAXEVANIDOU ZAFEIRO , GONZÁLEZ‐MARTÍNEZ SANTIAGO C. , CLIMENT JOSÉ. , GIL LUIS , EMERSON BRENT C. 
Published: June 2006

AbstractChloroplast microsatellites are becoming increasingly popular markers for population genetic studies in plants, but there has been little focus on their potential for demographic inference. In this work the utility of chloroplast microsatellites for the study of population expansions was explored. First, we investigated the power of mismatch distribution analysis and the FS test with coalescent simulations of different demographic scenarios. We then applied these methods to empirical data obtained for the Canary Island pine (Pinus canariensis). The results of the simulations showed that chloroplast microsatellites are sensitive to sudden population growth. The power of the FS test and accuracy of demographic parameter estimates, such as the time of expansion, were reduced proportionally to the level of homoplasy within the data. The analysis of Canary Island pine chloroplast microsatellite data indicated population expansions for almost all sample localities. Demographic expansions at the island level can be explained by the colonization of the archipelago by the pine, while population expansions of different ages in different localities within an island could be the result of local extinctions and recolonization dynamics. Comparable mitochondrial DNA sequence data from a parasite of P. canariensis, the weevil Brachyderes rugatus, supports this scenario, suggesting a key role for volcanism in the evolution of pine forest communities in the Canary Islands.