bluuebunny/crossref_metadata_2025 huggingface dataset:
Speech Content and the Emergence of Inequality in Task Groups
Authors: Shelly Robert K. , Shelly Ann C.
Published: April 2009

We examine how the content of actors’ speech and the frequency with which they make contributions affect the emergence and legitimation of inequality in task groups. Previous research has focused on classifying acts, the smallest meaningful units of speech, such as providing opportunities to others to speak, making task relevant suggestions, and positively or negatively evaluating the contributions of others. We also employ a classification scheme based on the cognitive complexity of spoken language in the turn. This scheme is based on an interpretation of the cognitive development model posited by Piaget. In addition to the complexity of language, we analyze speech group members employ to organize to solve the task. These classifications rely on the entire content of the turn rather than the more atomistic act. Data analyzed are from 33 groups of students performing different types of tasks. We employ structural equation models to identify how acts and content are related to one another in the observed interaction patterns in groups. Applications of these insights are explored in the discussion.
How Minorities Prevail: The Context/Comparison–Leniency Contract Model
Authors: Crano William D. , Seyranian Viviane
Published: April 2009

The pioneering efforts of Moscovici in the late 1960s motivated social psychologists to understand how minority groups affected the majority, and conversely, how the majority affected the minority. The underlying processes of influence have been found to be quite different, and understanding their operation provides insight into the processes of social influence, persuasion, and intragroup conflict and cooperation. This review tracks some of the development of this progression and details some contributions to understanding fundamental features of the influence process that have been uncovered as a result of this work. We consider major explanatory models, with particular emphasis onCrano's (2001)context/comparison model, and its allied leniency contract, a comprehensive account of the conditions that prevail when majorities and minorities wield influence. Finally, how this work informs important processes of influence in the world outside the laboratory are discussed.
Lower‐Status Participation and Influence:Task Structure Matters
Authors: Alexander Michele G. , Chizhik Alexander W. , Chizhik Estella W. , Goodman Jeffrey A.
Published: April 2009

Status hierarchies readily form in groups and,once established,limit lower‐status group members’ opportunities for contributing to and influencing group decisions.Recent findings,however,suggest that the type of task on which a group works may allow lower‐status individuals to break through power and prestige orders in a cooperative way while conflicting with ideas of their higher‐status group members.In this article,we review a research program that investigates how task structure relates to status and influence in small groups.In one experiment, using groups of three female students as participants,we found that open‐structured tasks allow lower‐status group members to participate,receive positive evaluations,and improve their status more than closed‐structured tasks.In a second experiment, using groups of two female students and a female experimenter as participants,we found that open‐structured tasks and lower‐status confederates foster more divergent thinking and indirect influence than closed‐structured tasks and higher‐status sources.Our findings contribute to the understanding of how immediate problem‐solving environments contribute to status change and influence in small groups.
Entrepreneurial Self–Efficacy: Refining the Measure
Authors: McGee Jeffrey E. , Peterson Mark , Mueller Stephen L. , Sequeira Jennifer M.
Published: April 2009

A growing number of studies on entrepreneurial motivation, intentions, and behavior include entrepreneurial self–efficacy (ESE) as an explanatory variable. While there is broad consensus among researchers on the importance of including ESE in an intentionality model, there remain inconsistencies in the definition, dimensionality, and measurement of ESE. This study takes an important step toward refinement and standardization of ESE measurement. Within a new venture creation process framework, a multi–dimensional ESE instrument is developed and tested on a diverse sample that includes nascent entrepreneurs. Implications for entrepreneurship theory and entrepreneurship education are discussed.
Can this Business be Rescued?
Authors: Ivanova Yuliya V.
Published: April 2009

This teaching case describes an ethical dilemma for a small business owner operating in the challenging business environment of Belarus, 2003. Each of his four options is a viable consideration depending on the perspective through which it is considered: his role as an individual, his role within his social network, and his role as a business executive. Students learn to evaluate each option and to make difficult decisions. The case is most appropriate for ethics or decision–making classes in the areas of Organizational Behavior, Leadership, or International Management. This case would also be relevant in an executive education program.
Does One Size Fit All? The Multiple Organizational Forms Leading to Successful Academic Entrepreneurship
Authors: Wood Matthew S.
Published: April 2009

This paper offers an integrative theory, through the use of transaction cost theory principles, that attempts to match the attributes of university–held innovations with the specific organizational form that best supports the identified attributes in innovation commercialization efforts. Two commonly utilized organizational forms are considered: the spin–off and the technology license agreement. Additionally, innovation transfer is conceptualized as a transaction and each of the organizational forms is considered an alternate governance mechanism for the management of the commercialization transaction. It is further conceptualized that by minimizing transaction costs, through the proper selection of the organizational form, universities may increase the odds of successful revenue generation from their entrepreneurial efforts. The overall goal of the paper is to enhance our understanding of proper organizational form–innovation attribute alignment as a key driver of innovation commercialization success, so that universities and their industry partners can increase their effectiveness in commercialization activities.
Business Networks and Economic Development in Rural Communities in the United States
Authors: Ring J. Kirk , Peredo Ana Maria , Chrisman James J.
Published: April 2009

Many rural communities in the United States are economically depressed. However, while poor rural communities are geographically isolated and small, they are likely to be rich in social capital. We first argue that the nature of the social capital in such communities can either facilitate or constrain the development of business networks among entrepreneurs. We then explain the community–level conditions that might increase the probability of business network effectiveness. The primary opportunities that such networks can exploit and their potential spillover effects on economic development are also identified. Finally, we provide directions for research that can contribute to better public policy decisions.
Mode of Induction of Ventricular Tachycardia and Prognosis in Patients with Coronary Disease: The Multicenter UnSustained Tachycardia Trial (MUSTT)
Authors: PICCINI JONATHAN P. , HAFLEY GAIL E. , LEE KERRY L. , FISHER JOHN D. , JOSEPHSON MARK E. , PRYSTOWSKY ERIC N. , BUXTON ALFRED E. ,   for the MUSTT Investigators
Published: April 2009

Introduction: Programmed stimulation is an important prognostic tool in the evaluation of patients with an ejection fraction ≤40% after myocardial infarction. Many believe that ventricular tachycardia (VT) requiring 3 ventricular extrastimuli (VES) for induction is less likely to occur spontaneously and has less predictive value. However, it is unknown whether the mode of VT induction is associated with long‐term prognosis.

Methods and Results: We analyzed a cohort of 371 patients enrolled in MUSTT who had inducible monomorphic VT and who were not treated with antiarrhythmic drugs or an implantable cardioverter defibrillator during the trial. Patients in whom sustained VT was induced with 1 or 2 VES or burst pacing (single VES n = 15, double VES n = 127, burst n = 7, total n = 149) were compared with those in whom VT was induced with 3 VES (n = 222). Compared with the others, patients requiring 3 VES were closer to their most recent myocardial infarction (17 vs 51 months, P = 0.035) and showed a trend toward a lower ejection fraction (26% vs 30%, P = 0.057). VT requiring 3 VES had a shorter cycle length (240 vs 260 ms, P < 0.001). Despite these findings, there was no difference in the incidence of arrhythmic death or cardiac arrest (HR 1.02; 95% CI 0.69‐1.51) or all‐cause mortality (HR 1.03; 95% CI 0.76‐1.39) according to the mode of induction in adjusted analyses.

Conclusions: The prognostic significance of VT induced by 3 VES is similar to that of VT induced by 1 or 2 VES, or burst pacing, in patients with coronary disease and abnormal LV function.
Dislocations at Prismatic Fracture Surfaces in Sapphire
Authors: López‐Cepero Jose Manuel , Wiederhorn Sheldon M. , Black David , Guin Jean‐Pierre , De Arellano‐López Antonio R. , Martínez‐Fernández Julian
Published: April 2009

Single‐crystal sapphire exhibits a highly anisotropic fracture behavior. The surfaces of specimens fractured along prismatic planes are wavy, with fractographic features appearing as small areas of contrast under an optical microscope. Optical microscopy, atomic force microscopy, X‐ray topography, and confocal microscopy are used to demonstrate a correlation between the areas of contrast and dislocations penetrating the sample surface. The surface features are argued to be a consequence of the stress field surrounding the dislocations, which deflect the crack approximately 10 nm normal to the surface as the crack cuts the dislocations. The lateral extent of measurable surface deflection is of the order of 5 μm. These images can be compared directly to show the equivalence of the position of the dislocations observed by X‐ray topography and the surface contrast observed optically.
The Role of Gender Identification in Social Dominance Orientation: Mediating or Moderating the Effect of Sex?1
Authors: Snellman Alexandra , Ekehammar Bo , Akrami Nazar
Published: April 2009

Previous research has shown that people's gender identification correlates with their social dominance orientation (SDO). A question is whether gender identification mediates or moderates the effect of biological sex on SDO. We examined the correlations of sex and gender identification with SDO using the Bem Sex Role Inventory in Study 1 and a gender diagnostic measure in Study 2. Both studies showed that gender identification was significantly associated with SDO. In Study 1, gender identification partially mediated the effect of sex on SDO; and in Study 2, this mediation was complete. There were no indications that gender identification moderated the effect of sex on SDO. The results are discussed against the background of the gender invariance hypothesis of SDO.
Ship Service Life and Naval Force Structure
Authors: KOENIG PHILIP , NALCHAJIAN DON , HOOTMAN JOHN
Published: April 2009

The Naval Sea Systems Command has conducted several interdisciplinary studies recently, motivated by a need to address the high cost and extended duration of naval vessel design and construction. Naval architecture and force structure studies have been key components of these efforts. Two general approaches are available: development of alternative future fleet design and programming concepts, and changes in ship expected service life policy. These are not mutually exclusive alternatives, service life is a key variable in future force planning regardless of any other variables considered. In this paper, issues associated with both approaches are described and discussed. Potential implications for future naval force structure planning are identified and recommendations for future work are suggested.
Differing acceptance of familiar and unfamiliar plant species by an oligophagous beetle
Authors: Kühnle Anne , Müller Caroline
Published: April 2009

The mustard leaf beetle, Phaedon cochleariae (F.) (Coleoptera: Chrysomelidae), is specialized to feed and develop on various species within the Brassicaceae. In this study, we investigated the acceptance of several host plant species (Brassica rapa L. and Sinapis alba L.), commonly used by the beetle (familiar plants), and of various unfamiliar plants, including systematically and chemically related [Bunias orientalis L. (Brassicaceae) and Tropaeolum majus L. (Tropaeolaceae), both Brassicales], as well as unrelated non‐host plant species [Plantago lanceolata L. (Plantaginaceae); Lamiales]. Emphasis was laid on the acceptance of the neophyte B. orientalis, and on underlying cues responsible for the acceptance of the various species. Behavioural responses to plant volatiles were studied using a static four‐chamber olfactometer. Stimulants and deterrents were investigated by bioassay‐guided solid phase extraction and semi‐preparative high performance liquid chromatography. A difference in acceptance of plant species was found: odours and polar compounds of all Brassicales evoked attraction and feeding stimulation, respectively, in Ph. cochleariae. Glucosinolates and their volatile hydrolysis products could be the main compounds that are involved in attraction of the beetles. In contrast, Ph. cochleariae did not respond to odours of the non‐host P. lanceolata, and some fractions of this plant had feeding‐deterrent effects, due to the presence of iridoid glycosides, among others. Although adult females accepted the neophyte B. orientalis for oviposition, neonate larvae did not survive on it. The flavonoid‐containing fraction of this plant was deterrent, whereas a similar fraction had been shown to cause some feeding stimulation when derived from S. alba. Differences in qualitative and quantitative composition of related metabolites lead to differentiated plant acceptance, proving the complexity of plant cues and of insect responses that determine host acceptance behaviour. The possibility of a diet breadth enlargement to B. orientalis and the role of Ph. cochleariae as a putative native biocontrol agent of this invasive plant are discussed.
Polar light regime and piscivory govern diel vertical migrations of planktivorous fish and zooplankton in a subarctic lake
Authors: Kahilainen K. K. , Malinen T. , Lehtonen H.
Published: April 2009

Abstract –  Seasonal variation in light intensity has strong impacts on invertebrate and vertebrate habitat selection creating trade‐offs between foraging gain and risk of death. Diel vertical migration (DVM) has received a particularly interest, but multitrophic level studies in lakes under polar light regime have not been conducted. Here, we examined habitat selection of pelagic zooplankton, planktivores and piscivores in subarctic Lake Muddusjärvi with polymorphic whitefish (Coregonus lavaretus (L.)). Seasonal change in light was hypothesized to be the most important abiotic factor inducing DVM, whereas predation was considered as an ultimate biotic factor. During period of mid‐night sun in June, no DVM was observed at any trophic level, whereas during normal day and night light in September planktivores and zooplankton migrated. DVM was top‐down controlled, where piscivorous brown trout (Salmo trutta L.) used pelagic habitat continuously inducing DVM of its main prey, pelagic whitefish morph, which cascaded to reverse DVM of zooplankton. Top‐down control of lower trophic level DVMs by piscivores might be more general pattern in lakes than previously considered.
An innovative method to measure skin pigmentation
Authors: Masuda Yuji , Yamashita Toyonobu , Hirao Tetsuji , Takahashi Motoji
Published: April 2009

Background/purpose: It is crucial to establish an accurate method for measuring skin pigmentation in cosmetic science and clinical dermatology. Here, we report a non‐invasive precise method for measuring skin melanin content.

Methods: In order to determine the concentrations of melanin and hemoglobin in skin, we used the spectrum resolution (SR) method. In brief, the absorption spectrum of the skin was calculated from the reflection spectrum using a spectrophotometer. The concentrations of melanin and hemoglobin were then determined using a multiple regression analysis, assuming that the absorption spectrum of the skin is expressed as a linear summation of the absorptions of melanin and hemoglobin according to the Lambert–Beer law. The skin changes in the volar forearm, which had been irradiated by ultraviolet rays (UV), were observed daily by the SR method.

Results: A multiple regression analysis with an absorption spectrum of 500–700 nm was performed. The multiple correlation coefficient was 0.993, resulting in a satisfactory precise estimate of the concentrations of melanin. After UV irradiation, the concentration of melanin monitored by the SR method increased until 8 days and decreased gradually afterwards.

Conclusions: The SR method allows the evaluation of the changes of epidermal melanin induced by UV irradiation.
Impact of different‐sized herbivores on recruitment opportunities for subordinate herbs in grasslands
Authors: Bakker Elisabeth S. , Olff Han
Published: April 2009

Abstract. Potential effects of herbivores on plant species diversity depend on herbivore size, species and density. In this study we examine the effect of different‐sized herbivores (cattle and rabbits) on recruitment of subordinate herbs in grasslands. We show that in a grazed floodplain, grassland plant species richness is mainly determined by the presence of many species of subordinate herbs. These herbs experience high colonization and extinction rates. We conclude that the creation of colonization opportunities for subordinate herbs plays a crucial role in maintaining plant species richness in productive grasslands. We found that cattle disperse large amounts of seeds via their dung, over ten times more than rabbits. Rabbits create more and on average larger bare soil patches than cattle. In a field experiment artificial disturbances improved germination success tremendously for four tested herb species. We found that bare soil is the best regeneration site, while cattle dung gave a too strong nutrient stimulus, resulting in tall vegetation and therefore light limitation. These results can be confirmed with results from field monitoring plots where plant species richness was positively related to the occurrence of bare soil patches. Therefore both large and small herbivores have a major impact on dispersal and colonization, but for different reasons. Cattle are identified as most important for seed dispersal whereas rabbits have a main effect as creators of disturbances. These results emphasize the importance of distinguishing between herbivore species in assessing their (potential) effects.
Distribution and species richness of woody dryland legumes in Baja California, Mexico
Authors: Garcillán Pedro P. , Ezcurra Exequiel , Riemann Hugo
Published: April 2009

Abstract.We analysed the biogeographic patterns of woody legumes in the Baja California peninsula, NW Mexico. From the specimen labels of eight herbaria, we digitized 4205 records from 78 species, and projected them onto a grid of 205 cartographic cells (20’ longitude × 15’ latitude). Most species followed distribution patterns that coincide with floristic subdivisions of the peninsula. Endemism is high, reaching 60–70% in the centre of the peninsula, where the driest deserts are found and where significant floristic changes took place during Pleistocene glacial events. The number of cartographic cells (i.e. their geographic ranges) were log‐normally distributed, as has been reported for many other taxa. Floristic richness was found to be clumped around some cells where the observed richness is significantly higher than could be expected from chance variation. We tested the hypothesis that these ‘hotspots’ could be attributable to great collection efforts or to large land surfaces, but we still found 16 cells where richness is significantly high once these two factors are accounted for. Species richness and micro‐endemism increase towards the south, conforming to Rapoport's rule that predicts that species ranges become smaller towards the equator while richness increases. The floristic hotspots for woody legumes in Baja California occur in the Cape Region and along the Sierra de la Giganta in the southern Gulf Coast, where 77% of the total peninsular legume flora can be found. These hotspots are mostly unprotected, and should be considered priority areas for future conservation efforts.
Consequences of shrub expansion in mesic grassland: Resource alterations and graminoid responses
Authors: Lett Michelle S. , Knapp Alan K.
Published: April 2009

Abstract.In the mesic grasslands of the central United States, the shrubCornus drummondiihas undergone widespread expansion in the absence of recurrent fire. We quantified alterations in light, water and N caused byC. drummondiiexpansion in tall‐grass prairie and assessed the hypothesis that these alterations are consistent with models of resource enrichment by woody plants. Responses in graminoid species, particularly the dominant C4grassAndropogon gerardii, were concurrently evaluated. We also removed established shrub islands to quantify their legacy effect on resource availability and assess the capability of this grassland to recover in sites formerly dominated by woody plants. The primary effect of shrub expansion on resource availability was an 87% reduction in light available to the herbaceous understorey. This reduced C uptake and N use efficiency inA. gerardiiand lowered graminoid cover and ANPP at the grass‐shrub ecotone relative to undisturbed grassland. Shrub removal created a pulse in light and N availability, eliciting high C gain inA. gerardiiin the first year after removal. By year two, light and N availability within shrub removal areas returned to levels typical of grassland, as had graminoid cover and ANPP were similar to those in open grassland. Recovery within central areas of shrub removal sites lagged behind that at the former grass‐shrub ecotone. These results indicate that the apparent alternative stable state ofC. drummondiidominance in tall‐grass prairie is biotically maintained and driven by reductions in light, rather than resource enrichment. Within areas of shrub removal, the legacy effect ofC. drummondiidominance is manifest primarily through the loss of rhizomes of the dominant grasses, rather than any long‐term changes in resource availability.C. drummondiiremoval facilitates grassland recovery, but the effort required to initiate this transition is a significant cost of woody plant expansion in mesic grasslands. Prevention of woody plant expansion in remnant tall‐grass prairies is, therefore, a preferred management option.
Dry vegetation in relation to the physical environment in the Baja California Peninsula, Mexico
Authors: Villers‐Ruiz Lourdes , Trejo‐Vázquez Irma , López‐Blanco Jorge
Published: April 2009

Abstract. An ordination analysis of vegetation and flora of Los Cabos Region, Baja California Peninsula, Mexico and its relationships with their environment and geomorphic characteristics was studied at 38 sites, selected based on ecoregion mapping units (EMU) previously delineated for the study area. Multivariate methods were used to analyse the relationship between physical characteristics of the environment and the two primary vegetation types, the Dry tropical forest (DTF) and the Xerophilous scrubland (XS), which together represent 83% of the vegetation cover in the study area. Sites were grouped based on both physical characteristics and relative abundance of plant species. The results of the statistical analysis suggest that altitude, rainfall, temperature, and lithology can help explaining differences between these important vegetation types. In the case of XS, the morpho‐physiognomic characteristics of vegetation in each site discriminated between two scrub types.
The influence of environmental factors on the spatial distribution of saxicolous lichens in a Norwegian coastal community
Authors: Bjelland Torbjørg
Published: April 2009

Abstract. The effects of vegetation cover, radiation, micro‐habitat variables and maritime influence on the floristic composition of a saxicolous community in Vingen, western Norway were studied. Particular emphasis is put on the local distribution of Fuscidea cyathoides, Ochrolechia tartarea, Ophioparma ventosa and Pertusaria corallina. Very little of the variation in the lichen community composition is directly related to measured micro‐environmental variables but variance partitioning shows that vegetation cover explains more of the floristic variation than radiation, maritime influence and microhabitat variables. Logistic regression analyses nevertheless indicate that the micro‐environment influences the spatial distribution of the four species. The high fraction of unexplained floristic variation, 91%, is suggested to result from (1) lack of fit of data to the response model; (2) some influential environmental variables that have not been recorded; (3) local historical factors that affect present day distribution and/or (4) apparent randomness in colonization. The results also agree with the view that the four lichen species in this study are able to co‐exist in the long‐term because of different spatial distributions resulting from different strategies with respect to ecology, dispersion and interaction.
Variation in modern pollen from tropical evergreen forests and the monsoon seasonality gradient in SW India
Authors: Barboni D. , Bonnefille R. , Prasad S. , Ramesh B.R.
Published: April 2009

Abstract. This study analyses the pollen signature of tropical lowland forests (< 1000 m a.s.l.) in the Asian monsoon climate. Its aim is to investigate how well the pollen data can reproduce the vegetation patterns in tropical India, and how the variations in the pollen composition are related to the gradient of decreasing plant moisture availability (measured by the ratio of actual over equilibrium evapotranspiration) that is associated with the strong seasonality of precipitation that characterizes the monsoon climate regime.

We used canonical correspondence analysis (CCA) to relate the variations in the pollen composition of 71 surface soil samples from evergreen and semi‐evergreen forests distributed along the western coast of south India (8° 48’ N‐15° 08’ N), with the climate characteristics of the sampling sites. We show that variations in plant moisture availability strongly determine variations in the pollen composition; for example evergreen and semi‐evergreen forests can be distinguished on the basis of their pollen assemblages. Variations in the mean temperature of the coldest month associated with elevation also determine distinct pollen assemblages; for example evergreen forests above 800 m a.s.l. present different pollen signatures than those below this altitude/temperature limit. Variations in the relative abundance of some pollen taxa are strongly related to plant moisture availability and taxa indicators of climate can be identified. Hence, modern pollen assemblages from tropical forests in south India carry considerable information about vegetation patterns and climate. Paleoclimatic changes, notably in the monsoon season, could be quantified.
Plot sizes used for phytosociological sampling of European vegetation
Authors: Chytrý Milan , Otýpková Zdenka
Published: April 2009

Abstract. In European phytosociology, variable plot sizes are traditionally used for sampling different vegetation types. This practice may generate problems in current vegetation or habitat survey projects based on large data sets, which include relevés made by many authors at different times. In order to determine the extent of variation in plot sizes used in European phytosociology, we collected a data set of 41 174 relevés with an indication of plot size, published in six major European journals focusing on phytosociology from 1970 to 2000. As an additional data set, we took 27 365 relevés from the Czech National Phytosociological Database. From each data set, we calculated basic statistical figures for plot sizes used to sample vegetation of various phytosociological classes.

The results show that in Europe the traditionally used size of vegetation plots is roughly proportional to vegetation height; however, there is a large variation in plot size, both within and among vegetation classes. The effect of variable plot sizes on vegetation analysis and classification is not sufficiently known, but use of standardized plot sizes would be desirable in future projects of vegetation or habitat survey. Based on our analysis, we suggest four plot sizes as possible standards. They are 4 m2 for sampling aquatic vegetation and low‐grown herbaceous vegetation, 16 m2 for most grassland, heathland and other herbaceous or low‐scrub vegetation types, 50 m2 for scrub, and 200 m2 for woodlands. It has been pointed out that in some situations, sampling in either small or large plots may result in assignment of relevés to different phytosociological classes or habitat types. Therefore defining vegetation and habitat types as scale‐dependent concepts is needed.
BOOK REVIEWS
Authors: van Andel Jelte
Published: April 2009

Book reviewed in this article:

Gurevitch, J., Scheiner, S.M. & Fox, G.A. 2002. The Ecology of Plants. xvi + 523 pp. Sinauer Associates, Sunderland, MA, USA. ISBN 0‐87893‐291‐7 (hardcover). Price: USD 89.95.
The role of refugia and dispersal in primary succession on Mount St. Helens, Washington
Authors: Fuller R.N. , del Moral R.
Published: April 2009

Abstract. An intense lateral blast devastated Mount St. Helens in 1980, but forest understory species survived in some north‐slope ‘refugia’. We explored the effects of refugia on colonization of barren pumice in 1997 and 1998, 18 yr after the eruption. The seed rain of 23 colonizers came mostly from populations that had previously established in refugia. Parachutists had small, vagile seeds, parasailors had winged seeds, and tumblers were blown along the ground. The latter two groups are heavier and dispersed more slowly, but are more likely to survive. The proportion of the vegetation represented by wind‐dispersed species increased with distance from refugia. Parachutist's density declined with time and proximity to refugia. As vegetation adjacent to refugia developed, populations of parasailors and tumblers expanded, foreshadowing their dominance in more remote pumice. Refugia played a critical role in determining the rate and course of succession by providing fertile islands that permitted pioneers and dry meadow species to establish near barren pumice. Species that survived in refugia played a negligible role in colonization. This study showed that when refugia contrast sharply with new substrates, they accelerate recovery by facilitating the invasion of pioneer species.
Avoiding misinterpretation of biotic interactions with the intertypeK12‐function: population independence vs. random labelling hypotheses
Authors: Goreaud F. , Pélissier R.
Published: April 2009

Abstract.The interactions between plants of different species, age or size play an important role in the dynamics of an ecosystem and can induce specific structures. These interactions can be studied by analysing the spatial structure of the corresponding bivariate patterns. The intertypeL12‐function has recently been successfully used in many papers for that purpose. However, when interpreting the results obtained with ecological data, at least two different null hypotheses – independence or random labelling – can be appropriate, depending on the context of the study and the nature of the data. As these two hypotheses correspond to different confidence intervals, an inappropriate choice of the null hypothesis can lead to misinterpretations of biotic interactions when studying ecological data. This problem has rarely been mentioned in the literature.

In this paper we clarify the differences between these two null hypotheses, and illustrate the risk of misinterpretation when using an inappropriate null hypothesis. We review the main characteristics of these two hypotheses, and analyse the spatial structure of both real data from forest stands and simulated virtual stands of different structures. We demonstrate that the risk of misinterpretation is quite high, and that extreme misinterpretations, i.e. cases leading to opposite conclusions in terms of spatial interaction, can occur in a significant number of cases. We therefore propose some guidelines to help ecologists avoid such misinterpretations.
The influence of Prosopis canopies on understorey vegetation: Effects of landscape position
Authors: Schade J.D. , Sponseller R. , Collins S.L. , Stiles A.
Published: April 2009

Abstract. The influence of canopy trees and shrubs on under‐storey plants is complex and context‐dependent. Canopy plants can exert positive, negative or neutral effects on production, composition and diversity of understorey plant communities, depending on local environmental conditions and position in the landscape. We studied the influence of Prosopis velutina (mesquite) on soil moisture and nitrogen availability, and understorey vegetation along a topographic gradient in the Sonoran Desert. We found significant increases in both soil moisture and N along the gradient from desert to riparian zone. In addition, P. velutina canopies had positive effects, relative to open areas, on soil moisture in the desert, and soil N in both desert and intermediate terrace. Biomass of understorey vegetation was highest and species richness was lowest in the riparian zone. Canopies had a positive effect on biomass in both desert and terrace, and a negative effect on species richness in the terrace. The effect of the canopy depended on landscape position, with desert canopies more strongly influencing soil moisture and biomass and terrace canopies more strongly influencing soil N and species richness. Individual species distributions suggested interspecific variation in response to water‐ vs. N‐availability; they strongly influence species composition at both patch and landscape position levels.
Competitive and facilitative relationships among three shrub species, and the role of browsing intensity and rooting depth in the Succulent Karoo, South Africa
Authors: Carrick Peter J.
Published: April 2009

Abstract. The nearest‐neighbour technique is used to infer competition and facilitation between the three most abundant species in a semi‐arid region of western South Africa. Relationships among the shrubs Leipoldtia schultzei and Ruschia robusta, which are leaf‐succulent members of the Mesembryanthemaceae (‘mesembs’) and Hirpicium alienatum a non‐succulent Asteraceae, were compared on two adjacent sites with different histories of browsing intensity. Competition was more prevalent and more important than facilitation. The only evidence for facilitation was found at the heavily‐browsed site where the palatable Hirpicium was larger under the unpalatable Leipoldtia. Generally the prevalence and importance of competition was reduced at the heavily‐browsed site. Strong evidence was obtained for intraspecific competition in each of the three species; also, competition was evident between the two mesembs, where Leipoldtia was competitively dominant over Ruschia, although neither species inhibited Hirpicium. Minimal competition between the mesembs and the asteraceous shrub was interpreted in terms of differentiation in rooting depth, and competition within the mesembs, in terms of overlap in rooting depth. The mesembs had the bulk of their roots in the top 5 cm of soil, while the asteraceous shrub had the bulk of its roots, and all its fine roots, at greater depths. The shallow‐rooted morphology of the mesembs is well adapted to utilize small rainfall events, which occur frequently in the Succulent Karoo, and do not penetrate the soil deeply. Modifications of existing methods are applied for analysing nearest‐neighbour interactions.
Relationships between species richness patterns in deciduous forests at the north Estonian limestone escarpment
Authors: Ingerpuu N. , Vellak K. , Liira J. , Pärtel M.
Published: April 2009

Abstract.The flora of the deciduous forests at the base of the north Estonian limestone escarpment is species rich, with an exceptionally high number of rare bryophyte species. Relationships between species richness of bryophyte and herb layers and biotic and environmental conditions were studied, using General Linear Mixed Models. Human disturbance (waste deposit, tree damage etc) was significantly negatively correlated with species richness of both plant layers. Soil nitrogen content was negatively and soil water retention positively correlated with bryophyte species richness, while herb richness was unrelated to soil factors. After eliminating the effects of environment, negative correlations in species richness and cover between the bryophyte and herb layers were discovered on finer scales (1 m2), referring to biotic interactions. This relationship was obscured with the simple correlation analysis. On the other hand, the positive correlation in species pools between the bryophyte and herb layers (0.1 ha) was insignificant. The species pools of both bryophyte and herb layers were significantly positively correlated with the species richness of the tree layer. In summary, bryophyte and herb layer richness responded differently to environmental conditions, but human disturbance significantly decreased the richness of both layers. Due to the uniqueness and small area of these forests we recommend protection and restoration of disturbed sites.
Use of the β‐function to estimate the skewness of species responses
Authors: Karadžić Branko , Marinković Saša , Katarinovski Dragan
Published: April 2009

Abstract. Response of a species to an environmental variable may be modeled and predicted using a wide spectrum of different functions. Contrary to other functions (Gaussian, polynomial etc), all parameters of the β‐function are interpretable in ecological terms. However, computational difficulties in the determination of the β‐function parameters initiated controversial debates on the applicability and usefulness of this function in vegetation modelling and gradient analysis. We propose a simple algorithm for fitting the β‐function to observed data. Analytic properties of the algorithm (its ability to recover the known species responses along gradients) are tested using a series of simulated data. In most cases the algorithm correctly estimated parameters of the simulated responses.
Survival and growth of tree seedlings in anthropogenically disturbed Mexican montane rain forests
Authors: Ramírez‐Marcial Neptalí
Published: April 2009

Abstract. The montane rain forest in Chiapas, Mexico has been subject to continuous human disturbance, mainly by wood extraction, cattle grazing and fire. To address the effect of this kind of disturbance regime on regeneration, survival and growth of naturally established tree seedlings were evaluated during a 3‐yr period in three forest stands which varied in frequency and intensity of human disturbance. Frequency of cattle browsing on transplanted seedlings of Cornus disciflora, Liquidambar styraciflua and Oreopanax xalapensis planted on different facing slopes was evaluated over an 18‐mo period, their survival and growth was also determined. The density of seedlings, number of species and survival of naturally recruited tree seedlings decreased with increased intensity of disturbance. Only seedlings of Pinus and Quercus species were recorded in heavily disturbed conditions. Seedlings grew more vigorously under moderately disturbed than in undisturbed or heavily disturbed conditions. More extreme microclimatic variation (air temperature, relative humidity and solar radiation) was recorded in heavily vs moderately disturbed forest. Survival and growth of transplanted tree seedlings differed with species. Grazing damage varied among seedlings located on different facing slopes. Plants located on NE facing slopes survived better than those on other slope positions. The mean proportion of surviving individuals of L. styraciflua (80%) and C. disciflora (78%) was higher than those for O. xalapensis (60%). A higher number of C. disciflora and O. xalapensis seedlings were grazed than L. styraciflua in any slope orientation treatment. The results suggest that human disturbance negatively affects natural recruitment, reduces richness of tree seedlings and favours a small number of tree species.
Propagule banks and regenerative strategies of aquatic plants
Authors: Combroux Isabelle C.S. , Bornette Gudrun
Published: April 2009

Abstract. The role of the propagule bank in aquatic plant maintenance was studied in two riverine wetlands. Four sites were selected, characterized respectively by flooding, drying up, both disturbances operating, and neither operating. Our hypothesis was that recolonization after drying up would mostly involve seeds and buds from the propagule bank, whereas recolonization after floods would mostly involve rhizomes. Dry sites were characterized by a high density of seeds, and a high similarity between seed species and established vegetation. Unspecialized fragments remaining in wet parts of the sediment probably also contribute to species maintenance. Species maintenance in sites subjected to flooding was highly dependent on deeply anchored rhizomes, as indicated by the strong floristic similarity between species that occur in the established vegetation and rhizomes in the bank. Regeneration of the community after scouring floods also involved seeds, some species being able to flower under water. When scouring flooding and drying up were superimposed, regenerative strategies exhibited in the bank did not simply result from the ‘addition’ of the two disturbance effects. When the disturbances did not occur too closely together in time, species were able to survive either by: (1) producing many propagules under aquatic conditions or (2) coping with the temporal variability by producing several types of propagules.
Reproducibility of vegetation cover estimates in south‐central Alaska forests
Authors: Helm D.J. , Mead B.R.
Published: April 2009

Abstract. Reproducibility of vegetation measurements is critical for large‐scale or long‐term studies, where numerous observers collect data, but past studies have questioned repro‐ducibility of some techniques. Five methods of evaluating understory composition were appraised for reproducibility among six observers in two forest types in south‐central Alaska: ocular estimates in quadrats, overall community species rank and cover estimates, nested rooted frequency, horizontal‐vertical profiles, and pin drop (systematic points). One forest type was selected to represent structure of coastal communities, another to represent structure of interior Alaska communities. Three general methods of evaluating reproducibility were considered: standard deviations (precision among observers), components of variance (percentage of total variance attributable to observers), and analysis of variance (significance of observer variance). Observer variances were generally similar among techniques and significant in most cases. No technique stood out as being more reproducible than others. Features of techniques other than reproducibility may be more important when selecting a technique. Management decisions based on vegetation cover data should consider the observer errors involved as well as biological significance.
Spatial structure of Aspidosperma polyneuron in two semi‐deciduous forests in Southeast Brazil
Authors: Fonseca Marisa Gesteira , Martini Adriana Maria Zanforlin , dos Santos Flavio Antonio Maës
Published: April 2009

Abstract. Description of the spatial structure of vegetation is the first step in generating hypotheses regarding underlying processes. It is also important to take into account variation in spatial structure between different localities to be able to distinguish between life history traits and the influence of environment on population processes. Correlogram analysis was used to examine spatial recruitment and mortality patterns of Aspidosperma polyneuron, an emergent tree species, at Reserva Municipal de Santa Genebra (SG), a forest fragment in southeast Brazil. The spatial structure of individuals was compared with two areas with similar physiognomy, one in the same forest and another at Mata do Ribeirão Cachoeira (RC), a semi‐deciduous forest located ca. 14 km away. Seedling, sapling and adult mortality occurred in clumps, while seedling recruitment occurred mostly in one region of the area. The spatial pattern varied among the three study areas, and the differences were higher between fragments than within SG. The adults showed a negative correlation in space with saplings and seedlings in one of the SG areas, which could be a consequence of intraspecific competition, or the influence of density or distance dependent natural enemies. However, this pattern was not observed in the other areas. The results suggest that the mechanisms governing the spatial population dynamics of A. polyneuron vary among nearby and similar localities.
Early post‐fire succession in northwestern Patagonia grasslands
Authors: Ghermandi Luciana , Guthmann Nadia , Bran Donaldo
Published: April 2009

Abstract. Large‐scale disturbances, notably fire and grazing, structure grass and shrubland dynamics in semi‐arid environments. We studied early post‐fire succession in two burned grasslands, one unburned grassland, and one shrubland near the burned area. We observed three processes: (1) establishment of a ‘phantom’ community comprised of fugitive species. Although transient, these species increase diversity and recharge the seed bank before the next disturbance; (2) regeneration of the original community by persistence of resprouter species and by auto‐replacement; (3) early stages of invasion by seedlings of the shrub Fabiana imbricata, which germinate next to shrubland and create new F. imbricata patches. Weed invasion was principally due to the ruderal exotic species Verbascum thapsus from the nearby road verge and by rapid increase of Rumex acetosella cover, another exotic species present before the fire. Although post‐fire climatic conditions are particularly important in semi‐arid environments, succession depends greatly on the regeneration strategies and dispersal abilities of the species present in the burned area. The phantom community occurs only at the first stage of succession when there is little competition for resources. We could call this process ‘the race for occupation of the area’. The second stage, when competition for resources becomes progressively more important, could be called ‘the effort to maintain space’.