Contagious Pattern Research Articles

Ecology of Fear in a Colonial Breeder: Colony Structure in Ground-Nesting Great Cormorants Phalacrocorax carbo Reflects Presence of Predators

Ground-nesting Great Cormorants were monitored in three neighbouring colonies at Lake IJsselmeer, The Netherlands. Using aerial photographs taken during peak breeding time, nest density and nearest neighbour distance were determined for four sequential years. In addition, species and number of predators were determined. In total, five mammalian and nine avian predatory species were associated with the Cormorant breeding colonies. Spatial distribution of nests mostly showed dispersed and random patterns rather than a contagious pattern. The latter distribution, with less distance between nests than expected both from a random and equal distribution pattern, was found in the colony of De Ven in 2013 during the last year of its existence. The predator Red Fox Vulpes vulpes arrived at the colony in 2010. In all three colonies, nest density was highest and nearest neighbour distance shortest in colonies with the highest number of predators. At low to moderate predatory pressure, ground-nesting Cormorants left free space between nests that was used by adult birds during take-off and landing. During the last years of its existence the shrinking colony of De Ven showed an almost circular shape, with an extreme nest density and the lowest edge-to-surface area ratio. But with Foxes present, breeding at the fringe still caused greater losses due to direct predation. Breeding success fluctuated synchronously between colonies but was lower in colonies where the number of predators was higher. The arrival of Red Foxes in De Ven caused extreme losses of young and over the years resulted in a strong decline in number of breeders, eventually leading to complete abandoning of the site in 2014. Large gulls formed another important group of predators but did not cause the Cormorants to abandon the breeding site. In the Vooroever colony, bush and tree cover supplied shelter and allowed birds to breed in greater density without causing nearest neighbour density to decrease, as was the case when no cover was available. Greater nest density and reduced nearest neighbour distances are considered to be a pro-active response by individual birds to the presence of predators. When predator numbers increased, the within-colony open spaces that normally exist under circumstances of moderate density were filled up with nests, leaving little or no room for landing and departure. This leads to reduced edge effects and a circular shape of the colony, thereby potentially limiting predation risk. As a consequence of extreme high nest densities, breeding success was lower due to interference by other Cormorants. This study is the first to show that colony structure in waterbirds is affected by forces of attraction and repulsion between founding birds that are predator driven.

HERB DIVERSITY AND THEIR MEDICINAL USES IN BIODIVERSITY CONSERVATION AREA OF JNANABHARATI CAMPUS, BANGALORE UNIVERSITY, KARNATAKA

Unnoticed, breeding beneath the canopy in the woods, the herb layer serves a special role in maintaining the structure and function of forests, this stratum remains an underappreciated aspect of forest ecosystems. The Bangalore University, Jnanabharathi campus, historically being a scrub forest facilitating the growth of enormous vegetation ranging from large canopied trees to understory layer comprising of herbs and grasses. The present study was intended to assess the herbs diversity, richness and medicinal use to emphasize its role in tropical dry forest ecosystems, using a quadrate method. A total of 61 species were recorded, comprising of 52 species of herbs, representing 28 families, of which (77%) belongs to native and (23%) exotic (non-native) category. In addition to herbs four species of grass and five climber species of procumbent were also recorded in the same quadrate. Desmodium triflorum with1014 individuals and (IVI = 11.76) was found to be dominant species followed by Evolvulus alsinoides, Vicoa indica and Calyptocarpus vialis. Astraceae and Fabaceae was the most abundant family followed by Lameaceae and Acanthaceae. The diversity indices were estimated to determine the richness, diversity and evenness of herbaceous species, among three sectors, sector-1 is found to have Shannon index of 3.14 and Simpson index of 0.95, where highest Evenness index of 0.64 was associated with sector-3 followed by Sector-8 and Sector-1. From the study it was also revealed that all the three sectors were significantly depicting clumped or contagious pattern of herb distribution. The study indicates that understory herbaceous layer plays very important role in regeneration of canopy species in scrub forest and it support regeneration of many medicinal herbs. Hence University authorities should protect herb layer from fire, grazing and other anthropogenic disturbances.

COVID-19 Infection Process in Italy and Spain: Are Data Talking? Evidence From ARMA and Vector Autoregression Models.

COVID-19 (coronavirus disease 2019) has spread successfully worldwide in a matter of weeks. After the example of China, all the affected countries are taking hard-confinement measures to control the infection and to gain some time to reduce the significant amount of cases that arrive at the hospital. Although the measures in China reduced the percentages of new cases, this is not seen in other countries that have taken similar measures, such as Italy and Spain. After the first weeks, the worry was whether or not the healthcare system would collapse rather than its response to the patient's needs who are infected and require hospitalization. Using China as a mirror of what could happen in our countries and with the data available, we calculated a model that forecasts the peak of the curve of infection, hospitalization, and ICU bed numbers. We aimed to review the patterns of spread of the virus in the two countries and their regions, looking for similarities that reflect the existence of a typical path in this expansive virulence and the effects of the intervention of the authorities with drastic isolation measures, to contain the outbreak. A model based on Autorregressive and moving average models (ARMA) methodology and including Chinese disease pattern as a proxy, predicts the contagious pattern robustly. Based on the prediction, the hospitalization and intensive care unit (ICU) requirements were also calculated. Results suggest a reduction in the speed of contagion during April in both countries, earlier in Spain than in Italy. The forecast advanced a significant increase in the ICU needs for Spain surpassing 8,000 units by the end of April, but for Italy, ICU needs would decrease in the same period, according to the model. We present the following predictions to inform political leaders because they have the responsibility to maintain the national health systems away from collapsing. We are confident these data could help them into decision-taking and place the capitals (from hospital beds to human resources) into the right place.

Are there any other safe haven assets? Evidence for “exotic” and alternative assets

This paper empirically investigates the existence of possible safe haven properties across “exotic” and alternative asset classes during the Global Financial Crisis (GFC) and Eurozone Sovereign Debt Crisis (ESDC). We extend the existent safe haven literature by focusing on a new dataset into a dynamic framework, which takes into account the fractional structure of the assets and is suitable to identify their recursive relationship, as well as the specific points in calendar time at which the assets act as safe havens. The main results indicate that the safe haven hypothesis is accepted for gold along with wine, commodities, crude oil and shipping index, although across different turmoil periods. On the other hand, real estate seems to display signs of contagious pattern during the last decades’ turmoil period, while rare coins show some weak evidence of contagious behavior at the beginning of GFC. These results imply that investors and portfolio managers should search for “new” safe haven assets during a turbulent and ultra-low interest rate period in order to improve their portfolio diversification strategies.

Community Composition and Distribution Pattern of Herbaceous Flora in Holi Area of District Chamba in Himachal Pradesh

The present study was carried out in Holi Forest Range of district Chamba, which is the north-west district of Himachal Pradesh and is located between latitude 32o17’412’’ to 32o26’541’’N and longitude 76o31’504’’ to 76o35’385’’E. The territory is completely mountainous with altitude varying from about 2,000 feet (610 m) to about 21,000 feet (6,400 m) above the mean sea level. The quantitative information of herbs was collected from different sites i.e., Deol, Kut, Dal, Lahaud Dhar. Frequency (%), Density (plants m-2), Basal Area (cm2), Importance Value Index (IVI) and A/F ratio of plant species at different sites were recorded. Poa alpina was found to have highest frequency (90%) closely followed by Jurinea dolomiaea (80%) and Biebersteinia odora has the lowest frequency of 10%. Poa alpina has the highest density (60.6 plants m-2) at Dal followed by Gentiana kurrooa (35.8 plants m-2). Moschela esculenta was found to have highest basal area (1.234 cm2) at Kut. Viola serpens was the dominant species with highest value of IVI (78.77) closely followed by Poa alpina (65.91), Gentiana kurrooa (65.37) and Jurinea dolomiaea (65.36). Most of the species were distributed randomly followed by contagious pattern of distribution and least species were reported for regular distribution pattern.

Variation in Species Distribution Pattern and Dominance with Altitude and Aspect of Garhwal Himalayan Oak Forest

An investigation was conducted in an Oak forest of Garhwal Himalaya in relation to aspect and altitude. Major dominant tree, shrub and herb species were compared for density, A/F ratio and IVI values. Quercus leucotrichophora, Rhododendron arboreum, Lyonia ovalifolia, Myrica esculanta, Pinus roxburghii, Pyrus pashia, Benthamedia capitata and Lindera pulcherrima were most dominant tree species among all studied altitudes. Q. leucotrochophora showed contagious pattern in the north facing aspect and changed to random pattern in the south facing aspect at upper and middle altitudes. R. arboreum and M. esculanata also showed same changes in their distribution at middle and lower altitudes. In the shrub layer, the contagious pattern was changed to random pattern from north facing aspect to south facing aspect and vice versa. Herb species were mostly recorded in contagious pattern and the change of distribution was found for few species.

Phytosociological analysis of woody vegetation under burnt and unburnt oak dominated forest at Pauri, Garhwal Himalaya, India

The present study was carried out in oak (Quercus leucotrichophora) dominated forest of Pauri. Two permanent plots were selected of which one was BPS and other was UBPS. The vegetational data were analysed for both the sites i.e., floristic composition, density, basal cover, A/F, Shannon Wiener index and Simpson’s index of dominance (cd). A total of 6-8 trees species and 24-26 shrub species were found on both BPS and UBPS. BPS showed maximum density than UBPS. Contagious pattern of distribution was common. This paper represents a close association among man, fire and forest ecosystem.

Comparative study of shrub diversity in lower Dachigam Kashmir Himalaya

The present study was conducted in two different ecosystems, that is, Site I (village site) and Site II (protected site) in the lower part of Dachigam National Park (Jammu and Kashmir) in all seasons during 2010-2011. Site I is located towards the periphery of the National Park near habitations and is under heavy grazing pressures while Site II is located inside the National Park with mild interferences and is a controlled site. The values of diversity (H=2.228) as well as richness index (R= 0.867) were higher for Site II while dominance index showed higher value at Site I (C = 0.113). The evenness index showed more or less similar values for both sites (Site I = 0.497 and Site II = 0.499). The frequently occurring dominant shrub species during the study period based on importance value index (IVI) were Plectranthus rugosa, Rosa webbiana, Indigofera heterantha, Cotoneaster nummilaria and Daphnae oleoides at Site I and Indigofera heterantha, Clematis montana, Rosa macrophylla, Clematis grata and Rosa brunoni at Site II. The abundance to frequency ratio (A/F) indicated that most of the species present contagious pattern of distribution. Key words: Shrub, biodiversity, species, grazing, Dachigam.

Contagious deposition of seeds in spider monkeys' sleeping trees limits effective seed dispersal in fragmented landscapes.

The repeated use of sleeping sites by frugivorous vertebrates promotes the deposition and aggregation of copious amounts of seeds in these sites. This spatially contagious pattern of seed deposition has key implications for seed dispersal, particularly because such patterns can persist through recruitment. Assessing the seed rain patterns in sleeping sites thus represents a fundamental step in understanding the spatial structure and regeneration of plant assemblages. We evaluated the seed rain produced by spider monkeys (Ateles geoffroyi) in latrines located beneath 60 sleeping trees in two continuous forest sites (CFS) and three forest fragments (FF) in the Lacandona rainforest, Mexico. We tested for differences among latrines, among sites, and between forest conditions in the abundance, diversity (α-, β- and, γ-components) and evenness of seed assemblages. We recorded 45,919 seeds ≥5 mm (in length) from 68 species. The abundance of seeds was 1.7 times higher in FF than in CFS, particularly because of the dominance of a few plant species. As a consequence, community evenness tended to be lower within FF. β-diversity of common and dominant species was two times greater among FF than between CFS. Although mean α-diversity per latrine did not differ among sites, the greater β-diversity among latrines in CFS increased γ-diversity in these sites, particularly when considering common and dominant species. Our results support the hypothesis that fruit scarcity in FF can ‘force’ spider monkeys to deplete the available fruit patches more intensively than in CFS. This feeding strategy can limit the effectiveness of spider monkeys as seed dispersers in FF, because (i) it can limit the number of seed dispersers visiting such fruit patches; (ii) it increases seed dispersal limitation; and (iii) it can contribute to the floristic homogenization (i.e., reduced β-diversity among latrines) in fragmented landscapes.

Shredders are abundant and species-rich in tropical continental-island low-order streams: Gorgona Island, Tropical Eastern Pacific, Colombia

Macroinvertebrate shredders may have been overlooked in tropical streams due to the geographi- cal bias of early studies, methodological limitations, and the complex influences of local-scale factors. While shredders seem to be scarce in most oceanic island streams, we here test if they are abundant in a continental island. Gut content analyses of benthic macroinvertebrates were used to identify shredding taxa in streams located in different types of forest in Gorgona Island (Tropical Eastern Pacific). General dietary overlap (GO) was quantified and relative biomass, relative frequency and the leaf litter percentage in the guts were used to establish the relative importance of each taxon in the shredding guild. Various indices were used to identify the spatial arrangement (i.e. contagious or random) of each taxon and shredding guild among streams. We identified 31 shredding taxa that were divided into specialist-shredders (14 taxa), generalist-shredders (10), and collector-shredders (7). There was a complete GO (0.75, p<0.001) for the guild. Cockroaches (Epilampra) were the most represented shredders due to the greatest contribution to guild total biomass and to the highest content of leaf litter in their guts. These organisms were more important than shrimps and crabs in terms of abundance and biomass in leaf pack samples. Potimirin shrimps ranked second and Stenochironomus midges ranked third. Among aquatic insects, other secondarily important species were Leptohyphes (Ephemeroptera), Macrelmis, Anchytarsus and Tetraglosa (Coleoptera). Ten taxa exhibited contagious spatial pattern and twenty-one exhib- ited a random distribution. Resource distribution (i.e., leaf packs) between streams was random too. The guild was contagiously distributed, but this result could be highly influenced by the taxa with contagious distribution. Mean abundance, richness and mean biomass of shredders were not significantly correlated with any of the environmental variables measured. Three factors seemly explain the high richness and abundance of shredders in Gorgona Island: (1) its continental origin, (2) its current proximity to the continent (35 km), and (3) the high diversity and availability of leaf litter and woody debris inputs to the streams. Although crabs, shrimps, aquatic insects and semiaquatic-cockroaches coexisted in Gorgona Island, the latter were the most important leaf litter shredders in terms of biomass. Rev. Biol. Trop. 62 (Suppl. 1): 85-105. Epub 2014 February 01.

Mining Maximal Adjacent Frequent Patterns from DNA Sequences using Location Information

rapid development of bioinformatics has resulted in the explosion of DNA sequence data which is characterized by large number of items. Studies have shown that biological functions are dictated by contagious portions of the DNA sequence. Finding contiguous frequent patterns from long data sequences such as DNA sequences is a particularly challenging task and can pave the way towards new breakthroughs. Apriori based techniques were among the first to be used in frequent contagious pattern mining. Later improved approaches like GSP, Prefix Span were also applied but the approaches required either large number of sequence scans, generated large number of candidates or required higher number of intermediate sequential patterns. In this paper an improvement of the positional based approach for contagious frequent pattern mining is DNA sequences is proposed. The proposed algorithm improves the existing positional based approach by introducing a new amalgamated sorting and joining technique which helps to reduce time and space complexity. The proposed approach outperforms traditional existing contiguous frequent mining approaches.

Epidemiology of scabies prevalence in the U.K. from general practice records

Scabies is a contagious parasitic infestation which causes an allergic reaction to just a few mites. To examine the epidemiology of scabies consultations in the U.K. by age, sex, region of the country and time. Data were obtained from the THIN (The Health Information Network) database provided by EPIC U.K. in which each consultation episode is coded according to a 'READ' code. Data were available for 1997-2005 inclusive (9 years) for approximately 8·5% of the U.K. population from 12 regions of the U.K. We used harmonic analysis to model the data over time and derived cycle amplitudes and phases for each region in the U.K. There was a significantly greater infestation rate among females with a relative risk of 1·24 (P < 0·001) relative to males. The age group 10-19 years had the highest infestation rates (with rates of 4·55 per 1000 and 5·92 per 1000 for males and females, respectively). The middle age groups had the smallest infestation rates. A cycle with length of between 15 and 17 years was derived, and the phase times of the cycles for each region suggested a progression of the disease originating from the North East, spreading to Northern parts of the U.K. and then to the Midlands and the South. The study confirms earlier studies with regard to the age/sex distribution of scabies. We suggest a contagious pattern of spread of scabies infestation in the U.K. with an epidemic cycle length of 15-17 years.

Comparative study of herb layer diversity in lower Dachigam National Park, Kashmir Himalaya, India

The present study was conducted at two different ecosystems that is, site I (pastureland) and site II (forest) in the lower Dachigam National Park of Kashmir, Himalaya. The pasture site is located outside the National Park and is under grazing whereas forest site is located inside the National Park and is protected. The study was done on seasonal basis and the average results revealed comparatively more or equal values of diversity (H′) for both sites (site I = 2.435 and site II = 2.395) while dominance index showed higher value at site I (average = 0.147). The richness index (average = 3.842) and equability index (average = 0.90) both showed higher value at site II. Seasonal trend of Shannon diversity (site I = 3.03, site II = 2.87), richness index (site I = 3.70, site II = 5.83) and evenness or equability index (0.94, site I and II) depicted highest value during summer season whereas lowest variation in Shannon diversity and richness index was observed in winter season at both sites. However, dominance index was recorded lowest in summer season at both sites (site I = 0.06 and site II = 0.07) hence inversely related to diversity (H′). The frequently occurred dominant species during prominent seasons based on importance value (IV) wereCynodon dactylon, Salvia moorcroftiana and Thymus serphyllum at site I and Fragaria nubicola, Galinsoga parviflora, Stipa sibirica and Viola indica at site II. The abundance to frequency ratio (A/F) indicated most of the species performed contagious pattern of distribution. Key words: Biodiversity, community structure, seasons, species, grazing.

Effect of forest fire on trees, shrubs and regeneration behavior in Chir Pine forest in northern aspects under Solan forest division, Himachal Pradesh

Effect of forest fire on woody vegetation and regeneration behavior was studied in Chir pine forest situated between 1150-1800 m in Solan Forest Division in Himachal Pradesh, India. Four fire affected Sites and one control Site were surveyed for floristic composition, density, basal area, IVI, A/F, Shannon-Weaver index, Simpson’s Index of dominance (Cd), Species richness (d), Sorenson index (S) and natural regeneration potential of tree and shrubs. A total of 3 tree species and 10 shrub species were recorded on the five experimental sites. Fire resistant species were observed more in selected Chir pine forests. There was not observed any consistent trend for density, basal area, IVI, H. Sorenson’s index of similarity between fire affected and control sites for trees. Density and basal area in fire affected sites were lesser than control sites for shrubs. Contagious pattern of distribution for trees and shrubs was common. Seedlings density of trees and shrubs was higher on occasional fire affected sites than control sites. Density of saplings of trees was higher in control sites than fire affected sites.

Stem Borers of Teak and Yemane in Sabah, Malaysia,with Analysis of Attacks by the Teak Beehole Borer (Xyleutes ceramica Wlk.)

Infestations by stem borers in teak (Tectona grandis) and yemane (Gmelina arborea) plantations were surveyed at seven locations in Sabah, Malaysia in March, 1998. The teak beehole borer (Xyleutes ceramica) and the collar ring borer (Endoclita aroura) were found to attack teak and yemane. X ceramica accounted for most of the boring attacks in teak plantations, damaging 10.3-65.2% of the planted trees, except at one location where no stem borer attack was detected. The number of past and present attacks per tree ranged from 0.27-1.28 and 0.01-0.62, respectively. In contrast, E. aroura was of minor importance, attacking 6.9% or less of the planted trees. Analysis of spatial distribution of past attacks by the teak beehole borer in young teak stands revealed a contagious pattern. The past attacks were heavier on bigger trees. Both past and present attacks were concentrated in the lower part of the trunk, less than 1 m from the ground level. In young stands of yemane, an unidentified lamiine cerambycid damaged 0.0-14.1% of the trees, whereas the teak beehole borer damaged 7.6-12.2% of the trees.

Disregulation of proopiomelanocortin and contagious maladaptive behavior.

Self-injurious behavior (SIB) is an untreatable and often life-threatening problem among individuals with developmental disorders, especially those diagnosed with autism. Functioning, relationships and processing of the proopiomelanocortin (POMC) system are "uncoupled" in subgroups of self-injuring individuals resulting in different ratios of ACTH and opioids in the bloodstream, particularly under conditions of stress. In this study, relations between SIB and POMC were evaluated in a multi-year study of the largest prospective sample studied to date. Observations were collected on palmtop computers for 45 treatment-resistant patients who exhibited chronic SIB. Behavior of each subject was observed in natural settings without disruption or intrusion, for continuous, 2.5-h periods, two times a day (morning and afternoon), 4 days a week for two consecutive weeks, for a total of 40 h/subject. Blood was collected in the morning, late afternoon and immediately after an SIB episode on two separate occasions separated by at least 6 months. Levels of beta-endorphin (beta E) and ACTH were assayed by RIA. We discovered that the SIB was the best predictor of subsequent SIB. Moreover, the majority of subjects exhibited this contagious pattern of SIB. Levels of POMC fragments were reliable over a 6- to 9-month period. Subjects exhibiting POMC disregulation characterized by high morning levels of beta E had the highest transitional probabilities of SIB (i.e. contagious patterns; F=8.17, P<0.01). These findings suggest that subjects with "contagious" SIB may represent a behavioral phenotype associated with disregulated expression of the POMC gene.

Strategies to identify dangerous electricity pylons for birds

Bird electrocution rates in Secanos de Lerida, an important bird area in central Catalonia (northeast Spain), were estimated based on 804 visits to 507 electric pylons between 1995 and 1999. Electrocution caused a minimum of 160 victims on 67 pylons. Victims were corvids (36%), diurnal birds of prey (60%) and owls (4%). Electrocution rates ranged between <0.01 birds pylon−1 · year−1, in the less risky areas, and 0.20 birds · pylon−1 · year−1, in the areas with higher risk. The number of electrocution victims per killing pylon ranged from 1 to 12. Casualties occurred in a fairly contagious pattern, since 50% of deaths took place on only 2% of the visited pylons, and 50% of the killing pylons accumulated 80% of the victims. Univariate analysis revealed that the technical design of the pylons was very important in determining the potential danger of electrocution (metal crossbows were found to be the most dangerous design, followed by earthed flat pylons and vaults). Most mortality (97%) could be eliminated if all technically dangerous pylons were modified, but these would entail 67% of the pylons in the study area. Modelling the presence of carcasses under the pylons was used to identify the pylons which concentrate casualties, so that a 'preferred pylon' approach could be used to allocate mitigation resources. A single under-line inspection identified 78% of the pylons causing bird casualties in the area, which were responsible for 91% of the deaths. Information collected during this single inspection was used to build a logistic model which allowed the correct classification of most of the dangerous pylons missed in the first inspection. This approach revealed that geographical location and habitat setting were as important as technical design in determining the actual risk of electrocution. In that way, up to 99% of mortality can be eliminated by modifiying only 23% of the pylons in the area.

Influence of the spatial distribution pattern of prey among patches and spatial coincidence on the functional and numerical response of Phytoseiulus persimilis (Acarina, Phytoseiidae)

Abstract: In a model system composed of 16 leaf disks (Phaseolus vulgaris L.) distributed uniformly in an arena (50 × 50 cm), the influence of both the spatial dispersion pattern of prey (eggs of Tetranychus urticae Koch) and the transit time of the predator between patches (leaf disks) on the overall functional and numerical response of Phytoseiulus persimilis Athias‐Henriot was studied. Regardless of the pattern of the prey and the transit time of the predator, the functional response curves showed the response type 2. The handling time of the predator became significantly longer when the prey was in contagious pattern than in uniform pattern (1.52‐1.60 versus 0.68‐0.90 h). The number of prey consumed and the number of eggs laid per female P. persimilis decreased significantly at the initial prey density, which was more than 20 per patch. When the transit time of the predator was long, the effects of coincidence between predator and prey on both the number of prey and the number of eggs of the predator were significant. Low degree of spatial coincidence merely reduced the number of prey consumed and the number of eggs laid per predator. The number of eggs per predator was not related to the prey density at this condition. Based on these results, it was suggested that a density‐dependent dispersion pattern of prey and coincidence can determine the overall functional response type of the predator in a complex system consisting of many heterogenous patches, such as in fields, and that the prey density‐dependent functional response of the predator could be possible.

Colonization of Sibbaldia tetrandra Cushions on Alpine Scree in the Pamiro-Alai Mountains, Central Asia

The population of Sibbaldia tetrandra, a cushion plant, on the scree slope at 3800 m a.s.l. in the Pamiro-Alai Mountains consists of isolated individuals with positively skewed size distribution. Direct competition among isolated individuals is improbable. The differences in cushion size are due mainly to the age of individuals and the local site quality. Linear relationship between the growth in height of a cushion and its lateral growth was found. Frost injuries are more extensive in the small cushions, but the proportion of afflicted plants is greater in the large ones. Slightly contagious spatial pattern resulting from the environmental heterogeneity was detected. Seventeen species were observed to invade the cushions. Total biomass of intruding species is highly correlated with the cushion volume as well as with biomass. Species diversity increases with cushion area. A log-linear relationship between the number of invading species and cushion area was found. Both the number and cover of the species occurring outside of the Sibbaldia tetrandra cushions are negatively correlated with the cover of Sibbaldia tetrandra. The spatial pattern of Sibbaldia populations differs considerably between the study plot on a flat site and that on the scree slope. On the flat site, Sibbaldia forms a carpet consisting of individuals which cannot be clearly distinguished from each other. There also, the number and cover of the other species increases, and the most successful species are those which are capable of colonizing Sibbaldia cushions.

Compliance of a biennial mullein (Verbascum sinaiticum Benth.) to erratic desert floods in the Negev highlands, Israel

Wadis of the Negev desert highlands are characterised by irregular flash floods and, consequently, their beds typically comprise coarse gravel. The biennial Verbascum sinaiticum Benth. tends to establish temporary stands on such wadi gravel beds, and these exhibit a contagious pattern of distribution. V. sinaiticum, which is native to the Afro-montane region, acquires a fugitive character in the Negev. Its seeds germinate mainly on the third or fourth days after wetting. Optimal germination was obtained in continuous light at 25°C; a gradual increase in Nacl, up to 80 m M caused a delay in germination and reduced the daily rate. Irregular fluctuation of the water regime and the unstable nature of the wadi beds are essential for the establishment of V. sinaiticum. Flash floods are also necessary for its existence: they provide periodic reformation of the disturbed habitat, removal of potential competitors, dispersion of the seeds of V. sinaiticum and wash-out of excess salts. Another mullein, V. fruticulosum Post, a perennial herb, occupies the shoulders of the same wadis, as well as the terraces above them. Its distribution is sparse and the pattern tends to be random. The rôle of floods in the allopatric distribution of the two species of Verbascum is discussed.