Intensity Disturbance Research Articles

Phytoplankton species diversity control through competitive exclusion and physical disturbances

Competitive exclusion theory suggests that phytoplankton species number in an assemblage at equilibrium will be limited to the number of simultaneously limiting resources, generally three or fewer. However, natural phyto‐plankton assemblages usually exhibit high species diversity, hence the concept of Hutchinson's “paradox of the plankton”. Recent works have suggested that this apparent paradox is a result of disturbances intermediate in frequency relative to the time period necessary for species succession to lead to equilibrium conditions (sensu Connell's intermediate disturbance hypothesis [IDH]). Moreover, evidence indicates that disturbances of intermediate intensities are also conducive to maintenance of high species diversity in phytoplankton communities. Using a long‐term data record from hypereutrophic subtropical Hartbeespoort Dam (South Africa) that was typically dominated by a single species, but annually subjected to physical disturbance, we demonstrate here that disturbances can indeed enhance phytoplankton species diversity. However, these data fail to support Connell's IDH per se, as moderate‐and high‐intensity disturbances yielded similarly high species diversity. These data also suggest that community resilience (the ability or time to return to predisturbed conditions) is negatively related to disturbance intensity, such that higher intensity disturbances maintained high diversity for longer periods of time relative to lower intensity disturbances.

BREEDING BIRD RESPONSES TO THREE SILVICULTURAL TREATMENTS IN THE OREGON COAST RANGE

Silvicultural alternatives to clear-cutting have been suggested to promote development, retention, or creation of late-successional features such as large trees, mul- tilayered canopies, snags, and logs. We assessed bird response to three silvicultural alter- natives to clear-cutting that retained structural features found in old Douglas-fir (Pseudo- tsuga menziesii) forests and that imitated natural disturbance regimes more closely than did traditional clear-cutting: (1) small-patch group selection treatment representing a low- intensity disturbance; (2) two-story treatment, representing a moderate to high-intensity disturbance; and (3) modified clear-cut treatment, representing a high-intensity disturbance. We counted diurnal breeding birds 1 yr prior to and 2 yr after harvest to estimate effects of the silvicultural treatments on bird communities compared with uncut controls. The small-patch group selection treatment was most similar in species composition to control stands. The two-story treatment was more similar to the modified clear-cut treatment. Ten bird species remained abundant following the small-patch group selection treatment. They declined in abundance in modified clearcuts and two-story stands. These species included four neotropical migratory species and five species with restricted geographic ranges and habitat associations. Nine species increased in response to moderate and/or high-intensity disturbances. This group included a larger proportion of species that were habitat generalists. Silvicultural treatments imitating low-intensity disturbances were most effective in retaining bird communities associated with mature forest; high-intensity disturbances such as the two-story and modified clear-cut treatments greatly altered bird community composition. Bird responses to the silvicultural treatments that we studied indicate that a variety of stand types is needed to meet needs of all species.

Roles of succession, light, nutrients and disturbance on population vigor and maintenance of the rare plant Solidago shortii (Asteraceae)

Results of field and glasshouse experiments on Solidago shortii, and our observations on this species over many years, were used to construct a conceptual model of the roles of succession, light, soil nutrients and disturbance on population vigor and maintenance of this federal-endangered species. As cover of woody vegetation increased at a population site between 1986 and 1992, number of flowering ramets of S. shortii significantly decreased but number of vegetative ramets remained nearly constant. Adult plants transplanted into a redcedar thicket and those shaded in a glasshouse produced many fewer flowering ramets and capitula per flowering ramet and less biomass and had higher mortality than those in the open. Seedlings/juveniles shaded in a glasshouse had significantly less dry biomass; lower RGR, NAR, leaf area and root/shoot ratio and higher LAR, SLA and LWR than nonshaded ones. In a field site and glasshouse, fertilized plants (NPK) consistently had more flowering ramets and capitula per flowering ramet than nonfertilized ones. Hierarchy of dry weight of plants grown in a glasshouse in soils derived from five types of bedrock was phosphatic limestone > calcareous shale > sandstone > black shale = dolomite. Flowering and biomass production in the field-fertilizer and soil-type experiments were associated closely with levels of P. Number of flowering ramets significantly increased in plants transferred from shaded to nonshaded glasshouse conditions, but no such increase occurred after opening the canopy above plants in a thicket. Both high light and high nutrient levels apparently are necessary to maintain high vigor of S. shortii. In areas subject to invasion by woody plants, periodic high intensity disturbance may be required to prevent population extirpation.

Multi-scale analysis of disturbance regimes in the northern Chihuahuan Desert

Remote sensing facilitates cross-scale validation, enables analysis of processes and patterns in time and space, and is thus viable for the conduct of earth system science. Multi-scale analyses of natural vegetation patterns and processes in the northern Chihuahuan Desert show that natural vegetation is capable of recovering from short-term, high intensity disturbances such as an atomic bomb blast. In contrast, mesquite dunelands persist on other sites grazed before the blast, showing the Chihuahuan is less resilient to long-term low intensity disturbances. A geographic information system (GIS) was used to register historical Landsat Multi-Spectral Scanner (MSS) data acquired over Trinity National Historic Site (TNHS), New Mexico, and the vicinity. Aerial and ground photography provide supporting detail, at finer scales, regarding the distribution and pattern of natural vegetation at TNHS Ground Zero and adjacent weapons impact targets. Aside from initial mechanical or thermal damage to vegetation from the first atomic test over a half century ago, analyses of vegetation at satellite and airphoto scales show no apparent persistent blast effects around TNHS.

Selection harvests in Amazonian rainforests: long-term impacts on soil properties

Surface soil properties were compared among disturbance classes associated with a single-tree selection harvest study installed in 1979 in the Brazilian Amazon. Response variables included pH, total N, total organic C, extractable P, exchangeable K, Ca, Mg, and bulk density. In general, concentrations of all elements displayed residual effects 16 years after harvests with N, P, K, and C being inversely related to disturbance intensity while Ca and Mg levels as well as pH were directly related. Elemental contents exhibited fewer residual effects except in the cases of Ca and Mg contents which generally increased with disturbance intensity. Higher intensity disturbance classes were associated with increased bulk density. Soil impacts apparent after 16 years suggest a combination of direct effects of harvests (e.g. as in the case of bulk density) combined with indirect influences of the ecophysiology of the Cecropia sp. which dominate disturbed areas.

Canopy Gaps and the Landscape Mosaic in a Coastal Temperate Rain Forest

We studied canopy gaps over a range of stand ages and site moisture classes in the temperate rain forest of Clayoquot Sound, southwestern British Columbia, Canada. We tested predictions about the landscape mosiac at three levels of resolution: the forest as a whole, gaps, and gapmakers. In addition to canopy gaps arising from the patchy mortality of dominant trees (developmental gaps), we described the prevalence and characteristics of gaps arising from edaphic and topographic features. Roughly 56% of the forest ares is influenced to some degree by canopy openings (canopy gap + expanded gap), with 30% of forest area in canopy gaps averaged over all sites (14% developmental canopy gaps and 16% in edaphic canopy gaps). Within the most intensively sampled biogeoclimatic subzone, 73% of gaps were developmental in origin. The majority of edapthic gaps result from streamcourses. Though percent area in developmental canopy gaps was similar across stand age classes, gaps and gapmaker were more common in old growth than in mature stands. Most developmental gaps resulted from the mortality of more than one tree: 96% of the developmental gaps had more than one gapmaker, and 50% had three or more. Mature stands had a significantly higher number of gapmakers per gap than old—growth stands. Old—growth forests were thus dominated by many small gaps and mature forests by fewer larger gaps. Drier and wetter sites had more gapmakers per gap than did stands on mesic sites. The number of decay classes of gapmakers in developmental gaps increases with number of gapmakers per gap, indicating that larger gaps represent the combined effects of distinct mortality events separated in time, rather than single large events. Gapmakers in developmental gaps were distributed broadly and evenly over the range of decay classes, suggesting a continuous pattern of recruitment of gapmakers rather than larger episodic mortality events. The snapping of boles and standing death were the most common modes of gapmakers mortality, together accounting for 76% of the mortality of gapmakers. Uprooting was the least common mode of gapmaker mortality in both mature and old—growth forests (23.6% and 15.6%, respectively; 20.6% of all gapmakers) and uprooting was more common in drier and wetter sites than in mesic sites. These general trends in gap—phase structure and gap formation processes are consistent with data on gaps and forests age structure collected elsewhere on the British Columbia coast, suggesting that a regime of small—scale, low—intensity disturbance is common in the old—growth forests of coastal British Columbia. We estimate that, in the absence of large—scale disturbances, turnover time for this forest is between 350 and 950 yr, resulting in ubiquitous late successional character throughout the landscape mosaic. Silvicultural practices intended to emulate the natural disturbance regime of these forests should create small gaps of 3—10 trees in an otherwise continuous forest matrix and should retain substantial late—successional characteristics within managed forests.

Cognitive Status and Postoperative Pain

The purpose of this study was to assess older adults to determine (a) the course of postoperative pain, (b) influences of pain and analgesics on mental status, and (c) relationships among age, mental status and pain. Sixty adults, aged 50-80 yr, who had total hip replacement surgery were included in this study. All subjects had met a preoperative criterion for mental status. Data collection took place over 5 days following surgery. Pain intensity and distress were assessed three times a day for 5 days. Recalled night pain intensity, pain distress, and sleep disturbance from pain were assessed daily in the early morning prior to assessment of mental status. Although no within day or day-to-day pain patterns were observed, the greatest decreases in pain occurred during the first 2 days. Night pain also improved after the third day. One-third of subjects recorded one or more episodes where mental status declined below criterion after surgery. Multivariate analysis indicated that pain, not analgesic intake, predicted mental status decline. Age was not related to pain or mental status. In general, pain was poorly managed in this group of subjects. The results suggest an explanation for acute confusion in older patients after surgery and recommend improved pain management.

The Effects of Hurricane Hugo on Bats of the Luquillo Experimental Forest of Puerto Rico

Natural disturbances can have large effects on ecosystem structure and function depending on their scale, intensity, and frequency. On 18 September 1989 Hurricane Hugo struck Puerto Rico, with the eye of the hurricane passing within 10 km of the Luquillo Experimental Forest. This provided a rare opportunity to evaluate the effects of an infrequent but large scale and high intensity disturbance on tropical bat species. Data on demographic parameters of three common phyllostomid bats (Artibeusjamaicensis, Stenoderma rufum, and Monophyllus redmani) were examined for three years prior and three years after the hurricane. Population levels as estimated by captures per net hour of all three species were affected by Hurricane Hugo. Populations of A. jamaicensis and M. redmani returned to predisturbance levels within two years. In contrast, population levels of S. rufum declined to about 30 percent of prehurricane levels and have not recovered after three years. Moreover, telemetry data indicate that foraging and home range size expanded to encompass an area approximately five times larger than its prehurricane size. The cost of foraging, in terms of time and energy, may be considerably elevated over prehurricane scenarios. In fact, a significant change in the age structure of the population (juvenile individuals have been absent from the population since Hurricane Hugo) as well as significant decline in the percent of reproductively active females indicate a failure to reproduce in the posthurricane environment.

The smoothing properties of some new shapes for transmission functions in Fourier space a real case study on exemplary noisy Auger spectra

Two new shapes for transmission functions (both derived from the sigmoidal function) in Fourier space have been applied to filtering of noisy Auger spectra differing from one another in their Fourier characteristics of noisy components. The results have been compared with an optimum transmission function designed by P. Marchand and L. Mermet [Rev. Sci. Instr. 54 (1983) 1034]. The comparison shows a better filtering efficiency for the new transmission functions within a low intensity disturbance regime, provided their parameters are within a range of limits dependent on the value of the characteristic frequency of the main feature in the spectrum. Additionally, in the case of a spectrum recorded with a low ratio of the sampling interval to the width of the line, a criterion for effective smoothing has been found.

Cognitive status and postoperative pain: Older adults

The purpose of this study was to assess older adults to determine (a) the course of postoperative pain, (b) influences of pain and analgesics on mental status, and (c) relationships among age, mental status and pain. Sixty adults, aged 50–80 yr, who had total hip replacement surgery were included in this study. All subjects had met a preoperative criterion for mental status. Data collection took place over 5 days following surgery. Pain intensity and distress were assessed three times a day for 5 days. Recalled night pain intensity, pain distress, and sleep disturbance from pain were assessed daily in the early morning prior to assessment of mental status. Although no within day or day-to-day pain patterns were observed, the greatest decreases in pain occurred during the first 2 days. Night pain also improved after the third day. One-third of subjects recorded one or more episodes where mental status declined below criterion after surgery. Multivariate analysis indicated that pain, not analgesic intake, predicted mental status decline. Age was not related to pain or mental status. In general, pain was poorly managed in this group of subjects. The results suggest an explanation for acute confusion in older patients after surgery and recommend improved pain management.

Mass Movement Effects on Grassland Vegetation and Soils on Santa Cruz Island, California

Abstract Two types of mass movement are studied to test the hypothesis that spatial heterogeneity would affect species richness of grassland communities. Rotational slumps are low-moderate intensity disturbances that generate a variety of new microhabitats (scarp and toe versus flatter middle). Concave shallow slips are higher intensity disturbances that create one new type of soil microhabitat (uniform exposed subsoil inside). Plant species response fails to conform to predictions that heterogeneity would foster greater species richness. The more intense slip disturbance provides sites for four new species to colonize, but the overall landscape richness is lower than elsewhere. The new colonizers are mostly shrubs characteristic of nearby coastal sage communities. Most native perennials are only in non-slip areas. The most successful colonizers are the dominant introduced European annuals, which occur everywhere. The greater heterogeneity of slumps does not affect richness of the grassland community. All...

Mood disturbance following increased training in swimmers.

Twelve male swimmers were studied psychologically before, during, and after 10 d of increased training. Daily training distance was increased from 4,000 to 9,000 m.d-1, and intensity was maintained at 94% of VO2max. Three of the swimmers were unable to tolerate the increased training load, and they did the same distance at slower speeds. Swimmers completed the Profile of Mood States, a muscle soreness scale, and a 24-h history each morning prior to the first of two daily training sessions. Changes across days were evaluated statistically with a one-way repeated measures ANOVA. Significant (P less than 0.005) increases occurred in the ratings of exercise intensity, muscle soreness, depression, anger, fatigue, and global mood disturbance, along with a reduction in general sense of well-being. Swimmers were classified as "responders" or "non-responders" on the basis of distress patterns using separate physiological and psychological criteria, and these classifications were performed in a double-blind setting. Close agreement (89%) was achieved between the psychometric and physiological judgments, and the physiological results appear in related papers. It is concluded that significant psychometric changes occur with an intense 10-d training regimen, and these alterations resemble those observed in swimmers exposed to increased training across several months. These findings underscore the potential utility of monitoring mood states in the prevention of staleness.

Immunologic and Virologic Status of Multitransfused Patients: Role of Type and Origin of Blood Products

An immunologic and virologic work-up was undertaken in 425 symptom-free multitransfused patients with hemophilias or hemoglobinopathies living in France. Patients were entered into five groups according to the type of blood product they received: local factor VIII, a mixture of local and imported factor VIII, imported factor IX, local factor IX, washed red blood cells. The overall prevalence of IgG antibodies to the lymphadenopathy-associated virus (LAV) was 45%. The highest rate was observed in hemophiliacs who received factor VIII concentrates prepared from plasma collected mainly on the American continent; intermediary values were found for hemophilic patients treated with local factor VIII or factor IX concentrates; and the lowest values were found for those who were treated with washed red blood cells. Lymphadenopathy, decreased skin hypersensitivity reactions, relative lymphopenia, and altered ratio of T lymphocyte subsets occurred at significantly higher rates in patients positive for LAV antibody, although such abnormalities were also encountered in LAV serologically negative patients. A correlation between treatment intensity and immunologic disturbances was found in patients infused with factor VIII preparations, irrespective of their positive or negative LAV antibody status. This study has shown the prominent role of LAV in the occurrence of immunologic disturbances in multitransfused patients. However, allogenic or altered proteins present in factor VIII but not in factor IX concentrates seem to play a role of immunocompromising agents. The interplay between LAV and additional factors possibly leading to acquired immunodeficiency syndrome remains to be analyzed.

Immunologic and virologic status of multitransfused patients: role of type and origin of blood products. By the AIDS-Hemophilia French Study Group

An immunologic and virologic work-up was undertaken in 425 symptom-free multitransfused patients with hemophilias or hemoglobinopathies living in France. Patients were entered into five groups according to the type of blood product they received: local factor VIII, a mixture of local and imported factor VIII, imported factor IX, local factor IX, washed red blood cells. The overall prevalence of IgG antibodies to the lymphadenopathy-associated virus (LAV) was 45%. The highest rate was observed in hemophiliacs who received factor VIII concentrates prepared from plasma collected mainly on the American continent; intermediary values were found for hemophilic patients treated with local factor VIII or factor IX concentrates; and the lowest values were found for those who were treated with washed red blood cells. Lymphadenopathy, decreased skin hypersensitivity reactions, relative lymphopenia, and altered ratio of T lymphocyte subsets occurred at significantly higher rates in patients positive for LAV antibody, although such abnormalities were also encountered in LAV serologically negative patients. A correlation between treatment intensity and immunologic disturbances was found in patients infused with factor VIII preparations, irrespective of their positive or negative LAV antibody status. This study has shown the prominent role of LAV in the occurrence of immunologic disturbances in multitransfused patients. However, allogenic or altered proteins present in factor VIII but not in factor IX concentrates seem to play a role of immunocompromising agents. The interplay between LAV and additional factors possibly leading to acquired immunodeficiency syndrome remains to be analyzed.

Scattering from a hard corrugated wall: An exact solution in the two-dimensional case

We present a method for computing exactly the intensities diffracted by a hard corrugated wall potential. We use a two-dimensional corrugation of any amplitude and calculate the source function by means of special points in the lattice unit cell. Our procedure is shown to be convergent, it is compared with the NN′ method and with the Fourier expansion method. The use of special points, about which a theoretical summary is given, allows us to consider rather small matrices to invert (64 × 64 or 128 × 128). Symmetrical cases are discussed and are shown to yield reduced matrix sizes. Our method is applied to the calculation of the intensity disturbances induced by the emergence of a beam. The validity of the eikonal approximation is also discussed.

Interrupted ongoing behaviour in two species of vole ( Microtus agrestis and Clethrionomys britannicus). I. Response as a function of preceding activity and the context of an apparently ‘irrelevant’ motor pattern

Microtus agrestis and Clethrionomys britannicus were maintained under different home pen conditions and tested in a large alley. Ongoing behavioural sequences were continuously recorded and interrupted at set intervals by an overhead moving object. Two main problems were examined. First, does an animal's response to the experimental stimulus vary as a consequence of different ongoing behaviour? Secondly can systematic increases as well as decreases in a seemingly irrelevant (i.e. ‘displacement’) behaviour be observed? Consequences of the differences in temperament between the two species, of the different home pen conditions, and of different intensities of the experimental disturbance were also explored. When locomotor activity preceded the stimulus presentation, fleeing rather than just freezing was most likely to occur. The role of an underlying ‘activity tendency’ which need not be expressed in overt locomotion was suggested by the fact that the more docile Microtus was generally more active in the experimental alley, and also fled more than Clethrionomys even when the two species were matched for behaviours preceding the stimulus. This hypothesis was supported by the subsequent finding that locomotor behaviour which had ceased several seconds before the stimulus presentation also increased flight probability. Home pen cover plus trial number influenced flight probability and appeared to combine in their effect with one another and with ongoing locomotion. Other ongoing activities such as grooming appeared on occasion to be momentarily accelerated by the stimulus presentation, but were soon suppressed. Microtus groomed more after the stimulus presentation than during control trials. Clethrionomys groomed less. Microtus also groomed more and Clethrionomys less following a high intensity compared with a low intensity disturbance. These data suggested that the animals were most likely to groom when optimally ‘aroused’. A temporal analysis of grooming supported the basic model. A single unitary process, however, could not be assumed. The ‘disinhibition hypothesis’ was partly supported by the data for grooming, but possible limitations were noted. For example, the relation between grooming and subsequent locomotion was inconsistent. An increase in the apparent intensity of grooming after the stimulus presentation was occasionally observed. Home pen cover had minimal effect upon grooming, probably as a consequence of housing numerous animals together. The relevance of these findings to problems of behavioural integration, and most particularly to the issue of specific versus general motivational systems, is discussed.