Showing papers on "Disturbance (geology) published in 1981"

Intertidal landscapes: disturbance and the dynamics of pattern [Mytilus californianus, mussels]

Abstract: The mussel Mytilus californianus is a competitive dominant on wave—swept rocky intertidal shores. Mussel beds may exist as extensive monocultures; more often they are an everchanging mosaic of many species which inhabit wave—generated patches or gaps. This paper describes observations and experiments designed to measure the critical parameters of a model of patch birth and death, and to use the model to predict the spatial structure of mussel beds. Most measurements were made at Tatoosh Island, Washington, USA, from 1970—1979. Patch size ranged at birth from a single mussel to 38 m2; the distribution of patch sizes approximates the lognormal. Birth rates varied seasonally and regionally. At Tatoosh the rate of patch formation varied during six winters from 0.4—5.4% of the mussels removed per month. The disturbance regime during the summer and at two mainland sites was 5—10 times less. Annual disturbance patterns tended to be synchronous within 11 sites on one face of Tatoosh over a 10—yr interval, and over larger distances (16 km) along the coastline. The pattern was asynchronous, however, among four Tatoosh localities. Patch birth rate, and mean and maximum size at birth can be used as adequate indices of disturbance. Patch disappearance (death) occurs by three mechanisms. Very small patches disappear almost immediately due to a leaning response of the border mussels (0.2 cm/d). Intermediate—sized patches (<3.0 m2) are eventually obliterated by lateral movement of the peripheral mussels: estimates based on 94 experimental patches yield a mean shrinking rate of 0.05 cm/d from each of two principal dimensions. Depth of the adjacent mussel bed accounts for much of the local variation in closing rate. In very large patches, mussels must recruit as larvae from the plankton. Recovery begins at an average patch age of 26 mo; rate of space occupation, primarily due to individual growth, is 2.0—2.5%/mo. Winter birth rates suggest a mean turnover time (rotation period) for mussel beds varying from 8.1—34.7 yr, depending on the location. The minimal value is in close agreement with both observed and calculated minimal recovery times. Projections of total patch area, based on the model, are accurate to within 5% of the observed. Using a method for determining the age of patches, based on a growth curve of the barnacle Balanus cariosus, the model permits predictions of the age—size structure of the patch population. The model predicts with excellent resolution the distribution of patch area in relation to time since last disturbance. The most detailed models which include size structure within age categories are inconclusive due to small sample size. Predictions are food for large patches, the major determinants of environmental patterns, but cannot deal adequately with smaller patches because of stochastic effects. Colonization data are given in relation to patch age, size and intertidal position. We suggest that the reproductive season of certain long—lived, patch—dependent species is moulded by the disturbance regime. The necessary and vital connection between disturbance which generates spatial pattern and species richness in communities open to invasion is discussed.

Latitudinal structure and extension of the polar atmospheric disturbance

Abstract: The dissipation of solar wind energy in the upper atmosphere generates a disturbance whose morphology depends on local time, season, and magnetic activity. A statistical analysis of ESRO 4 data reveals that (1) in the afternoon/evening sector the disturbance boundary coincides with the region of electric current dissipation along the auroral oval; (2) in the midnight/early morning sector, dynamical effects extend the disturbance zone to lower latitudes, and this expansion is strongly dependent on season and magnetic activity; and (3) in the late morning sector, direct heating effects along the auroral oval are superimposed on the residuals of the early morning disturbance. These results are consistent with previous observations and provide new boundary conditions for upper atmospheric models.

Effects of Human Disturbance on Colonial Species, Particularly Gulls

Abstract: Colonial birds are particularly vulnerable to human disturbance because of the large concentrations of birds nesting in close proximity. Vulnerability varies depending on species, nest location, and the type of disturbance (see Manuwal 1978). Nearness to human activities is one key factor, as the potential for disturbance is much greater regardless of a species' intrinsic vulnerability. Mere distance is not sufficient to assess the potential for disturbance because the surrounding habitat affects human (or predator) access. Birds nesting a half mile from a town on an island surrounded by deep, rough waters are surely less vulnerable than those surrounded by solid ground. Similarly, nesting habitat is crucial: nests on cliffs are less accessible than are nests on flat ground, nests in trees are less accessible than are ground nests, and burrows are less accessible than are surface-areas. Ground-nesting species such as gulls, terns, and some herons, egrets, ibises, and cormorants are thus particularly vulnerable to human disturbance because they are accessible and often nest in close proximity to human activities. The types of human activity that affect colonial bird populations are varied, ranging from overall destruction to direct intervention such as entering colonies, collecting eggs, and killing adults, eggs, or chicks. The response of colonial birds to human activities varies markedly, but no species can withstand the direct effects of killing adults, eggs, or chicks for sustained periods of time. Assessing the effects of human disturbance on nesting colonial birds is a difficult task because the observer can never completely remove himself. The problem is further complicated by the decreased accuracy of success measurements with fewer egg or chick censuses. Observation of reproductive success from afar is usually impossible in the egg stage, and is complicated in the chick phase by the presence of vegetation and rocky or uneven terrain. Reproductive success can be lowered either directly by causing desertion of nests, eggs or young, by adults, or indirectly by causing thermal stress, predation, and cannibalism. In this paper I discuss the direct and indirect ways human activities affect colonial birds, particularly Larids, and I report on some of the sub-lethal effects of human disturbance including behaviors contributing to the lowered reproductive success. I present results on the behavioral responses of gulls, terns, and skimmers to human disturbance including decreased egg and chick attendance, shifts in the mate incubating, movements and entanglements of chicks, higher brood sizes, and greater aggressive interactions.

A Numerical Study on the Effects of Environmental Flow on Tropical Storm Genesis

Abstract: The role of the environmental wind in tropical storm genesis is studied using a numerical simulationmodel. The model used is an 11-level, primitive equation model covering a channel domain of 25° span withopen lateral boundaries at 5.5 and 30.5°N. A number of experiments were integrated for 96 h in which theinitial zonal mean flow was specified differently. The superposed initial wave disturbances were identicalin all experiments. The dynamic coupling between the upper-level winds and the low-level movement of the disturbance wasfound to be an important factor in explaining the role of the environmental wind in storm genesis. Anotherimportant factor is the impact of the low-level winds on the latent energy supply. This supply is affectedby the relative inflow into a disturbance and by the transfer of momentum from aloft into the boundarylayer in a large area surrounding the disturbance. According to the model results, the storm genesis potential is definitely biased toward easterly verticalshear ...

Response of a soft-bottom harpacticoid community to stingray ( Dasyatis sabina ) disturbance

Abstract: The recolonization by harpacticoid copepods of patches disturbed by stingrays [Dasyatis sabina (LeSeur)] feeding in a subtidal (2–3 m depth) site off the Florida gulf coast (Lat. 29°54.55′N, Long. 84°31.45′W) was followed. Samples from disturbed patches could no longer be distinguished from control samples in terms of numbers of harpacticoids 29 h after disturbance. No species became significantly disproportionately abundant during the recovery suggesting that small-scale natural disturbances are not an important organizing force in this community.

Intermediate levels of soil disturbance maximize alpine plant diversity

Abstract: The intermediate-disturbance hypothesis1–9 predicts that plant species diversity will be maximized at intermediate levels of vegetation disturbance (D). As yet, the only directly applicable data seem to be from Grime's1 study, which served more as a source of the conjecture than an independent test of it, and in which disturbance was not measured. Here I report an analysis of the relationship between soil frost disturbance and diversity of vascular plant species in Arctic–alpine fellfield vegetation in the White Mountains of interior Alaska. To study plant species diversity, a measure (SD) is calculated, which is affected by both the number of species (species richness, SR) and the evenness of their relative abundances. I show that intermediate levels of disturbance maximize SD by influencing the evenness of relative abundances, but not the overall number of species. Because disturbances caused by soil frost action and animals are frequent in many Arctic and alpine tundras, these results imply that disturbance could be an important factor in species diversity differences within and between tundra vegetation types. If theoretical predictions1–9 are confirmed by dynamic tests now under way, the theory could be applied to problems of tundra vegetation management such as revegetation and disturbance by trampling and vehicles.

Process Studies in Succession

Abstract: As the remainder of the chapters demonstrate, process studies of disturbance and succession are carried out on a number of different levels of ecological organization. Despite this diversity of approaches, however, none of these studies systematically addresses the importance of nutrient cycling processes in succession, and none directly discusses the possible contributions that ecosystem-level process studies can make to the understanding of plant succession (McIntosh 1980a, Chapter 3). Further, while all of the studies demonstrate the important of disturbance, only one provides a systematic framework by which disturbance may be characterized. Accordingly, we shall begin this chapter with a brief discussion of some of the interactions of ecosystem-level nutrient cycling with successional vegetation change. We shall then examine some of the general properties of disturbance regimes.

State-Space Models of Gravity Disturbance Gradients

Abstract: State-space models of gravity disturbance gradients are needed to design the Kalman filters used for gradiometer-aided inertial navigation. However, the physics of the gravity field guarantee that many of the cross-spectral densities of gravity disturbance gradients are nonrational. A procedure is demonstrated for fitting gravity disturbance correlation functions with finite-dimensional state-space models.

A critique of the disturbance theory of indeterminacy in quantum mechanics

Abstract: Heisenberg'sgendanken experiments in quantum mechanics have given rise to a widespread belief that the indeterminacy relations holding for the variables of a quantal system can be explained quasiclassically in terms of a disturbance suffered by the system in interaction with a quantal measurement, or state preparation, agent. There are a number of criticisms of this doctrine in the literature, which are critically examined in this article and found to be ininconclusive, the chief error being the conflation of this disturbance with the projection postulate. We present a critique of the disturbance theory based on the fact that the required disturbance will in general depend on the interaction time of the system and state-preparer. This point is exploited in the construction of a spin-interaction model which acts as a counterexample to the disturbance doctrine, while remaining faithful to the spirit of Heisenberg'sgedanken experiments. Several consequences of this result are discussed.

Psychiatric Disturbance in Mentally Handicapped Patients

Abstract: strual exacerbation of symptoms occurring at other times may indicate a premenstrual component. Dr Dalton insists that these women are not premenstrual sufferers but it is not at all clear on what grounds, clinical, hormonal or therapeutic, she advances this distinction. She must surely know too that symptom ratings in the various cycle ratings repeatedly show highand significant correlations from phasetophase, (Moos, 1969; Halbreich and Kas, 1977; Taylor, 1979). There are significant correlations too between ratings of dysmenorrhoea and premenstrual affective symp toms, premenstrual somatic symptoms and pre menstrual pain. Dr Dalton herself is clearly aware of the difficulty, for elsewhere she has drawn our attention to those †̃¿ unlucky sufferers' whose symptoms †̃¿ start a ovu lation, increase in severity during the premenstruum and resolve gradually during menstruation leaving only a few days in which good health is enjoyed' (Dalton, 1975). Indeed, one of the earliest papers on the subject, by herself and Dr Raymond Greene, (Greene and Dalton, 1953), so defined the syndrome as to include just such cases. Reproving Dr Sampson for using a definition which Dr Dalton herself pro vided over 20 years ago seems, if I may be permitted an indelicacy, a little below the belt. However, Dr Dalton does raise an interesting point when she doubts the wisdom of equating reporting with complaining. She is right to be cautious. A recent study of over 500 women attending GPs found that 95 per cent reported some kind of somatic, affective or behavioural change premenstrually (Clare, in prepar ation). Such changes appear ubiquitous and merely eliciting their presence tells us nothing. Nor, however, can one simply rely on the fact that women present for treatment, without knowing more than is usually provided about how they come to identify themselves as †̃¿ ill' and how they differ, if they do differ, from women who do not come forward. My one reservation concerning Dr Sampson's work relates to her use of sine curves in analysing the data from the diaries. Such a method presupposes a symmetry within the menstrual cycle such that the portion of the cycle in which the woman scores highly on individual symptoms is equal to the portion of the cycle in which she scores low, which is not necessarily so. It also presupposes a dip in symptom scores with a minimum score at some point in the cycle. A more appropriate approach, and one that fits the reality of symptom variation throughout the premenstrual sufferer's cycle, involves fitting poly nomials to the scores obtained on individual symp toms or factors and examining for significance of the resulting fit using the F-test, as in fitting a regression line. I doubt, however, if my reservation affects Dr Sampson's overall result. Dr Dalton may insist that †̃¿ progesterone is the specific treatment for premenstrual syndrome' but the fact remains that in the twenty years since this claim was first made, not a single properly controlled trial has shown it to be signi ficantly superior to placebo nor to the many other treatments, such as pyridoxine, diuretics, monoamine oxidase inhibitors and bromocriptine, on whose behalf others argue as enthusiastically as Dr Dalton argues for progesterone.

Issues in the Education of Emotionally Disturbed Children

Abstract: Major issues facing educators and clinicians in the field of emotional disturbance in children and youth are centered around providing appropriate services to this population Three major problems

Tephrochronology and its Application to Problems in New-World Archaeology

Abstract: Quaternary tephra layers abound in the Americas, especially in the western and central part. Few of them have been examined in detail. At present, New-World archaeologists use tephra horizons mainly as marker beds for correlation purposes and, where the local tephra sequence has been dated, as rough age indicators for their sites. They are beginning to realize the importance of tephra deposits as: (1) thick caps of sediment that can protect artifacts from disturbance and plunder; (2) indicators of ancient natural disasters; (3) potential sources for radiometric dates; and (4) material suitable for the application of approximate dating methods. Case histories from El Salvador, Central Mexico, and the Pacific Northwest are presented to demonstrate how useful tephra layers are to archaeologists.

Regional adjustment of inertial gravity disturbance vector measurements by optimal two-dimensional smoothing

Abstract: A two-dimensional signal processing algorithm is developed to obtain smoothed estimates of the gravity disturbance vector from vector measurements obtained by an inertial surveying system. The method differs from a conventional least squares regional adjustment of such measurements in that it accommodates a signal model in the smoothing process. Using principles from the physical theory of geodesy, it is shown that for a local region on the surface of the earth, an appropriate signal model is obtained by applying the two-dimensional Laplacian operator to a function representing the surface disturbance potential and equating the result to spatial white noise. The model of the vector measurement is the three orthogonal spatial derivatives of a three dimensional disturbance potential evaluated at the surface contaminated by additive white noise. The problem of simultaneous smoothing of all the gravity disturbance measurements from all survey traverses in the region is solved by representing the surface disturbance potential by a two-dimensional Karhunen-Loeve expansion that makes no specific reference to either the geometry or the ordering of the parameter space, thereby making no assumptions of causality, stationarity or isotropy. The problem of estimating the gravity anomaly and the two vertical deflection components reduces to estimating the Karhunen-Loeve coefficients which are uncorrelated and rapidly converging. Simulation results as well as smoothing of actual gravity disturbance vector measurements obtained by the U.S. Army Engineer Topographic Laboratories (USAETL) with the Rapid Geodetic Survey System (RGSS) at the White Sands Missile Range (WSMR) are presented in the paper. An analysis of these results shows that the optimal two-dimensional smoother obtains a performance benefit relative to conventional regional least squares by a factor of 2 and a benefit relative to single-traverse smoothed results by a factor of 4.

Disturbance of underground wilderness in karst caves

Abstract: Karst cave systems comprise very fragile ecosystems, each one of which is unique according to cave form and location. Any alteration to the form and/or to the atmosphere or the overlying surface and catchment area has repercussions throughout the ecosystem, which are detrimental to the cave to a greater or lesser degree. Four major types of disturbance are considered, and some implications for the successful management of the cavern environment are alluded to.

Detecting emotional disturbance with the Comrey Personality Scales.

Abstract: Previous investigations have provided evidence for the efficacy of Comrey Personality Scales in discriminating between emotionally “abnormal” and “normal” groups. These correlations are believed to have been attenuated by the presence of emotionally disturbed individuals in the “normal” groups. The Comrey Personality Scales and two questionnaires containing items on life adjustment and marital adjustment were administered to a new sample of “normals.” Substantial correlations between Comrey scales and these criteria of adjustment were found, confirming the hypothesis that Comrey scales are useful for detecting emotional disturbance. These results also support the hypothesis that past correlations between these scales and “abnormal” vs “normal” criteria have been attenuated by the presence of abnormals in the “normal” groups.