Benign Disturbance Research Articles

Flight responses of eastern gray kangaroos to benign or harmful human behavior.

Globally, wilderness is being converted for rural and agricultural land use. In countryside landscapes, many habitat structures remain intact, providing suitable habitat for wildlife species that can accurately assess novel risks and develop tolerance to benign disturbances. Associative learning that promotes avoidance and also facilitates desensitization to benign disturbance is key to persisting in these landscapes. Conversely, learning to distinguish and avoid negative interactions with humans, like hunting, is vital. To determine if eastern gray kangaroos are capable of learning from previous interactions with humans, we tested the flight responses of wild kangaroos which have previously experienced either low or high frequencies of harmful and benign encounters with humans. We found that eastern gray kangaroos rapidly habituated to benign disturbance as there was no significant difference in assessment distance between groups that previously experienced low or high frequencies of disturbance. The threat of harmful disturbances was not as quickly learnt, as groups that experienced low frequencies of harmful disturbance delayed flight longer than those experiencing frequent harm. We found that the influence of environmental and group parameters on a kangaroo's decision to flee depended on the intent and frequency of previous interactions with humans. Our study indicates that kangaroos are learning from previous encounters with humans, correctly assessing novel risks which may be contributing to their persistence in countryside landscapes.

Instability wave-streak interactions in a supersonic boundary layer.

Optimal initial conditions for transient growth in a two-dimensional boundary layer flow correspond to stationary, counter-rotating vortices that subsequently develop into streamwise elongated streaks, which are characterized by an alternating pattern of low and high streamwise velocity. For incompressible flows, previous studies have shown that boundary layer modulation due to streaks below a threshold amplitude level can stabilize the Tollmien-Schlichting instability waves, resulting in a delay in the onset of laminar-turbulent transition. In the supersonic regime, the linearly, most-amplified waves become three-dimensional, corresponding to oblique, first-mode waves. This change in the character of dominant instabilities leads to an important change in the transition process, which is now dominated by oblique breakdown via nonlinear interactions between pairs of first-mode waves that propagate at equal but opposite angles with respect to the free stream. Because the oblique breakdown process is characterized by a rapid amplification of stationary streamwise streaks, artificial excitation of such streaks may be expected to promote transition in a supersonic boundary layer. Indeed, suppression of those streaks has been shown to delay the onset of transition in prior literature. Consistent with those findings, the present study shows that optimally growing stationary streaks indeed destabilize the first-mode waves, but only when the spanwise wavelength of the instability waves is equal to or smaller than twice the streak spacing. Transition in a benign disturbance environment typically involves first-mode waves with significantly longer spanwise wavelengths, and hence, these waves are stabilized by the optimal growth streaks. Thus, as long as the amplification factors for the destabilized, short wavelength instability waves remain below the threshold level for transition, a significant net stabilization is achieved, yielding a transition delay that is comparable to the length of the laminar region in the uncontrolled case.

Benign neonatal sleep myoclonus

Benign neonatal sleep myoclonus (BNSM), first described in 1982 by Coulter and Allen [1], is the non-epileptic condition most frequently confused with epileptic seizures during infancy. The etiology is uncertain: transient dysfunction of the serotoninergic system, a benign disturbance of the brainstem reticular activating system involved with initiation and synchronization of sleep and a genetic predisposition have been suggested by some authors. However none of these mechanisms has been proved [1,2]. The prevalence is also unknown, but it is thought that the condition is under-recognized. It was first described in three boys and in most subsequent publications, the condition was more commonly described in boys. Very recently, it has been shown that BNSM is extremely frequent in the newborn offspring of opiate-dependent mothers [3]. Myoclonic jerks usually present within a few days of birth. In a detailed study of 38 patients with BNSM the jerks appeared within the first 16 days, (median 3 days) and remitted in the first 10 months (median 2 months) of life [4]. It is usually said that the jerks disappear by the age of 3 months, but Egger et al. [5] demonstrated that the condition could persist for months and years. In the first description of BNSM myoclonus was reported to be bilateral, synchronous, and to mainly involve the distal parts of the upper extremities, with flexion of fingers, wrist, and elbow [1]. It is usually de-

Disturbance and productivity as codeterminants of stream food web complexity in the Arctic

Disturbance and productivity are potentially interacting factors often thought to underlie the complexity of aquatic food webs. We tested predictions about the effects of disturbance (bed movement, total water column freezing) and productivity (as indicated by primary consumer biomass) on the structure of 19 stream food webs in arctic Alaska. We predicted that food webs subject to high levels of disturbance would have low connectance, low linkage density, and short food chains, while food webs of streams with more benign disturbance regimes would be more complex (i.e., a test of the “dynamic stability hypothesis”). We further predicted that food chain length would increase with productivity (i.e., testing the “resource‐availability hypothesis”). Connectance and linkage density were negatively related to bed movement but not to freezing. Food chain length was related to freezing but not to bed movement or productivity. The relationships among food chain length, freezing, and productivity were driven by the occurrence of fishless streams, which all froze during winter. Streams containing fish had longer food chains than fishless streams, and food chain length was positively related to productivity only when fishless streams were removed from analyses. Our results show that disturbance and productivity are codeterminants of stream food web complexity in the Arctic. Our data further suggest that colonization dynamics are an important factor controlling food web structure, highlighting the importance of idiosyncratic habitat and life history related factors that are often overlooked in theoretical studies.

Osgood-Schlatter Disease: Practical Treatment for a Self-Limiting Condition

Osgood-Schlatter disease is one of the most common causes of knee pain in active adolescents. It is a generally benign disturbance at the junction of the patellar tendon and the tibial tubercle apophysis, and treatment during its 12- to 24-month course should be matched to severity. Mild symptoms require only patient education and moderation of activity, but severe symptoms call for a period of rest (or, rarely, immobilization) followed by aggressive quadriceps strengthening. Other conditions such as Sinding-Larsen-Johansson disease may occur simultaneously, and long-term effects can include a prominence on the anterior knee or painful kneeling.

Benign and disruptive disturbances of the supervisory field

Inspired by Baranger, Baranger and Mom’s notion of psychoanalytic bastion, we describe an unconscious collusion between analytic supervisors and supervisees. This collusion’s purpose is to avoid the anxiety inherent in the psychoanalytic field and that enters unprocessed into the supervisory field. The supervisor/supervisee dyad’s emotional experience can be fleeting, with moderate intensity, but can slow down the process. This can happen sometimes in any supervisory situation. Or it can become permanent and with greater intensity and bring the entire process to a standstill and to a disruption of the supervisory field. We call the first situation a ‘benign disturbance of the supervisory field’, the second a ‘disruptive disturbance of the supervisory field’. We illustrate both disturbances using supervisory material. Our purpose is to show how to detect these disturbances, understand them, and manage them.

Frequency information in the vibration-cued escape hatching of red-eyed treefrogs

Incidental acoustic and vibrational cues generated by predators are a potential source of information for prey assessing risk. Substrate vibrations should be excited by most predators, and frequency, amplitude or temporal properties could allow prey to distinguish predator from benign-source vibrations. Red-eyed treefrog embryos detect egg predators using vibrations excited during attacks, hatching rapidly and prematurely to escape. We recorded vibrations in egg clutches during attacks by five species of predators and three common types of benign physical disturbance. We analyzed their frequency distributions to assess if and how frequency properties could be used to discriminate between vibration sources and used vibration playbacks to examine the effects of frequency properties on the escape hatching response. Vibrations produced by predators and benign disturbances generally have broad and overlapping frequency distributions, and all frequencies excited by attacks are also excited by benign disturbances. Decision rules based on the frequency distribution of vibrations alone would therefore result in either high levels of hatching in response to benign vibrations (false alarms) or common failures to hatch in response to predators (missed cues). Nevertheless, embryos hatch in response to predator and not benign disturbances in nature, and our playback results show that vibration frequency information is an important component of their hatching decision. Embryos combine frequency with temporal information to refine their hatching response. Moreover, comparing frequency spectra of predator and benign vibrations suggests that the presence of energy in frequencies outside the range characteristic of attacks might serve as an indicator of benign disturbance.

Predator transitions in stream communities: a model and evidence from field studies

The role of predators (particularly top predators such as fish) in structuring stream communities has been debated for 2 decades. Much of the debate may have been caused by the lack of a conceptual framework for evaluating predator effects in stream communities. First, I propose a general conceptual model of the factors (abiotic, such as stream permanence and disturbance regime; biotic, such as predation) that can influence community structure, and the conditions in which these various factors would be expected to be important. Hydrologic permanence and disturbance transitions separate streams where abiotic factors are most important in determining community structure from streams with relatively benign disturbance regimes where predation may be more important. Second, I focus on the potential effect of predators in perennial streams with relatively benign disturbance regimes. Such streams are divided longitudinally into sections where different types of predators might be important in determining community structure. Large invertebrates (stoneflies, dragonflies, shrimp, and crayfish) and salamanders may be the dominant benthic predators affecting species composition in small perennial fishless streams. A transition from invertebrate- and amphibian-dominated to fish-dominated systems may occur in larger, downstream sections (predator transition 1). In addition, longitudinal transitions in fish-assemblage structure from upstream tributaries to downstream main-channel fish assemblages (predator transition 2) may affect community structure. I present evidence supporting the above model and suggest experimental approaches to test the model. This conceptual framework may help in understanding the role of specific predators in determining prey distributions in many stream communities.

Temporal pattern cues in vibrational risk assessment by embryos of the red-eyed treefrog, Agalychnis callidryas

The embryos of red-eyed treefrogs, Agalychnis callidryas, use vibrations transmitted through their arboreal egg clutch to cue escape hatching behavior when attacked by egg-eating snakes. Hatching early increases the risk of predation in the water, so embryos should avoid it unless they are in danger. We exposed egg clutches to intermittent vibrations with different combinations of vibration duration and spacing to examine the role of simple temporal pattern cues in the escape hatching response. Stimuli were bursts of synthetic white noise from 0 to 100 Hz, including the range of frequencies with substantial energy in snake attacks, and had approximately rectangular amplitude envelopes. Embryos hatched in response to a small range of temporal patterns and not in response to many others, rather than hatching to most vibrations except for certain patterns perceived as safe. Neither cycle length nor duty cycle predicted hatching response, except at extreme values where no hatching occurred; the highest energy stimuli elicited little or no hatching. Both vibration duration and inter-vibration interval strongly affected the hatching response. The highest levels of hatching were to durations of 0.5 s combined with intervals of 1.5-2.5 s, and hatching decreased gradually with increasing difference of either duration or interval from these most effective stimuli. Vibration duration and interval appear to function as two necessary elements of a composite cue, rather than as redundant cues. This increases response specificity and reduces the range of stimuli that elicit hatching, likely reducing the chance of hatching unnecessarily in a benign disturbance. Vibration-cued hatching in A. callidryas embryos offers an opportunity to experimentally assess the behavioral decision rules underlying an effective and costly anti-predator defense.

The Louisiana Purchase, Expansion, and the Limits of Community: The Example of Arkansas

GIVEN THAT THE GREAT INNER CORE of the North American continent, called for a recent moment of its long history the Louisiana Purchase, has been for the past two centuries one of the most exploited spots on the face of the earth-chopped, sprayed, drained, filled, stripped, and ripped to the full limit of the human capacity to do these things-one hesitates to disturb it yet again. But this will be a relatively benign disturbance, limited in space and time to the small part of it that became the Arkansas Territory, harmless to the area and yet useful, one hopes, to our understanding of an important aspect of the American republican experiment. The plan here is to try to learn something about a very grand subject-the theory and practice of republicanism-through a case study of a rather modest area. To begin with the grand: part of the general restructuring necessary to the emergence of modern Western societies was both a reconception and a redefinition of the concept of community. Kinship linkings, the necessarily quite local standard that had served for centuries to define community, had to be supplemented by a standard that would allow for the creation of much larger communities. Community now pushed far beyond family connections. This created problems everywhere, but some of the most interesting ones appeared in the British colonial system. There, through a naturalization procedure authorized by Parliament in the late colonial period, persons routinely excluded from other colonial systems could find their way into that of Great Britain (a subject of the King of France, by contrast, would find a home in the dominions of the King of Spain only under exceptional circumstances).1 As a consequence, English North America by the time of the independence movement had become a place of striking heterogeneity. Among other things, this would mean that the most common way of defining a national community, which was, fundamentally, to rely upon the webbing of a long historical homogeneity, would not work. Complicating things even was the heavy reliance upon republican theory. In a traditional European setting, the relationship between members of a national community was not too pressing a matter, for all were tied together through a common relationship to their sovereign. But as the resistance movement in English North America came to rely and heavily upon republican concepts, to the point of rejecting outright the very notion of the monarch as the link between all members of the national community, it became and necessary to define the relationship of those members in a new way: not to a monarch but to each other. This, it should be noted, was not just a matter of interest to political philosophers (although in that remarkably philosophic age that would not have made it a preoccupation as peripheral as it would in our own). Concern with the communal relationship is present in the great document of separation, the Declaration of Independence, though it is, for most readers, lost under the attack upon the king. In the Declaration's penultimate paragraph-a place of prime significance in eighteenth-century writing-Thomas Jefferson turned from the British king to the British people, declaring their apathy toward the plight of their transatlantic brethren to be a collective forfeit of the bond of community.2 But to recognize the need for a new concept of community was not to define it. To that problem, a complicated solution emerged. Clearly, only the individual colonies could come anywhere near to being the imagined of modern nationalism.3 As such, they would obviously remain, renamed as states. But other forces-the existence of a common enemy, the prospect of postwar dismemberment, the need for a unified economic system-at once exposed the need for a larger community and strengthened the basis for one. The result was the Constitutional Convention and the more perfect Union of 1787, within which, and under a redefined federalism, state and national communities would presumably enjoy a harmonious, synchronized existence. …

Effects of recreational disturbance on the foraging behaviour of waders on a rocky beach

Oystercatcher Haematopus ostralegus, Curlew Numenius arquata and Redshank Tringa totanus reacted in a variety of ways to human disturbance. They delayed arrival and departed earlier when disturbed. Vigilance (scan rates) increased with the vigour of human activity and the birds were more vigilant in the higher shore zones, but there was no corresponding decrease in food searching (peck rates). Prey capture rates of Oystercatcher and Curlew apparently increased with moderately close human disturbance. Undisturbed birds may not have been foraging at maximum rates and rested periodically during the low tide period. Characteristic avoidance behaviour elicited by disturbance differed between the species; Curlew and Redshank typically stopped feeding and, if they left, flew away, whereas Oystercatcher walked away. This difference may be related to plumage crypsis. Flight distances of all species were very low. Habituation may be an important response to regular but benign disturbance, reducing the disturbance-induced decrease in feeding time to a level which may be compensated for, at least in summer, within the normal low-tide foraging period.

Osgood-Schlatter Disease

Osgood-Schlatter disease is one brief the most common causes of knee pain in active adolescents. It is a generally benign disturbance at the junction of the patellar tendon and the tibial tubercle apophysis, and treatment during its 12- to 24-month course should be matched to severity. Mild symptoms require only patient education and moderation of activity, but severe symptoms call for a period of rest (or, rarely, immobilization) followed by aggressive quadriceps strengthening. Other conditions such as Sinding-Larsen-Johansson disease may occur simultaneously, and long-term effects can include a prominence on the anterior knee or painful kneeling.

Experimental Studies of Caribbean Seagrass Bed Development

Processes important in the development of subtidal seagrass beds composed of Thalassia testudinum, Syringodium filiforme, Halodule wrightii, and many rhizophytic algal species were examined in situ for 52 mo in a coral reef lagoon on St. Croix, United States Virgin Islands. The study emphasized the early stages of development of the seagrass beds and the role played by colonizing rhizophytic algae. I tested the hypotheses that nutrient accumulation in the sediments limits seagrass recolonization, and that rhizophytic algae facilitate sediment nutrient accumulation by stabilizing the sediments and adding organic matter from rapidly decomposing thalli. Vegetation was removed from 0.25— and 1—m2 plots in 3 m of water. Plot treatments consisted of: (1) no further manipulation, (2) adding nitrogen plus phosphorus fertilizer to the sediments, (3) removing colonizing rhizophytic algae to minimize algal effects (e.g., sediment stabilization, organic input), and (4) removing colonizing algae and adding "plastic algae" to stabilize sediments without organic input. Plant densities, sediment grain size, redox potential, inorganic nitrogen concentrations in porewaters, and ammonium production rates were measured over time in all plots, including undisturbed controls. All recolonization occurred through vegetative propagation. The sequence of plant recolonization was unaffected by the treatments, corresponding instead to life history characteristics and nutrient requirements of the species involved. Rhizophytic algae invaded the plots within a few months, followed by the seagrass Syringodium, then Thalassia. The seagrass Halodule was insignificant in the recolonization. Densities of rhizophytic algae and Syringodium declined when the density of Thalassia reached 200 leaf shoots/m2. The rates of increase in seagrass leaf shoot densities and biomass were greatest in the fertilized plots, supporting the nutrient limitation hypothesis. Rhizophytic algae facilitated seagrass recolonization; seagrass densities, biomass, and porewater ammonium concentrations were lowest in plots where algae were removed. Sediment ammonium concentrations decreased when Thalassia became dominant. Ammonium production in the sediments increased as the plant community developed. The nitrogen required for Syringodium productivity was met easily by ammonium production, assuming no competition from Thalassia. In contrast, Thalassia accounted for >93% of the nitrogen required for total seagrass productivity, and ammonium production could supply up to 45% of this requirement. At the end of the experiment (52 mo), Thalassia density and ammonium production rates in the sediments were lower than in the surrounding undisturbed seagrass bed. The experiment provides evidence for a resource—ratio model where the rate of succession is controlled by a sediment nutrient supply that increases over time. The sequence of colonization is determined by relative rates of vegetative propagation by stolons and rhizomes across the sediment surface, which are inversely correlated with whole plant productivity and thus with requirements for nutrients. Algal colonizers tolerate low nutrients by having low productivities. The climax species Thalassia is a competitive species effective at exploiting the sediment nutrient resource. Co—existence, rather than replacement, of species occurs, despite a relatively benign disturbance regime.

Petit mal epilepsy. Results of a prolonged follow-up study of 117 patients.

Since the advent of electroencephalography, it has been clearly demonstrated that all epileptic seizures of brief duration are not petit mal. It is important that the physician who cares for epileptic patients be cognizant of this fact, since the treatment and prognosis of petit mal epilepsy differ in most respects from that of other types of epilepsy. Petit mal epilepsy is primarily a disorder of childhood and seldom continues into adulthood. It is a comparatively rare type of epileptic spell: of 15,102 epileptic patients, only 364 (2.3%) had "true" petit mal epilepsy. It is a relatively benign disturbance and rarely causes demonstrable evidence of pathological cerebral changes, except in those patients who have frequent attacks of petit mal status. Since patients with petit mal epilepsy are prone to develop major seizures, concurrent administration of petit mal and major motor anticonvulsants (combined therapy) is recommended.

Petit Mal Epilepsy

Since the advent of electroencephalography, it has been clearly demonstrated that all epileptic seizures of brief duration are not petit mal. It is important that the physician who cares for epileptic patients be cognizant of this fact, since the treatment and prognosis of petit mal epilepsy differ in most respects from that of other types of epilepsy. Petit mal epilepsy is primarily a disorder of childhood and seldom continues into adulthood. It is a comparatively rare type of epileptic spell: of 15,102 epileptic patients, only 364 (2.3%) had "true" petit mal epilepsy. It is a relatively benign disturbance and rarely causes demonstrable evidence of pathological cerebral changes, except in those patients who have frequent attacks of petit mal status. Since patients with petit mal epilepsy are prone to develop major seizures, concurrent administration of petit mal and major motor anticonvulsants (combined therapy) is recommended.