Ecosystem theory--论文代写范文精选

在美国最大城市的构成人群,在温和的观点来说,国家生态对新出现和重新出现的问题,如传染性的传播行为与慢性疾病。这里我们将扩展规模分析，对于城市种族隔离制度影响个人健康和健康行为,特别是免疫系统。下面的paper代写范文进行详述。

ABSTRACT
Holling [31] has argued, since most ecologies are nested hierarchies, that a relatively few processes, having distinct frequencies in space and time, structure ecosystems, entrain other variables, and set the rhythm of ecosystem dynamics at other scales. A critical feature of such hierarchies is the asymmetric interactions between levels. In particular, the larger, slower levels maintain constraints within which the faster levels operate. In that sense, then, slower levels control faster ones, but, in the context of a loss of ecological resilience at the larger scale, faster processes can affect slower ones by means of their ‘brittleness,’ a concept explored at more length for human populations below and in several other papers of this series (e.g. [32]). In Holling’s view [31], ecosystems are structured hierarchically by a small number of underlying processes into a small number of levels, each characterized by a distinct scale of ‘architectural’ texture and of temporal speed of variables. Each of the small number of processes influencing structure does so over limited scale ranges. The temporal and architectural structure of discrete ecosystem components are determined by three broad groups of processes, each dominant over different ranges of scale: micro, meso and macro. 10 According to Holling [31], the meso scale plays a particularly critical role. 

There, distinct disturbance phenomena are triggered at thresholds of tens of meters to kilometers. These driving variables of disturbance form the kind and amount of structure found at mesoscales by causing local events to cascade upward in scale to affect much larger landscape patterns. Analysis of the function of mesoscale process and structure thus provides the bridge between individual and global dynamics. The mesoscale of human ecosystems is the neighborhood. Elsewhere we have explored how vulnerable neighborhoods of marginalized communities in the largest US cities constitute ‘keystone populations,’ in Holling’s sense, for the national ecology of emerging and re-emerging infection (e.g. [33]), and more recently, in the spread of contagious behaviors associated with chronic disease [34]. Here we will extend this analysis downward in scale to examine some of the ways in which neighborhood structuring by the US system of de-facto urban Apartheid affects individual health and health behavior, in particular the decision of a developing immune system to adopt a predominant Th1 or Th2 phenotype.

Recent collapse of US minority urban neighborhoods 
By 1980 large US urban minority neighborhoods – the keystones for public health at both larger and smaller scales – had begun to reflect a relentless siege by forces ranging from ‘urban renewal’, to contagious urban decay, ‘planned shrinkage,’ and the effects of deindustrialization. We recapitulate something of that history. Urbanization of African Americans began at the start of the 20th Century. Small numbers migrated to Northern cities, and established themselves as “succession” communities in neighborhoods that had housed other ethnic groups seeking entry into American urban life. Gradually these urban communities expanded, incorporating later waves of immigrants, among them many who were forced out of agricultural work because of the mechanization of the farms. The integration of these newcomers into urban life was slow, yet the communities grew in complexity and organization, gaining political and economic power along the way [35]. 

As noted earlier, a series of policies hostile to poor urban neighborhoods undermined their physical and social infrastructures. In the most serious cases, urban renewal obliterated whole communities, which simply ceased to exist. Later policies of systematic disinvestment, including planned shrinkage, led to gradual destruction of individual buildings, and the outbreak of 11 widespread contagious urban decay which undermined wholesale the built environment. In either case, the functioning of social groups was fatally compromised by the alteration of the built environment within which they were embedded. In the case of Harlem, New York, an important African American community, a stage/state model has been proposed to describe community disintegration [36]. The model assumes a range of possible states of community organization, from the highly integrated “model community” at one end, to the very disintegrated “collection of individuals” at the other. 

The stage/state model postulates that communities are not statically set at a single point on this range. Rather, they are dynamic entities, constantly working to maintain internal organization. External stressors, such as a war, loss of employment in the community, outbreaks of contagious urban decay or epidemic disease, can destabilize a community and trigger its decomposition. The Stage/State Model postulates that the transformation from “model” to “collection” follows a spiral pathway, in which each turn of the spiral is triggered by a destabilizing event. Three turns of the spiral are proposed for Harlem. The first stage follows the initial loss of housing and is characterized by confusion in the population. Efforts were undertaken to reorganize the community, but the failure to rebuild the urban infrastructure created a barrier to full recovery. In the case of Harlem, further destabilization was caused by several factors, including the loss of manufacturing jobs and further loss of housing. 

This second stage was characterized by increasing disorder in the population. Along with the increase in disorder was an increase in the use and sale of psychoactive substances, and a decline in social controls on violence and related behaviors. The growing use of drugs, licit and illicit, was accompanied by a shift in social relationships. Drug behaviors, which had been confined to designated areas, were able to occupy more and more territory. The effects on family life were magnified. The likelihood of family trauma, family dysfunction and family separation increased dramatically. Although in previous eras the ‘home’ and the ‘street’ had been carefully separated from each other, with increasing community disintegration, the ‘street’ was able to invade the territory of the ‘home.’ 

This prepared the way for the incursion of crack cocaine in the mid- 1980’s [37-40]. The crack epidemic was extremely violent. Addiction to crack was very disabling, and involved a very large number of women. Both the noxious effects of crack, and the loss of the community-building efforts of women, contributed to further destabilization of the community, a stage characterized by ‘non-sense’ in the population. In this stage, it was common to observe scenes that were frankly unreal by any measure of life prior to the arrival of crack cocaine. At each level of scale – the personal, the family, the small group and the community – sharp changes in attitudes and behaviors have been documented. The exposure to trauma and violence has left psychological scars on a large portion of the population [41, 42]. 

The collapse of social relationships has increased the weight on individuals, as well as the sense of ‘individualism.’ The failure of group institutions has eroded the group power to contain and order behavior in public places. Further, behavior in public places has overwhelmed the interdiction to enter the home. The atomization of the population is one factor contributing to a marked loss of political participation and political consciousness among the population. The increasing political weakness of the group leaves it more vulnerable to majority decisions that are not in the best interest of the community. The siting of noxious facilities in vulnerable, disintegrating communities is one example. The argument presented here suggests that the experience of history has altered the functioning of the socio-geographic community of Harlem, and created heavy social, political and emotional burdens for all residents. The future course of individual and group life will be build from the experience of disintegration: the downward spiral towards non-sense thus sets the pathways to the next stage. The story of Harlem illustrates the experience of virtually every large African-American and Puerto-Rican urban community since the end of World War II. By 1980 this disruption had contributed materially to the milieu of ‘structured stress’ which has entrained immune development and function for many, if not most, community residents.

Discussion and conclusions 
Our approach, implicitly, extends Cohen’s vision of immune cognition one step by allowing day-to-day immune function to be ‘renormalized’ or ‘integrated’ into a longer-term developmental process, resulting in a ‘higher order’ cognitive decision regarding the binary shift from Th2 to Th1 immune phenotype. This is the ‘initiating event’ in the chain of causality resulting in asthma. It seems likely that a second iteration of our theory would be required to understand the ‘promoting process’ by which children with atopic phenotype are driven to asthma. This work remains to be done, but we might speculate that, once a Th2 phenotype has been expressed, a second iteration could involve a leptin-cortisol-modulated or driven switch between phenotypes expressive of specific immunoglobin G (IgG) vs. specific immunoglobin E (IgE) antibodies, IgE being the most characteristic ‘asthma antibody’. 

In essence, we propose that an immunocultural condensation affects such ‘higher order’ processes as well, so that the cognitive functioning of the embedding sociocultural network becomes coevolutionarily condensed, in a large sense, with immune developmental cognition, and with the subsequent ‘promotion’ to explicit asthma. Although some mathematical details of such ‘renormalized cognition’ are discussed in the Appendix, further theoretical development will clearly be necessary. A structured pattern of externally-imposed sociocultural or socioeconomic driving stressors has, at the population level, clear grammar and syntax: certain intercorrelated patterns of abuse and injustice are recognizable and ‘make sense’ within the system of American Apartheid, others do not. We have, for example, moved beyond mass killings and slave auctions, no small matter. 

As the Appendix shows, in some detail, the population-level ‘language’ of externally-imposed stress can very suddenly become closely coupled with the ‘language’ of sociocultural cognition in a kind of ‘phase transition’ to form a coevolutionary condensation. It is this joint object which then forms the embedding milieu for a child’s developing immune system. We claim that policies and practices of urban renewal and planned shrinkage affecting urban minority communities had, by 1980, interacted with the outfalls of a massive deindustrialization driven in no small part by the diversion of engineering and scientific resources into the Cold War [e.g. 43]. This synergism greatly affected community sociocultural networks, triggering a literal phase transition in their function, so that the externally-imposed structured stress became quite literally a part of the ‘higher order’ immune cognition associated with development, and rapidly expressed itself in a rising proportion of ghetto children who develop the atopic phenotype.

The mechanism may well enter into a feedback with similarly driven leptin-cortisol cycle dysfunctions leading to excessive weight gain. Sociocultural phase transitions, like many such, are likely to be difficult to reverse, and may be subject to a path-dependent ‘hysteresis’, requiring far more than the simple removal of the triggering structured stress to reverse Information-theoretic phase transitions may, then, tend to persist even when the conditions which triggered them are ameliorated. This is, essentially, because the internal grammar and syntax of an information source ‘makes sense,’ and the making-of-sense tends to be conserved in time and resist change. Elsewhere we have made a quantitative argument regarding such matters, in the character of ‘generalized Onsager relations’ [20-25]. Change, when it occurs, may, however, be very sudden. Thus corrective interventions against certain classes of problem – like the rise of asthma in minority urban communities – may not seem to work for a very long time, and will likely need to be highly proactive. The foremost intervention, of course, would be to significantly change the system of ‘structured stress’ which is the driving force behind the ‘asthma epidemic.’ Programs, policies and practices which further destabilize urban minority communities will likely exacerbate asthma and related patterns of chronic disease.

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