Community conditioning hypothesis

Matthews, R.A., Landis, W.G. and Matthews, G.B. (1996) The community conditioning hypothesis and its application to environmental toxicology. Environ Toxicol Chem 15 597—603. 

The pollution prevention principle presupposes that all environmental pressure is potentially harmful. Conservative approaches are necessary to protect the environment because multiple stressors due to the presence of low concentrations of more than one substance or unexpected effects of metabolites (e.g., hormone disruption) can never be excluded. This opinion is in line with the community conditioning hypothesis (Matthews et al. 1996), which states that ecological communities tend to preserve information about every event in their history, including stress by substances. It is also in line with the rivet hypothesis (Ehrlich and Ehrlich 1981), which presupposes that each loss of a species (equivalent to a rivet in the analogy) affects ecosystem integrity to a small extent, and, if too many rivets are lost, the system collapses. 

In order to incorporate the features that we have discussed, in the latter half of this chapter Matthews, Landis, and Matthews (1996) have proposed the community conditioning hypothesis. The community conditioning hypothesis is an explicit recognition of the historical and thereby nonequilibrium nature of ecological structures. The basic precept is that ecological communities retain information about events in their history. The information can be contained in a variety of formats, from the relative frequencies of alleles or mitochondrial DNA to the dynamics of predatory-prey and competitive... 

The community conditioning hypothesis places critical importance on the historical aspects of an ecological structure in the determination of stressor impacts. Therefore, no two ecological structures will ever be the same. 

Landis, W.G., A.J. Markiewicz, R.A. Matthews, and G.B. Matthews. 2000. Confirmation of the community conditioning hypothesis persistence of effects in model ecological structures dosed with the jet fuel JP-8. Environ. Toxicol. Chem. 19 327-336. 

The design of multispecies toxicity tests runs into a classical dilemma. If the system incorporates all of the heterogeneity of a naturally synthesized ecological structure, then it can become unique, thereby losing the statistical power needed for typical hypothesis testing. If multispecies toxicity tests are complex systems and subject to community conditioning, then the tests are not repeatable in the same sense as a single-species toxicity test or biochemical assay. 

A corollary is that almost all stressors leave lasting impacts and that the information is located in a variety of biotic and abiotic components. The hypothesis states that ecological structures are historical, unique, and complex. The hypothesis explicitly recognizes the importance of indirect effects in retention of information within systems and in impacting the outcomes of future stressor events. These features place community conditioning in opposition to equilibrium-based or threshold models prevalent in ecological risk assessment and environmental toxicology. 

So far we can conclude that it is possible to describe intentions in communicative acts with the help of qualitative changes in movements. Yet it is still unclear which changes are present, because MED only crudely describes qualitative changes on a holistic level. Single movement features are not captured by this method. Yet our hypothesis is confirmed that under high risk conditions, communicative acts are forced to a level where it is only difficult to assess them with generic coding methods. This situation has lead us to a series of new developments which we currently pursue. 

To illustrate the WoE approach we will apply it to the evaluation of toxicity as a cause or risk factor in the alteration of benthic community structure in a waterway (Figure 12.11). Extensive data on chemical concentrations in sediments are obtained at the site under investigation (A). Data on the chemical contaminants are matched with laboratory tests of sediment toxicity to the chemicals (B). A comparison of the chemical concentrations to the toxicity data indicates that the materials are toxic under laboratory conditions (C). A hypothesis is then generated that identifies the sediment under consideration as likely to be toxic. Sediment bioassays of the sediment can confirm the hypothesis (D). Since the assessment endpoint is the preservation of benthos, measurements are made of the benthic community structure in the region (E). Chemical concentrations and toxicity results are also compared to measures of benthic community structure. Chemicals that are positively associated... 

In particular, it has been suggested that chlorophyll concentrations in the euphotic zone at stations Climax and ALOHA document the impact of PDO, and specifically the climate shift of 1976-77 on oligotrophic gyre productivity (Karl, 1999 Karl etal., 2001b). The current hypothesis suggests a shift from a eukaryotic phytoplankton community to one dominated by nitrogen-fixing prokaryotes. The shift to prokaryotic dominance is caused by physical conditions... 

Our discussions with colleagues indicate that there is a wide range of opinions in the community on these issues. On one end of the spectrum is the desire to use our best understanding of proxies calibrated against modern or recent conditions to produce the quantitative estimates and uncertainties of paleoclimatic conditions desired by modelers and policy-makers. On the other end is the worry that we cannot assess the uncertainties because the uniformitarian hypothesis of time-invariance of the calibration is inherently untestable instead, we might focus on producing consistent interpretations, multiparameter reconstructions of likely conditions, or some other less-precise or less-quantitative though perhaps still-useful interpretation of the paleoclimatic data. 

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