What is the Body s Physiological Response to Continuous Stress Which Includes Three Phases

Vulnerability of Ecosystems to Climate

C. Boisvenue , S.W. Running , in Climate Vulnerability, 2013

4.12.1.2.3 Physiological Interactions

Physiological responses to changes in environmental conditions are highly dependent on the limiting factors of a particular site to forest growth, which, may vary seasonally for the same location. Some studies have found exponential decreases in productivity with decreased water availability ( Webb et al. 1983); others confirm strong correlations between precipitation and productivity (Fang et al. 2001; Knapp and Smith 2001). However, the relationship between productivity and precipitation is not always obvious at finer temporal or spatial scales, e.g., the correlation between interannual variability of both precipitation and productivity levels is not always strong (Brando et al. 2010). This is due to the multiple role of water in metabolic plant activity and in ecosystem level processes such as decomposition and mineralization.

Increasing temperature, which has been shown to have a positive effect on productivity (e.g., Toledo et al. 2011), also increases vapor pressure deficit of the air, thereby increasing transpiration rates. This results in adverse effects on drier sites in summer, unless stomata close in response to other changes, such as an increase in CO₂. Increases in night temperatures, if they exceed increases in daytime temperature, can also reduce stomatal conductance (Kirschbaum 2004). Some tree species seem to be able to alter certain traits in response to environmental conditions. One important trait that exhibits some plasticity is water use efficiency (WUE) (Bergh et al. 2003; Gagen et al. 2011). Physiological traits, such as number of stomata, WUE, and foliage light-use efficiency are thought to vary across ecosystem types, and even within a single tree canopy, but how these traits vary across species and time scales is still under debate (Nichol et al. 2002; Guo and Trotter 2004; Lagergren et al. 2005). In a subsequent section, we give an overview of the observed and modeled physiological responses to changing conditions, including changes in traits.

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Environmental Tolerance

Ü. Niinemets , F. Valladares , in Encyclopedia of Ecology, 2008

Physiological versus Ecological Optimum Ranges

The physiological response curve ( Figure 1 ) describes potential organism distribution limits along an environmental factor or resource gradient in the absence of competition by other species. However, the response of species growing intermixed with other species, the ecological response, is often different from the potential physiological response. For instance, different plant species can have similar optimum ranges for limiting soil resources such as phosphorus and nitrogen. In general, the optimum ranges for N and P are very high, often much higher than the availability of these nutrients in natural environments even for species generally considered characteristic to low-nutrient sites ( Figure 2a ). However, the species markedly differ in the efficiency of nutrient use, defined as the amount of biomass produced per unit nutrients taken up. Species with higher nutrient-use efficiency can achieve a greater share of soil nutrient resources and outcompete the species with lower nutrient-use efficiency ( Figure 2b ). At the same time, minimum nutrient concentrations are generally higher in plants with inherently large growth rates, and therefore the tolerance of nutrient deficiencies is lower for these species. This mechanism can explain why plant species with similar physiological optimum ranges for nutrients exhibit distinct differentiation along nutrient availability gradients ( Figure 2b ).

Analogously, interspecific differences in light-use efficiency can affect plant response to shade and high light. Many plant species can potentially colonize a wide range of light environments in the complete absence of competition, but there is a distinct separation of species along natural light gradients due to species differences in the efficiency of the use of either low or high light. Tree shade tolerance as defined in forestry textbooks and used to predict the succession of forest communities is not an absolute minimum light requirement, but a relative term that characterizes plant ecological tolerance to low light in multispecies forest stands.

Tolerance also varies with plant developmental stage. It is well-known that juveniles are more vulnerable to stressful conditions such as drought or heat than adult plants, while young woody plants can tolerate low light availability in the understory better than older plants that have larger amount of support structures relative to unit foliage biomass. These examples collectively illustrate the caveats of employing species physiological tolerance limits estimated commonly with young plants in predicting species distribution.

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Marine Life

Douglas Wartzok , in Encyclopedia of Ocean Sciences (Third Edition), 2019

Behavioral Responses

The behavioral and physiological responses of marine mammals to sound are affected by multiple factors: characteristics of the sound, such as frequency, rise time, intensity and energy; behavioral state of the marine mammal such as feeding, resting, migrating, or socializing; age; gender; season; location; prior exposure; and individual variation ( Ellison et al., 2011). In most cases, the limit of auditory detectability will be the threshold for any response. If a sound is above the background level and above the auditory threshold at a particular frequency, then the animal can detect that sound. Beluga whales (Delphinapterus leucas) detect the return of their echolocation signal when it is only 1   dB above the background and Blainesville beaked whales and gray whales react to playbacks of predator killer whale vocalizations when the signal is 0   dB above the ambient.

Beluga whales are more sensitive to ship noise when they are confined to leads (meters to hundreds of meters wide open water channels between ice sheets) than when not so confined. Migrating gray whales changed their orientation when exposed to a Low Frequency Active sonar that was in their migratory path but ignored the same signal source at even higher received sound levels when it was located seaward of their migratory path. Right whales (Eubalaena glacialis) and fin whales (Balaenoptera physalus) are more tolerant of stationary noise sources than those moving toward them, whereas bottlenose dolphins (Tursiops truncatus) show aversive behaviors in response to speedboats and jet skis even when they are not approaching. Humpback whales (Megaptera novaeangliae) respond at lower received levels to stimuli with sudden onset than they do to continuous sound sources. Cuvier's beaked whales (Ziphius cavirostris) respond to simulated naval sonar playbacks from nearby vessels at lower received levels than they do to real sonar from distant naval activities indicating a calibrated response to perceived risk based on distance (DeRuiter et al., 2013).

Repeated exposure to a sound source can lead to either habituation or sensitization. Beluga whales in the High Arctic have been recorded fleeing for >   80   km from the first icebreakers of the season and exhibiting a range of other behavioral changes at received sound levels between 94 and 105   dB re 1   μPa, yet 1 or 2   days later they showed no reaction to icebreaker sound of 120   dB re 1   μPa. A gray seal (Halichoerus grypus) that showed habituation to stimuli with a long rise time showed sensitization to loud, rapid onset stimuli (Götz and Janik, 2011).

The past decade has seen the development of increasingly sophisticated recording devices that can be attached to marine mammals. These tags can record received sound levels, animal vocalizations, details of animal underwater movements, and locations of animals when they surface. They have provided a better understanding of the responses of a number of species of cetaceans including beaked, sperm, killer, pilot, and blue whales and pinnipeds, primarily elephant seals, to underwater sound. The most consistent response is a reduction of foraging activity when the animal is exposed to increased noise levels. Diving patterns can also change and animals often move away from the sound source (Falcone et al., 2017; Goldbogen et al., 2013). The net effect of these responses is to decrease energy input and increase energy expenditure.

Even the same sounds presented to animals in the same activity patterns can evoke very different reactions. Controlled exposure experiments have demonstrated the probabilistic nature of marine mammal response to the received sound level. Fig. 1 shows the avoidance response of killer whales to playbacks of naval sonar. Responses can occur below received levels of 100   dB with a 50% probability of response at 142   ±   15   dB (Miller et al., 2014).

Fig. 1. Exposure:response curve showing the probability of onset of avoidance against received sound pressure level (dB_RMS re 1   μPa). The solid central line represents the posterior mean, followed by 50%, 95%, and 99% credible interval lines.

Adapted from Miller, P. J. O., Antunes, R. N., Wensveen, P. J. et al. (2014). Dose–response relationships for the onset of avoidance of sonar by free-ranging killer whales. Journal of the Acoustical Society of America, 135, 975–993 and reproduced with permission from the Acoustical Society of America.

The sensitivity of killer whales to sonar is somewhat surprising. Other cetacean species react to sonar similarly to the way they react to playbacks of killer whale vocalizations but their reactions to killer whale vocalizations are stronger than their reactions to sonar. They are responding to sonar as they would to a predator but not one that is perceived as threatening as a killer whale. This predator-response hypothesis (Harris et al., 2018) helps explain some of the variability in response to sonar. Prey have a long evolutionary history of evaluating the need to respond to a predator against the gains of continued foraging or social activity.

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Health Benefits of Bioactive Seaweed Substances

Yimin Qin , in Bioactive Seaweeds for Food Applications, 2018

9.4.8 Antiinflammatory and Antiallergic Properties

Inflammatory reaction is a physiological response by the vascular tissue system to foreign body invasion in which macrophages play an important role. Seaweed-derived polyphenols are known to have antiinflammation properties ( Le et al., 2009). During the antiinflammation process, polyphenols function through suppressing the release of inflammatory mediators or blocking their migration to target cells. Fucoidan was found to have similar properties (Fitton et al., 2007). Niu et al. (2003) used methanol to extract 39 species of seaweeds to assess the antiinflammatory properties. Results showed that 7 types of brown seaweeds and 11 types of red seaweeds showed positive results, whereas the extract from green seaweeds showed no activity. Among the 18 seaweeds that showed activity, Chorda filum was found to have the strongest activity.

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Ecology of Individual Insects

In Insect Ecology (Second Edition), 2006

Chapter 2 deals with physiological and behavioral responses to changing environmental conditions. Chapter 3 addresses physiological and behavioral mechanisms for finding and exploiting resources. Chapter 4 describes allocation of resources to various metabolic pathways and behaviors that facilitate resource acquisition, mate selection, reproduction, interaction with other organisms, etc. Physiology and behavior interact to determine the conditions under which insects can survive and the means by which they acquire and use available resources. These ecological attributes affect population ecology (such as population structure, responses to environmental change and disturbances, biogeography, etc., Section II), community attributes (such as use of, or use by, other organisms as resources, Section III), and ecosystem attributes (such as rates and directions of energy and matter flows, Section IV).

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Physiological Ecology of Forest Production

Joe Landsberg , Peter Sands , in Terrestrial Ecology, 2011

a Effects of Water Stress on Foliage

In a review of physiological responses of plants to moderate stress, Bradford and Hsaio (1982) noted that "the first sign of (longer-term) water stress is usually a restriction in foliage growth". Using data from crop plants they developed a simple analysis demonstrating a strong feedback effect – a reduction in the amount of foliage results in less photosynthesis and assimilation, hence less foliage production and so on. Of course, reductions in foliage area also result in reduced transpiration. The study by McDowell et al. (2008) showed that tree mortality during drought may be a result of hydraulic failure per se for isohydric seedlings or trees near their maximum height, or carbon starvation caused by prolonged stomatal closure in response to hydraulic failure. Biotic agents may exacerbate drought-induced stress.

Severe or prolonged stress not only results in reduction in leaf emergence and foliage expansion, but also causes leaf senescence. This was clearly demonstrated by Linder et al. (1987) (discussed in Section 4.4.5), who showed that, after a period of adequate water followed by drought there was massive foliage loss in non-irrigated P. radiata trees, and stem diameter decreased. Raison et al. (1992a,b), reporting on the same experiment, found that needle length, weight, specific leaf area and rates of production were all strongly influenced by the duration and severity of water stress. Borchert (1980) and Reich and Borchert (1982) demonstrated that leaf shedding, and the consequent improvement in the water balance of some tropical trees, triggered flowering. Thus water stress affects phenology.

Brix (1972) found that irrigation caused an increase in leaf size in Douglas fir – and hence in leaf area. In the year following irrigation, leaf size was not different between irrigated, fertilized, and irrigated   +   N-fertilizer treatments, but leaf number was greatly increased by treatments. Stem growth was increased by irrigation and fertilizer combined in the treatment year and somewhat less by irrigation alone. There was a strong irrigation–fertilizer interaction: the response to the combined factors was about twice as much as the sum of the responses to each separately. Brix concluded that water stress had a more adverse effect on cambial growth than on photosynthesis.

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The Estuarine Quality Paradox Concept☆

Michael Elliott , Victor Quintino , in Encyclopedia of Ecology (Second Edition), 2019

Estuarine Resilience, Environmental Homeostasis and the Stress-Subsidy Continuum

With regard to organismal physiological response and stress tolerance, Margalef (1981) emphasized that stress leads to organisms implementing homeostasis as a stress-reduction or stress-avoidance mechanism (see also Costanza et al., 1992). Odum (1985) then regarded stress as a detrimental or disorganizing influence and McLusky and Elliott (2004) considered that with regard to polluting effects, stress reduces the fitness-for-survival. Individual organisms have an ability, termed homeostasis, to adapt to and withstand changes in environmental conditions that may be outside their optimal ranges. This is expanded here to the term environmental homeostasis to emphasize the ability of each level of biological organization, be it at the individual, population, community or ecosystem level, to withstand/tolerate/adjust/adapt to stressors. Thus, environmental homeostasis here is taken to be the ability of the estuarine organisms to achieve a stable state by compensating for the estuarine environmental physico-chemical variability; this may also be regarded as ecological robustness in which the resistance of the ecosystem to change and the resilience of the ecosystem to recover from change become emergent properties (Borja et al., 2010a; Duarte et al., 2015; Tett et al., 2013). Hence it is concluded here that homeostasis can operate at any level of biological organization: individual (physiological) homeostasis, population homeostasis, community homeostasis and ecosystem homeostasis. It is hypothesized that in estuaries, the high natural variability and environmental homeostasis may increase resistance and resilience and an ability to withstand stress, both natural and anthropogenic. Therefore, the background of high estuarine variability (i.e., noise) increases the difficulty of detecting anthropogenic perturbation signals.

Given the above and using Odum׳s (1985) framework of symptoms in naturally-stressed areas, in estuaries salinity decrease is not a stress but a subsidy (Costanza et al., 1992). Whitfield et al. (2012) show the dominant effect of salinity, through the so-called Remane diagram, and Basset et al. (2013b) show the effects of such environmental variables which create estuaries as the sites of multiple ecotones, each spreading across the range of environmental tolerances of organisms (Smyth and Elliott, 2016; Solan and Whiteley, 2016). If an estuary had high levels of natural stress, irrespective of anthropogenic stress, then there would be severe adverse consequences whereas there are not and therefore the system copes with that stress. Hence instead of considering estuaries as naturally stressed areas, they should be considered as areas with a subsidy rather than a stress, that is, as a perturbation with a positive effect on the system (Costanza et al., 1992). The positive effect being the ability of estuarine organisms to tolerate the adverse and variable environmental conditions by capitalizing on the lack of inter-specific competition which leads to high population densities. Hence the natural estuarine system is maintained by providing a benefit for those species adapted to the inherently variable conditions. Therefore, those estuarine environmental managers who require to detect change need to determine whether natural stress is occurring, in particular whether salinity decrease is a stress or, for a brackish community, the stress would be in not experiencing a decrease in salinity. Thus reduced and highly varying salinity may only be a stress for a marine-dominated or marine-derived estuarine community. In essence, if a species is typically estuarine then the conditions are a subsidy, generating benefits whereas if a species in not adapted to estuarine conditions then these are a stressor.

Because of the many quality assessments linked to the EU Water Framework Directive (Borja et al., 2010b; Hering et al., 2010), there are numerous studies which define and quantify the way in which the estuaries respond to human activities. As shown by Elliott and Whitfield (2011), the estuarine functioning, such as the ability to support high predator populations of fishes and overwintering birds, does not rely on a high biodiversity per se. The biodiversity-ecosystem functioning (BEF) debate, that is, that a high diversity is required for successful functioning and vice versa, seems to be well developed and agreed for terrestrial, freshwater and microbial systems (e.g., Strong et al., 2015; Loreau et al., 2002, and papers therein), but little considered for estuarine and other transitional waters. Estuaries and other transitional waters thus become an anomaly in this in that they function successfully precisely because they have a low biodiversity. Therefore, analyses of ecosystem structure (which often rely on diversity measures of various types) related to human impacts are not sufficient and so ecosystem function has to be given more importance. This then has to be incorporated into the conceptual models, such as by Costanza and Mageau (1999), which aim to assess estuarine ecosystem vigor (based on function) together with organization (i.e., structure).

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The Contribution of Root – Rhizosphere Interactions to Biogeochemical Cycles in a Changing World

Kurt S. Pregitzer , ... Andrew J. Burton , in The Rhizosphere, 2007

7.4 SUMMARY: CASCADING CONSEQUENCES OF ALTERED PRIMARY PRODUCTIVITY

It seems clear that the physiological response of plant root systems to a changing environment will cascade through terrestrial ecosystems to alter higher trophic levels (decomposers), which further regulate the flow of energy and nutrients in terrestrial ecosystems. A major uncertainty in our ability to predict ecosystem response to changing atmospheric chemistry is the extent to which fine root growth and tissue chemistry will be altered as the Earth's atmosphere changes. For example, we still do not understand how atmospheric N deposition will alter root growth, root mortality, and root tissue chemistry. Part of this problem is likely related to the issue of exactly how we define the pool of carbon and nutrients in fine roots. We also believe that the inherent physiological responses of plants to altered atmospheric CO₂ and soil N availability will depend on their life histories, and that mechanistic responses will not always follow the same path. Together, the underlying physiological responses of primary producers and microbial decomposers regulate the cycling of C and N in terrestrial ecosystems. In many regions of Earth, atmospheric CO₂ will increase in concert with increasing N deposition, but far too little attention has been given to the interaction of these changes in atmospheric chemistry. The impact of the interaction between elevated atmospheric CO₂ and O₃ on soil C storage clearly demonstrates why it is important to examine the interacting effects of our changing atmosphere. If we deliberately set out to understand how variable plant root and microbial physiology are to changes in atmospheric CO₂ and soil N, it should be possible to build a deeper understanding of the fundamental processes controlling ecosystem response to climate change.

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Impact of Extreme and Infrequent Events on Terrestrial Ecosystems and Biodiversity

Thomas Kitzberger , in Encyclopedia of Biodiversity (Second Edition), 2013

Cascading Effect Across Hierarchical Levels Ultimately Affecting Ecosystem Functions

Extreme climate events can produce physiological responses that exceed acclimation capacity of individuals. If severe enough, these responses may translate into fitness of individuals and population demography (e.g., increased mortality); and if occurring in dominant or key structuring species, they may influence community structure and composition and ultimately produce alteration of ecosystem functions such as primary productivity, water regulation, carbon fixation, and nutrient cycling ( Jentsch et al., 2011).

This area of research is related to a relatively new area of manipulative event-based experiments that started in the early 1990s and gained momentum during the last decade (Jentsch et al., 2007). Experiments have the advantage over observational studies of ongoing or past extreme events of allowing adequate replication and control of event characteristics (magnitude, duration, timing, etc.), thus enabling the analysis of causal relations and the identification of thresholds beyond which individual allocation, population fluctuations, community structure, or ecosystem functions change significantly (Jentsch et al., 2007 and references therein).

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Exposure Science: Inhalation

C.P. Weisel , in Encyclopedia of Environmental Health, 2011

Biomarkers of Exposure

A biological marker of exposure is a physiological response or a chemical/biochemical measured within body fluids or tissues whose concentration is proportional to the exposure to the agent of concern. Biomarkers of inhalation exposure that have been measured include the parent compound or element, its metabolite or adduct. Body fluids that have been utilized include breath, blood, urine, hair, finger or toe nails, breast milk, adipose tissue, and nasal lavage. The presence of a biomarker is a confirmation that an exposure has occurred, provided that the biomarker measured is unique to a specific exposure agent. However, many metabolites or responses can be derived from various agents, thus a definitive statement about what the exposure was cannot always be made. Furthermore, biomarkers concentrations typically change over time in the body as the parent compound and the biomarker continue to be metabolized or excreted. The concentration change often follows an exponential time curve, whereas most measurements are made in samples collected at a single or a few points in time. Genetic polymorphisms in metabolic enzymes or phenotypes that induce or suppress metabolism can alter the rate of change in the biomarker concentration resulting in potential large interindividual differences in the biomarker levels from the same exposure. Thus, biomarker measurements in isolation of information about exposure do not provide complete information for determining when, how, and the magnitude of the exposure. The full use of biomarkers information to understand public health and potential evaluation of pharmacokinetic and pharmacodynamic changes in the body needs information about the time frame and route of the exposure to be fully useful.

There have been major developments in tools for the collection and analyses of biomarkers, particularly in the field of molecular biology that can assist in linking exposure to environmentally related disease. Biomarkers are being used to identify markers of genetic susceptibility to environmental agents and as intermediate markers of effect in the pathway from exposure to disease. Examining the continuum between exposure and disease combining environmental transport models with exposure models and pharmacokinetic/pharmacodynamic models will allow for potential prediction of adverse health outcomes from release of contaminants into the air; biomarkers are one component used to evaluate these models. Collection of biomarkers has been a major component of the National Health and Nutritional Examination Study (NHANES) undertaken by the Center for Disease Control and Prevention in the United States, and the data collected as part of NHANES provides a population-based distribution of the body burden of many contaminants. However, only limited exposure data are being collected to fully utilize that robust data set. The promise of biomarkers as a key component in exposure science and for understanding gene–environmental interaction is a developing and expanding field.

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