Disturbance (ecology)

In ecology, a disturbance is a temporary change in environmental conditions that causes a pronounced change in an ecosystem. Disturbances often act quickly and with great effect, to alter the physical structure or arrangement of biotic and abiotic elements. Disturbance can also occur over a long period of time and can impact the biodiversity within an ecosystem. Major ecological disturbances may include fires, flooding, storms, insect outbreaks and trampling. Earthquakes, various types of volcanic eruptions, tsunami, firestorms, impact events, climate change, and the devastating effects of human impact on the environment (anthropogenic disturbances) such as clearcutting, forest clearing and the introduction of invasive species[1] can be considered major disturbances. Not only invasive species can have a profound effect on an ecosystem, but also naturally occurring species can cause disturbance by their behavior. Disturbance forces can have profound immediate effects on ecosystems and can, accordingly, greatly alter the natural community. Because of these and the impacts on populations, disturbance determines the future shifts in dominance, various species successively becoming dominant as their life history characteristics, and associated life-forms, are exhibited over time.[2]

Contrasts - fire
Disturbance of a fire can clearly be seen by comparing the unburnt (left) and burnt (right) sides of the mountain range in South Africa. The veld ecosystem relies on periodic fire disturbances like these to rejuvenate itself.


Conditions under which natural disturbances occur are influenced mainly by climate, weather, and location.[1] Natural fire disturbances for example occur more often in areas with a higher incidence of lightning and flammable biomass, such as longleaf pine ecosystems in the southeastern United States.[3] Conditions often occur as part of a cycle and disturbances may be periodic. Other disturbances, such as those caused by humans, invasive species or impact events, can occur anywhere and are not necessarily cyclic. Extinction vortices may result in multiple disturbances or a greater frequency of a single disturbance. Immediately after a disturbance there is a pulse of recruitment or regrowth under conditions of little competition for space or other resources. After the initial pulse, recruitment slows since once an individual plant is established it is very difficult to displace.[2] Due to the varying forms of disturbance this directly impacts the organisms which will exploit the disturbance and create diversity within an ecosystem.

Cyclic disturbance

Damages of storm Kyrill in Wittgenstein, Germany.

Often, when disturbances occur naturally, they provide conditions that favor the success of different species over pre-disturbance organisms. This can be attributed to physical changes in the biotic and abiotic conditions of an ecosystem. Because of this, a disturbance force can change an ecosystem for significantly longer than the period over which the immediate effects persist. With the passage of time following a disturbance, shifts in dominance may occur with ephemeral herbaceous life-forms progressively becoming over topped by taller perennials herbs, shrubs and trees.[2] However, in the absence of further disturbance forces, many ecosystems trend back toward pre-disturbance conditions. Long lived species and those that can regenerate in the presence of their own adults finally become dominant.[2] Such alteration, accompanied by changes in the abundance of different species over time, is called ecological succession. Succession often leads to conditions that will once again predispose an ecosystem to disturbance.

Pine forests in the western North America provide a good example of such a cycle involving insect outbreaks. The mountain pine beetle (Dendroctonus ponderosae) play an important role in limiting pine trees like lodgepole pine in forests of western North America. In 2004 the beetles affected more than 90,000 square kilometres. The beetles exist in endemic and epidemic phases. During epidemic phases swarms of beetles kill large numbers of old pines. This mortality creates openings in the forest for new vegetation.[4] Spruce, fir, and younger pines, which are unaffected by the beetles, thrive in canopy openings. Eventually pines grow into the canopy and replace those lost. Younger pines are often able to ward off beetle attacks but, as they grow older, pines become less vigorous and more susceptible to infestation.[5] This cycle of death and re-growth creates a temporal mosaic of pines in the forest.[6] Similar cycles occur in association with other disturbances such as fire and windstorms.

When multiple disturbance events affect the same location in quick succession, this often results in a "compound disturbance," an event which, due to the combination of forces, creates a new situation which is more than the sum of its parts. For example, windstorms followed by fire can create fire temperatures and durations that are not expected in even severe wildfires, and may have surprising effects on post-fire succession.[7] Environmental stresses can be described as pressure on the environment, with compounding variables such as extreme temperature or precipitation changes—which all play a role in the diversity and succession of an ecosystem. With environmental moderation, diversity increases because of the intermediate- disturbance effect, decreases because of the competitive-exclusion effect, increases because of the prevention of competitive exclusion by moderate predation, and decreases because of the local extinction of prey by severe predation.[8] A reduction in recruitment density reduces the importance of competition for a given level of environmental stress.[8]

Species adapted to disturbance

Greece Forest Fire July 25 2007
Forest fire burns on the island of Zakynthos in Greece on July 25th, 2007.

A disturbance may change a forest significantly. Afterwards, the forest floor is often littered with dead material. This decaying matter and abundant sunlight promote an abundance of new growth. In the case of forest fires a portion of the nutrients previously held in plant biomass is returned quickly to the soil as biomass burns. Many plants and animals benefit from disturbance conditions.[9] Some species are particularly suited for exploiting recently disturbed sites. Vegetation with the potential for rapid growth can quickly take advantage of the lack of competition. In the northeastern United States, shade-intolerant trees like pin cherry[10] and aspen quickly fill in forest gaps created by fire or windstorm (or human disturbance). Silver maple and eastern sycamore are similarly well adapted to floodplains. They are highly tolerant of standing water and will frequently dominate floodplains where other species are periodically wiped out.

When a tree is blown over, gaps typically are filled with small herbaceous seedlings but, this is not always the case; shoots from the fallen tree can develop and take over the gap.[11] The sprouting ability can have major impacts on the plant population, plant populations that typically would have exploited the tree fall gap get over run and can not compete against the shoots of the fallen tree. Species adaptation to disturbances is species specific but how each organism adapts effects all the species around them.

Another species well adapted to a particular disturbance is the Jack pine in boreal forests exposed to crown fires. They, as well as some other pine species, have specialized serotinous cones that only open and disperse seeds with sufficient heat generated by fire. As a result, this species often dominates in areas where competition has been reduced by fire.[12]

Species that are well adapted for exploiting disturbance sites are referred to as pioneers or early successional species. These shade-intolerant species are able to photosynthesize at high rates and as a result grow quickly. Their fast growth is usually balanced by short life spans. Furthermore, although these species often dominate immediately following a disturbance, they are unable to compete with shade-tolerant species later on and replaced by these species through succession. However these shifts may not reflect the progressive entry to the community of the taller long-lived forms, but instead, the gradual emergence and dominance of species that may have been present, but inconspicuous directly after the disturbance.[2]

While plants must deal directly with disturbances, many animals are not as immediately affected by them. Most can successfully evade fires, and many thrive afterwards on abundant new growth on the forest floor. New conditions support a wider variety of plants, often rich in nutrients compared to pre-disturbance vegetation. The plants in turn support a variety of wildlife, temporarily increasing biological diversity in the forest.[9]


Biological diversity is dependent on natural disturbance. The success of a wide range of species from all taxonomic groups is closely tied to natural disturbance events such as fire, flooding, and windstorm. As an example, many shade-intolerant plant species rely on disturbances for successful establishment and to limit competition. Without this perpetual thinning, diversity of forest flora can decline, affecting animals dependent on those plants as well.

A good example of this role of disturbance is in ponderosa pine (Pinus ponderosa) forests in the western United States, where surface fires frequently thin existing vegetation allowing for new growth. If fire is suppressed, douglas fir (Pesudotsuga menziesii), a shade tolerant species, eventually replaces the pines. Douglas firs, having dense crowns, severely limit the amount of sunlight reaching the forest floor. Without sufficient light new growth is severely limited. As the diversity of surface plants decreases, animal species that rely on them diminish as well. Fire, in this case, is important not only to the species directly affected but also to many other organisms whose survival depends on those key plants.[13]

Diversity is low in harsh environments because of the intolerance of all but opportunistic and highly resistant species to such conditions.[8] The interplay between disturbance and these biological processes seems to account for a major portion of the organization and spatial patterning of natural communities.[14] Disturbance variability and species diversity are heavily linked, and as a result require adaptations that help increase plant fitness necessary for survival.

See also


  1. ^ a b Dale, V.; Joyce, L.; McNulty, S.; Neilson, R.; Ayres, M.; Flannigan, M.; Hanson, P.; Irland, L.; Lugo, A.; Peterson, C.; Simberloff, D.; Swanson, F.; Stocks, B.; Wotton, B. (September 2001). "Climate Change and Forest Disturbances". BioScience. 51 (9): 723–734. doi:10.1641/0006-3568(2001)051[0723:CCAFD]2.0.CO;2.
  2. ^ a b c d e Nobel, I. "The Use of Vital Attributes to Predict Successional Changes in Plant Communities Subject to Recurrent Disturbances".
  3. ^ F.,, Noss, Reed. Fire ecology of Florida and the southeastern coastal plain. Gainesville. ISBN 9780813052199. OCLC 1035947633.
  4. ^ Mock, K.E.; Bentz, B.J.; O'Neill, E.M.; Chong, J.P.; Orwin, J.; Pfrender, M.E. (2007). "Landscape-scale genetic variation in a forest outbreak species, the mountain pine beetle (Dendroctonus ponderosae)". Molecular Ecology. 16: 553–568. doi:10.1111/j.1365-294x.2006.03158.x.
  5. ^ Ham, D.L.; Hertel, G.D. (1984). "Integrated Pest Management of the Southern Pine Beetle in the Urban Setting". Journal of Arboriculture. 10 (10): 279–282.
  6. ^ Forest Practices Board. 2007. Lodgepole Pine Stand Structure 25 Years after Mountain Pine Beetle Attack. "Archived copy" (PDF). Archived from the original (PDF) on 2008-10-29. Retrieved 2007-05-12.CS1 maint: Archived copy as title (link)
  7. ^ Buma, B.; Wessman, C. A. (2011). "Disturbance interactions can impact resilience mechanisms of forests". Ecosphere. 2 (5): art64. doi:10.1890/ES11-00038.1.
  8. ^ a b c Menge, A (1987). "Community Regulation: Variation in Disturbance, Competition, and Predation in Relation to Environmental Stress and Recruitment". The American Naturalist. 130. doi:10.1086/284741. JSTOR 2461716.
  9. ^ a b Pringle, L. 1979. Natural Fire: Its Ecology in Forests. William Morrow and Company, New York. 27-29.
  10. ^ Marks, P.L. (1974). "The Role of Pin Cherry (Prunus pensylvanica) in the Maintenance of Stability in Northern Hardwood Ecosystems". Ecological Monographs. 44 (1): 73–88. doi:10.2307/1942319.
  11. ^ Bond, J (2001). "Ecology of sprouting in woody plants: the persistence niche". Trends in Ecology & Evolution. 16: 45–51. doi:10.1016/s0169-5347(00)02033-4.
  12. ^ Schwilk, D.; Ackerly, D. (2001). "Flammability and serotiny as strategies: correlated evolution in pines". Oikos. 94: 326–336. doi:10.1034/j.1600-0706.2001.940213.x.
  13. ^ Pringle, L. 1979. Natural Fire: Its Ecology in Forests. William Morrow and Company, New York. 22-25.
  14. ^ Sousa, W (1984). "The Role of Disturbance in Natural Communities". Annual Review of Ecology and Systematics. 15: 353–391. doi:10.1146/annurev.es.15.110184.002033.

External links

Biological dispersal

Biological dispersal refers to both the movement of individuals (animals, plants, fungi, bacteria, etc.) from their birth site to their breeding site ('natal dispersal'), as well as the movement from one breeding site to another ('breeding dispersal').

Dispersal is also used to describe the movement of propagules such as seeds and spores.

Technically, dispersal is defined as any movement that has the potential to lead to gene flow.

The act of dispersal involves three phases: departure, transfer, settlement and there are different fitness costs and benefits associated with each of these phases.

Through simply moving from one habitat patch to another, the dispersal of an individual has consequences not only for individual fitness, but also for population dynamics, population genetics, and species distribution. Understanding dispersal and the consequences both for evolutionary strategies at a species level, and for processes at an ecosystem level, requires understanding on the type of dispersal, the dispersal range of a given species, and the dispersal mechanisms involved.

Biological dispersal may be contrasted with geodispersal, which is the mixing of previously isolated populations (or whole biotas) following the erosion of geographic barriers to dispersal or gene flow (Lieberman, 2005; Albert and Reis, 2011).

Dispersal can be distinguished from animal migration (typically round-trip seasonal movement), although within the population genetics literature, the terms 'migration' and 'dispersal' are often used interchangeably.

Chamaenerion angustifolium

Chamaenerion angustifolium, known in North America as fireweed, in some parts of Canada as great willowherb, and in Britain as rosebay willowherb, is a perennial herbaceous plant in the willowherb family Onagraceae. It is also known by the synonyms Chamerion angustifolium and Epilobium angustifolium. It is native throughout the temperate Northern Hemisphere, including large parts of the boreal forests.

This species has been placed in the genus Chamaenerion (sometimes given as Chamerion) rather than Epilobium based on several morphological distinctions: spiral (rather than opposite or whorled) leaf arrangement; absence (rather than presence) of a hypanthium; subequal stamens (rather than stamens in two unequal whorls); zygomorphic (rather than actinomorphic) stamens and stigma. Under this taxonomic arrangement, Chamaenerion and Epilobium are monophyletic sister genera.Two subspecies are recognized as valid:

Chamaenerion angustifolium subsp. angustifolium

Chamaenerion angustifolium subsp. circumvagum (Mosquin) Hoch


A chronosequence describes a set of ecological sites that share similar attributes but represent different ages.A common assumption in establishing chronosequences is that no other variable besides age (such as various abiotic components and biotic components) has changed between sites of interest. Because this assumption cannot always be tested for environmental study sites, the use of chronosequences in field successional studies has recently been debated.

E. A. Johnson

Edward A. Johnson is a Canadian ecologist. His research focuses on the contact between the geosciences and ecology. :)

Johnson is currently a professor of biological sciences at the University of Calgary, located in Alberta. He was formerly the director of the Biogeoscience Institute (BGI) at the university, which promotes research in the Canadian rockies and surrounding areas, where he is involved in research programs.His research aims to incorporate the concept of natural disturbance into plant community organisation and dynamics. E. A. Johnson’s applied interests include but are not limited to global climate change, conservation biology, and ecosystem and fire management.Johnson is a member of the National Science Foundation (NSF) Community Surface Dynamics Modeling System, whichis a national effort that aims to coordinate surface dynamic modelling of the Earth’s surface. He is also a member of the Natural Sciences and Engineering Research Council (NSERC) Centres of Excellence in Sustainable Forest Management, NSERC Geomatics for Informed Decisions (GEOIDE), PAGSE (Royal Society of Canada), and he serves as the editor-in-chief of the journal Bulletin of the Ecological Society of America.E. A. Johnson has published four books that pertain to his areas of ecological interests. This includes the book titled Fire and Vegetation Dynamics which was published in 1992, which explores the dynamics of fires in the North American boreal forest. He published Forest Fires: Behavior and Ecological Effects in 2001. In 2005, he published Environmental Education and Advocacy which highlights the changing perspectives of ecology and education. In 2007 Johnson published Plant Disturbance Ecology: the Process and the Response.E.A. Johnson received the 1986 W.S. Cooper Award from the Ecological Society of America.

Fire regime

A fire regime is the pattern, frequency, and intensity of the bushfires and wildfires that prevail in an area over long periods of time. It is an integral part of fire ecology, and renewal for certain types of ecosystems. A fire regime describes the spatial and temporal patterns and ecosystem impacts of fire on the landscape, and provides an integrative approach to identifying the impacts of fire at an ecosystem or landscape level. If fires are too frequent, plants may be killed before they have matured, or before they have set sufficient seed to ensure population recovery. If fires are too infrequent, plants may mature, senesce, and die without ever releasing their seed.

Fire regimes can change with the spatial and temporal variations in topography, climate, and fuel. Understanding the historic fire regime is important for understanding and predicting future fire regime changes and the interactions between fire and climates.

Forest pathology

Forest pathology is the research of both biotic and abiotic maladies affecting the health of a forest ecosystem, primarily fungal pathogens and their insect vectors. It is a subfield of forestry and plant pathology.

Forest pathology is part of the broader approach of forest protection.

Human–wildlife conflict

Human–wildlife conflict refers to the interaction between wild animals and people and the resultant negative impact on people or their resources, or wild animals or their habitat. It occurs when growing human populations overlap with established wildlife territory, creating reduction of resources or life to some people and/or wild animals. The conflict takes many forms ranging from loss of life or injury to humans, and animals both wild and domesticated, to competition for scarce resources to loss and degradation of habitat.

Conflict management strategies earlier comprised lethal control, translocation, regulation of population size and preservation of endangered species. Recent management approaches attempt to use scientific research for better management outcomes, such as behaviour modification and reducing interaction. As human-wildlife conflicts inflict direct, indirect and opportunity costs, the mitigation of human-wildlife conflict is an important issue in the management of biodiversity and protected areas.

Insular biogeography

Insular biogeography or island biogeography is a field within biogeography that examines the factors that affect the species richness and diversification of isolated natural communities. The theory was originally developed to explain the pattern of the species–area relationship occurring in oceanic islands. Under either name it is now used in reference to any ecosystem (present or past) that is isolated due to being surrounded by unlike ecosystems, and has been extended to mountain peaks, seamounts, oases, fragmented forests, and even natural habitats isolated by human land development. The field was started in the 1960s by the ecologists Robert H. MacArthur and E. O. Wilson, who coined the term island biogeography in their inaugural contribution to Princeton's Monograph in Population Biology series, which attempted to predict the number of species that would exist on a newly created island.

Intermediate disturbance hypothesis

The intermediate disturbance hypothesis (IDH) suggests that local species diversity is maximized when ecological disturbance is neither too rare nor too frequent. At high levels of disturbance, due to frequent forest fires or human impacts like deforestation, all species are at risk of going extinct. According to IDH theory, at intermediate levels of disturbance, diversity is thus maximized because species that thrive at both early and late successional stages can coexist. IDH is a nonequilibrium model used to describe the relationship between disturbance and species diversity. IDH is based on the following premises: First, ecological disturbances have major effects on species richness within the area of disturbance. Second, interspecific competition results from one species driving a competitor to extinction and becoming dominant in the ecosystem. Third, moderate ecological scale disturbances prevent interspecific competition.

Disturbances act to disrupt stable ecosystems and clear species' habitat. As a result, disturbances lead to species movement into the newly cleared area. Once an area is cleared there is a progressive increase in species richness and competition takes place again. Once disturbance is removed, species richness decreases as competitive exclusion increases. "Gause's Law", also known as competitive exclusion, explains how species that compete for the same resources cannot coexist in the same niche. Each species handles change from a disturbance differently; therefore, IDH can be described as both "broad in description and rich in detail". The broad IDH model can be broken down into smaller divisions which include spatial within-patch scales, spatial between-patch scales, and purely temporal models. Each subdivision within this theory generates similar explanations for the coexistence of species with habitat disturbance. Joseph H. Connell proposed that relatively low disturbance leads to decreased diversity and high disturbance causes an increase in species movement. These proposed relationships lead to the hypothesis that intermediate disturbance levels would be the optimal amount of disorder within an ecosystem. Once K-selected and r-selected species can live in the same region, species richness can reach its maximum. The main difference between both types of species is their growth and reproduction rate. These characteristics attribute to the species that thrive in habitats with higher and lower amounts of disturbance. K-selected species generally demonstrate more competitive traits. Their primary investment of resources is directed towards growth, causing them to dominate stable ecosystems over a long period of time; an example of K-selected species the African elephant, which is prone to extinction because of their long generation times and low reproductive rates. In contrast, r-selected species colonize open areas quickly and can dominate landscapes that have been recently cleared by disturbance. An ideal examples of r-selected groups are algae. Based on the contradictory characteristics of both of these examples, areas of occasional disturbance allow both r and K species to benefit by residing in the same area. The ecological effect on species relationships is therefore supported by the intermediate disturbance hypothesis.

Investigative Biology Teaching Laboratories at Cornell University

The Investigative Biology Teaching Laboratories are located at Cornell University on the first floor Comstock Hall. They are well-equipped biology teaching laboratories used to provide hands-on laboratory experience to Cornell undergraduate students. Currently, they are the home of the Investigative Biology Laboratory Course, (BioG1500), and frequently being used by the Cornell Institute for Biology Teachers, the Disturbance Ecology course and Insectapalooza. In the past the Investigative Biology Teaching Laboratories hosted the laboratory portion of the Introductory Biology Course with the course number of Bio103-104 (renumbered to BioG1103-1104).

Jill F. Johnstone

Jill Johnstone was a professor in the Department of Biology at the University of Saskatchewan, where she started the Northern Plant Ecology Lab (NPEL) which she still runs. She primarily conducts research on plant ecology and environmental biology with an emphasis on how boreal forest and tundra are responding to rapid rates of climate change.

Marie-Josée Fortin

Marie-Josée Fortin (born October 21, 1958) is the Canada Research Chair in spatial ecology at the University of Toronto. In 2016, she was elected to the Royal Society of Canada. Fortin is currently a Professor in the Department of Ecology and Evolutionary Biology at the University of Toronto. Fortin completed her BSc in 1983, as well as her MSc in 1986 at the University of Montréal. In 1992 she graduated with her PhD at the State University of New York, followed by her Postdoctoral Fellow from 1992-1994 at Université Laval.Fortin focuses her current research on four subject areas: spatial ecology, spatial and landscape statistics, conservation, as well as disturbance ecology. These subjects include disciplines such as spatially-explicit modeling, spatial epidemiology, forest ecology, network theory, landscape genetics and geography. This research focuses on the maintenance of biodiversity within ecosystems and appropriate conservation strategies for species affected by land use and climate change. This includes the analyses of how environmental factors and ecological processes affect the movement, persistence, and range dynamics of species at the landscape and geographical range in both forested and aquatic environments.


Rhizopogon is a genus of ectomycorrhizal Basidiomycetes in the family Rhizopogonaceae. Species form hypogeous sporocarps commonly referred to as "false truffles". The general morphological characters of Rhizopogon sporocarps are a simplex or duplex peridium surrounding a loculate gleba that lacks a columnella. Basidiospores are produced upon basidia that are borne within the fungal hymenium that coats the interior surface of gleba locules. The peridium is often adorned with thick mycelial cords, also known as rhizomorphs, that attach the sporocarp to the surrounding substrate. The scientific name Rhizopogon is Greek for 'root' (Rhiz-) 'beard' (-pogon) and this name was given in reference to the rhizomorphs found on sporocarps of many species.

Rhizopogon species are primarily found in ectomycorrhizal association with trees in the family Pinaceae and are especially common symbionts of pine, fir, and Douglas fir trees. Through their ectomycorrhizal relationships Rhizopogon are thought to play an important role in the ecology of coniferous forests. Recent micromorphological and molecular phylogenetic study has established that Rhizopogon is a member of the Boletales, closely related to Suillus.

Robin Wall Kimmerer

Robin Wall Kimmerer (also credited as Robin W. Kimmerer) (born 1953) is Professor of Environmental and Forest Biology at the State University of New York College of Environmental Science and Forestry (SUNY-ESF).

She is the author of numerous scientific articles, and the books Gathering Moss: A Natural and Cultural History of Mosses (2003), and Braiding Sweetgrass: Indigenous Wisdom, Scientific Knowledge and the Teachings of Plants (2013).

She is an enrolled member of the Citizen Potawatomi Nation, and combines her heritage with her scientific and environmental passions.

Seed dispersal

Seed dispersal is the movement, spread or transport of seeds away from the parent plant. Plants have very limited mobility and consequently rely upon a variety of dispersal vectors to transport their propagules, including both abiotic vectors such as the wind and living (biotic) vectors like birds. Seeds can be dispersed away from the parent plant individually or collectively, as well as dispersed in both space and time. The patterns of seed dispersal are determined in large part by the dispersal mechanism and this has important implications for the demographic and genetic structure of plant populations, as well as migration patterns and species interactions. There are five main modes of seed dispersal: gravity, wind, ballistic, water, and by animals. Some plants are serotinous and only disperse their seeds in response to an environmental stimulus.


A stressor is a chemical or biological agent, environmental condition, external stimulus or an event that causes stress to an organism. Psychologically speaking, a stressor can be events or environments that an individual would consider demanding, challenging, and or threaten the individual's safety.An event that triggers the stress response may include:

environmental stressors (hypo or hyper-thermic temperatures, elevated sound levels, over-illumination, overcrowding)

daily stress events (e.g., traffic, lost keys, money, quality and quantity of physical activity)

life changes (e.g., divorce, bereavement)

workplace stressors (e.g., high job demand vs. low job control, repeated or sustained exertions, forceful exertions, extreme postures, office clutter)

chemical stressors (e.g., tobacco, alcohol, drugs)

social stressor (e.g., societal and family demands)Stressors have physical, chemical and mental responses inside of the body. Physical stressors produce mechanical stresses on skin, bones, ligaments, tendons, muscles and nerves that cause tissue deformation and in extreme cases tissue failure. Chemical stresses also produce biomechanical responses associated with metabolism and tissue repair. Physical stressors may produce pain and impair work performance. Chronic pain and impairment requiring medical attention may result from extreme physical stressors or if there is not sufficient recovery time between successive exposures. A recent study shows that physical office clutter could be an example of physical stressors in a workplace setting.Stressors may also affect mental function and performance. One possible mechanism involves stimulation of the hypothalamus, CRF (corticotropin release factor) -> pituitary gland releases ACTH (adrenocorticotropic hormone) -> adrenal cortex secretes various stress hormones (e.g., cortisol) -> stress hormones (30 varieties) travel in the blood stream to relevant organs, e.g., glands, heart, intestines -> flight-or-fight response. Between this flow there is an alternate path that can be taken after the stressor is transferred to the hypothalamus, which leads to the sympathetic nervous system. After which, the adrenal medulla secretes epinephrine. Mental and social stressors may affect behavior and how individuals respond to physical and chemical stressors.

Life requires everyone to make sudden and planned adjustments to meet its demands, but the greater the demand comes with a greater adjustment and possibly more stress. Determining the impact of these various stressors allow individuals to decide the relationship between the types of stressors and the degree of distress. Identifying the stressor-stress relationship must involve quantifying the impact of life demands and all stress spurred from it. To do this, subjective measures and objective measures will be used depending on the situation. Individuals determine the degree of adjustment themselves in subjective measures, but a degree of adjustment will be or has already been assigned to the individual in an objective measure. The degrees of adjustment are measured by life change units, where one unit equals a degree of adjustment necessary to cope with the life change. The practice of measuring life change units led to the creation of many scales composed of these units that are tailored to certain life events or situations, such as social readjustment and college students.

Once the relationship between the stressor (event) and the stress, the individual can then begin to focus on the stress magnitude and the stress itself. For life events with a lower magnitude of impact, the ability to cope and adjust may not be very complex and relatively brief. But for others, life events with high magnitudes can impact their lives in many ways for an extended amount of time. The various stressors listed above can all have events or stressors that range anywhere from minor to traumatic. Traumatic events are very debilitating stressors, and often times these stressors are uncontrollable. Traumatic events can deplete an individual’s coping resources to an extent where the individual may develop acute stress disorder or even post-traumatic stress disorder. Acute stress disorder is a psychological disorder where a traumatic event that is life threatening or threatens an injury causes a reaction of fear and helplessness lasting up to four weeks. Post-traumatic stress disorder has symptoms of lasting longer than one month, and the first symptom is a history of experiencing a traumatic event followed with a reaction of intense fear, helplessness, or horror. The traumatic event is persistently reexperienced in one of these ways: recurrent distressing recollections, dreams, flashbacks, illusions, or a sense of reliving the experience, and distress or physical arousal by reminders of this event. The individual suffers from a persistent avoidance of reminders of the event. People who have been abused, victimized, or terrorized are often more susceptible to stress disorders.

No matter the magnitude of the stressor and stress, most stressor-stress relationships can be evaluated and determined by either the individual or a psychologist. Without proper attention, stress can produce severe effects on mental health and the immune system, which can eventually lead to effects on the physical body. Therapeutic measures are often taken to help replenish and rebuild the individual’s coping resources while simultaneously aiding the individual in dealing with the current stressor.

Thomas T. Veblen

Thomas Thorstein Veblen (born 15 November 1947) is an American forest ecologist and physical geographer known for his work on the ecology of Nothofagus (southern beech) forests in the Southern Hemisphere and on the ecology of conifer forests in the southern Rocky Mountains of the U.S.A. He is an Arts and Sciences College Professor of Distinction at University of Colorado at Boulder, USA (2006).

Windshield phenomenon

The windshield phenomenon (or windscreen phenomenon) is a term given to the anecdotal observation that people tend to find fewer insects smashed on the windscreens of their cars now compared to a decade or several decades ago. This effect has been ascribed to major global declines in insect abundance.

Food webs
Example webs
Ecology: Modelling ecosystems: Other components

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