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.
David Wilkinson gives a thorough history of the hypothesis in his paper titled, "The disturbing history of the intermediate disturbance". In this paper, he explains that the idea of disturbance relating to species richness can be traced back to the 1940s in Eggeling 1947, Watt 1947, and Tansley 1949. Though studies supporting the hypothesis began in the 1960s, the first concrete statements of the intermediate disturbance hypothesis didn't occur until the 1970s. The hypothesis was initially illustrated using what has been referred to as a "hump-backed model", which graphed the proposed relationship between diversity and disturbance. This graph appeared first in Grime's 'Competitive exclusion in herbaceous vegetation' where it was used to show the relationship between species density and both environmental stress and intensity of management. The graph appears again in Horn's 'Markovian properties of forest succession' and Connell's 'The influence of interspecific competition and other factors on the distribution of the barnacle'. Though Grime was the first to provide a model for the relationship and Horn was the first to explicitly state the hypothesis, Connell is generally cited in text books and journals as the founder of the hypothesis.
The hypothesis caused concern among the marine science community because of the discrepancy with the 1976 Competition/Predation/Disturbance model proposed by Menge and Sutherland In this model, low disturbance influences high predation and high disturbance creates low predation, causing competitive exclusion to take place. Menge & Sutherland formulated a new model, one that incorporated Connell's ideas in a two part graph published in The American Naturalist (1987). This model proposes that predation, competition, and disturbance are all responsible for shaping the diversity of a community under certain circumstances.
Research regarding the effects of intermediate disturbance is ongoing. In one study, dry and tropical forest regions were compared to determine how the effects of IDH change due to varying climate. More recently, the intermediate disturbance hypothesis has been examined in marine and freshwater ecosystems and protist microcosms.
Debates over the validity of the IDH are ongoing within the discipline of tropical ecology as the theory is tested in various ecological communities. Other evidence exists for and against the hypothesis. The intermediate disturbance hypothesis has been supported by several studies involving marine habitats such as coral reefs and macroalgal communities. In shallow coastal waters off of south-west Western Australia, a study was conducted to determine whether or not the extremely high diversity observed in macroalgal communities was due to disturbance from waves. Using a numerical wave model to estimate the forces caused by waves, researchers were able to determine that there was a significant relationship between species diversity and disturbance index; this is consistent with the intermediate disturbance hypothesis. Furthermore, diversity was lower at exposed offshore sites where disturbance from waves was highest, and at extremely sheltered site where disturbance from waves was minimized. The study provided evidence that biodiversity in microalgal reef communities possess some relationship with their proximity to the outer edge of lagoon systems typical of the Western Australian coast. While this study may have been localized to the Western Australian coast, it still provides some evidence to support the validity of the IDH.
Additionally, a study done in the Virgin Islands National Park found that species diversity, in some locations, of shallow coral reefs increased after infrequent hurricane disturbance. In 1982, reefs in Kona, Hawaii were reported to have an increase in diversity after a moderate storm, although the effects of the storm varied with the reef zones. In 1980, Hurricane Allen increased species diversity in shallow zones of the Discovery Bay Reef in Jamaica because the more dominant corals were reduced; giving the other types a chance to propagate following the disturbance. Similar findings have been reported in shallow reefs in which dominant species of coral have suffered more damage than the less common species. While more long-term studies are required to completely support the Intermediate Disturbance Hypothesis, the studies that have been conducted thus far have proven that IDH does have some validity while attempting to describe the relationship between diversity and the rate of occurrences of disturbance in an area.
Even though the IDH was designed for species-rich environments, like tropical rainforests, "most studies that evaluate the IDH are based on limited data with: few species, a limited range of disturbance and/or only a small geographic area, compared with the scale of interest". In this experiment, Rogers, Poorter, Hawthorne, and Sheil evaluate the IDH on a larger scale and compare different tropical forest types in Ghana. Their dataset consisted of 2504 one-hectare plots with a total of 331,567 trees. These plots were divided classified into three forest types: wet (446 plots), moist (1322 plots), and dry forest (736 plots). They found that diversity does peak at intermediate level of disturbance but little variation is explained outside dry forests. Therefore, disturbance is less important for species diversity patterns in wet tropical rain forests than previously thought. The number of species was about the same for each forest type, and wet forests had only slightly fewer pioneer species, slightly more shade-tolerant and an equal number of pioneer light-demanders compared with the moist and dry forests. Their results generally supported the IDH as an explanation of why diversity varies across sites, but concluded that disturbance is less important for species richness patterns in wet tropical rain forests than previously thought.
IDH has been subject to criticism since its inception but not to the degree that other species density hypotheses have been. Recently there has been a call for a critical reassessment of IDH. Criticisms have focused on the increasing amount of empirical data that disagrees with IDH. This can be found within approximately 80% of over 100 reviewed studies that are examining the predicted peak of diversity in intermediate disturbance levels. The rationales behind these discrepancies have been leveled at the simplicity of IDH and its inability to grasp the complexity found within the spatial and intensity aspects of disturbance relationships. In addition, many IDH proven circumstances have been suggested to be a reflection of skewed research methods based on researchers looking for humped diversity-disturbance relations only in systems where they believed it has occurred. Other criticisms are suggesting several subtle theoretical issues with IDH. First, while disturbances weaken competition by reducing species densities and per-capita growth rates, it also reduces the strength of competition needed to push per capita growth into a negative territory and reduce density to zero. Second, intermediate disturbances slow competitive exclusion by increasing the long-term average mortality rate, and thereby reducing the differences in the average growth rates of competing species. The difference in the growth rates between competitively superior and inferior species determines the rates of competitive exclusion; therefore intermediate disturbances are affecting species' abundance but not coexistence. Third, intermediate disturbances temporarily affect relative species fitness. However, no matter what the rate of disturbance is, the species with favored fitness will out-compete the rest of the species.
Several alternative hypotheses have been proposed. One example is by Denslow, who states that the species diversity in a disturbance-mediated coexistence between species is maximized by the presence of a disturbance regime resembling the historic processes. This is because species generally adapt to the level of disturbance in their ecosystem through evolution (whether disturbance is of high, intermediate or low level). Many species (e.g. ruderal plants and fire-adapted species) even depend on disturbance in ecosystems where it often occurs.
Bacterivores are free-living, generally heterotrophic organisms, exclusively microscopic, which obtain energy and nutrients primarily or entirely from the consumption of bacteria. Many species of amoeba are bacterivores, as well as other types of protozoans. Commonly, all species of bacteria will be prey, but spores of some species, such as Clostridium perfringens, will never be prey, because of their cellular attributes.Copiotroph
A copiotroph is an organism found in environments rich in nutrients, particularly carbon. They are the opposite to oligotrophs, which survive in much lower carbon concentrations.
Copiotrophic organisms tend to grow in high organic substrate conditions. For example, copiotrophic organisms grow in Sewage lagoons. They grow in organic substrate conditions up to 100x higher than oligotrophs.Decomposer
Decomposers are organisms that break down dead or decaying organisms, and in doing so, they carry out the natural process of decomposition. Like herbivores and predators, decomposers are heterotrophic, meaning that they use organic substrates to get their energy, carbon and nutrients for growth and development. While the terms decomposer and detritivore are often interchangeably used, detritivores must ingest and digest dead matter via internal processes while decomposers can directly absorb nutrients through chemical and biological processes hence breaking down matter without ingesting it. Thus, invertebrates such as earthworms, woodlice, and sea cucumbers are technically detritivores, not decomposers, since they must ingest nutrients and are unable to absorb them externally.Dominance (ecology)
Ecological dominance is the degree to which a taxon is more numerous than its competitors in an ecological community, or makes up more of the biomass.
Most ecological communities are defined by their dominant species.
In many examples of wet woodland in western Europe, the dominant tree is alder (Alnus glutinosa).
In temperate bogs, the dominant vegetation is usually species of Sphagnum moss.
Tidal swamps in the tropics are usually dominated by species of mangrove (Rhizophoraceae)
Some sea floor communities are dominated by brittle stars.
Exposed rocky shorelines are dominated by sessile organisms such as barnacles and limpets.Feeding frenzy
In ecology, a feeding frenzy occurs when predators are overwhelmed by the amount of prey available. For example, a large school of fish can cause nearby sharks, such as the lemon shark, to enter into a feeding frenzy. This can cause the sharks to go wild, biting anything that moves, including each other or anything else within biting range. Another functional explanation for feeding frenzy is competition amongst predators. This term is most often used when referring to sharks or piranhas. It has also been used as a term within journalism.IDH
IDH may refer to:
Intermediate Disturbance Hypothesis
Interactive Data Handler
Intradialytic hypotensionIndex of biodiversity articles
This is a list of topics in biodiversity.J. Philip Grime
(John) Philip Grime is an ecologist and emeritus professor at the University of Sheffield. He is best known for his Universal adaptive strategy theory, for the unimodal relationship between species richness and site productivity (the "humped-back model"), for the Intermediate Disturbance Hypothesis, for the DST classification (dominants, subordinates and transients) and, with Simon Pierce (University of Milan, Italy), universal adaptive strategy theory (UAST) and the twin filter model of community assembly and eco-evolutionary dynamics.Grime's 1979 book Plant Strategies and Vegetation Processes has been cited more than 1,200 times. Together with many influential scientific papers, it has made him a highly cited scientist. In an interview Grime has stated that "Ecology lacks a Periodic Table", quoting Richard Southwood.Joseph H. Connell
Joseph Hurd Connell FAA (born October 5, 1923) is an American ecologist. He earned his MA degree in zoology at the University of California, Berkeley and his PhD at Glasgow University. Connell’s first research paper examined the effects of interspecific competition and predation on populations of a barnacle species on the rocky shores of Scotland. According to Connell, this classic paper is often cited because it addressed ecological topics that previously had been given minor roles. Together, with a subsequent barnacle study on the influence of competition and desiccation, these two influential papers have laid the foundation for future research and the findings continue to have relevance to current ecology. His early work earned him a Guggenheim fellowship in 1962 and the George Mercer Award in 1963.In 2010, a Symposium was held in his honour by the Ecological Society of America said that "Connell’s observations, insights, syntheses, and example have motivated education and research in population and community ecology for over six decades". Among his important works are the Connell–Slatyer model of ecological succession (facilitation, tolerance and inhibition) and the Janzen-Connell hypothesis that explains plant-species diversity in tropical forests. Other notable works are his 1978 intermediate disturbance hypothesis and his thirty-year study of corals in the Great Barrier Reef.He is a corresponding member of the Australian Academy of Science, a member of the American Academy of Arts and Sciences, and a Guggenheim fellow, and has received the Eminent Ecologist Award from the Ecological Society of America. He is a professor emeritus at the University of California Santa Barbara.Connell was elected to the Australian Academy of Science in 2002 as a Corresponding Fellow.Lithoautotroph
A lithoautotroph or chemolithoautotroph is a microbe which derives energy from reduced compounds of mineral origin. Lithoautotrophs are a type of lithotrophs with autotrophic metabolic pathways. Lithoautotrophs are exclusively microbes; macrofauna do not possess the capability to use mineral sources of energy. Most lithoautotrophs belong to the domain Bacteria, while some belong to the domain Archaea. For lithoautotrophic bacteria, only inorganic molecules can be used as energy sources. The term "Lithotroph" is from Greek lithos (λίθος) meaning "rock" and trōphos (τροφοσ) meaning "consumer"; literally, it may be read "eaters of rock". Many lithoautotrophs are extremophiles, but this is not universally so.
Lithoautotrophs are extremely specific in using their energy source. Thus, despite the diversity in using inorganic molecules in order to obtain energy that lithoautotrophs exhibit as a group, one particular lithoautotroph would use only one type of inorganic molecule to get its energy.Mesotrophic soil
Mesotrophic soils are soils with a moderate inherent fertility. An indicator of soil fertility is its base status, which is expressed as a ratio relating the major nutrient cations (calcium, magnesium, potassium and sodium) found there to the soil's clay percentage. This is commonly expressed in hundredths of a mole of cations per kilogram of clay, i.e. cmol (+) kg−1 clay.Mycotroph
A mycotroph is a plant that gets all or part of its carbon, water, or nutrient supply through symbiotic association with fungi. The term can refer to plants that engage in either of two distinct symbioses with fungi:
Many mycotrophs have a mutualistic association with fungi in any of several forms of mycorrhiza. The majority of plant species are mycotrophic in this sense. Examples include Burmanniaceae.
Some mycotrophs are parasitic upon fungi in an association known as myco-heterotrophy.Organotroph
An organotroph is an organism that obtains hydrogen or electrons from organic substrates. This term is used in microbiology to classify and describe organisms based on how they obtain electrons for their respiration processes. Some organotrophs such as animals and many bacteria, are also heterotrophs. Organotrophs can be either anaerobic or aerobic.
Antonym: Lithotroph, Adjective: Organotrophic.Planktivore
A planktivore is an aquatic organism that feeds on planktonic food, including zooplankton and phytoplankton.Population cycle
A population cycle in zoology is a phenomenon where populations rise and fall over a predictable period of time. There are some species where population numbers have reasonably predictable patterns of change although the full reasons for population cycles is one of the major unsolved ecological problems. There are a number of factors which influence population change such as availability of food, predators, diseases and climate.Recruitment (biology)
In biology, especially marine biology, recruitment occurs when a juvenile organism joins a population, whether by birth or immigration, usually at a stage whereby the organisms are settled and able to be detected by an observer.There are two types of recruitment: closed and open.In the study of fisheries, recruitment is "the number of fish surviving to enter the fishery or to some life history stage such as settlement or maturity".Relative abundance distribution
In the field of ecology, the relative abundance distribution (RAD) or species abundance distribution describes the relationship between the number of species observed in a field study as a function of their observed abundance. The graphs obtained in this manner are typically fitted to a Zipf–Mandelbrot law, the exponent of which serves as an index of biodiversity in the ecosystem under study.Species homogeneity
In ecology, species homogeneity is a lack of biodiversity. Species richness is the fundamental unit in which to assess the homogeneity of an environment. Therefore, any reduction in species richness, especially endemic species, could be argued as advocating the production of a homogenous environment.Treefall gap
A treefall gap is a distinguishable hole in a forest with vertical sides extending through all levels down to an average height of 2 m (6.6 ft) above ground. These holes occur as result of a fallen tree or large limb. The ecologist who developed this definition used two meters because believed that "a regrowth height of 2 m was sufficient" for a gap to be considered closed, but not all scientists agreed. For example, Runkle believed that regrowth should be 10–20 m (33–66 ft) above the ground. Alternatively, a treefall gap as "the smallest gap [that must] be readily distinguishable amid the complexity of forest structure."There is no upper limit in gap size. However, it must be caused by a tree or a large limb. For example, a field would not be considered a treefall gap.Tree falls are commonly caused by old age, natural hazards, or parasitic plants (e.g. certain epiphytes).