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The IntermediateDisturbance Hypothesis

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.

Intermediate Disturbance Hypothesis | Conservation | …

Abstract. A review of research on the effects of hurricanes on coral reefs suggests that the intermediate disturbance hypothesis may be applicable to shallow reef zones domi-nated by branching or foliaceous coral species that are especially susceptible to mechanical damage from storms. Diversity (H') increases because of an increase in evenness following destruction or removal of the species that was monopolizing the space. The intermediate disturbance hypothesis as presented by Connell focuses on changes in number of species, but should be expanded to include diversity (H') and evenness. It should also be modified to incorporate changes in living cover and the time elapsed since disturbances of varying intensities. This hypothesis predicts that when cover is high, diversity will be low. However, research on coral reefs does not consistently demonstrate aninverse correlation of coral diversity and coral cover. An increase in cover and decrease in diversity with depth would also be expected because deeper eef zones generally experience less disturbance. However, higher diversity (both H ' and species richness) is often associated with deeper zones. The effects of hurricanes on coral reefs will depend on the temporal and spatial scales under consideration, the life history characteristics and morphology of the dominant species, the depth of the reef zone, the ecological history of the site, and the influence of any additional natural or human stresses.

Intermediate Disturbance Hypothesis ..

Caswell’s (1978) intermediate disturbance hypothesis suggests that at low levelsof disturbance, a few competitively superior species will dominate communities resultingin low levels of diversity. At intermediate disturbance levels, frequent removal of thesespecies will provide space for others, resulting in high diversity. At very high levels ofdisturbance only a few very tolerant or opportunistic species will occur. This hypothesishas been tested in boulder fields where it seems to hold true (Sousa, 1979). Physicaldisturbance appears to play a role in structuring communities with limited disturbancepromoting biodiversity.

and (1999) Diversity in planktonic communities: an experimental test of the intertmediate disturbance hypothesis. Limnology and Oceanography, 44 . pp. 1114-1119. DOI .

Intermediate Disturbance Hypothesis - Encyclopedia of …

According to Connell�s intermediate disturbance hypothesis (IDH), diversity within a community is maximal at intermediate frequencies and intensities of disturbances. In order to test the IDH, disturbances of different frequencies and intensities were imposed on natural plankton communities in controlled field experiments. These disturbances consisted of an artificial deepening of the mixed layer, leading to the dilution of epilimnetic populations and to a higher level of nutrients. Intervals between disturbances ranged from 2 to 12 d. Different intensities of disturbance were caused by differences in the experimental mixing depth (150 and 225% of the original epilimnion depth). Investigation focused on the effect that disturbances had on the diversity of natural phytoplankton communities. Additionally, we were interested in determining the effect of grazing by zooplankton. The results of the field experiments show for the first time the applicability of the IDH to phytoplankton within complete planktonic communities. Diversity showed a clear maximum at the intermediate disturbance interval of 6 d. Similarly, species number peaked at intermediate interval length (6-10 d).

According to Connell�s intermediate disturbance hypothesis (IDH), diversity within a community is maximal at intermediate frequencies and intensities of disturbances. In order to test the IDH, disturbances of different frequencies and intensities were imposed on natural plankton communities in controlled field experiments. These disturbances consisted of an artificial deepening of the mixed layer, leading to the dilution of epilimnetic populations and to a higher level of nutrients. Intervals between disturbances ranged from 2 to 12 d. Different intensities of disturbance were caused by differences in the experimental mixing depth (150 and 225% of the original epilimnion depth). Investigation focused on the effect that disturbances had on the diversity of natural phytoplankton communities. Additionally, we were interested in determining the effect of grazing by zooplankton. The results of the field experiments show for the first time the applicability of the IDH to phytoplankton within complete planktonic communities. Diversity showed a clear maximum at the intermediate disturbance interval of 6 d. Similarly, species number peaked at intermediate interval length (6-10 d).

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Graph shows principles of Intermediate Disturbance Hypothesis: I

Science 199:1302 -1310): The Intermediate Disturbance Hypothesis (IDH) predicts that the highest species richness will occur at an intermediate level of intensity or frequency of natural disturbance.

Intermediate-Disturbance Hypothesis | Science

What regulates the number of species in a community, or "species diversity"? One hypothesis is that the diversity of species in a community is constantly changing (non-equilbrium). In this scenario, species diversity in a community is predicted to be greatest when disturbance to the environment is intermediate (Connell 1978, Sousa 1979). At high levels of disturbance, species that are good colonists are predicted to predominate, whereas at low levels of disturbance, competitively superior species are predicted to be the most abundant. At intermediate levels of disturbance both colonists and competitively dominant species overlap, leading to the highest species diversity. Today we will test the intermediate disturbance hypothesis by determining whether areas with intermediate disturbance by gophers have the greatest plant species diversity.

Intermediate-Disturbance Hypothesis

The Intermediate Disturbance Hypothesis (IDH) justifies that local is maximized when is neither too rare nor too frequent. At high levels of disturbance, due to frequent or human impacts like , 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.

Intermediate Disturbance Hypothesis - Revolvy

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. , 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. 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.

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