IDH has been subject to criticism since its inception but not to thedegree that other species density hypotheses have been. Recently therehas been a call for a critical reassessment of IDH. Criticisms havefocused on the increasing amount of empirical data that disagrees withIDH. This can be found within approximately 80% of over 100 reviewedstudies that are examining the predicted peak of diversity inintermediate disturbance levels. The rationales behind thesediscrepancies have been leveled at the simplicity of IDH and itsinability to grasp the complexity found within the spatial andintensity aspects of disturbance relationships. In addition, many IDHproven circumstances have been suggested to be a reflection of skewedresearch methods based on researchers looking for humpeddiversity-disturbance relations only in systems where they believed ithas occurred. Other criticisms are suggesting several subtletheoretical issues with IDH. First, while disturbances weakencompetition by reducing species densities and per-capita growth rates,it also reduces the strength of competition needed to push per capitagrowth into a negative territory and reduce density to zero. Second,intermediate disturbances slow competitive exclusion by increasing thelong-term average mortality rate, and thereby reducing the differencesin the average growth rates of competing species. The difference inthe growth rates between competitively superior and inferior speciesdetermines the rates of competitive exclusion; therefore intermediatedisturbances are affecting species' abundance but not coexistence. Third, intermediate disturbances temporarily affect relative speciesfitness. However, no matter what the rate of disturbance is, thespecies with favored fitness will out-compete the rest of the species.
Abstract theories are challenging to apply in the real world. For example, an observation that a species occurs somewhere says relatively little about its ability to persist in that location. The occurrence may represent a relic, a chance ephemeral occurrence, or a sink population (see source-sink dynamics in Table 1). Such fundamental challenges explain why ecological-coexistence theory has had little influence on conservation practice. Despite its focus on species persistence, such theory is hard to apply in practice. Demonstrations that species coexist in a persistent manner, rather than simply noting their occurrence in the same location, remain rare even in formal ecological studies (Siepielski and McPeek 2010). Despite its intuitive appeal, achieving demonstrable coexistence as ecologists might define it, is neither a practical nor a realistic conservation goal. Nevertheless, given that conservation can use any cost-effective combination of actions that can slow or prevent species loss, there is value in recognizing the conditions under which competitive exclusion is more or less probable or rapid. Coexistence theory thus offers some potentially useful insights about the role of disturbance.
Intermediate Disturbance Hypothesis - Encyclopedia of …
Our results support the intermediate disturbance hypothesis, with both highly mobile and relatively sedentary taxa conforming to the predicted bell-shaped curve.
Intermediate Disturbance Hypothesis : Wikis (The Full …
As biodiversity declines globally, it is becoming increasingly important to understand the processes that create and maintain biodiverse communities. We examined whether the extraordinarily high species diversity of macroalgal communities in shallow coastal waters off south-west Western Australia is related to wave-induced physical disturbance. We used the numerical wave model SWAN to estimate the hydrodynamic forces generated by waves in bathymetrically complex coastal reefs. Oscillatory water motion at the seabed during extreme wave events was used as an index of physical disturbance in macroalgal communities. There was a significant curvilinear relationship between species diversity and disturbance index, consistent with the intermediate disturbance hypothesis (IDH). Diversity was lower at exposed offshore sites where disturbance is likely to be highest and at very sheltered sites with the least disturbance. Our results match those from some other highly diverse habitats, including rainforests, grasslands and coral reefs in which patchy, stochastic disturbance regimes have been hypothesised to prevent the development of homogeneous climax communities, promoting spatiotemporal heterogeneity and increasing total system diversity. Our results represent important evidence in support of a role for the IDH in driving diversity in marine plant communities.
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Disturbance can be defined in many ways even by ecologists (see for example, Sheil 1999). In the present context, I propose a definition that implies reduced competition. Such events thus modify each species’ competitive environment and influence the realized niches and resulting distributions. In Appendix 1, I select a range of examples that show that disturbance often permits species to range beyond their more typical environmental conditions.
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Although species richness has been hypothesized to be highest at `intermediate ’ levels of disturbance, empirical studies have demonstrated that the disturbance