INTERMEDIATE DISTURBANCE HYPOTHESIS:

INTERMEDIATE DISTURBANCE HYPOTHESIS:

The Intermediate Disturbance Hypothesis  states that diversity is

maximized when ecological disturbance is neither too rare nor too frequent. At low levels of disturbance, more competitive organisms will push subordinate species to extinction and dominate the ecosystem. At high levels of disturbance, due to frequent forest fires or human impacts like deforestation, all species are at risk of going extinct(both r and k-selected species). According to intermediate disturbance theory, at intermediate levels of disturbance, diversity is thus maximized because both competitive k-selected selected and opportunistic r-selected species can coexist

      This coexistence is a result of the differing life history strategies of species,which dictate a preference for high or low disturbance. K-selected species tend to be more competitive, because they invest a larger proportion of resources into growth and competition and thus generally dominate stable ecosystems over long time periods. In contrast, r-selected species, which colonize open areas quickly, can dominate landscapes recently cleared by

disturbance. Therefore the areas where disturbance occurs frequently, but in intermediate magnitude both r-selected and k-selected species exist.

     The intermediate disturbance hypothesis is consistent with diversity patterns observed in natural and altered lotic ecosystems. Species diversity is reduced in stream habitats exposed to levels of disturbances that are severe. In addition, habitats with enhanced environmental consistency exhibit suppressed diversity even if adverse conditions (e.g., oxygen deficits) are not apparent. It is postulated that ‘undisturbed’ lotic systems are in fact ‘disturbed’ and that the high biotic diversity of natural streams is a function of moderate perturbation. Diversity is enhanced by the spatio-temporal heterogeneity resulting from intermediate disturbance, which maintains the   community in a non-equilibrium state (a state where both ‘k’ as well as ‘r’-selected species co-exist.