| Summary: | The changes in species diversity and composition of Cyperus conglomeratus plant community caused by anthropogenic disturbance were estimated and analyzed in four selected sites at southern Jeddah in Saudi Arabia. The ecological disturbances in the study area have their major effect on species richness, where about 76% of the perennial species in the study area were disappeared as the result of the human impact on C. conglomeratus community in the most disturbed sites. Interspecific competition results from C. conglomeratus indicated that it is a competitor species led to exclusion of the other species from the highly disturbed sites which affected by the Industrial City in Jeddah. Therefore, resulting in a remarkable decrease in species diversity (Shannon’s index = 0.664) coinciding with maximum dominance of C. conglomeratus (Simpson’s index = 0.656). The general trend of plant species richness and diversity in moderately disturbed sites in the study area showed remarkable increase in both richness (S = 16 species) and diversity (Shannon’s index = 1.792), coinciding with minimum dominance (Simpson’s index = 0.253). The resulting graphs of species abundance distribution models representing the highly disturbed sites tend toward geometric series pattern of species abundances, where one (C. conglomeratus) species dominate the community with the remainder fairly uncommon, assuming competitive exclusion and resource exhaustion in such degraded and harsh ecosystems. Keywords: Disturbance, Species diversity, Cyperus conglomeratus, Saudi Arabia
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