19. The fundamental niche allows more members of a species to survive in an ecosystem because that species has no competition for the resources it needs. A species in the realized niche can not have as many members survive because of interspecies competition.
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More of the species in the graph of a fundamental niche at left can survive as there is no interspecies competition. Not as many of the species can survive in the graph of a realized niche at right because there is interspecies competition for the resources there.
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Slichter