The article reviews the effects of urbanization on species richness, focusing on plants and non-avian animals. It highlights that urbanization can either increase or decrease species richness, depending on various factors such as taxonomic group, spatial scale, and intensity of urbanization. For most non-avian species, species richness tends to be reduced in areas with extreme urbanization, but moderate levels of urbanization can have varying impacts. Plant studies show a higher likelihood of increased species richness with moderate urbanization, while invertebrate and vertebrate studies show less consistent results. The review discusses possible explanations, including the introduction of nonnative species, spatial heterogeneity, intermediate disturbance, and scale. The article also explores the complex nature of urbanization's impact on biodiversity, noting both negative effects like species loss and positive effects like increased biodiversity due to high habitat heterogeneity and productivity.The article reviews the effects of urbanization on species richness, focusing on plants and non-avian animals. It highlights that urbanization can either increase or decrease species richness, depending on various factors such as taxonomic group, spatial scale, and intensity of urbanization. For most non-avian species, species richness tends to be reduced in areas with extreme urbanization, but moderate levels of urbanization can have varying impacts. Plant studies show a higher likelihood of increased species richness with moderate urbanization, while invertebrate and vertebrate studies show less consistent results. The review discusses possible explanations, including the introduction of nonnative species, spatial heterogeneity, intermediate disturbance, and scale. The article also explores the complex nature of urbanization's impact on biodiversity, noting both negative effects like species loss and positive effects like increased biodiversity due to high habitat heterogeneity and productivity.